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WAR DEPARTMENT
ENGINEER FIELD MANUAL
Volume II
MILITARY ENGINEERING
{TENTATIVE)
PART TWO
DEFENSIVE MEASURES
U S. Army Mary History institute
ENGINEER FIELD MANUAL
Volume II
MILITARY ENGINEERING
(Tentative)
PART TWO
DEFENSIVE MEASURES
PREPARED UNDER THE DIRECTION OF THE
CHIEF OF ENGINEERS
For sale hy the Superintendent of Documents, Washington, D. G.
Price 30 cents
PROPERTY OF US ARMY
UNITED STATES
GOVERNMENT PRINTING OFFICE
WASHINGTON : 1932
0<S~
Ob
pi, 2,
WAR DEPARTMENT,
Washington, June 25, 1932.
Part Two, Defensive Measures, Engineer Field Manual, Vol-
ume II, Military Engineering (Tentative), is published for the
information and guidance of all concerned.
[A. G. 062.11 (7-19-30).]
By order op the Secretary op War:
DOUGLAS MaoARTHUR,
General,
Chief of Staff.
Official :
C. H. BRIDGES,
Major General,
The Adjutant General.
LIST OF FIELD MANUALS
A MANUAL FOR COMMANDERS OF LARGE UNITS. (M. C. L. U.)
Vol. I. Operations. — >A guide for commanders and staffs for tactical
operations of large units.
II. Administration A guide for the administration of large
units in a theater of operations.
STAFF OFFICERS' FIELD MANUAL. (S. 0. F. M.)
Staff principles and functions applicable to the staffs of all units,
together with pertinent reference data.
BASIC FIELD MANUALS. (B. F. M.)
Training, administrative, and reference data applicable to more than
one arm, with special reference to the smaller units.
Vol. I. Field Service Pocketbook. (F. S. P.) — The individual.
II. Infantry Drill Regulations. (I. D. R.) — Drill, dismounted
ceremonies, and inspections ; the infantry pack, display of
equipment, and tent drill.
III. Basio Weapons. (B. W.) — Marksmanship and mechanical
training of the rifle, automatic rifle, pistol, machine gun,
37-mm. gun, 3-inch trench mortar, bayonet and grenade
instruction. Technique of fire (37-mm. gun, 3-inch trench
mortar, and machine gun) ; musketry and combat practice
of small units, instruments.
IV. Signal Communication. (S. C.) — Signal regulations and
technical information needed by officers and enlisted men
on signal communication duty of arms other than the
Signal Corps.
V. Transport. (T.) — Equitation, training remounts, use and
care of animals an.d of animal-drawn, pack, motor and
tractor transport.
VI. Administrative Regulations. (A. R.) — Army Regulations
essential to small units.
VII. Military Law. (M. L.) — The Manual for Courts-Martial,
including the Articles of War ; the Rules of Land Warfare,
including recent conventions relative to the sick and
wounded of armies in the field and to prisoners of war ;
an epitome of the legal principles applicable to military
forces when aiding the civil power.
VIII. Operations of Combined Arms (Small Units). (O. C. A.) —
The principles, doctrines, and methods governing the tacti-
cal employment of combined arms with reference to the
small units.
Ill
IV
LIST OF FIELD MANUALS
FIELD MANUALS FOR THE ARMS
The manual for each arm contains, primarily, the principles, doctrines,
and methods governing the employment of that arm and pertinent
reference data.
Infantry Field Manual. (I. F. M.)
Vol. I. Units other than Tanks.
II. Tank Units.
Cavalry Field Manual. (C. F. M.)
Field Artillery Field Manual. (F. A. F. M.)
Vol. I. Organisation and Drill.
II.. Tactics and Technique.
Coast Artillery Field Manual. (C. A. F. M.)
Vol. I. Harbor Defense, Railway and Tractor-drawn Units.
II. Antiaircraft Artillery Units.
Air Corps Field Manual. (A. C. F. M.)
Engineer Field Manual. (E. F. M.)
Vol. I. Engineer Troops.
II. Military Engineering.
Signal Corps Field Manual. (S. C. F. M)
Vol. I. Signal Corps Troops.
II. Signal Corps Operations.
TABLE OF CONTENTS
Chapter 1. Camouflage: Paragraph Page
Section I. General principles. _ 1-6 1-3
II. Reconnaissance- 7-11 3-4
III. Construction .1 12-27 4-31
Chapter 2. Field fortifications:
Section I. Principles of field fortification.- _ 28-34 33-37
II. The effects of projectiles 35-41 39-40
III. Underground water and its relation to fieldworks. . 42-44 41-42
IV. Standard types of field-works 45-78 43-103
V. Protected shelters...- 79-145 105-172
Chapter 3. Explosives and demolitions:
Section I. General principles - 146-155 174-182
II. Demolition equipment _ 156-169 184-191
III. Methods of handling explosives 170-201 192-221
IV. The demolition project 202-217 221-240
V. Mine warfare 218-227 241-244
FOREWORD
Engineer Field Manual, Volume II, Military Engineering, is a
compendium of technical information and suggestions as to
the conduct of the most common operations undertaken by engi-
neer troops in the theater of operations. The user of this
manual should recognize that local conditions in the field will
always profoundly affect the application of the principles and
formulas given herein. The manual contains suggestions and
guides to judgment rather than regulations to be rigidly
adhered to.
The manual will be published in three parts as follows :
Part One, Communications:
Chapter 1. Roads.
2. Bridges.
3. Military Railways.
4. Surveys and maps. (This chapter will be
published when it becomes necessary to
revise TM 2180-30 and 2180-37.)
Part Two, Defensive Measures :
Chapter 1. Camouflage.
2. Meld Fortifications.
3. Explosives and Demolitions.
Part Three, Construction and Utilities :
Chapter 1. General Construction.
2. Water Supply.
3. Light and Power.
ENGINEER FIELD MANUAL
VOLUME II, MILITARY ENGINEERING
(TENTATIVE)
PART TWO
DEFENSIVE MEASURES
(The matter contained herein supersedes IB 195-20, December 20, 1927
(including Changes No. 1, January 2, 1931), IB 195-25, December 1,
1927, IB 195-30, May 15, 1926 (including Changes No. 1, January 2,
1929), and IB 195-10, June 15, 1926)
Volume II supersedes the Engineer Field Manual, edition of 1918 (Profes-
sional Papers of the Corps of Engineers, IT. S. Army, No. 29)
CHAPTER 1
CAMOUFLAGE
Section I. General principles
II. Reconnaissance
III. Construction
Section I
GENERAL PRINCIPLES
1. Definition. — Camouflage is work done for the purpose of
deceiving the enemy as to the existence, nature, or location
of material, troops, or military works. The importance of
camouflage depends in general upon the activity and effective-
ness of the enemy's air service, although it is important to
camouflage against ground observation.
2. Basic principle. — The basic principle of camouflage is de-
ception. Deception is accomplished by suppressing all signs
of abnormal activity near the object or deceiving the enemy
as to the purpose of such activity; by making the object in-
distinguishable from its surroundings ; by making the object
appear to be something else ; or by complete concealment.
1
Paragraph
1-6
7-11
12-27
2
ENGINEER FIELD MANUAL,
3. Hostile observation. — Hostile observation may be of two
kinds, direct and indirect. Direct observation is by direct
vision, aided or unaided by field glasses or telescopes. It is
obtained from observation posts or aircraft. Indirect ob-
servation, whicb is by far the most dangerous, is from the
study of aerial photographs.
4. Patterns. — The pattern formed on aerial photographs by
the features of the terrain influences to a large degree the
measures taken toward deception or concealment. Patterns
may be large and simple or intricate and confused. Detection
by aerial photography is more difficult when an object is
located in terrain showing a complex photographic pattern.
Patterns are made by form, shadow, texture, and color.
a. . Form. — F orm is the most important element. Regular
forms quickly attract the eye, while irregular forms of human
origin are lost in the irregular forms of the natural features.
&. Shadow. — Shadow is what discloses form, and from the
shadow tne™experienced aerial photograph reader can visualize
the object casting it.
c. Texture. — Texture in camouflage is a quality opposed to
smoothn8!!S J ~{Jr polish and is illustrated by a rug of long nap.
The nap is composed of innumerable fine hairs, each one when
erect casting a shadow. When the rug is trod upon, the
hairs are pressed down and texture is lost. When brushed, the
hairs become erect and texture is regained. Substance with
much surface texture absorbs light and photographs dark ;
if location in texture and surface reflects light, it photographs
light. Grass or other vegetation possesses this property in
a marked degree. The longer it is the darker it appears in
the photographs, but when pressed down by the foot the
amount of shadow is lessened, and it consequently appears
lighter. Hence the obviousness from the air of a slight track
or path in grass which is quite inconspicuous from the ground.
d^^o^g^r-Color is the least important of the four elements
that contribute to form patterns in the photograph, as it can
be translated only into tones of black and white. Colors which
may appear to the eye to match the locality do not match in
photographs unless the texture of the material approximates
the texture of the locality. Painted canvas or burlap of the
same color as grass photographs much lighter on account of
reflection due to lack of texture.
ENGINEER FIELD MANUAL
3
5. Relative importance of camouflage requirements. — Field
experience has shown that the relative importance of .camouflage
requirements is about as follows :
a. Propet,eliaice_of position — 40 per cent.^
6. Camouflage disciptrn^«fcaffifn ;= oDservance of camouflage
regulations) — 25 per cent.
o. Proper erection of ^camouflaga material— 20 per cent.
d. Camouflage material used — 15 per cent.
6. Typay Of camouflage. — TKe : types of camouflage include —
a. Concealment, as by the use of screening to prevent direct
observation of our activities.
6. Variegated painting to deceive the observer as to the true
pattern of what he sees.
c. Fish nets hung with garlands of burlap or other material
to cover batteries and other objects to make a blurred and in-
conspicuous record on an aerial photograph.
d. Koad screens of natural or artificial material.
e. Dummies which, though visible to the enemy, confuse and
deceive him.
Section II
RECONNAISSANCE
7. Use of aerial photographs. — The most important means of
reconnoitering for camouflage information are aerial photo-
graphs. If possible, a complete series of photographs should
be used showing the terrain before occupation by our forces,
and from time to time thereafter, in order that the camouflage
measures adopted by us may conform to the requirements of
the locality and in order that errors in camouflage technique
may be discovered early.
8. TTse of maps. — By the use of accurately contoured maps
it is possible to determine what points in the terrain occupied
by our forces are directly visible from the enemy position. This
is of assistance in determining where road screening is worth
while.
9. Local material. — Camouflage reconnaissance should deter-
mine the location of local materials which can be used for ca-
mouflage purposes. These include principally brush and poles
and local commercial stocks of iron wire, lumber, chicken wire,
burlap, and paint.
4
ENGINEER FIELD MANUAL
10. Seasonal changes. — The entire position occupied by our
forces must be reconnoitered from time to time to determine
the effect of seasonal changes of vegetation upon camouflage
in the area. This reconnaissance is made partly by personal
visit and partly by the study of aerial photographs.
11. Reconnaissance and choice of positions. — The most im-
portant factor in the camouflage of a position is intelligent
reconnaissance. Whether or not the terrain has been photo-
graphed by the enemy has an important bearing upon the choice
of position. If it has not been photographed, the position can
be hidden in many ways, so long as the method is maintained.
If the terrain has been photographed, the position is best hid-
den by offering the least disturbance to the surroundings. The
points to be sought embrace —
a. Ease of access without making incriminatory tracks either
during installation, in supplying food and ammunition, or in
relieving personnel.
&. Natural concealment or ease of concealment by camouflage.
o. Defilading both from direct observation posts and balloons
or by flash in the case of artillery.
d. Suitable locations for auxiliaries to the main position such
as camps, kitchens, and latrines, easily camouflaged and easily
accessible yet not so close as to cause discovery of the main
position.
Section III
CONSTRUCTION
12. Camouflage materials. — a. Natural. — The best materials
for camouflage are natural ones, as they possess the textures
of the locality. The objection to them is that they must be
constantly renewed, whereupon the feet of the men replenish-
ing the camouflage tread down the area around the point to
be hidden until the position looks like a black bull's-eye in
the center of a white target.
(1) Natural materials include grass, weeds, foliage, branches,
vegetation of all kinds, sod, etc. They may be self-supporting
or erected on frames or wire. Natural materials must be re-
newed at short intervals, otherwise withering and fading will
cause detection of the position.
(2) Another class of natural camouflage material is debris
natural to the locality, such as is found in shell-torn villages
ENGINEER FIELD MANUAL
5
and battlefields. This debris may be so distributed over and
around positions that in the confused pattern of light and
shadow it will be impossible to distinguish anything suspicious.
&. Artificial. — Artificial camouflage materials for cover of
various kinds are furnished by the camouflage sections. The
most important of these are wire netting and fish net, both
garnished with burlap, grass, or other material in colors suited
to the terrain where they will be used.
(1) There are two methods of garnishing wire or fish nets
with burlap :
(a) The better method is to knot burlap strips into the wire
or fish net. Strips 5 feet long and 1 inch wide are woven
and knotted at each end into the wire or net. The proportion
of bare space in a covering of this type is about 30 per cent.
(See fig. 1.) The strips are thinned out gradually at the edges.
The strips give the approximate texture to the cover when
correctly colored to the surroundings. The thickly woven cen-
tral portion serves to conceal what may be under it and the
thinned edges cast a faint, indeterminate shadow which, merg-
ing into the inequalities of the terrain, renders it unnoticeable
in aerial photographs. Since the thinned edges allow objects
under them to show, the cover must be much larger than the
object over which it is placed.
(6) The other method is to slash a lightweight burlap by
cutting slits from 6 to 15 inches long in various directions and
then stretching the burlap on wire netting or fish net so that
about 75 per cent of the wire is covered with burlap and the
rest is bare. The burlap is tied to the wire at 1-foot intervals
with strong twine. The texture of this covering causes it to
photograph lighter than the knotted burlap net.
(2) Wire netting 6 feet wide is cut into standard lengths of
30 feet. Burlap strips are woven into this wire, which is then
rolled up ready to transport. Inasmuch as covers of various
dimensions are built up from these, the thinned portion is
furnished in separate rolls which are used for the edges of the
cover when erected. Every accomplished requisition for wire
netting should contain about 15 per cent of thinned strips
which should be distinctively marked. Particular care should
be taken, when slashed burlap is used on these strips, to see
that the burlap overlaps from 6 to 12 inches on one side and
one end, otherwise the sheets of burlap will shrink away from
Figure 1. — Framework and cover
ENGINEER FIELD MANUAL
7
the edges of the strips or wire and each individual strip will be
outlined on an aerial photograph by a black border.
(3) The sizes of fish nets recommended for future use are
32 by 40 feet for 6-inch guns or larger, 32 by 32 feet for
3-inch guns, and 10 by 10 feet or 16 by 16 feet for machine
guns.
(4) Fish nets, because of their portability, are used prin-
cipally for mobile artillery, which carries them as a part of
its equipment. Wire netting is used for batteries or guns
in more or less stabilized positions, for observation posts, dug-
out and mine entrances, and sometimes for concealment of
concentrations of troops. It is supported on wire frames
stretched on posts and strongly guyed. It has the advantage
of being rigid enough to bridge considerable gaps between
supports without sagging, of being more permanent, and, in
case of fire, of not dropping the whole fabric on men and
materiel underneath ; but it is more bulky than fish nets and
less easily moved. For spoil covers, and when material is
laid directly on the surface desired to be rendered inconspicuous,
painted burlap may be used. Its efficiency is very limited,
however, as such a practice, though covering up obvious
differences in color or value, shows both form and shadow.
(5) Garlands are made of two or three strips of burlap
l 1 /! by 6 inches, tied together about 1% inches from one end.
These knots are then secured to a light wire framework so that
they are approximately 8 inches apart. They are useful for
screens for thickening overhead cover, at entrances to shelters,
etc. (See fig. 1.)
(6) Colors of fish net and wire netting camouflage must be
standardized, because material must be used over a wide front
and during changing seasons. As a rule, mottled patterns are
best for general use. Solid-color patterns are objectionable.
Some experiments will be needed to find colors and patterns
adapted to use in America. In general, the standard colors
will be the six used in France : No. 1, a light yellow ; No. 2,
dark green ; No. 3, yellow ocher ; No. 4, brown earth color ; No.
5, reddish brown ; and No. 6, dark reddish brown.
13. Standard method of erecting wire frame for wire net-
ting or net covers. — a. There are many problems which demand
flat-top covers, usually of wire netting, but sometimes of net,
of various 'dimensions and irregular size. Often no material for
the support can be had except wire from the engineer dumps.
ENGINEER FIELD MANUAL
9
6. (1) The following method of erection is easy and expe-
ditious even for men without experience. It lends itself to any
size or shape, and may be used to support either a finished
cover or plain wire netting as a base for natural materials.
(See fig. 2.)
(a) Posts should be made about 3 inches in diameter, cut
square at the top, and sharpened at the bottom.- They are
placed preferably about 12 feet apart in each direction though
conditions often necessitate a greater distance.
(6) The outside rows of posts should be driven in the ground
•just far enough to stand alone, and strong guy stakes should
be driven about 12 feet from them.
(c) Two nails should be driven in the head of each post,
about 1 inch apart. (See fig. 3.)
(d) The end of the wire, No. 8 or 9, should be wound fast
around the head of the first post, then taken with a turn around
the guy stake and back over the top of the post between the
nails, forming a double guy.
(e) The wire should then be stretched along the line of the
posts by several men, being supported by a nail about 1 foot
below the top of the last post of the row, then given a turn
around the guy stake and brought back and made fast to the
top of the post. Cut the wire from the coil at this point. ( See
(f ) The wire should then be pushed up over the tops of all
the posts in the row and seated between the nails, thus stretch-
ing it tight.
Figure 3. — Detail of flat-top wire frame
fig. 2.)
10
ENGINEER FIELD MANUAL
(g) Proceed similarly with each parallel line of posts, then
in the same manner run wires at right angles to the first series,
forming squares.
(h) Run diagonal wires across each line of posts, placing
the wire between the nails.
(i) Tighten all guy wires by twisting with a rack stick or
large nail. 'Tighten the diagonal wires in the same manner at
all crossings. This will tighten the whole frame.
(j) Drive the nails home, to avoid catching the cover when
spread. If poles are of even height and flat topped, the nails
may be dispensed With, though they assist greatly in quick'
work.
(2) This method is quick and gives a rigid and lasting
frame. After erection any of the interior posts may be shifted
in position to accommodate battery needs without affecting the
stiffness of the frame. By placing additional posts on the edges
and wiring them in accordance with the previously mentioned
principles, any irregular shape may be made. If only hard,
steel wire is obtainable, it is easily annealed by heating it until
red hot in a fire and allowing it to cool gradually. It is im-
possible to do good light work with hard wire.
14. Erection of natural materials.- — a. In the use of natural
materials, which are always the best when properly and in-
telligently handled, care must be taken to place the materials
in their natural positions, otherwise they will reflect light
differently and show in aerial photographs. For instance,
cut grass thrown over a path lies flat and photographs nearly
as light as the path itself. A thatched cover of branches,
particularly evergreens, reflects light to such an extent as to
photograph nearly white. Branches thrown on upside down, as
is generally the practice with untrained men, photograph al-
most white. The underside of a leaf is a very different color
from the upper side. Also branches should not be thrown
on camouflage material with the stem out. Trees do not grow
that way.
6. In making a cover of natural material two methods are
successful :
(1) On a standard wire frame erect a flat top of two layers
of wire netting separated about 4 inches by brush placed be-
tween the layers. This will serve to stick the covering material
in, the two layers holding the branches or cuttings upright.
They will invariably fall flat if only one layer of netting is used.
ENGINEER FIELD MANUAL
11
(2) Stretch wires overhead at different heights and in sev-
eral directions. Fasten them to trees or posts and suspend
small trees, branches, or shrubs by their tips from these wires.
A natural appearance is then presented to the eye or lens.
o. In case paint or solutions preserving the natural color
of the foliage are not used the materials must be renewed at
night upon the earliest indication of deterioration.
d. When a position placed in thick woods in leaf is presum-
ably to be occupied after leaves fall, a cover of brown burlap
may be stretched over the position. As the leaves fall, thin-
ning the natural cover, they will be caught on the burlap, and
when the trees are bare the cover will present the leaf-covered
appearance of the ground.
e. Where some thinning out of trees in a wood for a position
or path is necessary, it is often sufficient to bend saplings and
small trees over the thinned space, fastening them with wires.
15. Road screening. — a. Road screening is erected to prevent
balloon or terrestrial observers from seeing traffic pass along
visible roads. Its purposes are to prevent the enemy intelli-
gence observers from counting the road traffic, and so esti-
mating what troop movements are taking place in our areas,
and to keep the enemy from observing and shelling vehicles
moving over an exposed road. The first purpose is at times
most important.
6. Most roads may be sufficiently screened by a lateral screen,
6 to 12 feet high. This must be guyed solidly to the ground
with good stakes to keep the wind and shells from knocking
it down. It should be 20 to 50 yards from the road to allow
free room for guy wires. When the road is on a high embank-
ment, the screen must be close to the edge of the road. Gaps
must be left at intervals in the screening for lateral communi-
cation. In a salient, lateral screening may be necessary on
both sides of a road to prevent enemy observation. Figures
4, 5, and 6 give details of lateral screenings.
c. When a road is nearly perpendicular to the front, it may
be economical to echelon the screening, as shown in Figure 4.
The angle of these wings of screening, their length, and dis-
tance apart can be easily estimated by drawing a diagram show-
ing the road and the enemy's line of sight. Care must be taken
to have plenty of overlap between successive screens.
66842°— 32 2
12
ENGINEER FIELD MANUAL
d. A road perpendicular to and sloping downward toward the
front must often be cross screened. It may require lateral
screening also. Figure 7 gives details of cross screening.
e. Road screening can be made either from natural materials
available in the vicinity, such as brush and cuttings, or from
artificial camouflage materials, such as plain burlap or wire
netting garnished with camouflage material or burlap strips.
(1) Brush either cut on the site and woven with smooth wire
into a screen, or fabricated in rolls at some favorable point
and hauled to the site for erection, makes a very durable road
screen for lateral and echelon screening. Figure 6 gives details
of fabricating screen from brush.
i (2) Wire netting garnished with camouflage material in the
same manner as described in paragraph 12 can be used. A
more satisfactory method of garnishing is by means of burlap
strips of alternate light and dark color as shown in Figure
5. The alternating color is used to secure greater opacity.
Plain material is probably as effective. When wire netting is
used for overhead cross screening, a 3-foot width is used. The
burlap strips are made 2 inches wide and 12 feet long. These
strips are woven once across the netting and back again, leav-
ing two 3-foot ends hanging below. These dangle down and
allow high loads to pass through but obstruct the view to a
6-foot depth.
(3) Plain burlap is suitable for either lateral or cross screen-
ing. It should be used for overhead cross screening if avail-
able on account of its light weight. It should be slashed, as
shown in Figure 7, to cut down wind resistance. Plenty of
holes are necessary to let the wind blow through, and these
should be small and close together, rather than large and un-
duly separated. Otherwise even strong screens will blow
over.
f. Overhead road screening is generally only necessary for
short stretches, and then perhaps only 6 to 12 separate screens
need be erected. This requires poles 20 to 25 feet long, usually
made by splicing 2 short ones. The amount of road screening
necessary to hide all visible important roads from enemy ob-
servers varies widely with the terrain. The opacity necessary
for road screening varies with the distance from the enemy
observer. A good rule is that three-fourths of the surface of
the screening should be opaque.
ENGINEER FIELD MANUAL
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ENGINEER FIELD MANUAL
Figure 6
16
ENGINEER FIELD MANUAL
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ENGINEER FIELD MANUAL
17
16. Snow camouflage. — a. It is virtually impossible to camou-
flage in snow. Time expended in such work is almost wholly
wasted. Available labor is much more profitably expended in
digging under such circumstances. However, if an attempt at
camouflage is insisted upon, it is well to keep the following in
mind : Trails track with mud and snow. They melt out early
and leave a black line. Snow falls through camouflage material
and the holes show dark. It soon melts off the warm roofs of
dugouts.
6. The remedies are as follows :
(1) When snow first falls, keep activity at a minimum. Often
snow soon melts in places and it is only on the first clear morn-
ing that an unbroken white sheet exists. Then enemy aircraft
is unusually active, like hunters after a snowstorm.
(2) Cover trails, dugout roofs, etc., with fresh snow. Renew
this covering as often as needed. Cover parts of camouflage
with something to hold snow and then scatter snow on' this
sheet. The entire surface need not be covered, but the form
should be broken up with the snow.
(3) If any white cloth is available, use this in patches to
cover the camouflage. Cloth in the quantities necessary is so
difficult to obtain that it would probably only be furnished for
areas where snow lies unbroken on the ground for long periods.
17. Observation posts. — a. Observation posts are of two
classes :
(1) For close observation in the trench, system or trenches
themselves.
(2) For distant observation, such as observation posts for
intelligence, for artillery adjustment, or for both.
6. Any observation post which shows artificial construction
is apt to be useless. It will almost certainly be noted and,
when most needed, will be destroyed by the -enemy. Hence,
effective camouflage is especially important for observation
posts. Observation posts should preferably be located in one
of two ways :
(1) Underground where natural folds or slopes allow cham-
bers and loopholes to be made from within, leaving the terrain
undisturbed, access being provided through a shaft or tunnel.
(2) Concealed in some existing structure or object
o. Trench observation posts are useful only when occupied
trench lines are within a few hundred yards of each other. A
standard type of camouflaged provision for such posts consists
18
ENGINEER FIELD MANUAL
of a wire frame with a cement coating, simulating the material
of the parapet. (See fig. 8.) These camouflaged observation
posts have loopholes covere'd with painted wire gauze, and are
placed at the end of a short sap from the trench, the observa-
tion post forming the overhead cover. They are not armored
and depend on their likeness to the parapet for protection.
Posts for close observation located out from trenches are often
spotted by the trails or saps leading to them. These latter
can generally be hidden or they can be given a false objective.
Figure 8. — Camouflaged cover for observation post
d. Observation posts for artillery and intelligence should
have the greatest command possible and may be at considerable
distances back of the lines, equipped with high-power telescopes.
They can often be successfully concealed in old buildings,
cellars, trees, etc. A well-concealed observation post in a tall
tree, in woods subject to gas attacks, is very valuable, for the
observer may remain above the gas long after the woods must
be evacuated by those on the ground. Loopholes for artillery
and intelligence observation posts must be of considerable size
to accommodate instruments and two or three observers. It
is essential that the exterior of the loopholes should be irregu-
lar in shape and the observation post must be so constructed
ENGINEER FIELD MANUAL 19 '
OBSERVATION POSTS
UPPfR. O HE LOCATED IN WOODJ • LOWER.
ONE 111 HEDGE,
Figure 9
20
ENGINEER FIELD MANUAL
that the light from behind may not show through. It is often
necessary to provide a curtain to close the loophole when not
in use.
18. Cave shelters. — a. Dugouts built in deliberately planned
defense lines can be successfully hidden under a cover of camou-
flage, providing the position fits into woods, clumps of trees
or brush, or into broken-up terrain. If the dugouts must be
built in open fields, the camouflage will show up, especially
after exposure for some time, but it is worth while anyway
to conceal the working party and the exact nature and state
of the work. It might be practicable, at times, to use false
work to deceive the enemy as to the connection between these
dugouts and the trench system when the trenches are put in
later.
&. The exact location of dugouts may be concealed by cov-
ering the entrance niche so that it does not show. The disturb-
ance of earth should be minimized and the spoil covered by
sod, brush, or artificial material, which is placed directly on
the spoil and should have a contour very nearly that of the
original surface, or the entire surface in that area should be so
irregularly broken up by scattering the parapet or digging up
the soil, that the dugout roof will be lost in the confusion.
19. Communications. — a. Telephone and telegraph air lines
may be rendered less conspicuous by painting tops of poles
dark green or black, by sodding spoil at the base of poles, and
by cutting the grass close up to the poles when mowing a
field. Telephone lines in trenches are difficult to conceal. The
trench is almost certain to show unless great care is taken in
concealing it. Trenches should be dug under cover of hedge-
rows, trees, etc., when possible. When placed in the open, the
trenches must be concealed by covering with camouflage
material.
6. Roads, railroads, and paths can not be hidden .except for
short lengths, but they can be controlled so that their true
objective is not discovered. Narrow-gauge tracks along the edge
of a road do not show except where the road makes a right-
angle turn. There the railroad curve will show if not covered.
The spur of a railroad, road, or path branching off from the
main road to a military position is generally very important
evidence of the exact whereabouts of the position, and so the
location of this turnout should be selected and hidden care-
ENGINEER FIELD MANUAL
21
fully so as to escape detection. For instance, a spur run into
a wood should, if possible, take off where the main line is
obscured in the woods, or a narrow-gauge spur from a main
line to a battery or dump on' a road should have its turnout
curve hidden under camouflage and then should follow up the
road to the battery,
c. To avoid tracks —
(1) Use existing roads and paths wherever possible.
(2) Build new roads and paths under cover, using natural
cover as much as possible. Do not cover a trail with straight
lines of material. The lines will show. Cover it with irregu-
lar patches, not necessarily contiguous and preferably not of
the same material. For instance, mix brush patches with
artificial material.
(3) Carry new roads and paths past the position to another
road, a house, or a dummy position. Make sure that the road
is used past the true position.
(4) When new paths can not be avoided make them follow
existing lines, such as fences, hedges, ditches, edges of plowed
fields, or the like. Keep the paths narrow and avoid cutting
corners.
(5) Confine traffic to one route. Keep this route narrow and
confine traffic to the route by the liberal use of trip wires.
20. Command, posts. — a. Command posts are important tar-
gets and should be hidden. Arrangements should be made to
cover the vehicles at headquarters with a screen, and a screen
should conceal vehicles stopping at the message center. This
must be done cleverly, otherwise the enemy will soon learn
that a large horizontal screen is a sign indicating a head-
quarters.
&. The location of smaller command posts is apt to be dis-
closed by the telephone lines converging on them. These lines,
whether overhead or in a trench, show, because they are
straight and because they cut across natural lines. The 100 to
300 yard lengths of telephone wires converging on a command
post should be hidden. The telephone trench should follow
along existing ground lines or the uncovered wires should be
laid in an existing ditch or on the bare ground, and the forma-
tion of paths along the wires should be prohibited.
21. Artillery. — a. Artillery batteries may be camouflaged by
an overhead covering of camouflage material erected as de-
22
ENGINEER FIELD MANUAL
scribed in paragraph 13. Seventy-flve-mm. guns and 155-mm.
howitzers require 6% feet headroom from gun pit to camouflage
material. Heavy and medium field artillery require 7% to 9
feet headroom. The higher camouflage material stands, the
more shadow it causes and the greater its visibility. Nets
only 2 or 3 feet above the ground cast very trifling shadows;
hence it is desirable to dig down 3 or 4 feet for light field
artillery and 5 to 6 feet for heavy and medium field artillery.
This, of course, has the additional advantage of providing
protection against shell bursts. Pathways in and around the
battery should be wired off to keep men from cutting corners
and thereby spreading the paths.
6. An embrasure must be provided in the camouflage mate-
rial large enough to permit the guns to fire through required
angles of fire without hitting the inflammable camouflage mate-
rial. There are three main types of embrasures, the split type
which is most common, the rolling embrasure, and the counter-
weighted embrasure. (See figs. 10, 11, and 12.)
o. Blast marks show on aerial photographs as white blurs
in front of each gun. These can be hidden by covering them
with branches held in place by driving a few 12 or 18 inch
stakes at intervals in the blast marks. This camouflage may
have to be renewed frequently. It should be distributed so as
not to cover exactly the blast mark but so as to break up the
pattern.
d. Heavy artillery requires better camouflage than lighter
artillery because it remains in one position longer and re-
quires a more elaborate firing position. A concentration of
heavy artillery can be hidden only partially ; firing positions
are usually very large and very obvious. A railroad spur posi-
tion can be concealed for two or three weeks in case it is
very important that the initial installation and firing be secret.
22. Dumps. — a. In general, dumps are so large and the ac-
tivity around them so intense that their concealment is rarely
practicable. The building of new dumps or the refilling of old
ones reveals plans of attack. A good camouflage measure for
large dumps in rear areas is to scatter buildings irregularly
or to place the buildings in and around woods and clumps of
bushes so as to make poor night bombing targets. A dump
should not be near any landmarks easily visible at night, such
as a large white building or a distinctive body of water. If
ENGINEER FIELD MANUAL
* ' ' - - .: ' -s
MOST COMMOM TYPE OF EMBRASURE
Each half of ZMbRAsuee covee istheown
>6ACfO FOE/ n^M<f
f LAW OF EMBF2A3UEE- SHOWN -A&OVE.
EM5RA5URE TO BE POLLED -BACiO
Figure 30. — Types of embrasure
ENGINEER FIELD MANUAL
• Pf Lv/PCCTlVf •
PfTAIL ■ or£M0XJJu&t
•DfTAIUT-OF -COVNTfiLy WEIGHTED •
■ EMfciCAJ'Ue.e -TO-v/IMULATE-AHEDGC-
vJ'UFFICIENT^ANP &AGv/- TO &ET.
PLACEDAT- LOWER^ eND TO HOLP-
EMPJLAJ'UJLC- VPJLIGHT; FJ (L-MLV-
E>R,AC£ THE- VPR.IGHTJ\ PLACE' •
:OM UPPEEj J"lDt- OF ZMbZsAJ'VRJE
■MAK.E OVEICHAUG-CAMOVHACE IfLUGUlAV-
Figure 11. — Counterweighted embrasure
ENGINEER FIELD MANUAL
<HUBJ)LEJ TO \/f?ilY- lrt-<SIZ£
■ TO ■ FIT- CONDlTlOHJ ■
DETAILS- Of £M£>£AJ-U/l£ MJDF
w/m- e&uj'/t crtfvAux pr- raise
Figure) 12. — Embrasure details
26
ENGINEER FIELD MANUAL
bombing activity becomes intense and effective, large dumps
must be broken up and scattered. This dispersion, of course,
complicates the system of supply.
I). More effective measures must be adopted for the smaller
forward dumps subject to shell fire. These are as follows (see
fig. 13) :
(1) Locate dumps, as far as requirements of service and
the labor of construction will permit, in places favorable for
concealment in woods, in scattered brush or trees, in a quarry,
or, for engineer and ration dumps, in a village. Avoid im-
portant crossroads, a lone building or group of buildings, or
the immediate vicinity of a battery.
(2) Lay out the dump so that the material is scattered and
fits in with the natural features of the terrain as far as pos-
sible. Small artillery dumps may be well concealed and per-
fectly accessible by placing the ammunition boxes irregularly
at the bottoms of hedgerows.
(3) Cover piles of material with sufficient screening to pre-
vent the enemy from seeing the quantity of stores on hand.
(4) Bestrict traffic to a few routes so that tracks will not
indicate the nature of the place. If possible, provide return
routes for wagons and trucks so that their turning will not
mark up the area.
23. Camps. — a. Camps must be located all over the forward
areas, especially during an advance. Shelter tents can usually
be hidden with a reasonable expenditure of effort by placing
them irregularly among bushes and trees and by covering them
over with brush and grass. Out in the open they may be
grouped irregularly under a single cover of artificial camouflage
material or of brush supported on wire.
b. The concealment of troops is much simpler in woods and
villages than in the open, and such locations should be utilized
to the fullest extent. In woods, if not very thick, use over-
head cover of proper color or cover tents with branches or brush,
and avoid all regularity in placing tents or shelters. In
villages, utilize to the utmost capacity existing buildings, walls,
basements, etc. A shelter in a tumble-down or roofless en-
closure may be disguised by leaning broken timbers against
the wall above the shelter to represent fallen rafters, and scat-
tering dirt, brick dust, or debris over the shelter. In yards,
shelters should be scattered and placed near fences, hedges, or
ENGINEER FIELD MANUAL
Figure 13. — Ammunition dump located between two roads on
hillside
66842"— 32 3
28
ENGINEER FIELD MANUAL
trees. Disguise them with paint blotches, mud, or tar, and
throw brush or grass on them. Especially cover up the ends
and entrances.
c. To conceal a bivouac in the open, cover the area with
camouflage material on a standard wire cover. Grass or hay
may be used, as the bivouac is temporary. About 5 square
yards of cover per man is sufficient. The wiring is to be erected
as described in paragraph 13. The wires may serve as sup-
port for tent ridges. In covering any large area, care must be
taken to come exactly to the existing edge of a field. Half
covered fields, or those where edges of cover do not exactly
coincide with existing boundaries, are very evident in photo-
graphs. When a cover occupies exactly the same area as the
field underneath it, even if the color is not exactly the same,
it appears in photographs as though some normal agricultural
development had taken place.
d. Large tents can be treated in exactly the same way as
shelter tents. The irregular grouping of the tents to fit in
with existing concealment is the most essential feature. j(See
fig. 14 ® and ®.)
24. Buildings in general. — a. Buildings, on account of their
height, always cast strong shadows and, as they have rectangu-
lar forms, are easily picked out on aerial photographs. It is
almost impossible to conceal a building, except a very small
one, so that it will not show in a photograph. Therefore the
siting of buildings is of the greatest importance, and no build-
ing layout in forward zones should ever be drawn up without
considering carefully all camouflage measures.
Z>. Eighty per cent of the value of the camouflage of buildings
lies in their correct location.
(1) Woods should be used for locations of buildings to the
utmost possible extent.
(2) If scattered clumps of trees or bushes exist, tie the
buildings into them ; avoid the open as far as possible. Never
arrange buildings in rows nor space them regularly.
(3) If one building in a regular layout be detected, the
whole group can easily be destroyed by bombing.
c. A flat-roofed building is less visible than a peak-roofed
one, because, with the sun on one side, the hard straight line
in the latter between the side in light and that in shadow is
very conspicuous.
ENGINEER FIELD MANUAL
® DETAIL ELEVATION
tiyirjr r?/rrr.
TENTS
SMALL TMTS GROUPED UNDER ONE WAS* OF
OMOl/FLAGE UR.QF TEMTJ WITH WIRESET1
COVERFp WITH t>WH.
Figure 14
30
ENGINEER FIELD MANUAL
d. If new boards, bright tin, or corrugated iron are used for
roofs, they must be painted in a flat color or daubed with tar or
mud to remove the shining or conspicuous color. Old boards
are better than new; rough boards are better than dressed.
Tar paper is a good covering. The rougher the surface the
less conspicuous the building is in the photograph.
e. After any conspicuous color in buildings is neutralized,
bushes and brush should be piled irregularly on the roof. It is
not necessary to cover it entirely, but by letting some brush
extend beyond the roof lines the rectangular form is broken up.
Increase this breaking up of form by placing bushes or brush
on the ground, extending irregularly from the building. As
the airplane view gives the appearance of flattening out all
objects in the landscape, this method, if well carried out, will
give the appearance from the air of bushes or blurs and render
it almost impossible to distinguish objects clearly enough to
bomb them.
25. Airdromes. — Airdromes are subjected to severe bombing.
They are the favorite target of enemy bombers. The camou-
flage measures to be adopted consist in the irregular scatter-
ing of the hangars and barracks to fit the concealing features
of the terrain and, if need be, in reducing the visibility of the
individual hangars by covering them with a dull rough sur-
face. The whole gives a target hard to locate in the first
place, and hard to hit if it is located. Hangars and barracks
are very often successfully hidden in woods. However, they
should not be concentrated in a small wood or along an edge
of a wood, because a wood is visible at night and if one is
known to be fully occupied it can be bombed with effect. It is
better to scatter the hangars widely ; some in woods and some
off alone in the open. This scattering of hangars and locating
them in places favorable for concealment are facilitated by
locating hangars 300 to 500 yards from the flying field and
taxying the machines between the hangars and the field. Tar-
ring roads leading to the airdrome aids materially in
concealment.
26. Camouflage in open warfare. — a. Effective camouflage is
a far more difficult problem in open warfare than in a stabi-
lized position, inasmuch as the requisite time and labor are
more available in the latter case, and because it is more diffi-
cult to conceal moving objects than stationary ones. Also, it
ENGINEER FIELD MANUAL
31
is more important to conceal stationary objects. However, the
principles of camouflage apply equally to open warfare and,
while their proper application is less vital than in stabilized
situations, it is nevertheless important. It is impossible to
conceal from a reasonably alert enemy, especially if he pos-
sesses a good air force, that there is activity of some kind tak-
ing place in a certain area. The problem therefore is to de-
ceive him, not as to the presence of our troops in this area,
but as to the nature of our operations, the exact location of
individual units and the extent of our strength, and to supple-
ment this deception with such measures of concealment as may
be applied.
&. Dummy bases, dumps, camps, railways, and other mili-
tary essentials, not too well nor too slovenly camouflaged, may
be advantageously employed to mislead the enemy as to our
numbers, dispositions, and objectives.
Table I. — Transportation of camouflage materials
Article
Unit
Weight
per unit
in
pounds
Number of units per load
Escort
wagon
1-ton
truck
2-ton
truck
3-ton
truck
Burlap
Wire netting (with stripped bur-
lap).
Wire netting (chicken wire) 1J4-
in. mesh.
Fish uet 32 ft. by 40 ft
32 ft. by 32 ft._
Fish nets
Poles 12 to 15 ft., top diameter 2 in.
Stakes 3 ft. long, diameter 3 in
Wire, smooth, No. 8 to No. 16
yd.
Sq. yd
20 sq.
roll.
100 by 3 foot
roll.
Per net
do
Per sq. yd...
Each
do.
250 ft. coil...
1.2
42
60
140
115
1
115
8
100
1, 100
30
30
10
12
1,200
18
250
20
1, 100
30
30
10
12
1,200
18
250
20
1, 600
60
60
20
24
2,400
36
500
40
1, 875
100
35
3,600
54
750
60
27. Reference data. — a. Road camouflage. — Bill of materials
for one mile of lateral road screening, 12 feet high :
3-ton
truck loads
360 each, poles, 12 to 15 feet, top diameter 2 inches 5
750 each, stakes, 3 feet long, diameter 3 inches 3
30,000 feet smooth wire, No. 9 to No. 16 2
1,800 yards fabricated brush rolls, 12 feet wide 24
Or 7,200 yards burlap, plain, 36 inches wide 1
Or 3,600 yards wire-netting camouflage, 6 feet wide 3
Vi keg staples or nails.
32
ENGINEER FIELD MANUAL
6. Overhead camouflage. — Bill of stakes and wire required
for supports for each 1,000 square yards of camouflage
covering :
17 stakes, 2% feet long and 3 inches in diameter.
(67 poles, 5 to 8 feet long, 3 to 4 inches in diameter.
1.8 rolls wire No. 8, No. 9, or No. 10, smooth.
1.2 rolls wire No. 14 or No. 16, smooth.
5 pounds nails.
CHAPTER 2
FIELD FORTIFICATIONS
Paragraph
Section I. Principles of field fortification 28- 34
II. The effects of projectiles 35- 41
III. Underground water and its relation to fleldworks — 42— 44
IV. Standard types of fleldworks 45- 78
V. Protected shelters 79-145
Section I
PRINCIPLES OF FIELD FORTIFICATION
28. Organization of the ground. — a. Definition. — The organ-
ization of the ground is the utilization of the terrain to secure
the most effective tactical disposition of the troops thereon by
taking advantage of the naturally defensive features and im-
proving them by the use of field fortifications.
6. Composition. — A defensive position consists of a system of
mutually supporting defensive areas or tactical localities of
varying size, each with a definite assignment of troops and
mission.
c. Sectors. — The commander of a force on the defensive di-
vides his front into sectors and assigns them to the several units
for occupation, organization, and defense. The sector in the de-
fensive corresponds to the zone of action in the offensive. While
the extension of sector boundaries to the front defines the re-
sponsibilities of the several units for distant defense, the fire
of units for close defense can not be restricted to lanes leading
straight to the front. Each unit on the defensive must also be
given the definite mission of covering the front of adjacent units
by flanking fire in close defense. By application of the princi-
ple of mutual support, dead spaces are eliminated, and all parts
of the terrain immediately in front of a position are covered
by the fire of the defense.
d. Combat groups. — The combat group is the smallest tacti-
cal locality. All other tactical localities are made up of com-
bat groups. It is occupied by a force varying from a squad to
a platoon, disposed in groups of from four to eight men, to
33
34
ENGINEER FIELD MANUAL
cover by fire a definite portion of the terrain. The funda-
mental principle of the defensive tactics of the combat groups
is that each combat group should be able to cover by fire its
own front, the fronts of the adjacent combat groups of the
same echelon, and the unoccupied intervals between it and
these adjacent combat groups.
e. Strong points. — A strong point is composed of several com-
bat groups disposed laterally and in depth and commanded gen-
erally by a company commander. The garrison of a strong
point is usually a company, but it may be held by a force
varying from two platoons to two companies, depending on
the terrain and other conditions. The combat groups of a
strong point are located with a view to resistance to the front
and flanks and, if necessary, to the rear. When fully organ-
ized a strong point should be capable of a protracted all-around
defense.
f. Line of resistance. — The line of resistance of any defensive
position is the line on which the principal defense of the posi-
tion is made. It usually is the forward line of the combat
echelons. After long occupation it may develop into a continu-
ous trench or parallel. The line of resistance of the principal
defense or battle position of a defensive system is called the
main line of resistance and is the base or reference line which,
governs the location of all elements of the defensive system.
g. Support line. — Long occupation of a position generally will
lead to the construction of parallels connecting the combat
groups in support of the line of resistance. This line of
trenches, practically continuous, and from 100 to 300 yards in
rear of the line of resistance, is known as the support line of
the position.
h. Centers of resistance. — A center of resistance is composed
of several strong points disposed laterally and in depth and
commanded by a single officer, generally a battalion com-
mander. The garrison of a center of resistance is usually a
battalion, but in exceptional cases may consist of a battalion
with one or two rifle companies attached. One or more
(usually two) of the rifle companies are located on the line
of resistance and the remainder of the garrison is held in
battalion reserve. The function of the battalion reserve is to
counterattack when the integrity of the center of resistance
has been seriously threatened. Should the tactical situation.
ENGINEER FIELD MANUAL
35
prevent counterattack, the reserves must stop or delay the
further advance of the enemy and must accordingly be pre-
pared for defense to the front, flanks, and rear. Therefore
they organize strong points so located as to afford mutual
support with reserve units of adjacent battalions and to cover
the foreground by fire at least as far to the front as the
supports.
i. Battalion reserve line. — The general line on which the for-
ward elements of companies in battalion reserve are disposed
is called the battalion reserve line. This line is from 400 to
900 yards in rear of the line of resistance (300 to 600 yards
in rear of the support line). Some of the combat groups should
be on the forward slope of commanding ground in order to
cover the foreground by fire at least as far to the front as the
support line and to render mutual support between adjacent
strong points. Between the strong points the battalion reserve
line may be located on the reverse slope, and such location
may be advantageous for the formation of counterattacks.
Regimental reserve line. — In the defensive the regiment
deploys with one or two battalions as combat or first line bat-
talions and one or two reserve battalions. The combat bat-
talions organize centers of resistance as described heretofore.
The primary mission of the regimental reserve is to maintain
the integrity of the sector of the battle position held by the
regiment and its principal means is the counterattack. To
meet a situation where the centers of resistance in front have
been overrun by the enemy and the counterattack is not prac-
ticable, the regimental reserve organizes for stubborn resistance.
The organization usually consists of a row of strong points
prepared for all-around defense and located not only for mu-
tual support between themselves and the regimental reserve
units of adjacent regiments but also for the support of front
centers of resistance, particularly their flanks. The general
line on which the forward elements of companies in regimen-
tal reserve are disposed is called the regimental reserve line.
It is usually located from 400 to 900 yards in rear of the
battalion reserve line, 800 to 1,800 yards in rear of the line of
resistance. Due to the necessity of covering the foreground
by fire at least as far as the battalion reserve line and render-
ing mutual support between adjacent strong points, some of the
combat groups of the strong points organized by the regimental
36
ENGINEER FIELD MANUAL
reserve should be on the forward slope of commanding ground.
In the intervals between strong points the regimental reserve
line may be located on the reverse slope should the terrain
be favorable. Machine guns located on the regimental reserve
line should be able to place defensive fires in front of the line
of resistance.
29. Battle position. — The term battle position is applied to
the belt of ground organized as above described consisting of
three approximately parallel rows of strong points as follows :
A forward row of strong points embracing the main line of
resistance and the support line, a second row of strong points
embracing the battalion reserve line, and a third row embracing
the regimental reserve line.
30. Outpost area. — The enemy situation permitting, every
battle position should be covered by an outpost to the front.
The area in front of the main line of resistance of the battle
position occupied by the outpost is called the outpost area.
When practicable the line of resistance of the outpost in posi-
tion defense should be located at least 1,500 yards In front
of the main line of resistance in order to prevent the enemy
from emplacing machine guns within reach of the latter.
31. Reserve battle position. — In any defensive situation the
commander must always consider the possibility of defeat in
the selected battle position and the necessity of continuation
of the defense farther to the rear. Such a position is desig-
nated as the reserve battle position.
32. Switch, positions. — In addition to the several positions or
organized areas of a defensive zone paralleling the front,
additional positions are provided oblique to the front and con-
necting the forward position or areas with those in rear. These
oblique positions, designated switch -positions are established
on the flanks of localities in the defensive system where, due
to lack of natural defensive strength or for other reasons, there
is a probability of an enemy penetration.
33. Defensive works. — The defensive works constructed con-
sist of:
a. Machine-gun emplacements and fire trenches located, con-
cealed, and constructed to develop the fire power of the de-
fenders and to protect the occupants from the effect of hostile
fire.
6. Obstacles so located as to be covered throughout by the
fire of the defense (otherwise they are of no value) and to
ENGINEER FIELD MANUAL
37
hold the attacking forces under the effective fire of automatic
weapons. The bulk of the obstacles used in the organization
of a battle position are artificial, and of these the wire entangle-
ment furnishes the best obstacle for the least expenditure of
time and labor.
c. Approach trenches. — Approach trenches are constructed
approximately perpendicular to the front to provide covered
communication between the front and rear elements of a
defensive position.
d. Switch trenches running obliquely between trenches paral-
leling the front of a battle position and the approach trenches,
particularly between the battalion and regimental reserve lines.
A switch trench differs from an approach trench in that it is
located primarily for combat, though it may also serve as a
communication trench.
e. Observation posts. — As required.
f. Command, posts. — As required.
g. Aid stations. — As required.
h. Communications. — In a defensive system, where roads and
trails do not exist or are inadequate, a sufficient number must
be constructed or existing ones must be improved to provide
adequate means for the prompt movement of reserves, for the
bringing forward of supplies and ammunition, and for the
evacuation of wounded and of salvaged materials. When a
stream lies within or closely in rear of the battle position,
numerous crossings, supplementing those at the established
toads, should be provided in order to facilitate the movement
of troops across country and to provide alternative stream
crossings in case those on established routes of traffic are
shelled.
i. Shelters designed to protect the defenders from the con-
centrated fire of the enemy.
j. Dummy works may be constructed and occupied areas
connected by dummy trenches in order to confuse the enemy
as to the defensive dispositions.
34. Relative importance of works. — a. The positions or areas
of a defensive system should generally be organized in the
following order :
(1) The battle position;
(2) The outpost area;
(3) The reserve battle position;
(4) Switch positions;
38
ENGINEER FIELD MANUAL
but the order of importance may be changed by the situation,
as, for example, in taking up the defensive following an offensive
the organization of the battle position and that of the outpost
area are practically of equal importance.
b. (1) The relative importance of the elements of organiza-
tion of a battle position may be taken as follows :
(a) Machine-gun emplacements.
(b) Reasonable field of fire.
(c) Fire trenches on line of resistance and support line.
(d) Continuous obstacle in front of line of resistance.
(e) Obstacles protecting combat groups of front line strong
points.
(f) Temporary command posts, observation posts and aid
stations, and routes of communication.
(g) Completion of trenches and obstacles in front line strong
points. Shelters.
(h) Fire trenches and obstacles on battalion and regimental
reserve lines.
(i) Completion of trenches and obstacles in centers of
resistance.
0) Permanent command posts, observation posts, aid sta-
tions, and shelters.
(fc) Completion and improvement of trenches and obstacles
in the position.
(2) The foregoing list should not be taken to mean that
each item of work is completed before the following item is
begun. In practice, work proceeds simultaneously on several
items. Those items which can usually be completed within six
hours, and which may be said to fall in first group priority,
include —
Machine-gun emplacements (open type).
Reasonable field of fire.
Squad trenches, simple standing type on line of
resistance.
Continuous obstacle in front of line of resistance.
Shallow connecting trenches between squad trenches on
lines within combat groups.
Command posts ; observation posts ; aid stations.
Camouflage.
ENGINEER FIELD MANUAL
39
Section II
THE EFFECTS OF PROJECTILES
. 35. General. — The penetration and effects of small-arm and
artillery projectiles are very variable. Fortifications must be
designed with large factors of safety. However, maximum prob-
able penetrations and effects must be kept in mind, so that
works may be strong enough to resist the fire that can be
brought against them without an unnecessary expenditure of
labor and material.
36. Penetration of rifle bullets. — a. The United States Army
rifle, M1903, caliber .30, is a fair example of the small arm
used by the various nations. It can be fired at a maximum rate
of 20 shots per minute. With the present 150-grain bullet it
has a flat trajectory giving a wide danger zone at all prob-
able ranges. The maximum ordinate at 500 yards is 2 feet ; at
1,000 yards, 14.5 feet ; and at 2,500 yards, 271 feet. The new
boat-tail bullet, weighing 172 grains, gives a flatter trajectory
and a much greater range.
&. The following table gives approximate maximum penetra-
tions in various materials of the 172-grain bullet, which are
somewhat greater than the penetrations of the service 150-
grain bullet:
Table II. — Maximum penetration of 172-grain tmllet in inches
Material
Range
200 yards
600 yards
1,500
yards
Armor .-. ---
0. 30
0.10
0. 10
8.00
7.00
6.00
4.00
4. 00
4.00
Concrete, 1-2J4-5 mix . . _ _.
1.65
1.20
1.10
Oak.._
20.00
20.00
12.00
12.00
11.00
11.00
27.00
27.00
27. 00
60.00
40.00
30.00
1 Greater penetrations may occur when bricks are laid in soft mortar and bullets
strike in mortar.
37. Penetration of automatic rifle and machine-gun bul-
lets. — a. Caliber .30 automatic rifle and machine-gun bullets
have the same penetration as rifle bullets.
40
ENGINEER FIELD MANUAL
b. Caliber .50 machine-gun bullets penetrate at short range
up to 1 inch of special steel (tank) armor.
38. General rule for the penetration of armor by small-
arm bullets. — It may be taken as a general rule that specially
designed armor-piercing rifle and machine-gun bullets at their
most favorable ranges can penetrate special steel (tank) armor
twice their caliber in thickness, and that armor of greater
thickness gives protection against them.
39. Penetration of 37-mm. projectiles. — a. The 37-mm. pro-
jectile fired from the service piece with a muzzle velocity of
1,300 feet per second penetrates 0.625 inch of special steel
(tank) armor at 300 yards range.
6. A projected 37-mm. gun having a muzzle velocity of 2,000
feet per second has been tested and penetrates 1 inch of special
steel (tank) armor at 300 yards range.
40. Effects of artillery fire. — a. Light artillery projectiles,
75-mm. (3-inch) to 105-mm. (4-inch), inclusive, produce in-
appreciable effects upon trenches and shelters, but are most
effective against exposed personnel by reason of their frag-
mentation.
b. Medium and heavy artillery projectiles, 4.7-inch (120-mm.),
to include the heaviest types, are used for the destruction of
shelters, trenches, and other types of fortifications. The fol-
lowing table gives some conception of their relative effective-
ness, but it must be borne in mind that craters vary greatly
with the nature of the soil and depth to which the shell pene-
trates before explosion. This penetration is dependent upon
both the kind and setting of the fuze and also upon the soil.
The tabular dimensions must be considered as average.
Table III. — Probable crater dimensions in feet in virgin soil
Penetration 1 to 2
Penetration 3 to 4
lengths
lengths
Caliber
Diameter
Depth
Diameter
Depth
156-mm. (6-inch)
11.8
3.5
11.5
5.0
220- mm. (8.7-inch)
15.0
4.5
18.0
7.5
370-mm. (14.6-inch) _.
20.0
7.0
33.0
20.0
41. Effects of trench mortar and airplane bombs. — a.
Trench mortar bombs have a high angle of fall and can reach.
ENGINEER FIELD MANUAL
41
defiladed objects. Due to their low velocity, they have little
penetrative power. On the other hand, they carry heavier
bursting charges than artillery projectiles of corresponding
weight and caliber. They are consequently especially effective
•when used against entanglements or other obstacles, and pro-
duce serious destructive effects when they fall within trenches.
&. Airplane bombs have low velocity and little penetrative
power. They carry heavy bursting charges, produce many frag-
ments, and are frequently of large size. The present tendency
is toward an increase in size and destructive power. They
have in the past been used chiefly against large targets in rear
of the combat units; for example, concentrations of reserves,
roads, and railroads, ammunition and supply dumps, higher
headquarters, cantonments, and cities.
Section III
UNDERGROUND WATER AND ITS RELATION TO
FIELDWORKS
42. General. — The possible presence of underground water
should always be considered before starting the construction of
extensive fieldworks. In some localities it is so close to the
surface that even the simplest trench digging can not be under-
taken and all defensive works have to be parapets, breastworks,
or other structures built entirely above the ground level.
43. Forms in which underground water occurs. — a. Under-
ground water occurs in three forms: As a saturated zone at
the surface, as ground water, and as water-bearing horizons.
(1) Saturated surface layers. — Saturated surface layers are
found in localities where the formation underlying the subsoil
is impervious. Such formations usually consist of clay or rock
containing a considerable percentage of clay. If this under-
lying rock is entirely impermeable there will be dry ground
below and cave shelters may be built by sinking through the
saturated ground into the dry ground below taking care to
seal the shaft through the saturated layer. Such a procedure
is not recommended, however, and should be utilized only when
shelters can not be located elsewhere. The surface zone of
saturation is usually deepest on the flats and shallowest on
the slopes and summits. Its total depth will rarely exceed 5
to 7 feet and will vary somewhat with the season. Hence
shelters constructed during the summer may be dry when
42
ENGINEER FIELD MANUAL,
constructed, only to be flooded during the winter. Flood plains
of streams are usually saturated at certain seasons and should
be avoided as much as possible when planning fieldworks.
(2) Ground water. — The upper surface of ground water in
localities where it occurs is roughly parallel to the surface of
the ground. The depth to the ground water surface depends
chiefly on the character of the rock formation and the quantity
of rainfall. In pervious or almost pervious strata the zone of
saturation is usually below the depth required by military works,
while impervious or only partly pervious rocks hold the water
near the surface. Depth also varies according to the season.
In general the depth from the ground surface to the upper level
of ground water is a maximum in the spring and a minimum
in the fall and may vary as much as 10 to 12 feet. It may be
determined by examining wells and springs or by sinking some
shafts or bore holes. No fieldworks can be maintained below
the upper level of the ground water.
(3) Water-bearing horizons. — Water-bearing horizons are
formed when a pervious or fractured stratum is contained be-
tween two impervious layers. Such a formation seriously
interferes with the construction of underground works and may
prohibit them if the amount of water is considerable. The base
of a limestone formation resting on clay is almost invariably a
locus of water.
b. Faults. — A fault is a dislocation of geological formation
caused by a slipping of rock masses along a plane of fracture.
If a fault traverses a water bearing bed which is under hydro-
static head the water may reach the surface or may penetrate
a zone of fracture along the fault, forming a saturated zone of
considerable width. The siting of trenches or cave shelters
across or near faults should be avoided unless it has been estab-
lished that the faults are not water bearing.
44. Investigation for ground water. — Geological maps, if
available, assist in investigating for underground water. It
should be understood that the data they show are general in
their application and that any specific location should be in-
vestigated on the spot. The presence of underground water
and the ground formation can best be determined by test pits
or bore holes, and such tests should be made before any exten-
sive fieldwork construction is undertaken. Outcroppings of
underground water in the form of springs and swamps and
local wells indicate the location of the ground-water level.
ENGINEER FIELD MANUAL
43
Section IV
STANDARD TYPES OF FIELD WORKS
45. Clearing field of fire. — a. Large scattered trees, if left
standing, give less cover to an attacker than if cut down, and
are sometimes useful as range marks. Unless they can be
entirely removed or converted into dead abatis, only the lower
branches should be cut off. Thick brushwood left standing
may sometimes serve as an obstacle, but infantry can usually
pass with ease any but the thickest growth of this kind.
Therefore it is imperative to clear such growth. It is rarely
possible or desirable to undertake the wholesale clearing of
woods, and the work is usually restricted to clearing the under-
growth and removing the lower branches of the larger trees.
Narrow lanes running obliquely in front of a line to be de-
fended may be entirely cleared through woods and swept by
machine-gun fire.
i>. The following tools will be found useful in clearing
woods : Double-bitted axes, brush hooks, canthooks, hatchets,
machetes, mattocks, and cross-cut saws. In situations whete
extensive clearing is necessary those classes of the above tools
not found in quantity in the equipment of combat units should
be procured from the larger engineer supply establishments.
Large trees may be cut down by the use of explosives, but
the lack of large quantities of explosives for this purpose ordi-
narily makes it impracticable.
o. The following figures will be found useful in estimating the
time required for a given job of clearing. The unit in each
case is 100 square yards.
(1) Area is covered with, brush up to 6 inches in diameter
and contains about 25 trees, 6 inches to 2 feet in diameter:
Chopping or sawing down trees and clearing brush, 5% man-
hours.
(2) Area is covered with undergrowth and some small trees
not exceeding 12 inches in diameter : Chopping or sawing down
trees and clearing brush, 2 man-hours.
(3) Area is covered only with small brush : Clearing, 1
man-hour.
46. Trench traces. — Five standard trench traces are shown
in Figure 15 : The traversed, wavy, octagonal, zigzag, and
echelon. The one most suitable to the tactical situation and
66842°— 32 4
.44
ENGINEER FIELD MANUAL
the terrain should be employed, combinations and modifications
being made to meet the requirements of special conditions.
47. Standard trench profiles. — a. Trenches constructed in the
face of the enemy and under difficult conditions necessarily
vary in profile in order to meet those conditions, but standard
profiles are prescribed for use except where Unusual conditions
require modification or do not admit of complete execution.
The standard profiles shown should be used in all instruction
"17
General trace
tine
J-
Traversed
General trace tine
16 I 6 16
- — paces — spaces?* — paces
J.n:n- 13-0 \ 4-0'
liL
•es — A
-p x
//^Qenerat trace >^
Oct agonal
The angte the diagonal makes
with front is variable! to
conform with ground
requirements and'enetny
Echelon
Figure 15. — Standard trench traces
and training. They give a comparatively wide trench. Experi-
ence teaches that the advantage of additional protection offered
by a narrow trench is more than offset by the freedom of cir-
culation provided by the wider trench and by the fact that
the wider trench is not easily blocked by cave-ins. Officers
and men should familiarize themselves with these profiles so
as to avoid confusion and loss of time in constructing trenches
under difficult conditions. Figure 16 shows the terms adopted
for the various parts of a standard trench. The standard pro-
ENGINEER FIELD MANUAL
45
files are shown in Figures 17 to 23. The development of a
simple standing trench into the A or B standard type is shown
by Figure 20.
h. The following remarks apply to the standard profiles.
(1) The simple standing trench (fig. 17) is unrevetted and
provides no room for circulation in rear of the firing line. It
Enetnp
J^eOefment
sprain
Figure 16. — Trench nomenclature
is the first profile sought when trenches must be constructed
rapidly, but should be developed to type A in order to provide
better cover and communication, as soon as time, labor, and
material permit.
^l-S'-Jr' 4-0"
}
Figure 17. — Standard profile, simple standing trench
(2) Type A (figs. 18 and 21) is unrevetted (except for the
parapet of the fire trench and the fire step) and therefore is
the standard for hard ground, where the excavated slopes will
stand without revetment. In soft ground this profile should be
developed to type B as soon as time, labor, and material permit.
(3) Type B (figs. 19 and 22) is deeper and wider than type
A, with the lower half of the trench revetted throughout with
46
ENGINEER FIELD MANUAL
A-frame supports and the upper half unrevetted, with wide
berms on easy slopes -so as to avoid blocking of the trench by
cave-ins under shell fire.
Figdrb 18. — Standard profile, fire trench, type A
c. Figure 23 shows a wide communication trench (type C)
used in special cases for main thoroughfares in order to provide
ample room for the increased traffic, Utter bearers, etc.
Figure 19. — Standard profile, fire trench, type B
d. The berms at top of A-frames (see figs. 22 and 23) may
be omitted at first, if necessary to save time and labor, and
the ground above sloped as shown by broken lines in the draw-
ings. These berms, however, should be constructed as soon
as opportunity affords, in order to prevent the earth above from
falling into the bottom of the trench and blocking the drain.
e. The height of parapet adopted as a standard for fire
trenches (1 foot 6 inches) should be varied to suit conditions
ENGINEER FIELD MANUAL
47
of terrain requiring more command, or where ground water
or hard rock is encountered, making the excavation of the
trench to full depth impossible. In such a case the profile of
Rtrados
C* 3sa.ft.Exc.
^)irt from C disposed of at C
- ■ A ■ - -A'
- J>
-Simple standing trench, showing development into stand-
ard fire trench, types A and B
Figure 20.-
the trench, except for the parados, will remain the same, all
parts of the trench bearing the same relation to each other,
although the distance of any particular part above or below
ground level will vary from the distance shown on the drawings.
Figure 21.-
Ground Line^
IKSsfttExc
J Jbr use Without A. Fhitnes
Also shows development to type J)
U_ i
-Standard profile, communication trench, type A
f. The fundamental dimensions of standard profiles are —
(1) Height of fire crest above fire step — 4 feet 6 inches.
(2) Height of parapet — 1 foot 6 inches.
(3) Height of parados — 2 feet.
(4) Depth of type A trenches — 5 feet.
(5) Depth of type B same as A plus 1 foot for A-frames —
6 feet.
(6) Bottom width of all trenches (except broad communica-
tion trench) — 2 feet.
(7) Width of all herms (including fire step) — 1 foot 6 inches.
48
ENGINEER FIELD MANUAL
(8) Uwrevetted slopes (in excavation) — approximately 3 on 1.
(9) The excavated profile for type A fire trench — same as
that required for type A communication trench, except for the
additional excavation necessary to provide a 1% foot fire step.
(10) The excavated profile for type B fire trench — same as
that for type B communication trench.
Figure 22. — Standard profile, communication trench,- type B
(11) Kuling dimensions (top width by depth) :
Fire trench Communication trench
Type A, 6y 2 by 5 feet 5 by 5 feet
Type B, 8 by 6 feet 8 by 6 feet
Figure 23. — Standard profile, communication trench, type C
48. Breastworks.— If the need for additional command, or
the presence of water, rock, or very hard material, makes the
construction of standard trenches impracticable, breastworks
must be constructed. The profile of the breastworks should
approximate the standard trench profile as nearly as possible.
A parados should be constructed to protect against the back
blast and fragments from shells. In some cases the entire pro-
ENGINEER FIELD MANUAL
'49
tection above the fire step may be constructed in fill and be
revetted, as shown in Figure 24. Traverses are provided as in
standard trenches. Careful provision for drainage in wet soils
may greatly reduce the height of the breastworks and conse-
quently the labor required for their construction.
49. Trench intersections. — An approach trench should enter
a traversed parallel at the rear of a traverse. If it continues
beyond the parallel it should leave it at a point not less than
25 yards from the point of entrance. The trace of the parallel
between these two points should be modified to provide easy
communication. A better solution is to provide two independ-
ent crossings, in order that traffic may not be blocked if one of
these crossings is destroyed.
JJornm Pit vitk
tntanaiement. Pit-
h
Gabions-^ SSH*** ^^M^/y/Z/^f I stioufd t>c flooded
Figure 24. — Breastworb in wet soil
50. Length of excavation for a given general trace. — If the
length of the general trace of a trench line is known the actual
length of trench to be dug may be found by multiplying by the
appropriate coefficient, as follows :
Type of trench trace Coefficient
Traversed. 1. 33
Octagonal. 1. 09
Zigzag. 1. 07
Echelon. 1. 08
51. Estimates of time, labor, and tools. — a. Table IV gives
figures for use in estimating time, labor, and tools required for
trench construction. It is applicable to day work by inexperi-
enced men using pioneer tools. The figures given represent the
best performance that can be anticipated from large groups of
soldier labor.
6. Estimates must be reduced from the totals indicated by
Table IV for night work, rain or other unfavorable weather
conditions, and annoyance by enemy fire, in the discretion
and based upon the experience of the estimating officer. Night
work is about one-half as effective as day work. Night work
50
ENGINEER FIELD MANUAL
should be planned to take full advantage of moonlight hours,
and the duration of the moon and probable cloud conditions
should be carefully considered when preparing estimates.
Table IV. — Day work, single relief, using pioneer tools 1
Soil
Number cubic feet of excavation per man in—
1 hour
2 hours
3 hours
4 hours
5 hours
6 hours
7 hours
8 hours
Hard -._
Medium _.
Soft 3 __.
15
23
30
24
37
50
32
49
66
40
60
80
47
71
94
54
81
108
61
91
121
67
100
133
' This table contemplates a rest of 10 minutes every hour after the first hour.
' All must be loosened with a pick. Requires 2 picks to 1 shovel.
! Requires little or no picking. Requires 1 pick to 2 shovels.
Table V. — Hours required, to complete Sty-foot and 5-foot tasks;
or if not completed, percentage finished in 8 hours (day work,
using pioneer tools)
Nature of soil
Type A unrevetted
Type B revetted
Fire trench
Communication
trench
Fire and communi-
cation trench
One re-
lief
Two re-
liefs
One re-
lief
Two re-
liefs
One re-
lief
Two re^
liefs
3M
feet
5
feet
m,
feet
5
feet
3M
feet
5
feet
3M
feet
5
feet
feet
5
feet
3K
feet
5
feet
85%
6.5
6.0
Very hard
Average...
Light...
90%
5.25
3.5
60%
8.0
5.75
5.5
3.5
2.5
7. 25
5.0
3.5
7.0
4.0
3.0
80%
6.5
4.5
4.0
2.75
2.0
5. 75
4.0
3.0
70%
7.5
5.25
50%
70%
90%
6. 75
4.5
3.5
52. Bevetments. — a. A revetment is a retaining wall or fac-
ing for maintaining earth slopes at a steeper angle than their
natural angle of repose.
b. Revetments may be classified as follows:
(1) The retaining wall type, which is self-supporting and acta
on the gravity principle for retaining walls. It is largely used
in connection with fills, parapets, and breastworks.
(2) The surface or superficial type, which must be supported
and acts largely by protecting the revetted surface from the
ENGINEER FIELD MANUAL
51
disintegrating and erosive effects of weather and from abrasion
due to occupation of trench. When strongly constructed it
may also serve to retain loose materials and prevent settlement.
It is principally used in cuts.
c. A good revetment must possess the following qualities :
(1) Simplicity of detail.
(2) Adaptability to available materials.
(3) Ease of fabrication and erection.
(4) Low fragmentation under shell fire.
(5) Ease of removal from obstructed trenches.
d. In general, revetments should be constructed only when
obviously required and should not be more extensive than
necessary. They require a great deal of labor and material
and should, therefore, be avoided if possible. On the other
hand, during long occupation of trenches and when time, labor,
and materials are available, extensive revetments make the
garrison more comfortable and reduce maintenance.
e. If the sides of the excavation are carefully sloped the
amount of revetment required is greatly reduced. Uneven-
ness causes rain to lodge in or erode the surface, to soak into
the earth, and results in the rapid disintegration of the slope.
The steeper the slopes of a trench are the greater is the need
for revetment to prevent them from caving.
f. The interior slope of the parapet of fire trenches (not the
entire front slope) is always revetted. In addition, only the
lower 2 or 3 feet of a trench usually require revetment. For
standard profiles, as illustrated by Figures: 18 to 23, inclusive,
this involves revetment to the level of the fire step or lower
berm. Such revetment supports portions of the trench subject
to the most wear, preserves drainage, is seldom injured by the
enemy's fire, and preserves the profile of the bottom of the
trench for clearing after a cave-in.
53. Retaining wall types of revetment. — a. As these revet-
ments must be self-supporting, they should always take the
form of a properly built retaining wall. The thickness at any
level should be at least one-half the remaining height and
the average thickness not less than one-third of the total
height.
b. Sandbag revetment is easily and quickly constructed, does
not splinter from shelling, and is especially useful for emer-
gency work, for repairs, crowning, and revetting the interior
slopes of parapets.
52
ENGINEER FIELD MANUAL
c. (1) The standard sandbag is 14 by 26% inches flat,
with an attached tie string 3 inches from the top of the bag.
When filled three-fourths full each bag weighs from 45 to
75 pounds, depending upon the material and whether it is wet
or dry, averaging approximately 65 pounds, and fills a space
approximately 4% by 10 by 19 inches. Thus 10 linear feet of
parapet revetment, as illustrated in Figures 18 and 19, require
Figure 25. — Sandbag revetment
48 sandbags, and 10 linear feet of revetment for front slope
and parapet, as illustrated by Figure 25, require 156 sandbags.
(2) Sandbags 18 by 32 inches flat have been issued in the
past. When filled three-fourths full they weigh approximately
135 pounds and fill a space approximately 6 by I6V2 by 25
inches. A small sandbag 12% by 25 inches flat was extensively
purchased during the World War. When filled three-fourths
full it weighs approximately 45 pounds and fills a space
approximately 4 by 9 by 18 inches.
ENGINEER FIELD MANUAL
53
d. When laying sandbags attention should be paid to the fol-
lowing points :
(1) Tuck bottom corners of bags in before filling.
(2) Fill bags uniformly about three-fourths full.
(3) Build revetment at slope of from 3 on 1 to 4 on 1.
(4) Lay bags with beds perpendicular to slope.
(5) Lay bottom row headers on prepared bed. Alternate in-
termediate rows as stretchers and headers and complete with
a top row of headers.
(6) Lay bags with seams and choked ends inward.
(7) Break joints and beat bags into a rectangular shape
with the back of a shovel.
(8) A sandbag revetment will last much longer if wire net-
ting, preferably doubled, is placed over the face.
e. Sod revetment is more durable than sandbag revetment,
and its use is recommended where sods can be obtained in suf-
ficient quantity. Sods are cut 18 by 9 inches, laid grass down
except the top layer, and pinned together with wooden pegs.
The principles given in (3), (4), (5), (7), and (8) above for
sandbag revetment apply.
f. Stones and bricks may be used for revetment in the form
of retaining walls laid dry, in which case a slope of not steeper
than 4 on 1, beds at right angles to the face, and broken joints
are especially important. Due to the danger from flying splint-
ers in case a stone revetment is hit by a shell, its use is not
recommended where other material is available. If used in a
parapet it should always be crowned with earth-filled sandbags.
54. Surface types of revetment. — a. This form of revetment
consists of two parts — the revetting material which retains the
earth and the supports which hold the revetting material in
place. It is most useful in retaining the slopes of trenches,
since little additional excavation is needed.
6. The revetting material may consist of expanded metal, wire
netting (chicken wire), corrugated iron sheets, brushwood
hurdles, burlap, canvas, poles, brush or lumber, or combina-
tions of these materials, depending on the materials available
and the nature of the soil.
o. The supports for the revetment may be —
(1) Standard A-frames for use in the bottom third of the
trench, placed 3 feet center to center and supporting revetting
material described above. (See figs. 26 and 27.) Methods of
54
ENGINEER FIELD MANUAL
placing these frames around corners in traversed trenches are
shown in Figure 28.
(2) If A-frames are not available and the soil permits, the
revetment may be supported by means of pickets driven into
the bottom of the trench and braced, as shown in Figure 29.
-3-0--
/ /
-2-0~-
"T"
Strap Iron re^i'
End Elevation
Side Elevation
Figure 26. — Standard A-frame
.4-6'-
-3-6'-
Straplroti £*J£*e-'0'
Side Elevation End Elevation
Figure 27. — Special A-frame for use in communication
trench, type C
(3) Anchored revetting pickets are used when revetting
front slopes of fire trenches (fig. 30), or in other special cases
where high revetment is required. Revetting pickets should be
from 2 to 3% inches in diameter, straight, pointed at the
small end, and driven into the ground from 1 to 1% feet. Light
ENGINEER HELD MANUAL
56
ENGINEER FIELD MANUAL
angle-iron pickets may also be used. Lateral spacing of pickets
varies with the soil and the character of the working mate-
rials. For example, burlapped chicken, wire requires more
Figure 29. — Braced revetting pickets
closely spaced supports than sheets of corrugated iron. Simi-
larly, sand requires more support than firm clay. Spacing may
vary from 1% to 6 feet. Anchor pickets should be driven firmly
Figure 30. — Method of wiring and anchoring revetment
into solid ground 8 to 10 feet from the edge of the trench, stag-
gered so as to avoid forming a plane of weakness parallel to
the trench, and inclined so as to be perpendicular to the direc-
tion of pull on the anchor wire. Anchor wires, preferably
ENGINEER FIELD MANUAL
57
No. 14 American wire gauge, should pass at least four or five
times between picket and stake. Each strand should take a
round turn around the head of the anchor picket and then
the strands should be twisted together with a short stick to
tighten them.
(4) Struts resting against opposite walls of a trench are for
use only in narrow, deep trenches in which there is little
circulation, as iii shell slits for protection against shell fire.
d. Expanded metal and wire netting are used most effec-
tively either alone or in combination with burlap, canvas, or
similar materials. The burlap checks evaporation and pre-
vents disintegration and erosion, and the metal or netting
supports the burlap. If burlap or similar material is not avail-
able, grass, leaves, twigs, etc., may be substituted with good
results.
e. In placing expanded metal or wire netting revetment (fig.
31), the following operations are necessary:
(1) Cut vertical grooves for the anchor pickets throughout
the length of the bay at the spacing decided upon.
(2) Drive the two end pickets of each bay first and anchor
them back loosely.
(3) Stretch the metal or a double thickness of netting be-
hind the two end pickets, holding it taut until these pickets
are pulled into their grooves by tightening the anchor wires.
(4) Drive remaining pickets and anchor them back, thus
drawing the revetting material tight against the surface to be
revetted.
f. A continuous brush revetment of the superficial type may
be constructed by driving pickets from 2% to 3 inches in
diameter at about 1-pace intervals along the face of the sur-
face to be revetted and about 4 inches from it. The tops
of the pickets should project above the ground. The space
behind the pickets is then packed with small straight brush
laid parallel to the surface and held in place by the pickets,
which are drawn back firmly by means of wire and anchor
pickets.
55. Brush work. — a. In practically all wars brush has been
used extensively in the revetment and improvement of earth-
works. While its value in modern warfare is not always
commensurate with the labor and skill involved in its use, its
58
ENGINEER FIELD MANUAL
flexible utility and ready availability in forested areas will
still result in its extensive use in the future. At times it
may be the only material available. It may be used as hurdles,
gabions, fascines, continuous revetment already described, or
any combination of these.
6. Almost any kind of brush, reasonably straight, tough,
flexible, and free from refractory branches, dangerous thorns,
Figure 31. — Constructing wire-mesh revetment
or other objectionable characteristics is suitable ; but willow,
birch, ash, hickory, hazel, and similar woods are desirable.
Split bamboo of pliable dimensions, reeds, and vines are also
valuable. Brush for weaving should not be more than an inch
in diameter at the butt. That to be used without weaving
may be of larger size. When cut, brush should be assorted
in sizes for the various uses and made up in bundles weighing
ENGINEER FIELD MANUAL
59
40 to 60 pounds, the butts in one direction. Poles of 2% inches
diameter at the butt or larger are not bundled but are piled
together. They are used for posts, pickets, struts, binders,
grillage, and similar purposes. It is frequently best to
fabricate hurdles, gabions, or fascines at the point where the
brush, is cut, later transporting the finished brushwork to the
point of use.
c. (1) A brushwood hurdle is a woven revetment unit, usu-
ally 6 feet long and of the required height. (See fig. 32.)
It is constructed on sharpened pickets which are driven 18
J)rushwood
}'tol~J>ia. Jjutts
<a1ternatit\g
» . o-c
Figure 32. — Brush hurdle
inches into the ground. The pickets are about 2 inches in
diameter and are spaced approximately 1 foot 8 inches apart —
that is, four pickets to a hurdle. The two outer pickets should
be about 6 inches from the ends of the hurdle except when
woven with, vines or other very flexible material.
(2) To construct the hurdle, drive the pickets into the
ground firmly, and run two strands of plain wire, 14 or 16
A. W. G., along the pickets near the ground, taking a turn round
each picket. Twist these wires together until they are quite
tight, then weave the brushwood in and out of the pickets,
beginning at the bottom and keeping it pressed firmly down
on the wire. Each length of brushwood should pass alternately
66842°— 32 5
60
ENGINEER FIELD MANUAL
in front and rear of the picket. If the brushwood is not long
enough to reach the length of the hurdle, twist another piece
to it or tie a piece to it with wire. Since it is seldom possible
to bend a piece of brushwood round the end picket and take
it back along the hurdle, it should be allowed to extend about
6 inches beyond the end picket in weaving and later cut off.
Continue until halfway up and insert a couple of strands of
wire, twisted as before. Complete the hurdle and finish in the
same way with wire along the top. Then sew the hurdle in
three or four places from top to bottom with plain wire using
a double or saddler's stitch. Saw off the ends flush. Three
men should make a hurdle in half an hour.
(3) When placing the hurdle the bank should be cut away
to a proper slope as indicated by the profile sketches. The
hurdle should be laid against the bank and the pickets driven
into the ground 18 inches. The tops of the pickets are then
anchored as has been described for other surface revetment
types.
d. (1) A gabion (fig. 33) is a cylindrical basket with open
ends, made of brush woven on pickets. The usual dimensions
are 2 feet outside diameter and 2 feet 9 inches height of
wattling. On account of the sharp curvature of the form,
somewhat better brush is required for gabions than for hurdles.
(2) The gabion form, Figure 33©, is of wood, 21 inches in
diameter, with equidistant notches around the circumference,
equal in number to the number of pickets to be used, not less
than 8 and not more than 14. A smaller number is used if the
brush is large and stiff, and a large number if it is small and
pliable. The notches should be of such depth that the pickets
will project 1 inch outside the circle. The pickets should be
1% to 1% inches in diameter, 3 feet 6 inches, long, and sharp-
ened, half of them at the small end and half at the large end.
(3) To make a gabion the form is placed on the ground and
the pickets are driven vertically in the notches, large and small
ends down alternately. The form is then raised a foot and
held by placing a lashing around outside the pickets, tightened
with a rack stick (fig. 33 ©). The wattling is woven from
the form up to within 1 inch of the tops of the pickets. The
form is then dropped down, the gabion inverted, and the
wattling completed to within 3 inches of the ends of the
pickets. If the brush is small, uniform, and pliable, pairing
will make a better wattling than single strands. If not for
ENGINEER FIELD MANUAL
61
immediate use, the gabion must be sewed as described for
hurdles. Three men should make a gabion in an hour.
(4) Gabions may be made without the forms, but the work
is slow and not so regular. The circle is struck in the ground
and the pickets driven at the proper points. The weaving is
Figure 33. — Brush gabi'
done from the ground up. The entire time of one man is
required to keep the pickets in proper position.
(5) If brush is scarce, gabions may be made with 6 inches
of wattling at each end, the middle left open. In filling, the
open part may be lined with straw, grass, brush cuttings, or
grain sacks, to keep the earth from running out. Also iron
gabions may be constructed and carried in engineer supply
establishments.
62
ENGINEER FIELD MANUAL
e. (1) A fascine (fig. 34) is a cylindrical bundle of brush
closely bound. The usual length is 18 feet and the diameter
9 inches when compressed. Lengths of 9, 6, and 3 feet, when
needed, are conveniently obtained by sawing a standard
fascine into pieces.
(2) Fascines are made in a cradle which consists of five
trestles. A trestle is made of two sticks about 6% feet long
and 3 inches in diameter, driven into the ground and lashed
at the intersection as shown in Figure 34 ©.
Figube 34. — Brush fascine
(3) To build a fascine, straight pieces of brush, 1 or 2 inches
at the butt, are laid on the trestles, the butts projecting at
the end 1 foot beyond the trestle. Leaves should be stripped
and unruly branches cut off or partially cut through, so that
they will lie close. The larger straighter brush should be laid
on the outside, butts alternating in direction, and smaller stuff
in the center. Dispose the brush so that the fascine is of
uniform size, strength, and stiffness from end to end.
(4) When the cradle is nearly filled the fascine is com-
pressed or choked by the fascine choker (fig. 34©), which con-
ENGINEER FIELD MANUAL
63
sists of two bars 4 feet long joined 18 inches from the ends
by a heavy chain or wire 4 feet long. To choke, two men
standing on opposite sides pass the chain under the brush
and exchange bars. Then they bear down on the long ends
until the fascine is properly compressed.
(5) When a large number of facines is required and brush is
plentiful at one point, a portable frame as illustrated by
Figure 35 may be constructed. It is used at the site of the
brush, one man being assigned to each lever, and the completed
fascines are transported where needed. Such a frame speeds
up the compressing and binding processes.
(6) Binding is done with a double turn of wire, 12 or 14
A.W.G. The fascine should be bound in 12 places, 18 inches
apart, the end binders 3 inches outside the end trestles.
(7) Improvised binders may be made from rods of live brush ;
hickory or hazel is the best. Place the butt under the foot
and twist the rod to partially separate the fibers and make it
flexible. A rod so prepared is called a withe. To use a withe,
make a half turn and twist at the smaller end, pass the withe
around the fascine and the large end through the eye. Draw
taut and double the large end back, taking two half hitches over
its own standing part.
(8) When the fascine is choked and bound, saw the ends off
square 9 inches outside the end binders. After a cradle is
made, as illustrated in Figure 34 © , four men can make one
fascine per hour, with wire binding. Withes require one man
more. A frame, as illustrated in Figure 35, speeds up the
work but requires a larger working party.
f. Hurdles make an excellent surface revetment and are used
extensively for that purpose. Gabions are used principally in
the construction of parapets and breastworks in wet ground
(fig. 24), and to a limited extent in the repair of caved-in
trenches. Fascines may be used to advantage at the back edge
of the firing step ; that is, at the top of the surface revetment
of the lower third of a standard profile. They stand wear
much better than sandbags. Fascines may also be used in
connection with the footings for gabions and as a crown for
gabion, hurdle, or other types of revetment. Figure 36 illus-
trates a gabion and fascine breastwork topped with sandbags.
56. Revetting materials carried in engineer supply estab-
lishments. — Sandbags, corrugated iron, expanded metal, metal
64
ENGINEER FIELD MANUAL
lath, wire netting (chicken wire), pickets (including light angle-
iron pickets), and binding wire are normally carried in the
Figure 35. — Portable frame for compressing fascines
engineer sections of army depots, corps parks, division dumps,
and division distributing points. Except for sandbags, which
ENGINEER FIELD MANUAL
65
are standardized as noted in paragraph 53 c (1), they are
commercial articles purchased in the open market as required.
57. Machine-gun emplacement with splinter-proof cover. —
A simple type of machine-gun emplacement, with splinter-proof
cover for guns and crew, accommodating a section of two guns,
iw shown in Figure 37. This type may be used in connection
with existing trenches or in an isolated position with or without
concealed approaches.
Figure 36. — Gabion and fascine breastwork topped with sandbags
Table VI. — Machine-gun emplacement — Bill of material and
worlc data for Figure 37
Emplace-
ment for
2 guns
Logs, 6 inches in diameter, 8 feet long
Logs, 4 inches in diameter, 10 feet long —
Poles, 2 inches in diameter, 6 feet long „
Timbers, 6 by 8 inches, 3 feet long
Boards, 1 by 12 inches, 2 feet long...
Stakes, 12 inches long
T bases, standard
Corrugated iron or roofing paper square feet.
Camouflage material do,-.
Sandbags
Wire, smooth, No. 10. feet.
Brush, for revetting steps _ bundles.
Excavation . cubic feet.
Work:
Excavation in hours, 12 men
Eevetting, roofing, etc., in hours, 12 men
Total in hours, 12 men - _ -
8-hour shifts, 12 men __ _-.
24
220
40
4
5
200
2
750
1,900
240
500
1
1,500
10
11
24
ENGINEER FIELD MANUAL
67
58. Reinforced concrete emplacement. — Figure 38 shows an
emplacement providing protection against 210-mm. (8.25-inch)
shells. A shelter of the same dimensions, but without loopholes,
may be used for sheltering two gun crews to operate machine
Broken Sock
Bursting layer used on Zexposed sides in
soft groundJfc&'iDide by Z : 0'deepand JW
in front of wall extending SWbeyond matt)
All stirrups-*
strands of&iron
wire. Average
spacing 1^
/ <> e-o-'i — . -?o-
-3-0
All reinforcing grids J
off iron bars spaced §
q 8'c.toc in squares a. ijtj
•' wired together. Grids \
" to be covered by 3'
of concrete. The ends
af all bars bent {cold}
-180'toadia.tfjr
Sand bag protection for
door extending from
ground to roof.
® Plan
Figure 38. — Shellproof machine-gun emplacement
guns from near-by open emplacements. In this case it should
be lowered so as to be more easily concealed, and the thickness
of the floor may be reduced to 12 inches. Due to the large
amount of material and more or less elaborate construction
plant required, the use of concrete emplacements is restricted
68
ENGINEER FIELD MANUAL
to positions not under direct observation of the enemy and pro-
vided with good transportation facilities, preferably near a light
railway line.
Section A A
Section
Top tBottom Bates
4Anjles r-Z-J.JM
Note:
Mix 1:2:4- by volume
If reinforcing bars are left out
the thickness of the roof and
front walls shoutd be 5-0"
Vhen 13eams are not available
place a layer of heavy wire mesti
J' from the surface of the ccilinp
in addition to a grid of f rein'
forcing bars spaced in squares
S'c toe.
~*-J>rill 2 holes I'd. ate'ei
4.-G*
SPlates t£~-/ : /p*'-6-farmorJteel)
® Section and details of sliding panels
Figure 38. — Shellproof machine-gun emplacement
A minimum period of two weeks must be allowed for the
hardening of Portland cement, so that the emplacement may be
considered effective, and one month for it to attain practically
ENGINEER FIELD MANUAL
69
full strength. Newly developed quick-hardening alumina cement
attains an effective strength in 24 hours. In soft ground, in
order to prevent shells from penetrating and exploding under
the floor, a course of broken rock, as indicated in the drawing,
or concrete bursters, should be placed protecting the exposed
sides. The embrasure is fitted with a pair of armor-steel panels
sliding in metal grooves set in the concrete. The steel panels
are sufficiently thick to withstand a direct hit by a new type
37-mm. projectile. They may be moved in the grooves by means
of a pinch bar inserted in the holes, drilled in the plates, so
that an aperture is left only sufficiently wide to fire through
in the desired direction. By installing the steel panels it is
practicable to provide an arc of fire of 60°. Bill of material
and work data are given below :
Table VII. — Shellproof machine-gun emplacement-
teriul and work data for Figure 38
-Bill of mar
Item
Weight
in tons
Amount
Cement.
Sand
Broken stone or gravel-.
Water
I beams, 5-inch
Iron wire for stirrups, iMs inch (No. 4)
Round iron bars for reinforcing grids, % inch
Embrasure panels, complete, consisting of---
2 armor steel plates 1)4 inches by 1 foot; 1H
inches by 4 feet 6 inches.
4 angles, 2 by 2 by % inch by 12 feet 6 inches.
2 plates, H by 5J4 inches by 12 feet 6 inches.
Sandbags.. ___
T base, standard
Bunk, 4-man, double-deck
Camouflage screen
Plank, 2 inches for forms _ --.
Posts, 2 by 6 inches, for forms
Broken stone for burster course
Total weight (approximate) -
Excavation for emplacement
Excavation for burster course
Volume of concrete
Work:
Excavation, 20 men -.
Erecting forms, placing burster layer, etc., 20
men -
Mixing and placing concrete.--
Total (material at the site, 20 men)
Total 8-hour shifts, 20 men
Period for hardening (minimum):
Portland cement
Alumina cement
19.5
46.5
93
29
.07
3.4
.5
3.6
1. 1
31
103 barrels (3.8 cubic
feet per barrel).
32 cubic yards.
64 cubic yards.
7,000 gallons (approxi-
mate) .
27—9 feet long.
4—5 feet long.
1,500 linear feet.
6,500 linear feet.
l.
375.
1.
1.
5,600 square feet.
900 square feet.
550 lineal feet.
21 cubic yards.
50 cubic yards.
21 cubic yards.
70 cubic yards.
9 hours.
10 hours.
20 hours.
39 hours.
5.
2 weeks.
24 hours.
70
ENGINEER FIELD MANUAL
59. Obstacles. — a. Principles of design and construction. — In
the design and construction of obstacles the following principles
should be observed :
(1) The obstacle should afford the attacker neither cover
nor concealment while holding him under the effective fire of
the defense.
(2) By employing types of low visibility, by avoiding regular
geometric layouts with lines terminating in angles indicative
of the location of flanking machine guns, the organization of
the defense, especially the machine-gun locations, is withheld
from the enemy. The obstacles should present a confused,
irregular, and unsystematic appearance. Such obstacles give
little indication of the defensive organization and are difficult
to range upon. The attacker has difficulty in determining when
the obstacle lias been breached or destroyed. The construction
of straight lines of obstacles that indicate the location of
machine guns must always be avoided.
(3) While being sufficiently dense to prevent easy penetra-
tion, an obstacle should not be so heavy as to be readily visible
on an airplane photograph. A thin, broad, irregular obstacle,
preferably a wire entanglement, is of low visibility, more
difficult to destroy by fire, and quite as effective as the same
amount of material in a denser structure. Such an obstacle
will frequently escape detection from the air.
(4) Several comparatively narrow belts of obstacles,
separated by intervals, are more effective than the same
material in a single belt. If additional protection is required,
another belt should be added rather than broaden the existing
one. Belts should be of such width, however, that a single shell
burst, even that of a large trench mortar bomb, can not make a
passable breach through the obstacle. Belts should be from
4 to 10 yards wide and the intervals between them from 15
to 40 yards.
(5) It is- not usually the wire entanglement itself which
shows on an airplane photograph, but rather the increased
length of grass, untrodden plowed ground, and other changes
in surface texture resulting from the presence of the obstacle.
Paths following the edges of obstacles and passing through the
gaps in them frequently indicate their presence on airplane
photographs.
ENGINEER FIELD MANUAL
71
(6) Wire entanglements should be constructed in accordance
with standard designs.
(7) Obstacles should be of the simplest possible design so
that they may be quickly, easily, and quietly erected by aver-
age troops with average training, in the dark and in the pres-
ence of the enemy.
(8) Obstacles should be strongly anchored to the ground
and well supported so that they can not be easily pushed
aside or otherwise removed.
(9) The first element erected should afford immediate pro-
tection, after which the construction is continued to the rear.
(10) Wire should be strung loosely, for if taut it is more
readily cut by wire cutters and shell fire. Ordinary procedure
results in loosely strung wire.
(11) The construction should require the minimum number
of men, who should not be bunched in groups vulnerable tQ
fire.
(12) Speed in construction is obtained by means of —
(a) Simple design.
(6) Careful organization of work and supply of material.
(e) A systematic procedure, having the form of a drill in
which each man has simple and definite tasks.
{d) Selection of especially skilled men for the actual con-
struction, the less skilled men being employed carrying
materials.
(13) The obstacles should be of a type not easily destroyed
by fire, either hostile or friendly. It is desirable that frontal
fire should pass over the obstacle rather than through it. The
obstacle should not interfere with the defender's view or fire.
(14) The gaps should be closed when not in use by means
of portable obstacles. Gaps should be covered by fire, espe-
cially gaps that have been made by the enemy. Portable
obstacles should be available for quickly closing gaps made
by the enemy.
6. Materials. — (1) Barbed wire is encountered in various
styles. The standard is the familiar 2-wire type of No. 12,
A. S. & W. gage wire with four-point barbs, spaced approxi-
mately 4 inches apart. The length on a commercial reel, as
shipped from the factory, is about 420 yards, and the weight
of a full reel about 100 pounds, plus the weight of the reel,
72
ENGINEER FIELD MANUAL
about 5 pounds. Keels of about one-half the foregoing size
are also obtainable, and are desirable. Hand bobbins are
usually made up at the rear from the large size reels, contain
25 yards of wire, and weigh from 7 to 8 pounds each. They
are always used when constructing entanglements.
(2) To make bobbins, secure 1-inch round or square sticks
approximately 2y 2 feet long. When necessary round off the
ends to facilitate handling. It is desirable to drive 8-penny
or 10-penny nails through the stick about 8 inches from each
end. Improvise trestles similar to those used in making fas-
cines. Pass a pick handle, piece of pipe, or other suitable
article through the reel, and place in the trestle so that the
Figure 39. — Making bobbins
wire may be unreeled from the bottom. Two men work at
making bobbins, one at the bobbin and one at the reel, alternat-
ing duties from time to time. The bobbin man fastens the end
of the wire to one of the nails in a bobbin stick and draws the
wire out over a measured distance of 25 yards. The man at
the reel controls the movement of the reel by hand or by
braking with a stick. The bobbin man grasps the stick at the
center with both hands and keeps his hands in this position
while making the bobbin. Maintaining a constant strain on
the wire, he moves toward the reel at the same time winding
the wire on the bobbin by overhand movements so that the
wire is passed alternately over and around first one end of the
stick, then the other, coming to rest on the nails, as illustrated
in Figure 39. When the 25-yard length of wire has been wound
ENGINEER FIELD MANUAL
Y3
the wire is cut and the free end marked with white rag or
tape and secured. The result is a compact bobbin of light
weight. One man can easily carry four such bobbins, two in
each hand, or six on a stick on his shoulder.
(3) Wooden pickets are cut in near-by woods or are shipped
from the rear. They should range in diameter from 2% to 4
inches, and should be cut 5 feet long for the high entangle-
ment and 2 feet 6 inches for the low type. Pickets split
from a log by quartering should be avoided, as they increase
materially the visibility of an entanglement.
(4) Figure 40 illustrates standard types of screw pickets,
the helix permitting them to be screwed noislessly into the
ground.
(5) Figure 41 illustrates standard types of angle-iron pickets.
60. Table of wire-entanglement materials. — The following
table gives data relative to standard entanglement materials :
Table VIII. — Wire-entanglement materials
Weight
in
pounds
Length
in
feet
Number
easily
carried by
1 man
Weight
of man
load
"Wooden picket, long, 3 to 4 inches diameter...
12-10
5
3
36-48
"Wooden picket, short, 2 to 3 inches diameter..
4-8
2
8
32-48
Screw picket, long _
9
4 10
4
36
Screw picket, medium _
2 8
6
36
4
1 9
8
32
10
6
4
40
3 8
36
Full reel wire, 420 vards (approximate) _ _
105
1,200
1 52.5
Bobbin, 25 yards
7-8
75
4-6
28-48
• Full-sized reels are carried by two men upon their shoulders by means of a picket
passed through the hole in the reel.
61. Types of entanglements. — a. The following obstacles
may be considered standard and methods for their construction
are outlined :
(1) High-wire entanglement.
(2) Double-apron fence.
(3) Low-wire entanglement.
(4) Belts of Ribard wire or concertina.
(5) Portable wire obstacles.
ENGINEER FIELD MANUAL
75
b. The following table gives data relative to the material
required for 1,000 yards of single-belt entanglement:
Table IX. — Material required for 1,000 yards of single-belt
entanglement
Type of entanglement
§8
la
a
3
S3
°S
a-9
High-wire
Double-apron..
Low wire
Ribard (2 cylinders
side by side)
Concertina (2 cylinders
side by side)
4-strand wire fence
'320
640
640
302
M8
38
29
Pounds
> 5,040
3,990
3,045
5,670
7,875
1,155
Pounds
Pounds
2,367
623
1,315
< 600
600
1 For front anchorage if used.
3 Plus 3 if front anchorages are used.
3 Plus 315 if front anchorages are used.
< 1,100 feet of rods.
Figure 41. — Angle-iron pickets
62. General remarks on wire-entanglement drills. — The fol-
lowing remarks and precautions are applicable to all entangle-
ment drills.
a. The line of stakes toward the enemy for high wire and
the center line for double apron and low wire should be traced
and marked in the manner described for trenches. The use of
tracing tape is highly desirable for night work in the presence
of the enemy.
b. The men are given numbers in the order in which they first
proceed to work, each having definite, limited tasks. They start
66842°— 32 6
76
ENGINEER FIELD MANUAL
at intervals, so that men doing different tasks will not be
bunched, exposed to fire, or interfere with each other. One
row of pickets is set by pacing. The others are placed by eye,
using the paced row as a guide. The elements nearest the
enemy should be placed first, and work continued to the rear.
c. Pickets should be carried under the left arm and placed
on the ground with the right hand so that the end of the screw
or the point of the picket faces the enemy, indicating the spot
at which the picket is to be erected. For carrying, all bundles
of screw and iron pickets should be wrapped with a sandbag
and secured in at least two places by a turn of plain wire with
the ends twisted together. Enough end to this wire must always
be left so that it can be untwisted by hand without pliers. Bun-
ENGINEER FIELD MANUAL
77
dies of long wooden pickets should be tied together in at least
two places with plain wire. Short wooden pickets are best car-
ried in sandbags, a suitable number in each bag; two bags are
tied together and slung over the shoulder. Screw pickets must
be screwed in so that the eyes are parallel to the length of the
' JO-O'
4 Paces _
JO-O'
jo-o~
Figure 43. — Double-apron fence
entanglement, and the eye points in the direction from which
the men are working ; that is, toward the starting point. Com-
pliance with this rule facilitates placing wires. Wooden pickets,
used as holdfasts (anchors), should be driven in approximately
at right angles to the stay wire to be attached to them, but screw
anchorage pickets must be placed in prolongation of this stay
wire.
78
ENGINEER FIELD MANUAL
d. In running out barbed wire two men work together; one
man walks out with the bobbin, unwinding as he goes, and the
other stretches the wire and fastens it to the pickets.
e. In the erection of the entanglement the following rules
should be observed:
(1) Men fastening the wires must always work| facing the
enemy.
Figure 44. — Low-wire entanglement
(2) To fasten wire in top eye of screw picket, pull the fixed
wire (the one leading toward the starting point) taut and slip
the wire up into the eye, turn the running end up over the
eye, thus threading the wire in the eye. Then take a turn with
the running end over the standing end and around the picket
below the eye. (See fig. 45.)
(3) To fasten the wire in a lower eye of a screw picket
when there is already a wire in the top eye —
(a) Pull the standing end taut and slip the wire up into
the eye. Then take a bight on the running end, pass it around
the picket above the eye, and take a turn with the bight on the
running end. (See fig. 45.)
ENGINEER FIELD MANUAL
79
(6) If one eye is on the opposite side of the pickets from
the others, the wire must be forced down into the eye, and
the bight on the running end passed around the picket under
the eye.
(4) The foregoing rules (2) and (3) apply whichever way
the wiremen are working, from right to left or left to right,
Figure 45. — Proper method of fastening wire to screw pickets
and if carried out, the wire will be firmly fixed in the eye
and can not slip up or down the picket ; also, if one bay is cut,
the wire in the bays on either side remains taut and does not
slip through the eyes.
(5) Wires are fastened to wooden pickets as shown in Figure
46.
(6) To fix one wire to another a short length of smooth wire
may be used or the two wires may be twisted together by
80
ENGINEER FIELD MANUAL
means of a rack stick as shown in Figure 47. This is the
better method and is known as " windlassing."
(7) Each member of a wiring party is equipped with a rack
or windlass stick.
Figure 46. — Proper method oC fastening wire to wood pickets
f. The carrying parties indicated in paragraphs 63, 64, 65,
and 69 can carry at one trip all the material required for 50
yards of entanglement. If a round trip to the dump requires
more time than the construction of 50 yards- of the obstacle,
Figure 47. — Method of fastening two wires together by
" windlassing "
the strength of the carrying party must be increased accord-
ingly. Specially skilled crews of piekfcd men, undisturbed,
have erected wire entanglements in less than one-quarter of
the time stated in Table X, paragraph 78.
ENGINEER FIELD MANUAL 81
63. Drill for erecting high-wire entanglement.
SO yards high-wire entanglement (two rows of stakes)
Material
Wiring party
Carrying party
8 bundles (32) long pickets.
40 25-yard bobbins barbed wire.
1 noncommissioned officer
(carries pliers).
16 men (each carries a stick).
1 man, carrier.
1 noncommissioned
officer.
18 men.
Nos.
First task
Second task
Third task
N.
C. 0.
Leads party to
head of work.
Paces front panel and indicates location of pickets; su-
pervises work.
1
2
Each man carries
out one bundle
pickets.
Place pickets of front panel.
String bottom horizontal
wire, zigzag panel.
3
4
Place pickets of rear panel.
String first diagonal wire,
zigzag panel.
5
6
Screw in pickets of front
panel
String second diagonal wire,
zigzag panel.
7
8
Screw in pickets of rear
panel.
String top horizontal wire,
zigzag panel.
9
10
Each man carries
out four bobbins
barbed wire.
String bottom horizontal
wire, front panel .
String bottom horizontal
wire, rear panel.
11
12
String first diagonal wire,
front panel.
String first diagonal wire,
rear panel.
13
14
String second diagonal
wire, front panel.
String second diagonal
wire, rear panel.
15
16
String top horizontal wire,
front panel.
String top horizontal wire,
rear panel.
17
Carry out 4 bobbins barbed
wire.
Note. — Nos. 1 to 4 place pickets lightly in ground. In stringing, odd numbers run
out coils, even numbers fix wire to pickets.
Each additional row of high-wire entanglement
Material
Wiring party
Carrying party
4 bundles (16) long pickets.
1 noncommissioned officer.
1 noncommissioned
officer.
32 25-yard bobbins.
10 men.
12 men.
Note. — A drill for erecting the additional row of high-wire entanglement may be
readily improvised based upon the above drill for the first row.
82 ENGINEER FIELD MANUAL
64. Drill for erecting double-apron fence.
50 yards double-apron fence
Material Wiring party Carrying party
4 bundles (16) long pickets. 1 noncommissioned officer 1 noncommissioned
4 bundles (32) anchor pickets. (carries pliers) . officer.
32 25-yard bobbins barbed wire. 9 men (carry rack sticks). 15 men.
Nos.
First task
Second task
Third task
Fourth task
Fifth task
N.C.
0.
Carries out 1 bundle long pickets. Paces off and indicates to Nos. 1, 2, and 3
location of pickets. Supervises work.
1
Each car-
ries out 1
bundle
long pick-
ets.
Lay out and
screw in
pickets of the
center line.
Run out front
diagonal wire.
Run out bot-
tom horizon-
tal wire of
fence.
Run out rear
diagonal wire.
2
Fasten front
diagonal wire
on anchor
pickets.
Fasten bottom
horizontal
wire of fence
on pickets,
Nos. 2 and 3
working on
alternate pick-
ets.
Fasten rear
diagonal wire
on long pick-
ets.
3
Fasten front
diagonal wire
on long pick-
ets.
Fasten rear
diagonal wire
on anchor
pickets.
4
Each car-
ries out 1
bundle an-
chor pick-
ets.
Lay out and
screw in
front anchor
pickets. No.
4 places pick-
ets at head
of work.
"Run Ant" fffii
J\ LI 11 \J Lit LULJ
wire, front
apron.
XV LI 11 ISL1 1 oCv
ond horizon-
tal wire of
fence.
Run out top
horizontal
wire, rear
apron.
5
Windlass trip
wire to diag-
onal wire.
Fasten second
horizontal
wire of fence
on pickets.
Windlass top
horizontal
wire to diag-
onal wire.
6
Lay out and
screw in rear
anchor pick-
ets. No. 7
places pick-
et at end of
work.
Run out sec-
ond horizon-
tal wire, front
apron.
Run out third
horizontal
wire of fence.
Run out sec-
ond horizon-
tal wire, rear
apron.
7
Windlass sec-
ond horizon-
tal wire to
diagonal wire.
Fasten third
horizontal
wire of fence
on pickets.
Windlass sec-
ond horizon-
tal wire to
diagonal wire.
8
Carry out 32 bobbins of
barbed wire.
Run out top
horizontal
wire, front
apron.
Run out top
horizontal
wire of fence.
Run out trip
wire, rear
apron.
9
Windlass top
horizontal
wire to diag-
onal wire.
Fasten top
horizontal
wire of fence
on pickets.
Windlass rear
trip wire to
diagonal wire.
Note. — Diagonal and apron wires begun and finished on end anchor pickets.
Horizontal wires on fence not carried down to end anchor pickets.
ENGINEER FIELD MANUAL 83
65. Brill for erecting low-wire entanglement.
50 yards low-wire entanglement
Material
Wiring party
Carrying party
3 bundles medium pickets (1 of
6, 2 of 5 each).
4 bundles (32) anchor pickets.
24 26-yard bobbins barbed wire.
1 N. C. 0. (carries pliers).
6 men (carry rack sticks).
IN. C. 0.
13 men.
Mos.
First task
Second task
Third task
Fourth task
Fifth task
Sixth task
N.C.
0.
Carries out 1 bundle medium pickets. Paces off and indicates to Nos. 1 and 2
location for their pickets. Lays out own pickets. Supervises work.
1
Carries out
] bundle
medium
pickets.
Carries out
1 bundle
medium
pickets.
Lay out and
screw in
center line
of pickets.
String and
fasten
front diag-
onal wire.
String and
windlass
top hori-
zontal
wire,
front
apron.
String and
windlass
top hori-
zontal
wire, rear
apron.
2
Carries out
1 bundle
anchor
pickets.
Carries out
1 bundle
anchor
pickets.
3
Carries out
1 bundle
anchor
pickets.
Carries out
1 bundle
anchor
pickets.
Lay out and
screw in
outer an-
chor pick-
ets.
String and
windlass
trip wire,
front
apron.
String and
fasten
horizontal
wire, cen-
ter line.
String and
windlass
second
horizontal
wire, rear
apron.
4
Carries out
4 bobbins
barbed
wire.
Carries out
4 bobbins
barbed
wire.
5
Carries out
4 bobbins
barbed
wire.
Carries out
4 bobbins
barbed
wire.
Lay out and
screw in
inner an-
chor pick-
ets.
String and
windlass
second
horizontal
wire,
* front
apron.
String and
fasten
rear diag-
onal wire.
String and
windlass
trip wire,
rear
apron.
6
Carries out
4 bobbins
barbed
wire.
Carries out
4 bobbins
barbed
wire.
Note. — No. 3 places anchor picket at head of work. No. 5 places anchor picket
at foot of work. Diagonal wire of rear apron and horizontal wire on center line of
pickets are not carried down to end anchor pickets. Low-wire entanglements are
slow to erect at night, owing to the difficulty of seeing the pickets.
66. Ribard wire. — a. The elements of Ribard wire consist of
seven wire circular frames 3 feet 4 inches in diameter, spaced
3 feet 4 inches apart, and on which are stretched six longi-
tudinal strands and three diagonal strands of barbed wire. By
twisting the elements in opposite directions from each end they
can be closed up for transportation. When extended each
84
ENGINEER FIELD MANUAL
element has a length of 20 feet. Figure 48 shows a portion
of an element extended. Its chief advantages are its low
visibility, portable character, resistance to destruction by
artillery, and rapidity of erection.
6. Figures 49 and 50 show the method of making up the
Ribard coils. Circles of heavy (about No. 5) smooth steel wire,
each containing a 6-pointed star of No. 12 smooth wire, are
first made up as shown in Figure 49. These are then placed
in a frame as shown in Figure 50 and three diagonal barbed
wires are placed between the circles connecting opposite vertices
of the triangles. Finally, six, horizontal wires are added
Piguke 48. — Partially opened Ribard element showing stapling and
connecting the points of the" stars. The elements are then
removed from the frame. Two men grasp the ends. Both
twist strongly to the right, approaching each other at the same
time. The cylinder closes into a compact coil, which is then
placed on the ground compressed with the feet, and tied with
tracing tape. Usually two men work at each table making
circles and three men at each frame wiring the circles together.
The average time per cylinder is 20 minutes. Seventy yards
barbed wire, 30 yards heavy steel wire for circles, and 40
yards light smooth wire are required. One Ribard element is
a load for one man.
67. Barbed-wire concertinas. — a. Like the Ribard element,
this type of obstacle is prepared in advance and in the field
-3-4'-
M.
supports
ENGINEER FIELD MANUAL
Figure 49. — Table for making Ribard circles
ir-e-zt-s'tottj-
Figure 50. — Frame for constructing Ribard elements
86
ENGINEER FIELD MANUAL
needs only to be opened out, supported on a wire strung
between posts, and stapled to the ground.
6. Draw on the ground a circle 4 feet in diameter. Place
nine posts — an odd number is essential— equally distant,
approximately 17 inches apart around this circle and drive
them, leaving a height of 5 feet above ground. Angle-iron
pickets are much easier to work with than wooden ones. One
100-yard coil of barbed wire is required per concertina, with
® Element collapsed © Method of making concertina ele-
and prepared for ments with either plain or
carrying barbed wire
©Concertina extended
Figure) 51. — The concertina
short lengths of plain wire for fastening. The unit party is
three men. No. 1 works inside the framework ; Nos. 2 and 3
run out the coil, No. 2 helping No. 1 if necessary.
Average time per concertina is 20 minutes. Take two com-
plete turns around the nine posts with No. 12 plain wire, or
four turns with No. 14 wire, and bind these turns together at
ENGINEER FIELD MANUAL.
87
each interval between posts, so as to form a secure end ring
for pulling the concertina out. Fasten the end of the barbed
■wire to the plain wire and take 24 turns with it around the
posts in a spiral form, binding two consecutive turns together
at every other interval, using No. 14 to No. 20 plain wire for
binders. Make two turns with plain wire and make fast. It
assists to have a nonagonal-shaped framework to fit inside
the top of the pickets, so as to keep them properly spread out.
It is easily removed when the concertina is finished.
c. The easiest method of carrying is to wire a slat to each
face of the closed roll, the slats parallel to each other. The
points 90° from the slat fastenings are then lightly tied with
tape. The concertina can easily be carried by two men, or
With reasonable ease by one man if in the open.
68. Ribard and concertina entanglements. — a. Ribard ele-
ments and concertinas open out to a length of about 20 feet
and are formed into an entanglement by tying end to end. The
elements are supported between posts spaced 20 feet apart
and carrying a taut top horizontal wire, to which the elements
are secured. Each coil should also be stapled, in at least three
places to the ground, with a staple as shown in Figure 48. The
entanglement may be thickened in depth as desired by adding
successive lines. Figure 52 shows the manner in which Ribard
or concertina elements are arranged to form an entanglement.
6. The entanglement has the advantages of low visibility,
rapidity, and ease of construction once the elements are pre-
pared, and difficulty of destruction by artillery owing to its
strength and resiliency. Being stapled to the ground, it is
difficult to pass, and in double lines with a top horizontal wire
it forms an exceedingly efficient barrier.
69. Drill for erecting Ribard wire or concertina entangle-
ment.
50 yards double-belt Ribard wire or concertina
Material
Wiring party
Carrying party
4 bundles (16) long pickets.
4 anchor pickets.
14 coils Kibard wire or concer-
1 noncommissioned officer
(carries pliers).
1 noncommissioned
officer, 20 men.
tina.
2 50-yard coils barbed wire.
30 wire staples.
24 8-inch pieces No. 18 plain
10 men (Nos. 1 and 2 each
carry 12 pieces plain wire;
9 and 10 each carry 15
staples; all carry rack
sticks) .
wire.
88 ENGINEER FIELD MANUAL
50 yards double-belt Ribard wire or concertina — Continued
Nos.
First task
Second task
Third task
Fourth task
Fifth task
N. C.
0.
Carries out 4 anchor pickets. Paces off distances and locates pickets. Super-
vises work.
1
2
Carry out 4
long pickets
each.
Each lays out
and screws
in 4 long
pickets.
Open out and
place in front
line of pickets
1 Ribard ele-
ment or con-
certina.
Wire coils together in both
belts, No. 1 working on
enemy side, No. 2 opposite.
3
Open out and
place in front
line of pickets
1 Ribard ele-
ment or con-
certina.
Open out and
place in sec-
ond line of
pickets 1 Ri-
bard element
or concertina.
Run horizon-
tal wire
along top of
pickets,
first row.
4
Fasten wire
to pickets.
5
Carries out 1
Ribard ele-
ment or con-
certina and
cuts tape.
Lays out and
Screws in 4
anchor pick-
ets.
Open out and
place in front
line of pick-
ets 2 Ribard
elements or
concertinas.
Open out and
place in sec-
ond line of
pickets 2 Ri-
bard ele-
ments or con-
certinas.
Windlass
coils to wire
at 3 points
between
each 2 pick'
ets.
6
Carry out 2
Ribard ele-
ments or
concertinas
and cut tie
tapes.
Carry out 1
Ribard ele-
ment or con-
certina coil
and cut tie
tapes.
Run horizon-
tal wire
along top
of pickets,
second row.
7
Open out and
place in front
line of pick-
ets 2 Ribard
elements or
concertinas.
Open out and
place in sec-
ond line of
pickets 2 Ri-
bard ele-
ments or con-
certinas.
Fasten wire
to pickets,
8
Windlass
coils to wire
at 3 points
between
each 2 pick-
ets.
9
Carry out 1
coil barbed
wirft.
Open out and
place in front
line of pick-
ets 1 Ribard
element or
concertina.
Open out and
place in sec-
ond line of
pickets 2 Ri-
bard ele-
ments or con-
certinas.
Staple down
both belts.
10
Note. — Nos. 6, 7, 8, 9, and 10 place coils in intervals between pickets in tasks
Nos. 1 and 2.
70. The knife rest or cheval-de-frise. — The knife rest con-
sists of a framework of wood or iron, upon which is strung
barbed wire. It is sometimes called a cheval-de-frise. The
ENGINEER FIELD MANUAL
90
ENGINEER FIELD MANUAL
framework, if the iron type, may be made collapsible and
hence easier to transport, as well as being more difficult to
see and stronger than the wooden type. In shape, the frame-
work of the knife rest is of the same appearance as a common
sawbuck. Figure 53 shows its construction. Chevaux-de-frise
are frequently used to stop temporary gaps in entanglements.
® Without wire
Figure 53. — Knife rest or etieval-de-frise
to barricade trenches leading toward the enemy, and to barri-
cade roads and streets.
71. The gooseberry and the hedgehog. — a. The gooseberry,
illustrated in Figure 54, consists of barbed-wire balls con-
nected by spirals of the same material. It is used principally
to block trenches. For this purpose the balls should be made
with a diameter slightly greater than the width of the trench
ENGINEER FIELD MANUAL
91
in order that, when jammed into place, they will be more
difficult to remove. They may also be used to make emergency
repairs to existing obstacles.
The imishect
Gooseberry -u)ou*vct
Spirall,y -witkharhed
•wire. iWtenect at
points -with smooth,
■wife.
Connected to
another berry bj»
a spiral coil.
Taken off the -pegs
and opened -up
lorming a Sphere
8 or 10 turns around
the pegs, fastened
at two places with
small smooth -wire
Figure 54. — The gooseberry
6. The hedgehog.— The nature and manner of construction of
this obstacle are illustrated in Figure 55. It is used in the same
way as the gooseberry.
Figuhe 55. — The hedgehog
72, Abatis. — a. Dead abatis. — Dead abatis is made by felling
trees toward the enemy and placing them so closely together
that the branches form a barrier against an advance. The
66842°— 32 7
92
ENGINEER FIELD MANUAL
difficulty of passage is increased by the addition of barbed-
wire interlaced in the branches of the trees. The wire lacing
also makes the removal of the barrier more difficult. This type
of barrier is highly efficient as a rapid means of blocking a
road lined with trees. In the case of a road between two rows
of trees the trees on bath sides are so felled that their tops
interlock, making the barrier as dense asi possible. Trees are
preferably only partially cut through when felled so that their
removal may be more difficult. Dead abatis has the disadvan-
tages of being conspicuous and also inflammable when dry. For
these reasons it is often worth while to go to the greater labor
of building live abatis for defenses in a wood.
6. Live abatis. — (1) In the organization of woods, where the
growth is suitable, it is possible to form a barrier by bending
down, interlacing, and tying the easily bent saplings and lower
branches of adjacent trees in such a way that the obstacle is
invisible to both ground and air observers. (See fig. 56.) This
type of barrier is usually constructed in extended depth and is
practically impassable to advancing infantry, unless the circum-
stances are such that trench knives or axes can' be used.
(2) It is sometimes the practice in connection with the use
of live abatis to augment its impassability by the addition of
a number of plain or barbed wires strung from sapling to sap-
ling or tree to tree. The use of pickets in this situation should
be avoided as they increase the visibility of the barrier.
(3) In the organization of fairly dense woods abatis is not
always continuous ; gaps are left at points which would natu-
rally be the avenue of approach of advancing elements. These
lanes of access are directed toward lines of supplementary bar-
riers of double-apron or high-wire entanglement, there being
definite lanes cut through the woods along the enemy side of
these barriers, and bounded by them and the abatis. These
lanes are under fire from well-placed flanking weapons and are
under good observation. The object of this type of organization
is to held the enemy into zones from which he can not easily
find an exit and which are swept by the fire of automatic
weapons.
(4) Lanes should not be too wide, as they then become
visible from the air. It is possible in fairly dense woods to
clear lanes 6 to 20 feet wide and to bring together the branches
overhead, thus concealing their position.
ENGINEER FIELD MANUAL
93
73. Inundations. — Inundations form serious obstacles to the
attacker. They also may seriously limit counterattacks. They
are created by building dams at suitable points. An exten-
sive survey is frequently a necessary preliminary step to deter-
mine the area and depth to be inundated and height and best
® Dead abatis protecting hasty trench in woods
©Dead abatis blocking road with live abatis on its flank
Figure 56. — Abatis
location of the dam. In a stream with a firm bottom it requires
at least 4 feet of water to be a serious obstacle to infantry
and 6 feet as a minimum should be sought. If the bottom is
soft, or if the inundation is combined with other obstacles,
a lesser depth suffices. A barbed-wire entanglement prepared
in advance and inundated is a most formidable obstacle.
94
ENGINEER FIELD MANUAL
Inundations are very effective obstacles against tanks or any
form of vehicle.
74. Tank obstacles. — a. The most effective defense against
tanks is the 37-mm. gun or other infantry accompanying gun
of greater caliber. The use of tank obstacles presupposes a pas-
sive defense, although such obstacles should not limit or impede
counterattacks. The construction of tank obstacles involves a
great deal of time, labor, and for many types a great deal
of material.
b. Points at which advancing tanks are limited as to their
lines of approach ; for example, causeways passing extensive
swamps, roads through timber heavy enough to serve as an
effective tank obstacle, and the entrances to the stone villages
Figure 57. — Antitank ditch
of western Europe, are the most favorable locations for tank
obstacles. Their construction is not usually warranted except
in such favorable locations.
o. Trenches and entanglements are not usually effective ob-
stacles against tanks. However, trenches filled with wire may
hold up or delay the infantry accompanying the tanks and
thereby break up the attack. Heavy abatis may serve as an
effective obstacle ; light and live abatis generally do not, Light
tanks can penetrate woods when the large trees are scattered
and the undergrowth is not excessively heavy.
d. Figure 57 shows the minimum excavation that can be
considered an effective tank obstacle. The earth may be scat-
tered and the ditch camouflaged to the point that it is invisible
to approaching tanks. A ditch blocking a road may be sup-
plied with a camouflaged bridge adequate for the normal traf-
fic of the defenders but not strong enough to carry the enemy
tanks.
ENGINEER FIELD MANUAL
95
e. Heavy obstacles consisting of concrete blocks, railroad
rails imbedded in the ground or in concrete, and rubble masonry
have been used. Such obstacles should be designed by the
engineers when the need for their use arises, due considera-
tion being given to the size and power of the tanks they are
to withstand.
75. Antitank mines. — a. Antitank mines are land mines, of
the controlled or contact type, buried in the ground or scat-
tered on the surface and camouflaged, used to destroy or dis-
able enemy tanks. The controlled mines will rarely be used.
In the few situations where mines of this type are advantageous
the destruction of enemy personnel and materiel in general
will be the object sought for. They will infrequently be used
against tanks alone. Contact mines find their greatest applica-
tion in position warfare where there is ample time to bury
them carefully in mine fields and to camouflage the spot where
each mine is buried. In open warfare antitank mines must
be scattered on the surface, concealed in the grass, or other
vegetation. The ease with which they may be discovered and re-
moved by troops detailed to accompany the tanks for that pur-
pose makes their effectiveness in open warfare problematical.
6. Antitank mines of the contact variety will invariably be
placed at intervals over an area to form a mine field. The
following principles govern the location and layout of mine
fields :
(1) The mine field should be used in connection with tank
obstacles, natural or artificial, so that tanks in avoiding the
obstacle will pass over the field. An exception to this rule
occurs when mines are planted within wire entanglements to
destroy any tanks that attempt to open lanes through the en-
tanglement for the attacking infantry. Figure 58 shows the
use of a mine field with an antitank obstacle on a road.
(2) The mine field, regardless of whether it is composed of
mines buried in the ground or merely placed on the surface,
must be carefully camouflaged. A bombardment by artillery
will destroy a mine field. If the regular arrangement of mines
in a field is disclosed to the enemy by spots on an aerial
photograph he will destroy it by artillery fire or arrange for
the removal or destruction of the mines by troops accompanying
the tank attack.
(3) To prevent the removal of the mines the mined area
should be covered by small-arms fire of the defenders.
96
ENGINEER FIELD MANUAL
(4) The mines in a field should be in at least two rows,
laid checkerboard fashion. The intervals between adjacent
mines in a row must be so small as to prevent a tank from
passing through the row without exploding at least one mine.
The distance between rows should not exceed twice the interval
between mines in a row. Sometimes, in order to economize on
material and labor, transverse beams or sleepers are laid
across adjacent mines. The interval between mines may then
be greater than the width between treads of the tank. This
scheme has the disadvantage that mines will often be set off
outside the area of the tank. Unless excessively large charges
have been used, in which case no economy of material is
TF —Anti-tank. Pitch
* * Anti-tanK Mines
woods
Figure 58. — Antitank obstacle with mines
effected, no damage is done to the tank. It has the advantage
that mines may be set off under the belly of the tank over which
the tank would pass unharmed if the beams were not used.
(5) To prevent the defenders from entering the mine field
with vehicles, guns, or tanks by accident or through ignorance
of the location of the field, the mined area must be definitely
located on maps and, in addition, the area should be wired
in with bands of entanglement.
c. The amount of explosive which should be used in an anti-
tank mine depends on the size of the tanks against which
the mines are to be used. A comparatively small charge
exploded under any part of a tank will disable it, wherea's it
requires a very large charge outside the area covered by the
tank to do any damage. It is more desirable to prepare a
larger number of mines with smaller charges from the available
supply of explosive and space them more closely, so that any
explosion that occurs will be under the tank setting off the
charge, than to concentrate the available explosive in com-
ENGINEER FIELD MANUAL 97
paratively few mines, widely spaced. The material that will
ordinarily be used as the charge in antitank mines is our stand-
ard explosive triton as issued. However, it may often be
necessary to use high-explosive shells of various calibers. The
following table gives data as to the disabling effect of various
charges on certain types of tank used during the World War
and suggestions as to the size of charges to be used against
similar tanks.
TART.rc X. — Disabling effect of various charges on certain types
of tank
Nature, size, and location of charge
Degree of disablement
Mark V star
Light Renault
One 3-inch high-explosive shell buried 6
inches under track.
One 3-inch Stokes mortar high-explosive
shell buried 6 inches under track.
One 6-inch high -explosive shell buried 6
inches under track.
One 3-inch high-explosive shell on ground
under belly.
One 6-inch high-explosive shell on ground
under belly.
2 pounds triton buried 6 inches under track
15 pounds triton buried 6 inches under track.
30 pounds triton buried 6 inches under track.
15 pounds triton buried 1 foot in ground 2
feet from tank.
25 pounds triton buried 1 foot in ground 2
feet from tank.
15 pounds triton buried 1 foot in ground 5
feet from tank.
50 pounds triton buried 1 foot in ground 5
feet from tank.
2 pounds triton on ground under belly
None
None. Very slight
damage.
Permanent
No test
Permanent-.
No test
Permanent
Permanent. Very
extensive de-
struction.
No test___
.do..
_do_„.
_do_...
_do._.
Permanent.
No test.
Do.
Permanent.
Permanent. Com-
plete destruction.
Temporary. Con-
siderable repair
required.
No test.
Do.
Temporary.
Permanent.
None. No dam-
age.
Temporary.
Do.
Note. — The Mark V star (British) is a heavy tank weighing about 33 tons and
carrying a crew of 8.' The Renault is a light tank weighing 7}4, tons and carrying a
crew of 2.
Minimum charges for antitank mines:
Against light tanks similar to the Renault-
One 75-mm. high-explosive artillery shell, or one 75-mm. infantry howitzer
shell, or 5 pounds of triton or its equivalent in other loose explosive.
Against medium tanks (15 to 20 tons in weight)—
Two 75-mm. high-explosive artillery shells, or two 75-mm. infantry howitzer
shells, or one 155-mm. high -explosive artillery shell, or 10 pounds of triton
or its equivalent in other loose explosive.
Against heavy tanks similar to the Mark V star (British)—
One 155-mm. high-explosive artillery shell.
15 pounds of triton or its equivalent in other loose explosive.
98
ENGINEER FIELD MANUAL
d. Figure 59 shows a mine for which only standard demoli-
tion equipment is required. This mine may be built to accommo-
date any size of charge. The wooden case may consist of a
suitable ammunition packing case or other box. In case one
or more shells are to form the charge a proper sized box to hold
A Box
B Explosive Shell
C Wooden Cradle
D Strap Iron Ties
E Tetryl Caps (Duplicate)
F Instantaneous Fuses ft>up.)
G Fricton Fuse Lighters (Mupti-
cafe. Stapled to wall of Box)
H Wooden Plunger
J Strap Iron Guides (For plunger)'
K Cross He Wire (Set. Fuse Lighters)
L Tie Wires
M Wooden Cross Bar (Size varied
to break under various loads)
N Breaker Block
O Wooden Lid
A Box. K Wooden Plunger
B Explosive Charge E Friction Fuse Lighter (Stapled to matt of Boxi.
C Tetryt Cap F Wooden Cross Bar (Size varied to break under
D Instantaneous Fuse various toads)
O Breaker Block L Safety Pin (f 2d. nail. To be removed after
H Wooden Cover mine is placed)
J Tie Wires M Cross tie Wire (Between fuse lighters)
N Strap Iron Guides (fbr plunger)
Figure 59. — Antitanls mine
the shell or shells laid on their side together with the firing
mechanism shown in the illustration of the standard mine is
prepared. The two tetryl caps are inserted in the well in the
booster charge of the shell. Unless the booster charge is left
in the shell the tetryl caps may fail to explode the cast triton
in the shell.
ENGINEER FIELD MANUAL
99
e. The items of the standard demolition equipment used ir
the above described mine are susceptible to deterioration by
moisture. The mine must, therefore, be carefully waterproofed.
This may be accomplished by wrapping the box with two courses
of tarred paper and sealing all joints in the paper with roofing
tar. A more suitable means of detonating the charge in land
mines is under investigation and will be available in the future.
f. Figure 60 shows the slight modifications in the mine and
the arrangement for setting off the charge by a trip wire.
This arrangement finds application when mines are to be used
in connection with wire entanglements.
A J3ox
£ Explosive Charge
J) Instantaneous Fuses
E Smooth Wire
FJlavbed Wire
Figure 60.-
G3arbed TVire
Entanglement
H Tetryl Caps
C Friction Fuse Litht&rS
(Stapled to roatl ctf£ox)
Antitank mine with a trip wire
76. Latrines. — a. Latrines should be located in offsets from
trenches, usually not more than 50 yards away from and in
a place convenient of access for the men who will use them.
They should not be located in dugouts, except in very large
ones where special provision is made for ventilation. They
should not be located near points which are likely to draw fire.
6. Accommodation both in latrine and urinal facilities should
be 'proVided for at least 2 per cent of the command. If a
trench system is to be occupied a considerable time, facilities
should be provided for at least 5 per cent of the command.
c. Types. — (1) Bucket type. — Any type of bucket or can,
provided with a seat and cover, may be used. The buckets are
100
ENGINEER FIELD MANUAL
placed in an excavation from which tliey can be easily removed,
and a routine arrangement made for emptying them. This
system is used only where deep latrines can not be constructed.
(2) Deep latrines. — The straddle type (fig. 61), and the box-
seat type (fig. 62), are the usual types. Pits should be dug
Figure 61. — Deep latrine, straddle type
6 to 8 feet deep and, when filled to within 2 feet of the top,
should be completely filled with earth and a new latrine dug.
d. Urine troughs or tubs should be provided in every latrine ;
troughs may be easily made of standard corrugated-iron sheets.
77. Ladders and steps. — a. Ladders form the most satisfac-
tory means of exit from trenches for the purpose of attack.
ENGINEER HELD MANUAL
101
Permanent ladders 5 feet long and in sufficient numbers for
patrols are ordinarily fixed to the front wall of a trench.
b. In preparation for attack a large number of loose ladders
should be placed in the parallels of departure. When the
attack is about to start these may be supplemented by taking
Figure 62. — Deep latrine, box-seat type
up trench boards and using them as ladders, after knocking off
alternate crosspieces,
c. Steps. — To permit travel over the surface of the ground at
night, ladders, steps, or ramps should be provided along the
communication trenches throughout the position. Steps may
be cut into the earth and revetted. Figures 63 and 64 show
simple types of sortie ladders and steps.
ENGINEER FIELD MANUAL
103
78. Estimates. — a. Tables XI and XII contain estimates for
certain types of works in order that approximate computations
may be made. It must be borne in mind that the figures in
the tables are approximations only, based upon average con-
ditions, day work, and engineer tools. The actual time and
labor necessary vary greatly with such elements as training
and morale of personnel, weather, soil conditions, proximity
and activity of the enemy, kind and number of tools available,
whether the work is done by day or night, and many other
contingencies which the estimating officer must evaluate to the
best of his experience and ability. For night work add 50 per
cent to man-hours in tables. For infantry tools add 40 per
cent to man-hours in tables. The personnel indicated in Table
XII represents the maximum number of men that can ordi-
narily be used effectively on the given item of work.
Table XI. — Time and labor estimates
Description of work
Re-
sults
Man-
hours
Reference
in this
manual
Remarks
Excavation cubic feet..
Trenches, type A, unrevetted —
Fire_ linear feet..
Communication do
Revetment (front slope of trench only):
Sandbag type linear feet_.
Wire-mesh type do
Automatic-rifle emplacement
Machine-gun emplacement:
Shallow type
Standing type
Splinter-proof type, double emplace-
ment
Reinforced concrete type
Emplacement for 37-mm. gun
Emplacement for 3-inch mortar
Wire entanglement:
High-wire entanglement (two rows of
, yards..
Double-apron fence do —
Clearing the field of fire: 2
Small brush square yards..
Undergrowth and some small trees
square yards..
Brush and trees do
100
5
5
50
50
100
100
100
i 720
3
24
Table IV.
Fig. 18...
Table V..
Fig. 21...
Table V..
Fig. 25...
Fig. 31...
Fig. 37.
Fig. 38.
Fig. 42.
Par. 61..
Fig. 43.
Par. 61.
Par. 45.
.do...
-do...
Materials at
site.
Do.
Do.
Do.
Do.
1 Plus the time necessary for the concrete to reach its effective strength. (See
par. 58.)
1 This contemplates fairly complete clearing, including removal of debris. A
light clearing or thinning out to improve the field of fire can be accomplished in less
time.
104
ENGINEER FIELD MANUAL
Table XII-
-Approximate time and labor estimates for hasty
works 1
Work
Number
of men
Number of man-hours in—
Soft soil
Average
soil
Hard
soil
Company command post, hasty '_.
Company observation post, hasty 1
Light 2-man shelter in trench *
Aid station, local, hasty 1
Battalion observation post, hasty
Battalion command post, hasty 1 .-.
Battalion aid station, hasty 1
2-3
2
2
2-4
2-4
8-16
8-16
24
12
12
24
20
100
100
1 Plans for these works are not given, as the nature of the work must be adapted to
the terrain features available. The working parties and man-hours given are the
minimum required in order to provide protection comparable to that given other
elements of the defense in a hasty organization of the ground.
2 For plans see See. V.
6. These tables should be of value to commanders and staff
officers in determining the extent to which it is possible to or-
ganize any given front in a given time with a given number of
men. They are also of value as a measure of the efficiency of
the troops, and especially of the junior officers who actually
supervise the work. Time allowances are liberal and troops who
do not come up to these standards are below average.
o. Estimates for defensive positions involve a summation
based upon the total length of the various types of trenches
to be dug, the number of emplacements for infantry weapons
to be constructed, the drainage requirements, and trench acces-
sories contemplated. Table XI gives time and labor figures,
which should be carefully weighed in view of local conditions,
for the more important units in this summation. Highly organ-
ized positions, particularly those containing many light and
heavy shellproof shelters, require large quantities of materials,
the procurement and transportation of which are separate prob-
lems of great magnitude. There is a most important distinction
between the works that are characteristic of a hasty organiza-
tion and of a deliberate organization. Hasty organization is
understood to mean one that can be installed during a single
day ; that is, in six to eight hours, and with no materials except
for wire entanglements. Deliberate organization requires much
time, labor, and materials, accordingly it should not be under-
taken except on the orders of higher commanders, usually the
ENGINEER FIELD MANUAL
105
commander in chief, who alone is qualified to decide whether
the situation calls for such effort and who alone can make
available the great supplies of materials and other facilities.
d. The following general rules for the execution of the work
after estimates have been made are applicable to all details
of field fortification :
(1) Assign to each organization the construction of the works
it will itself occupy and defend.
(2) Assign to each organization the work it is best equipped
and trained to perform.
(3) Assign work of general interest, such as clearing the
.field of fire, improvement of routes, etc., to special units and
attached troops.
(4) Avoid the splitting up of any unit amongst a large num-
ber of tasks, especially if they are widely distributed. Assign
as few different tasks as possible and all in the same locality.
(5) Avoid the shifting of units or individuals from one task
to another.
(6) Avoid the assignment of men from different organizations
to the same task.
(7) Avoid the splitting of units or violation of tactical integ-
rity. Use complete squads, complete platoons, and even complete
companies as far as possible.
(8) If there be not enough men for all tasks in the allotted
time, make sure that the most important tasks will be completed
on time, and others as far as possible.
(9) It will never be possible to observe all of the foregoing
rules, precisely. Each should be given all the weight that the
situation permits.
Section V
PROTECTED SHELTERS
79. Classification of shelters based on degree of protec-
tion. — Protected shelters are classified according to the degree
of protection they afford, as follows :
a. Splinter-proof shelters protect against rifle and machine-
gun fire, splinters of high-explosive shell, and grenades, but
not against direct hits by 3-inch shells. They require only
that an overhead cover of compact earth of about 1 foot in
thickness (or its equivalent in other material) be securely
supported. When these shelters are numerous and are care-
fully located, casualties may be greatly reduced.
106
ENGINEER FIELD MANUAL
6. Light shelters protect against direct hits, and in some
cases against a continued bombardment by 3-inch shells.
c. Light shellproof shelters protect against continuous bom-
bardment by all shells up to and including the 6-inch.
d. Heavy shellproof shelters protect against continuous bom-
bardment by at least 8-inch shells. Some types may be proof
against larger shells or against all types of artillery fire.
80. Classification based on method of construction. — Shel-
ters may further be classified as to the method of construction,
which depends on the character of the ground, the materials
available, and the protection required. The classification is — •
a. Surface shelters. — These structures, or at least the greater
portion of them, are built at or above the surface of the
ground. This type has a maximum of observation and facility
of exit and requires a minimum of labor ; on the other hand,
it is relatively conspicuous, requires considerable cover ma-
terial, and provides the least protection. Shelter of this type
is seldom used for the protection of personnel in advanced
lines, unless it can be concealed in woods, on a steep reverse
slope, or among the buildings of a village, or unless the under-
ground water level is so close to the surface that the cut-and-
cover type can not be used. One exception to this rule, how-
ever, may be the reinforced concrete shelter, though this type
often approaches cut-and-cover construction. Light shelters,
consisting of almost any type of small improvised shed covered
With a layer of earth, may be used for the protection of am-
munition and stores. These shelters should be of small
capacity, well dispersed, and carefully concealed.
6. Cut-and-cover shelters. — (1) This type consists of an open
excavation in which the framework for the shelter is placed,
after which the excavation is back-filled around and over the
framework to the level of the original surface, or somewhat
above. To increase the resisting power of the overhead cover,
concrete, steel beams, broken stone, and other materials of
high resistance to penetration are used in the roof construc-
tion. It is a type intermediate between the surface and the
cave shelter.
(2) The cut-and-cover shelter, comparing it with the cave
shelter, is adapted for use as dressing stations because it is
easily cleaned, is well ventilated and lighted, and facilitates
the ready admission and evacuation of casualties. Out-and-
ENGINEER FIELD MANUAL
107
cover shelters are generally more quickly constructed but re-
quire much larger quantities of material than cave shelters.
They do not resist intensive shelling as well and are more
difficult to conceal than cave shelters.
(3) When surface and underground water or the hardness
of underlying rock makes the construction of cave shelters im-
practicable, cut-and-cover shelters may be used. They are
also used where need for rapidity of exit prohibits the use of
cave shelters (as in important machine-gun shelters in or near
the front line) ; in wooded areas or in buildings where conceal-
ment is easy and where ample material is available ; in situa-
tions requiring immediate shelter which can be most quickly
obtained by this type.
(4) A cut-and-cover shelter providing protection against
6-inch shell does not usually present great difficulties, but it is
generally impracticable to attempt to get protection by cut-and-
cover methods against heavier shell without constructing the
shelters partially or entirely of concrete.
c. Concrete shelters. — With an adequate supply of plant, ma-
terials for the aggregate and for forms, protection may be ob-
tained by either surface or cut-and-cover methods by the con-
struction of concrete shelters.
d. Cave shelters. — (1) Cave shelters are constructed entirely
below the surface of the ground by mining methods and have
a cover of undisturbed or virgin earth. They are the least
conspicuous of all types and afford the greatest protection
which can be secured before the shelter is completed. They
require a minimum of material. They also afford a minimum
of observation, worse living conditions than other types, greater
difficulty of exit, and their drainage may be difficult.
(2) Cave shelters should be constructed in preference to
other types whenever material and time are available and
physical and ground-water conditions permit. It is difficult
if not impossible to increase the overhead protection of these
shelters after completion, since the protection depends upon
the depth at which the chamber is built. For this reason it is
important not to underestimate the amount of protection needed
when the depth is determined. On the other hand, it is equally
important not to overestimate the amount of protection needed,
because of the time, labor, and material involved in going to
unnecessary depths.
66842°— 32 8
108
ENGINEER FIELD MANUAL
81. Choice of type. — The type adopted should be suitable to
all the conditions of the case ; each selection is a separate and
distinct problem. The more important considerations are as
follows :
a. The use for which the shelter is designed. This is usually
the most important consideration and depends on the tactical
situation.
6. The terrain, with especial reference to slope and its effect/
on the type of entrances and the rapidity with which overhead
cover can be gained, wooded areas and buildings which pro-
vide materials and facilitate concealment, and the disposal
of spoil. Reverse-slope positions are difficult for the artillery
to hit and are usually easily drained.
c. The subsurface conditions, such as extent and character
of underlying rock, position and thickness of impervious and
water-bearing strata, and the amount of water to be controlled.
(See Sec. III.)
d. The facilities available, including time, personnel, tools,
material, and transportation.
82. Protection against aerial bombing. — In future wars air-
planes and dirigibles will undoubtedly play an even more
active part than in the past. Consequently, protected shelters
may be necessary in rear areas for security against enemy aerial
bombing.
83. Location. — a. Shelters should be near the combat or as-
sembly positions of the troops occupying them. This rule, of
the utmost importance near the front, is of relatively less im-
portance toward the rear.
6. The facilities for cover and concealment afforded by the
terrain influence the location of shelters. Steep reverse slopes,
quarries, etc., can be prepared to afford excellent shelter with
comparatively little labor. Every advantage should be taken
of any natural shelter in the locality, tactical considerations
permitting.
c. Splinter-proof and light shelters are the only types per-
mitted in the outpost lines and main line of resistance. Cave
shelters are located in rear lines, off communication trenches,
switch trenches, and in strong points in the reserve line.
84. Facility of exit. — a. Facility of exit is secured by de-
signing shelters of small capacity, a minimum depth below
ENGINEER FIELD MANUAL
109
ground, and having unrestricted entrances. It is particularly
important near the front.
&. Large shelters are provided with at least two entrances
and preferably with a third for emergency use. This supple-
mentary exit should emerge in a different trench from the
other two, or at least at some point well concealed or camou-
flaged, permitting the garrison to escape and launch a counter-
attack on an enemy attacking the main entrance. Entrances
should be spaced to avoid the danger of one shell burst block-
ing two of them (a minimum of 40 feet apart and separated
by a traverse or angle in the trench). Large systems of cave
shelters should be constructed to provide one entrance for
every 25 men.
85. Concealment. — a. It is important that the location and
number of shelters be concealed from hostile observation.
6. Surface shelters to be inconspicuous must be hidden by
existing features of the terrain, as in a wood or among build-
ings in a village.
e. For concealment, cut-and-cover shelters must be kept low.
The surface of the ground where disturbed must be restored
to its previous appearance. Necessary measures should be
taken to conceal the work while in progress.
d. Cave shelters are the easiest to conceal, as they do not
disturb the natural surface of the ground. However, it is
difficult to dispose of the spoil without attracting the attention
of the enemy.
e. It is very important during construction to conceal all
signs of activity. Construction materials and excavated earth
must be carefully camouflaged and strict camouflage discipline
demanded of the men carrying on the work. .
f. Concealment is facilitated by placing the entrance to a
shelter in a trench, thereby providing a protected outlet and
inlet and avoiding overground trails or footpaths
86. Observation. — Shelters should, if practicable, be provided
with means of observation, such as loopholes in a surface
shelter or a periscope in the roof of a cave shelter. The
upper end of the periscope should be camouflaged.
87. Drainage, ventilation, and gas proofing. — a. Drainage. —
(1) In the case of surface shelters, drainage presents few
difficulties.
110
ENGINEER FIELD MANUAL
(2) In the case of deep shelters, it sometimes becomes a
complex problem which includes the following elements :
(a) The exclusion of surface water from the entrance.
(6) The exclusion of seepage from the chambers, shafts, and
galleries.
(0) The removal of water that has collected in the chambers
and galleries.
6. Ventilation. — In the hasty or splinter-proof shelter, ven-
tilation presents no problem ; but in the cave shelter, with its
underground chambers, it becomes of vital importance. Ven-
tilation is provided by the entrances and by openings through
the roof, all so equipped that they can be closed to exclude
gas. For further details see paragraphs 136, 137, and 138.
c. It should be possible to make all shelters, and particularly
those below ground, gas tight. A shelter not in use should be
sealed to exclude gas, otherwise, casualties may occur when it
is again used. For details of gas proofing see paragraph. 129.
88. Requirements for shelters in advanced positions. — a.
Shelters in advanced lines should be —
(1) Well distributed, placing the troops close to their combat
positions.
(2) Constructed without going to great depths in order to
provide for ease of exit.
(3) Provided with, a direct and easy exit (even at some
sacrifice of cover).
(4) Of small capacity (from two to eight men).
(•5) Of a type that can be rapidly constructed.
(6) Concealed as thoroughly as possible.
These requirements limit the type to the splinter-proof or the
light shelter.
6. The construction of light shelters is usually started by
infantry holding the front lines. They are located in the
individual rifle pits or in the trenches resulting from organizing
the position. To prevent caving, they are lined with logs or
timber, depending upon material available. They should have
at: least 4 feet of cover. For construction details see
paragraphs 116 to 135, inclusive.
89. Requirements for shelters in rear positions. — Shelters
in rear positions may be larger and deeper than those at the
front. The occupants have more time to emerge after the
ENGINEER FIELD MANUAL
111
warning of the attack has been received, and can occupy their
positions more deliberately. They can be given the maximum
of overhead cover in order to withstand the bombardment of
heavy shells, giving the troops occupying them the necessary
rest and feeling of security. These shelters are built entirely
below ground, if underground water conditions permit, and
are carefully hidden from enemy aerial observation.
90. Thickness of overhead cover. — The thickness of over-
head cover is governed by —
a. The artillery fire to be resisted.
6. The character of the covering material.
c. The arrangement of the successive layers.
d. The interior construction of the shelter.
91. Materials employed. — Materials for overhead cover fall
into two main classes :
ft. Virgin soil (in undisturbed condition) existing in the case
of cave shelters. — This is the best form of cover if sufficient
thickness can be provided. It may, however, particularly in
soft ground, be reinforced by the addition of a bursting layer
consisting of any of the following materials :
(1) Concrete slab bursters, which are described in para-
graph 103.
(2) Broken stone or brick, layer at least 18 inches thick.
(3) Layer of I-beams, reinforced concrete beams, or rails
set on edge and firmly wired together.
6. Artificial substitutes used in all forms of cut-and-cover and
surface shelters. — Artificial substitutes in addition to earth are
employed in the construction of cut-and-cover and surface shel-
ters. Protection is usually secured by alternating layers of
various resisting materials; but to acquire a degree of protec-
tion equal to that of the deepest cave shelters would cause the
mound to project too far above the ground and would involve
too great a quantity of material. Consequently cut-and-cover
and surface shelters (other than those of concrete) are designed
for protection against calibers less than 8 inches.
92. Thickness of cover for various shells. — ai. The following
table may be used for computing the thickness of cover required
for various shells under different ground conditions. (See
Sec. II.)
112 ENGINEER FIELD MANUAL
Table 'Kill.— Minimum thickness in feet of overhead cover
Nature of cover
Size of projectile
Rifle, machine
gun, fragments
CB
ja
CO
M
CD
J=
a
8
a
o
n
CD
M
0>
•s
a
00
K
0)
Xi
CJ
d
o
M
0>
S3
o
a
CN
M
0>
S3
CJ
a
CD
w
CO
S3
CJ
a
00
Reinforced concrete
1.0
1.5
2.0
3.5
2.4
3.6
4.8
3.4
5.1
5.0
6.0
7.0
11.0
Masonry, solid: Brick,
stone, plain concrete
7.5
10.0
17.5
37.5
9.0
12.0
21.0
Logs, 8" minimum diam-
eter wired
6.8
11.0
25.5
34.0
Crushed stone . .
8.4
18.0
24.0
Tamped or packed earth.
Loose earth. _
1.0
3.0
7.5
10.0
Cave shelters:
Sandstone or granite-
Soft limestone
Undisturbed earth
2.0
3.0
fi.O
6.0
9.0
12.0
8.0
11.0
17.0
10.0
15.0
25.0
13.0
20.0
30.0
14.0
21.0
32.0
17.0
27.0
40.0
24.0
36.0
48.0
Figures to the right of and below the heavy line are for shelters that would normally
be constructed by cut-and-cover methods; those to the left are normally for surface
shelters. The dividing line is not fixed, as the determination of the type depends on
the location, materials, and the labor and time available.
h. The figures in the table are for material of uniform char-
acter from the top of the chamber to within a foot of the
surface. If a tamping layer of soft material overlies rock,
the total depth from surface to chamber roof must be increased
by the effective depth of the tamping layer.
c. Excavation for cut-and-cover shelters reaches practical
limits at a depth of cut of about 12 feet below the surface.
AH shelters with a base to be placed lower than this should
be constructed by mining methods (cave shelters).
93. Layers; arrangement and number. — a. The strength of
the overhead cover depends as much on the manner in which
the various layers of covering are arranged as on the character
of the materials of which it is composed. The proper ar-
rangement of layers is shown in Figure 65.
b. Component layers consist of the following:
(1) Bursting layers must be provided for all cut-and-cover
and surface shelters to cause the force of the explosion to be
expended upward, due to lack of tamping effect. They are
effective against shells with instantaneous and short-delay
ENGINEER FIELD MANUAL
113
fuzes. The bursting layer may be made from any of the ma-
terials listed in paragraph 91a, should be in the form of an
umbrella, and should extend well beyond the shelter on the
sides and toward the enemy. It should extend, to a point well
beyond a line drawn tangent to the bottom edge of the shelter
at an angle of 45° to the vertical. Bursting layers should be
covered with not more than 9 inches of earth, which should
preferably be sodded. This serves to conceal the shelter, pre-
vents flying splinters, and reduces the disintegration of the
burster layer by several hits in the same place.
(2) Distributing layers of logs firmly wired together, steel
I-beams, rails, or concrete beams set on edge are essential to
distribute the strain and to prevent the penetration of shell
to V&aChstrA dry
virjjiiv earth
IVoaf «£ftin*i g" Shall
~IKrtrihutitt<J Inyer
Shodk-nKforhuvj cushion
Distributing Inj|«r
tOi4orhln<> cushion
Figure 65. — Diagrammatic section showing name, character, and correct
manner of placing successive layers of artificial cover
fragments. These layers are placed in accordance with prin-
ciples illustrated by the example in e below. The weight of
the over-head cover is carried by the lowermost distributing
layer which rests on berms left in the natural soil. Thus, the
weight of the cover and the shock of explosion are transmitted
to these berms rather than to the interior framework.
(3) Shock-absorbing cushions are essential beneath the burst-
ing layer, over the top of the inner framework, and between
the distributing layers. The one beneath the bursting layer
may be of loose or tamped earth, the others of tamped earth
or broken stone, except the one immediately above the shelter,
which should be of tamped earth. Fascines are sometimes sub-
stituted for tamped earth with satisfactory results. The omis-
sion of these shock-absorbing cushions is one of the most fre-
114
ENGINEER FIELD MANUAL
quent causes of the failure of cut-and-cover shelters. The top
and bottom cushions are the most vital, and under no circum-
stances should they be omitted.
c. Proper interior support is essential to secure the full value
of overhead cover. The clear span of the interior framework
must not exceed 6 feet 6 inches for cut-and-cover or 8 feet for
cave shelters. The figures for cover are based on the use of
these spans and upon the use of standard-size timbers prop-
erly supported. If these are not used, the cover provided, if
based on Table XIII, may be insufficient.
H. The shock Or blow of the explosion strikes the stiff dis-
tributor course and is spread over the cushion ; the latter ab-
sorbs part of it and further spreads its effect before it strikes
the next distributor course, where it is again spread over a
wider area, until finally, when the blow reaches the inner
shell of the shelter chamber, it is so distributed and absorbed
as to be sustained without rupture.
e. An example of the computation for cover to protect against
6-inch shell, using several classes of material, similar to that
used in Figure 65, is given. It is assumed that the material
available for cover consists of 8-inch diameter logs, standard
bursters and beams, and earth, the latter to be tamped or
packed. With the general number and arrangement of layers
determined on, it is desired to And the thickness of earth that
is to be distributed in the cover. From Table XIII the total
cover for tamped earth alone is 25.5 feet. Any other material
except loose earth reduces this figure by the ratio of thickness
used to thickness required if the material were to be used
alone. Thus reinforced concrete would be required in thick-
ness of 3.4 feet if used alone, but as 0.415 foot only is used
in one layer of concrete bursters, the layer has a value equiv-
alent to 12.2 per cent of the total thickness for the material
used alone. The following values are used in the above man-
ner in the computation of the percentage equivalence of the
whole thickness for each material used, except earth :
2 layers standard concrete beams- 0.83 foot thick (or high).
1 layer standard concrete burs-
ters .415 foot thick
1 layer of 8-inch diameter logs . 66 foot thick
Then the per cent of total cover allocable to these materials
ENGINEER FIELD MANUAL
115
Per cent
Concrete beams-
Concrete bursters.
Logs
(0.83h-3.4)X2= 48.8
0. 415H-3. 4 = 12. 2
0. 66 h-6. 8 = 9. 7
Per cent of cover allocable to tamped earth.
70.7
29.3
100.0
25.5X29.3 per cent=7.5 feet or four layers of equal thickness at
1.88 feet each.
94. Concrete as overhead cover. — a. Concrete, either plain
or reinforced, is a most effective shell-resisting material.
6. There are apparent drawbacks to the use of concrete in
active warfare, but some may be more apparent than real.
These drawbacks are —
(1) There are too many workers concentrated in a small area.
(2) Construction time is long when Portland cement is used.
(3) Cement at the front is likely to deteriorate; it is neces-
sary and difficult to keep it dry.
(4) Due to interruptions, it is often impossible to obtain a
continuous pour of concrete and a truly monolithic shelter.
c. The use of quick-hardening, or alumina, cement concrete
in place of standard Portland cement reduces the construction
time, because the former attains about 75 per cent of its full
strength in 24 hours, against 24 days for Portland cement con-
crete ; it also permits of work at relatively lower temperatures.
The final forms (beams, slabs, etc.) may be removed, if neces-
sary, about 30 hours after pouring alumina cement concrete.
d. Where the amount of concrete to be poured is relatively
large, and other conditions, as hostile interference and observa-
tion, do not control, concrete mixing should always be done
by power mixers if they can be obtained. The mixing of con-
crete by machinery should be made the rule, even in small
batches of a few yards, to reduce the time of the operation
and the number of men necessary.
e. The construction time includes the whole period of work
from commencement of labor to the time when the structure
becomes effective for use. The factor of transportation of
materials may have a delaying effect if the amounts required
are excessive. Comparing shelters of equal capacity and resist-
ance, the necessary transportation for materials for a concrete
116
ENGINEER FIELD MANUAL
shelter is, in most cases, considerably less than for a shelter con-
structed of lumber, logs, rails, concrete beams, and crushed stone.
f. Existing conditions may cause cement to deteriorate. The
ability to protect cement from deterioration increases in pro-
portion to the distance from the front line.
g. The liability to interruptions in pouring depends on the
location of the shelter with regard to the front line. The
shortened period of construction due to the use of machinery on
a well-coordinated job lessens the importance of this drawback.
95. Standard construction materials. — a. During the World
War standard materials were developed for use in the con-
struction of protected shelters and were distributed by engineer
agencies. Their use resulted in economy of material and labor.
The construction materials described are a result of experi-
ence in the World War and are given as a guide for establish-
ing standard materials under future similar conditions.
Z>. Cases will often occur where round timbers cut near the
site will have to be used in lieu of dimensioned lumber. The
following table gives a number of standard-size sawed timbers
and the round timbers which should be used in lieu of them.
Table XIV. — Equivalent timbers used as beams
Sawed
timbers,
width X
depth
Area
(square
inches)
Equiva-
lent
round
timber
diameter
in
inches
Area
(square
inches)
1X4
4
3
7. 1
1J4X6
9
m
15.9
2X4
8
4
12.6
2X6
12
5
19.6
2X8
16
6
28. 3
2X10
20
7
38.5
3X3
9
3H
9.6
3X6
18
6
28. 3
3X10
30
8
50. 3
3X12
36
9
63.6
4X4
16
5
19.6
SX10
50
10
78.5
6X6
36
7
38.5
8X8
64
10
78. 5
8X12
96
13
132. 7
8X14
112
14
154.0
8X16
128
15
177.0
12X12
144
14
154.0
Note. — The equivalent round timbers are also safe'as columns. In making up the
table, primary consideration was given to the resistance to bending. However, in
every case the round timber will resist more vertical shear than the timber of rec-
tangular cross section to which it is equivalent.
ENGINEER FIELD MANUAL
117
96. Dimensions governing standard shelter materials. —
The following tables give the sizes of the various classes of
galleries and shafts and include material lists for cases and
frames for these classes.
Table XV. — Dimensions of gallery anil shaft oases and frames
Size of —
Inside clear
Height
Width
6' 4"
8' 0'
6' 4"
6' 6'
6' 4"
3' 0'
4' 6"
3' 0'
2' 10"
3' 0'
2' 4"
2' 0'
Chamber gallery
Great gallery
Common gallery
Half gallery
Branch gallery
Small branch gallery.
Table XVI. — Material list, gallery ami shaft cases
Item
Great gallery
Common
gallery
Half gallery
Branch
gallery
Small branch
gallery
Cap
Sill
Post _
Spreader
Nails ^pounds. _
Weight. ..do
1-4X10X7'2"
1- 3X10X7'2"
2- 4X10X6'6"
2-lX10X6'6"
Yi lb. lOd.
385
1-3X10X3'6"
1- 3X10X3'6"
2- 3X10X6'6"
2-lX10X3'0"
Yi lb. lOd.
220
1-3X10X3'6"
1- 3X10X3'6"
2- 3X10X4'8"
2-lX10X3'0"
YiVo. lOd.
180
1-3X10X3'6"
1- 3X10X3'6"
2- 3X10X3'0"
2-lX10X3'0"
Yi lb. lOd.
150
1-2X10X2'4"
1- 2X10X2'4"
2- 2X10X2'6"
2-lX10X2'0"
Yi lb. lOd.
75
1 Nails for spreaders only.
Table XVII. — Material list, gallery and shaft frames
Item
Chamber
gallery
Chamber
gallery
Great gallery
Common
gallery
Cap, I-beam '
1-3X5X9'0"
2 standard
Beam shoe. _ _
Cap
2-3X10X9'0"
l^tX 6X9'0"
2-6X 6X6'6"
2-1X 6X8'0"
0.41b. lOd.
440
1-6X9X7'6"
1- 4X6X7'6"
2- 6X6X6'6"
2-lX6X6'6"
0.41b. lOd.
375
1-6X8X4'0"
1- 3X6X4'0"
2- 6X6X6'6"
2-lX6X3'0"
0. 2 lb. lOd.
255
Sill
Post
Spreader
2-fiX6X6'6"
Weight do
250
'I-beams 3"X5"X9% pounds per foot. *Nails for spreaders only.
Item
Half gallery
Branch
gallery
Small branch
gallery
Cap _..
1-6X6X4'0"
1- 3X6X4'0"
2- 6X6X4'8"
2-lX6X3'0"
0.21b. lOd.
195
1-4X5X3'8"
1- 3X4X3'8"
2- 4X4X3'0"
2-lX4X3'0"
0.21b. lOd.
80
1-3X4X2'6"
1- 3X3X2'6"
2- 3X3X2'6"
2-lX3X2'0"
0.2 lb. lOd.
35
Sill
Post
Spreader
Weight . --. . do -..
1 Nails for spreaders only.
118
ENGINEER FIELD MANUAL
97. Cases, gallery, and shaft. — a. The standard common gal-
lery case is shown in Figure 66. It is designed as a lining,
without additional lining material, for use in horizontal gal-
Spreader
-3o*-
5»10'«G'-6'
a^r 'adcrl ; 10*3 :
sill3'«10»3'-fi
/ -
o o
Elevation
u.
Convttvotv Gallery Case
Figubb 66.-
Improvlsed Qaltety Case
-Gallery cases
leries, inclined passages, and in shafts ; the dimensions of lum-
ber used vary with the size of gallery or shaft (Table XVI).
In horizontal and inclined passages the cases are ordinarily
Side Elevation
Corner Detail
Figure 67. — Improvised shaft set
placed in a vertical position and in shafts they are always
horizontal. When dimension lumber is not at hand, cases may
be improvised from round timber as shown in the figure.
ENGINEER FIELD MANUAL
119
&. The great gallery case finds little use except in the appli-
cation to special approaches or passages, as in first aid shelters.
When used in this way the cases may be narrowed to any width
desired for economy in excavation without sacrifice of space.
The use of the branch gallery case provides for the construct-
ion of the timbered light shelter shown in Figures 78 and 79.
It also fulfills the requirement for ventilation shafts in cave
shelters. The half and branch gallery cases serve for machine-
gun shafts, for emergency exits, or for access to observation
posts.
98. Frames, chamber, gallery, and shaft. — a. Standard
types of frames are shown in Figure 68. They are used in
horizontal or inclined passages or in shafts, to support the
accompanying sheeting which forms the lining of the passage
or shaft. For use in shafts all timbers of a frame should be
the same size as given for frame posts. The dimensions are
such as to permit a frame spacing of not over 4 feet on centers.
When dimension lumber is not available, frames can be impro-
vised from round timber as shown in the figure.
&. The chamber frame is designed for use in the rooms or
chambers of cave shelters. The posts may be furnished in 6 by
6 inch dimension timber or round logs at least 6 inches in
diameter at the small end. If the latter are used, they must
be straight and as free from knots as possible. Caps are 3 by
5 inch steel I-beams, 9 feet long, weighing 9% pounds per foot.
They are held on the posts by standard beam shoes fastened to
the posts by spikes or lag screws. A 2-inch notch is cut in the
floor to receive the bottom of the post. In soft ground, foot
blocks of 3 by 10 inch plank, 18 inches long, are placed under
the posts. In very soft ground, such as clay, the bottoms of the
posts should be sunk from 4 to 6 inches into the floor. If steel
I-beams are not available, 6 by 10 inch timber or two 3 by 10'
inch planks spiked together may be used for the cap.
99. Standard sheeting. — Sheeting is used for supporting the
ground between frames in chambers and galleries and in inclines
and shafts where frames rather than cases are used. Two-inch
sheeting is furnished for the roof and iy 2 -inch for the sides.
It is normally made in 5-foot lengths varying from 4 to 10
inches in width. For frame spacing of 3 feet center to center,
4-foot lengths of sheeting afford economy of material and work.
Boards selected from the side sheeting should be used for head
boards and stair risers which are W-i by 10 inches by 3 feet
120
ENGINEER FIEM> MANUAL
Standard Chamber Frame
I 1 \ ^ a- a-xic? sjiikcct ia$eOu>r \ J
^ *ik« 'Spreads* W
EmlEIaw Side Elevattotv
Improvised Chamber Frame
Figure 68. — Frames for chamber and gallery
ENGINEER FIELD MANUAL
121
6 inches in stepped inclines. If standard sheeting is not avail-
able and ground conditions are favorable, round poles 2% inches
in diameter at the butt and 4 to 5 feet long may be used instead.
100. Wedges. — Wedges are used for bracing timbers tightly
against the walls and roofs of excavations, holding them in place
until the settling of the ground has rendered displacement im-
possible. Wedges must be provided in large quantities and freely
used. The dimensions of the wedge are shown in Figure 69.
101. Sandbags. — The standard sandbag is 14 by 26% inches
flat, with an attached tie string 3 inches from the top of the
bag. When filled three-fourths full, it weighs from 45 to 75
pounds, depending upon the material and whether it is wet or
dry, and fills a space approximately 4% by 10 by 19 inches.
Other sizes of bags are frequently encountered.
102. Bunk posts. — Bunk posts are 4 by 4 inches and 2 by 4
inches, and are used for supporting the double tier of bunks
in shelters. The 4 by 4's should be placed under the caps of
the frames, thus providing additional support. In case stand-
ard materials are not available, round timber 4 inches in di-
ameter at the small end may be substituted.
103. Standard concrete bursters and beams. — Standard
bursters and beams are used in cave shelters to provide a
burster layer over entrances and in cut-and-cover shelters to
provide bursting and distributing layers. They provide an
efficient means of protection only when wired securely together,
and should never be used unless so secured. Loops are pro-
vided at the corners of the bursters and on top of the beams
for this purpose. Details are shown in Figure 69.
104. Use of lumber. — Commercial lumber cut to proper
lengths is used for props, bunks, gas curtain frames, battens
for holding timbers in place during construction, and for strap-
ping incline and shaft sets together, making bomb recesses,
baffle boards, etc. Scrap lumber obtained during cutting should
be used in conjunction with wedges for blocking timbers in
place.
105. Corrugated steel arches. — Arches are fabricated from
heavy corrugated steel. (Fig. 70.) They are classified as to
name and size as —
a. Two man, for splinter-proof and light shelters.
6. Light elephant, for splinter-proof and light shelters.
c. Elephant, for light Shellproof shelter.
122
ENGINEER FIELD MANUAL
106. Quick-hardening cement. — a. For war work when a
saving of days is essential, the use of quick-hardening or
MAde in lengths at eft. 12 ft. And 15ft.
VeigMJS'perft.
fbr 6'0'beam lift je'diA.roa or 'G<oire>
19ft. of fcdtA.rod or"£ivire
Concrete Burster
Burster Assembly
— 1-_
r
*■
\
\
Ui7eq§a
Figure 69. — Standard materials
alumina cement permits the construction of fleldworks of con-
crete which have an effective strength in 24 hours instead of
about the same number of days as is the case for Portland
ENGINEER FIELD MANUAL
height one
section ■i±* f
123
—z : z "—
Eteu^tiotv,
Jfo.US.U2G.
(05 'thicKaess)
Weight one
section JO'
3 "6 beveled
&3~'JO : G : ionj> jpaced
Z : 6"centers
Cross Stciion.
Elevation
Li$ht Elephant
4*J0"lreveled
^t&JO'Siltat each joint
-Z : 9~—
Elevation
Figure 70.-
66842°— 32 9
Elephant
-Corrugated steel arches
124
ENGINEER FIELD MANUAL
cement. Concrete made with quick-hardening or alumina ce-
ment also has a much higher ultimate strength than when
Portland cement is used.
6. The following table indicates the relative value of Port-
land and alumina cements. The data are taken from a series
of tests by the United States Bureau of Public Roads, a medium
mix being used.
Table XVIII.— Compressive strength of 6 by 12 inch concrete
cylinders, pounds per square inch
Age
1-2-4
1-3-6
Lumnite
Portland
Lumnite
Portland
24 hours ______ ___ _ _.
4,960
6,200
6, 318
346
1,276
2,867
2,303
3,465
3,689
7 clays _
468
814
28 days
Note.— The figures, 1-2-4, 1-3-6, indicate proportions by volume, of cement, fine
aggregate (sand), and coarse aggregate (gravel or broken stone), respectively.
107. Methods of excavation. — a. In earth the pick and shovel
are used to make the excavation, with the aid of such accessciry
tools as crowbars and pick mattocks. In advancing an incline
or gallery, care should be taken not to open up more ground
than is necessary to accommodate the timbering. Methods of
rock excavation are not discussed here for the reason that
shelter construction in rock is unusual.
b. Removal of the excavated material. — (1) In small head-
ings the excavated material or " spoil " is removed from the
working faces by shoveling it into bags which are carried
away to the place of disposal. In fairly large headings, wheel-
barrows and small tramcars may be used to convey the material
away. For large jobs, an electric railway installation may be
desirabl
…[truncated]