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FM 6-40
WAR DEPARTMENT
FIELD ARTILLERY
FIELD MANUAL
*
FIRING
FM 6-40
FIELD ARTILLERY
FIELD MANUAL
v«
FIRING
Prepared under direction of the
Chief of Field Artillery
UNITED STATES
GOVERNMENT PRINTING OFFICE
WASHINGTON: 1939
For sale by the Superintendent of Documents, Washington, D. C.
Price 25 cents
WAR DEPARTMENT,
Washington, October 10, 1939.
FM 6-40, Field Artillery Field Manual, Firing, is published
for the information and guidance of all concerned.
[A. G. 062.11 (7-14-39).]
By order of the Secretary of War:
G. C. MARSHALL,
Chief of Staff.
Official :
E. S. ADAMS,
Major General,
The Adjutant General.
ii
TABLE OP CONTENTS
Chapter 1. The Firing Battery. Paragraphs Pages
Section I. General 1-7 1-3
II. Precautions in firing 8-12 3-6
III. Posts and duties 13- 24 6- 10
IV. Organization of the position 25- 38 10- 16
V. Fire commands and their execu-
tion 39- 76 16- 35
VI. Examples of fire commands 77- 79 35- 40
Chapter 2. Elementary Ballistics and Disper-
sion, and Effects of Projectiles.
Section X. Elementary* ballistics and disper-
sion 80- 85 41- 48
II. Effect of projectiles 86- 89 49- 52
Chapter 3. Preparation of Fire.
Section 1. General 90- 94 53- 54
II. Preparation of fire with instru-
ments 95-109 54— 68
III. Firing charts 116-114 68- 74
IV. Survey operations, plans, and pro-
cedure 115-122 74— 87
V. Preparation of fire from firing
charts - 123-133 87- 99
VI. Schedule fires 134^142 99-120
Chapter 4. Conduct of Fire.
Section I. General 143-147 121-123
II. Attack of targets 148-151 123-125
III. Axial 152-156 126-135
XV. Lateral 157^164 135-146
V. Combined 165^-170 147-152
VI. Adjustment with sound-and-flash
units 171-174 153-154
VII. Conduct of fire with air observa-
tion 175-186 154-162
VIII. Conduct of fire by air observation
methods, using ground observers. 187-190 163-165
IX. Smoke 191-194 165-167
X. Gas 195-196 167-169
Chapter 5. Technique of Fire Direction.
Section I. General 197-201 170-173
II. Support by observed fires 202-203 173-177
III. Schedule fifes 204-207 177-180
IV. Ammunition requirements 208-212 180-182
Chapter 6. Dead Space, Visibility, and Calibra-
tion 213-215 182-187
Chapter 7. Service Practice 216-225 187-190
Index 191-198
III
FM 6-40
FIELD ARTILLERY FIELD MANUAL
FIEING
(The matter contained herein supersedes TR 430-85, September
2, 1930 (including Cl, January 2, 1932); and Parts One and Six,
Volume II, Field Artillery Field Manual, December 28, 1931.)
CHAPTER 1
THE FIRING BATTERY
Paragraphs
Section I. General 1- 7
H. Precautions in firing 8-12
III. Posts and duties 13-24
IV. Organization of the position 25-38
V. Fire commands and their execution 39-76
VI. Examples of fire commands 77-79
Section I
GENERAL
■ 1. Scope. — This chapter covers duties of personnel of the
firing battery (except those duties prescribed for the service
of the piece) and prescribes fire commands with explana-
tion of their execution. It governs primarily the division
artillery, but with obvious modifications applies to all types
and calibers.
■ 2. Terms used. — a. Firing battery, as used in this manual,
includes only that portion of a gun or howitzer battery at
the firing position, carriages unlimbered or uncoupled and
prepared for action.
b. Battery commander, as used in this manual, refers to
the officer commanding the battery or conducting the fire
of the battery.
c. Fire discipline is that condition, resulting from train-
ing and practice, which insures the orderly and efficient
functioning of personnel in the delivery of fire. The basis of
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FIRING
fire discipline is the thorough training of the individual
soldier.
■ 3. Training. — a. The object of training is the perfection
of fire discipline throughout the firing battery as a whole.
Training includes instruction in the care, preservation, de-
scription, and nomenclature of materiel; the acquirement
of a knowledge of the duties of all cannoneers in the squad
by each member thereof, and a thorough understanding of
fire command; and the development of manual dexterity and
teamwork in the mechanical operations involved. The
executive is charged with this training.
b. Gun squad training is the preliminary phase of train-
ing in fire discipline; firing battery instruction is the ad-
vanced phase. Training of the firing battery should be
started shortly after instruction of gun squads is begun.
c. Firing battery instruction is started in the gun park.
As proficiency is gained, the training advances to varied
terrain and simulated service conditions. Occupation and
organization of position under varied conditions, including
darkness and bad weather, should be practiced. Fire on
targets is first simulated, followed by subcaliber and service
practice.
d. Each battery should maintain a minimum of four
trained gun squads. Individuals of special aptitude should
be assigned appropriately to permanent positions, but at
drills posts should be changed frequently in order to develop
flexibility and permit the ready replacement of absentees or
casualties.
e. During maneuver or campaign as well as during the
training year, frequent drill of the firing battery is necessary
to maintain a high standard of fire discipline. However,
during actual firing, while correction of errors is necessary,
instruction in the service of the piece will be avoided since
it interferes with the effective delivery of fire.
■ 4. Accuracy and Speed. — Accuracy in the performance of
individual duties must be stressed; it is obtained by insistence
upon exactness from the beginning. Speed acquired by
prompt performance of individual duties in regular sequence
must not be stressed at the expense of accuracy
2
FIRING
5-9
■ 5. Lost Motion. — To eliminate the effects of lost motion,
settings must be made in a uniform manner as prescribed
for the particular piece or instrument concerned.
■ 6. Checking. — a. Frequent checks of setting and laying
are necessary to insure accuracy, both at drill and during
firing. Checking during firing is usually restricted to lulls
in action, except that when firing close to friendly troops
constant checking by the executive and assistant executive is
indispensable. It must be made with an absolute minimum
of delay in firing.
b. When a piece is discovered to have fired with an error
in laying, the error is corrected and reported immediately to
the battery commander. When a piece is plainly and unac-
countably in error, firing with it ceases and it is reported out
of action until the error is found and corrected.
■ 7. Uniformity. — Uniformity is necessary both in giving
and in executing commands. However, while instruction
always should conform to the spirit and principles of this
manual, latitude is allowed in the practical application,
thereof, and subordinates are encouraged to use their skill
and ingenuity in solving the problems which occur in
service.
Section II
PRECAUTIONS IN FIRING
■ 8. Reference. — Special measures peculiar to a particular
weapon will be found in the pertinent manual of the FM 6-
series for the Service of the Piece.
■ 9. Care of Materiel. — a. As soon as practicable after ar-
tillery materiel has been used, it is cleaned and put in order
under the supervision of an officer. Lost or unserviceable
parts are replaced or repaired. The work is not complete
until everything is again ready for immediate service.
b. Before the piece begins firing, the chief of section veri-
fies that the recoil mechanism contains the proper amount
of liquid; thereafter he carefully observes the functioning
of the recoil system.
3
9-10
FIRING
c. In the case of separate -loading ammunition, the powder
chamber is swabbed out after each round to extinguish
sparks. During firing, a pail of water is kept under each
piece and the bore is washed whenever fire is suspended for a
short time. Usually it is sufficient to wash the bore forward
a distance of 2 feet from the breech for light and medium
and 6 feet for heavy artillery.
d. During prolonged firing, it is desirable to rest each
piece at least 5 minutes of each hour.
e. When time permits during suspension of fire, the breech-
block is dismounted, cleaned, and oiled, and the bore cleaned
as prescribed in Technical Regulations for the materiel.
f. Permissible rates of fire for short bursts (up to 10 min-
utes) and for prolonged fire are given in FM 6-130; these
rates are exceeded only if the situation demands it.
H 10. Care of Ammunition. — Ammunition is sorted and
stored by lots. When received boxed or crated, it is kept
packed as long as practicable; after it is unpacked, it is pro-
tected from dirt and ground moisture by being placed on
paulins or raised off the ground. Each lot is covered by a
paulin or other material to protect it from rain and sun and
to keep the temperature uniform throughout that particular
lot. The paulin or other covering should be raised to allow
free circulation of air.
a. Projectiles. — Unpacked projectiles and complete rounds
are piled. Piles or groups are located 10 or more yards apart
and contain not more than one hundred rounds of 75 -mm
ammunition, fifty 155 -mm projectiles, or twenty-five 240-mm
projectiles. When piled, the height will not exceed five
layers for 75 -mm ammunition and three layers for 155 -mm
projectiles. Planks or brush are placed between layers.
Projectiles of 240-mm caliber are never piled but may be laid
horizontally. Care is taken to prevent injury to the rotating
bands ; they are always examined before firing and any burrs
removed with a file. Chemical shell are piled at a distance
from the battery, in a direction downwind from the prevail-
ing wind, and are inspected frequently for leakage. Adapter
plugs are left in projectiles until immediately before the fuzes
4
FIRING
10-11
are to be inserted , and the projectiles are not fuzed until
immediately before they are to be fired.
b. Powder charges . — It is especially necessary that powder
charges be kept dry and ventilated. They are kept in mois-
ture-proof containers until just before use. Powder charges
are so stored as to reduce the possibility of their ignition in
case of a flare-back or other accident at the piece.
c. Fuzes and primers. — Fuzes and primers are kept dry
and stored separately from the other components of the
ammunition. They are not carried on the person. Primers
are especially sensitive to shock. Fuzes are seated securely
(screwed home with the fuze wrench issued for that pur-
pose) before firing. If difficulty is encountered in screw-
ing home a fuze or if a fuze is otherwise defective, it is laid
aside temporarily and at a convenient time it is buried 3
feet deep or turned over at the position to ordnance person-
nel if available. Before returning ammunition to a vehicle
or container, a careful check is made to insure that the
combination fuzes are set at safety and that other types of
fuzes are removed from projectiles and properly stored or
disposed of otherwise. The precautions to be taken in the
use of any particular type of fuze are given in the Technical
Regulations pertaining to the materiel.
d. Misfires . — See the FM 6 -series for the Service of the
Piece.
■ 11. Unloading a Piece. — a. Unloading fixed ammunition or
projectiles is to be avoided whenever possible. If unloading
a piece becomes necessary, in case the projectile cannot be
extracted readily or becomes separated from the cartridge
case when the breech is opened, it is removed under the di-
rect supervision of an officer, using a rammer which bears
only on the projectile and provides for clearance around the
fuze.
b. When unloading fixed ammunition, the breech is opened
very slowly to reduce the likelihood of separating the car-
tridge case from the projectile and of scattering loose pow-
der from the propelling charge inside the breech. Should
the cartridge case separate from the projectile, the piece is
brought to the horizontal and the breech recess cleaned to
5
11-14
FIRING
remove the loose powder. When the rammer is used, the
recess in the -rammer head is inspected to insure that it is
free from foreign matter. Projectiles being removed should
be prevented from falling to the ground when forced to the
rear.
■ 12. Precautions in Handling Ammunition. — The following
precautions also are observed:
a. Ammunition is not tossed, rolled, or dropped.
b. Smoking in the vicinity of explosives is prohibited; care
is taken to avoid sparks or open flames nearby.
c. A round of ammunition held in preparation for reload-
ing the piece is kept free from the path of recoil.
d. Tampering with or disassembling any component of a
round is prohibited.
e. Any ammunition exposed to gas is wiped off immediately
with an oiled rag.
/. Personnel handling chemical projectiles are provided
with gas masks and gloves.
g. All rounds are examined before loading.
h. With pieces using separate loading ammunition, prim-
ers are not inserted until after the breechblock is closed and
locked in its recess.
i. When the long lanyard is used, it will not be attached
until the piece is otherwise ready to fire.
j. Pieces are examined before firing is begun to insure that
their safety features are in order and that the bores are
clear.
Section III
POSTS AND DUTIES
■ 13. General. — Individuals at the firing battery are dis-
mounted; they are not restricted to posts designated herein
when their duties require their presence elsewhere.
■ 14. Executives. — The post of the executive is a position
near the pieces from which he can best supervise the firing
battery and be in communication with the battery com-
mander. He should be able to see all the pieces and be seen
6
FIRING
14-16
by the chiefs of section, and his voice must be heard dis-
tinctly by all cannoneers. His principal duties are to —
a. Establish the firing battery in position.
b. Organize the position.
c. Comply with the fire commands of the battery com-
mander.
■ 15 Assistant Executive. — The post of the assistant ex-
ecutive when at the firing battery is in the vicinity of the
pieces where he can best perform his duties. His principal
duties when at the firing battery are to —
a. Assist the executive and to act as executive in the lat-
ter’s absence.
b. Supervise and check the work of gun squads.
■ 16. Chief of Piece Section. — The chief of a piece section
goes where he can control the service of his piece, hear
commands, and perform his duties effectively. A convenient
post is 2 yards from the end of the trail on the side oppo-
site the executive. His duties are —
a. To place the piece in position, to announce to his gun
squad its number in battery, to measure and announce the
minimum elevation (or range), and to enforce camouflage
and gas defense discipline,
b. To identify and point out to the gunner the aiming
point, the referring point, or the target.
c. To follow fire commands, but to repeat only such part
as may be called for by a member of his squad.
d. For direct laying in which his section is used, to assign
a part of the target to his gunner. (See the pertinent man-
ual of the PM 6-series for the Service of the Piece.)
e. For indirect laying, to indicate the general direction to
be given the piece and to operate the gunner’s quadrant
when used.
/. To show that his piece is ready to fire by extending his
right arm vertically as soon as his gunner calls “Ready.”
g. Except when otherwise prescribed, to give the command
fire, dropping his arm sharply to his side.
h. To execute prearranged fire when a written schedule
for it is furnished him.
7
16—17
FIRING
i. To supervise and check the work of the gun squad and
to report to the executive errors discovered in the laying;
for example, “No. 1 fired 5 mils right.”
j. To report when the piece is out of action and the
reason therefor; for example, “No. 1 (or so and so) out, must
dig trail trench deeper to reach that range.”
Jc. To conduct the fire of his section in fire at will and
at other times when so directed.
l. During firing, to watch the recoil system and measure
the length of recoil. To ascertain by inspection that the
recoil cylinder contains the proper amount of liquid and
that the pressure in the counterrecoil system is correct.
m. To have the section ammunition properly handled,
cared for, and stored by lot, and the materiel and equipment
cleaned as prescribed.
n. To keep the data for the gun book and data pertaining
to his piece.
o. To apply calibration corrections to his piece when and
as prescribed by the battery commander.
p . To enforce strict compliance with safety precautions.
■ 17. Ammunition Sergeant or Corporal. — The battery com-
mander will designate an ammunition sergeant or corporal.
His post is at the battery ammunition dump, if there is one;
otherwise, in the vicinity of the post of the executive. His
duties are to —
a. Have charge of such ammunition at the position as is
not issued to the sections.
b. Receive, inspect, sort, and care for ammunition not
delivered directly to sections.
c. Issue ammunition to piece sections, dividing each lot
equally among them.
d. Keep accurate records, by lot, of all ammunition issued
to the battery, tabulating receipts, issues, and expenditures;
prepare ammunition reports.
e. Keep the executive informed as to the amount and
kinds of ammunition on hand.
f. Dispose of ammunition left at positions, making the
necessary reports.
8
FIRING
IB— 22
■ 18. Telephone Operator. — The telephone operator is usu-
ally seated in rear of the battery and toward the windward
flank. His duties are to —
a. Have charge of and operate all telephone communica-
tion at the position.
b. Have ample slack wire left at the battery and to see
that the wire is not damaged during the occupation of posi-
tion.
c. Establish communication promptly and report to the
executive, “Communication established.’* To report to the
executive when communication is out.
■ 19. Linemen. — Linemen at the position of the firing bat-
tery are with, and under the command of, the telephone
operator.
■ 20. Recorder. — The battery commander designates a re-
corder. The recorder is seated beside the telephone opera-
tor. His duties are to —
a. Record all fire commands and messages*
b. Tabulate his record so that he can instantly give the
executive the setting for any piece.
c. Record the minimum elevation (or range) and the base
deflections.
d. Keep a file of fire schedules.
■ 21. Chief Mechanic. — The chief mechanic normally is at
the battery position. His duties are to —
a. Inspect materiel, observe the functioning of the pieces,
and make such repairs as can be made properly at the
position.
b. Assist the ammunition sergeant.
■ 22. Sentinels.— Sentinels are posted as the executive may
direct. Their duties are as follows:
a. Sentinels at pieces. — To alert gun squads, report un-
usual events, prevent pieces from being disturbed, and, upon
the signal for firing the normal barrage, to load and fire the
pieces until relieved.
b. Gas sentinels. — To keep gas alarms in serviceable condi-
tion, to be on the alert to discover gas, to sound the alarm,
and to give assistance in gas defense.
9
22-25
FIRING
c. Circulation sentinels. — To enforce orders with respect to
movement of individuals, animals, and vehicles in or near the
position.
d. Rocket sentinels. — To distinguish pyrotechnic signals;
to operate rocket boards; to call, “Barrage” immediately upon
seeing the barrage signal; and to report other signals in
accordance with his orders.
e. Security sentinels . — To prevent surprise, to assist in de-
fense, and to direct and guide authorized persons to the
battery position.
■ 23. Replacement of Casualties. — During action, casual-
ties are replaced as follows; the executive, by the senior
present; the assistant executive, not replaced; chief of piece
section, by the gunner (who continues to act as gunner also) ;
gunners and cannoneers, by redistribution of duties by the
chief of section or by the executive if necessary; others, as
the executive may direct. Permanent assignments and
reassignments are made by the battery commander as ap-
propriate. Casualties are reported to higher authority daily
or at such times as called for.
■ 24. Resupply of Ammunition. — Under the direction of the
battery commander, the executive, assisted by the ammuni-
tion sergeant, supervises the ammunition supply. As the
necessity for resupply is foreseen, the battery commander
requests the necessary amounts and types from the bat-
talion. The battery commander makes a daily ammunition
report to the battalion.
Section IV
ORGANIZATION OP THE POSITION
■ 25. Definition. — Organization of the position is the sys-
tematic performance at the firing battery position of all
functions which contribute to the prompt opening and de-
livery of accurate fire and to the concealment and protec-
tion of personnel, materiel, and ammunition. Organization
begins when the position is selected and is continuous
through occupancy.
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FIRING
26-28
■ 26. Order in Battery. — All carriages are unlimbered or
uncoupled and prepared for action. The pieces may be
placed in line at regular intervals or they may be placed
irregularly, in which case they are said to be “staggered.”
The pieces of a battery when staggered should not be so
separated as to preclude the direct control, by the executive,
of the firing battery as a whole. When the pieces are in
line and the interval between muzzles is 20 yards, they are
said to be at “normal” intervals. Pieces in position are
designated from right to left as No. 1, No. 2, No. 3, and No.
4, without regard to the permanent numerical designations
of sections.
■ 27. Occupation of Position. — a. When a position is oc-
cupied after dark or positions have been selected for each
individual piece, the executive designates to each chief of
section the position for his piece and the direction of fire.
Each chief of section conducts his section individually to
the position designated.
b. Where practicable, in order to avoid a multiplicity of
tracks, the position is occupied from the march formation.
The position is approached from a flank in section column.
When opposite the piece positions, the trucks or carriages
are halted in the track made by the leading vehicle or car-
riage; the pieces and caissons are uncoupled or unlimbered
and run into position by the cannoneers; trucks are un-
loaded; and the trucks or limbers are then moved on past
the position, leaving a single track passing the position.
c. The executive checks communication at the battery
and posts the telephone operator at the position from which
he will normally give commands.
■ 28. Laying the Battery for Direction. — The executive
lays the battery as commanded by the battery commander,
or, if no commands have been received, lays it parallel in
the direction indicated by the gun marker. In the latter
case, if no aiming point or compass has been indicated, he
should lay on a definite y-azimuth (par. 55) usually a mul-
tiple of 100 mils.
11
29-30
FIRING
■ 29. Referring Pieces. — a. To refer a piece which has been
laid for direction, an aiming point is announced and the
deflection is measured and recorded. The command for
referring is, for example:
AIMING POINT, AIMING STAKES.
REFER,
b. A common aiming point used for referring should be
fixed, continuously visible, and as distant from the battery
as possible. It should contain a clearly defined vertical line
or a definite point on which the gunners can lay.
c. When a common aiming point is used, aiming stakes
should be set up (for emergency use) at such a time as
does not interfere with the firing. When a common aiming
point is not used, the executive orders the aiming stakes set
up as soon as the position is occupied. The command is:
AIMING STAKES OUT.
d. Two aiming stakes are used for each piece. One stake
is set up at a convenient location at least 100 yards from
the piece; the other stake is set up at the midpoint between
the first stake and the piece. Both stakes are set up so
that they and the sight of the piece are on the same straight
line. Whenever aiming stakes are used, the pieces are also
referred to an auxiliary aiming point which is used in case
the aiming stakes are knocked down during firing. During
darkness, a light is attached to each aiming stake, the near
light lower than the far light. Each light is completely
screened except for a narrow vertical slit visible through the
sight.
■ 30. Displacement Corrections. — a. When a gunner sees
that his aiming stakes are out of line, he notifies the chief
of section (who notifies the executive) and uses the far stake
for laying until the piece can be moved or a correction is
authorized by the executive. The correction is made by the
gunner who —
(1) Lays on the far stake.
(2) Refers to the near stake.
(3) Lays on the far stake with the new reading.
(4) Realines the stakes (as soon as practicable) by mov-
ing the near stake.
12
FIRING
30-32
b. Lateral displacement is most likely to occur when the
axle of the piece is not level. This is particularly true of
materiel equipped with pneumatic tires. Lateral displace-
ment may be prevented by placing sandbags against the
outside of each wheel. When gun platforms are used, wheel
guides are constructed.
■ 31. Determining Piece Intervals. — If the pieces are stag-
gered, the executive determines the interval from No. 1 to
each of the other pieces by measuring or pacing the distance
from No. 1 along a line perpendicular to the line of fire to
points opposite each of the other pieces. These intervals
are recorded and used for forming the sheaf as explained
in paragraph 62.
II 32. Determining Minimum Range or Elevation. — a. As soon
as each piece is established in position and laid in the
direction indicated by the gun marker, the executive causes
the minimum range or elevation to be measured.
(1) Minimum range is used only in the hasty occupation
of a position and when the range to the mask does not exceed
600 yards. In such case, the executive selects the greatest
minimum range setting reported to him by the chiefs of
section, adds thereto the range in yards from gun to crest of
mask, and reports the sum to the battery commander; for
example, “Minimum range 1,600 (or so much)/’ Site zero
(or 300) is used in determining the minimum range setting
unless otherwise ordered. The foregoing is a rapid method
providing a satisfactory safety factor for clearing an unoccu-
pied crest.
(2) Minimum elevation is used in all cases except the
above. The executive —
(a) Selects the greatest minimum elevation reported by
the chiefs of section,
(b) Adds thereto the elevation (from Firing Tables) for
the piece -mask range for the type of available ammunition
having the lowest velocity.
(c) Adds two forks at the piece -mask range (from Firing
Tables) .
(d) If the mask is occupied by friendly troops, adds the.
value in mils of a height of 5 yards at the piece -mask range.
177568 °— 39 2 13
33—35
FIRING
(e) Reports the sum to the battery commander as the
minimum elevation.
b. The battery commander normally will advise the
executive as to the probable sector of fire and require a
report as to the minimum elevation throughout the sector.
A few probable critical points can be selected readily by
inspection and the minimum elevations determined for them.
In this way, accidents will be avoided in instances where the
mask is very irregular. The executive may be required to
determine minimum elevation for a particular projectile,
charge, and fuze; further, he may be required to determine
ft for each piece.
c. Pieces are not fired at a quadrant elevation less than
the minimum elevation or that corresponding to the mini-
mum range setting and site as determined by the executive.
If a fire command includes an elevation (or range) less than
the minimum elevation (or range), the executive reports to
the battery commander, “Minimum elevation (so much)*’ or
“Minimum range (so much) .”
■ 33. Opening Fire. — a. When the above operations have
been completed, the executive reports to the battery com-
mander, “Battery ready."
b. If complete fire commands are received before these
operations have been completed and if it is obviously safe
to fire, the opening of fire takes precedence.
c. Further steps in the organization of position are com-
pleted as rapidly as possible provided they do not interfere
with the fire.
■ 34. Improving Emplacements. — As time permits, such of
the following improvements are carried out as are appro-
priate for the type of materiel: construction of trail trenches,
backed by trail logs; leveling of the ground occupied by the
pieces; and construction of wheel platforms or firing-base
supports.
■ 35. Defensive Measures (FM 6-20). — a. References . —
Chapters 1 and 2, Engineer Field Manual, Volume II; Chap-
ter 8, Basic Field Manual, Volume I.
b. Concealment. — Positions should be concealed from en-
emy ground and air observation. To this end, the movement
14
FIRING
35-37
into position should be concealed, pieces irregularly emplaced,
camouflage correctly employed, circulation controlled, and
the use of lights and fires restricted. Measures for conceal-
ment must not delay preparations for promptly opening fire.
c. Protection . — The position must be prepared for defense
against artillery fire and direct attack by ground troops and
aircraft. Passive means, such as camouflage, cover, and con-
cealment, are used. Active defensive means comprise the
fire of small arms and of the pieces themselves. Construc-
tion work must harmonize with the camouflage scheme and
ordinarily be executed at night.
d . Gas defense . — Orders for gas defense should cover such
of the following as are appropriate: location, use, operation,
and maintenance of gas alarms; adjustment, removal, and
care of gas masks; reporting of gas attacks and of their ter-
mination; defensive measures; assistance for casualties; and
protection of material objects. All personnel must be in-
structed in defensive measures and selected individuals taught
gas protection.
■ 36. Reliefs. — During long-continued action, personnel is
divided into reliefs. Sentinels are posted at the pieces when
the latter are not actually firing, the remainder of each gun
crew being allowed to rest in sheltered positions near by.
■ 37. Records. — a. The following records are kept:
(1) Each chief of piece section keeps a notebook and data
for the gun book. In the notebook he keeps data of semiper-
manent value to his piece, such as calibration corrections,
base deflection, and data for defensive fires. The data for
the gun book are the number of rounds fired, defects, repairs,
and similar pertinent information.
(2) Each gunner records, on data boards set up for each
piece when necessary, base deflection, calibration corrections
when appropriate, minimum range or elevation, and data for
primary defensive fire missions. Base deflection and mini-
mum range or elevation are also entered on the shield of
pieces equipped therewith.
(3) Each cannoneer operating a fuze setter keeps, when
appropriate, calibration corrections for the fuze setter.
15
37-40
FIRING
(4) The ammunition sergeant keeps a record by lot of all
ammunition at the position, consisting of a tabulation of
receipts, issues, and expenditures, and reports of ammunition
expenditures. The ammunition report is prepared from
this record.
(5) The recorder keeps a record of all fire commands,
reports, and messages as prescribed in paragraph 20.
b. Extract copies of fire missions or fire schedules may be
furnished by the battery commander to each chief of piece
section and complete copies to the recorder. All schedules
are carefully preserved.
c. Except as prescribed no records of fire commands are
made.
■ 38. Evacuation of Casualties. — Firing is not interrupted
because of casualties. Available first aid is administered
immediately. The slightly wounded walk to battalion aid
stations; others, including gas cases, are removed by litter
or ambulance at appropriate times.
Section V
FIRE COMMANDS AND THEIR, EXECUTION
■ 39. Definitions. — a. Fire commands are commands which
convey all the information necessary for the commencement,
conduct, suspension, and cessation of fire, and activities inci-
dent thereto.
b, Firing data are the elements of a fire command which
prescribe the settings of instruments and fuzes in the firing
battery.
c. The base piece is the piece (usually No. 1) for which
initial data are computed and with reference to which data
for other pieces are found.
■ 40. Origin and Transmission. — Fire commands originate
with the battery commander. They are sent to the firing
battery by telephone, radio, signal flags, signal lamp, voice
relay, or messenger. The executive repeats the commands of
the battery commander to the gun squads, except as noted
herein.
16
FIRING
41-44
fl 41. Numbers. — Numbers are announced as illustrated in the
following examples:
10 One zero.
25 Two five.
300 Three hundred.
1,400 One four hundred.
6,000 Six thousand.
3,925 Three nine two five.
4,050 Four zero five zero.
10,300 One zero three hundred.
11,000 One one thousand.
100.7 One zero zero point seven.
245.4 Two four five point four.
■ 42. Repetition. — Fire commands are not repeated by any
member of the firing battery except on request of a subor-
dinate or when a fire command has manifestly been unheard
or misunderstood. The subordinate who fails to understand
elements of a fire command which pertain to his duties asks
his superior for them thus: “Site?** “Corrector?** The tone
of the reply is informatory and only loud enough for the
individual to understand it. Repetitions are prefaced by
“The command was (so and so) .”
■ 43. Initial Commands; Changes. — The fire commands for
the first firing from a position must contain all the elements
necessary to cause instruments and fuzes to be set and the
pieces to be laid, loaded, and fired. Thereafter the range or
elevation is announced and, unless otherwise w escribed, only
such other elements as are changed. When firing more than
one piece, a change for an individual piece or pieces will be
preceded by the command no. i (or other pieces) (so and
so) . An individual change is announced and set after any
general change of the same element.
■ 44. Opening Fire. — For the executive, the indication to
fire is the battery commander’s command for the range or
elevation, except when otherwise specified herein. Fire is
begun at the command fire; or no. i (or other piece) fire;
or resume firing. The command to begin fire is given by the
executive except in the following cases:
17
44-48
FIRING
a. By the chief of section during schedule fire and in fire
at will.
b. By the gunner during fire at moving targets with direct
laying. (See the pertinent manual in the FM 6 -series for
the Service of the Piece.)
■ 45. Ceasing Fire. — Fire is stopped by the executive’s com-
mand cease firing or suspend firing, but in emergencies
anyone present may give the command cease firing. Fire
always is stopped at the command cease firing, whatever
its source. When a piece has been loaded with HE shell and
the command cease firing has been given, the executive re-
ports to the battery commander, “No. 1 (or other pieces)
loaded,” and acts on the instructions received.
■ 46. Suspending and Resuming Fire. — The command sus-
pend firing is used when the battery is firing on a schedule
and a temporary stop is desired. The pieces are left loaded
and the laying conforms to the schedule. When fire may
be delayed more than a minute, the battery commander
should command: UNLOAD. At the command resume fir-
ing, fire is resumed in accordance with the schedule.
■ 47. Signals. — The commands fire and cease firing usually
are given by arm signals as well as by voice. The signal
for fire is to drop the right arm from a vertical position
sharply to the side or to point with the right hand at the
piece to be fired, extend the arm vertically and drop it
sharply to the side. The signal for cease firing is to raise
both arms vertically and hold them in that position until the
signal is understood by all concerned, or to give one long
whistle blast.
■ 48. Pieces To Follow Commands. — a. A fire command will
be followed by all pieces unless it includes no. (so and so)
adjust. This command may be given as the first element of
the fire command or may follow any other element of the
command except the range or elevation.
b. At the command no. (so and so) adjust, only those
pieces specified follow the subsequent commands.
c. To require the pieces that have not been following to
follow, BATTERY ADJUST, Or RIGHT (LEFT) ADJUST, is given as
18
FIRING
48-51
the first element of a subsequent fire command, which, in
prescribed sequence, will include appropriate data for such
pieces and the designation of pieces to fire and the method
of fire.
■ 49. Sequence. — a. The prescribed sequence of fire com-
mands is:
(1) Special methods of adjustment and particular mis-
sions.
(2) Direction.
(3) Converging sheaf.
(4) Deflection difference.
(5) Site.
(6) Projectile.
(7) Charge.
(8) Fuze.
(9) Fuze range or time.
(10) Pieces to fire.
(11) Method of fire.
(12) Use or discontinuance of use of quadrant.
(13) Range or elevation.
b. The commands for ceasing and suspending fire may be
given at any appropriate place in the sequence. When the
command refer is to be used as an element of a fire com-
mand, it follows the announcement of the aiming point.
The command record base deflection when used with refer
follows refer; otherwise it may follow the commands for
laying for direction; it is usually the last element announced.
■ 50. Commands for Special Adjustments and Missions. —
Appropriate types are: ON NO. (SO AND SO) ADJUST
SHEAF PARALLEL; INSTRUMENT DIRECTION, RIGHT
(LEFT) (SO MUCH) ; or LAY ON NORMAL BARRAGE, or
(ON SO AND SO) . The first two are not repeated verbatim
to the gun squads.
■ 51. Initial Direction. — The battery commander may di-
rect the initial laying of the battery for direction by com-
manding: A TARGET AND A DEFLECTION; AN AIMING
POINTED AND A DEFLECTION; A Y- AZIMUTH; or A
BASE ANGLE.
19
52-55
FIRING
■ 52. Changes in Direction, — After the battery has been laid
for direction initially, the battery commander announces
changes in direction by commanding: RIGHT (LEFT) (SO
MUCH), or BASE DEFLECTION RIGHT (LEFT) (SO
MUCH) , or by any of the means listed in paragraph 51.
Base deflection is a recorded deflection setting by which the
pieces of the battery are laid parallel and in a known
direction.
■ 53. Target. — The command is: TARGET (SO AND SO),
followed by a deflection. It is an order to use direct laying.
Each gunner is assigned his part of the target by his chief
of section; the latter also corrects the direction of his piece
during firing.
■ 54. Aiming Point and Deflection. — The battery com-
mander commands: AIMING POINT (SO AND SO) ; DE-
FLECTION (SO MUCH), or PLATEAU (SO MUCH) DRUM
(SO MUCH) . When the aiming point is not visible from all
pieces of the battery, the executive may set the announced
deflection on an aiming circle, sight on the aiming point,
using the lower motion, and lay the battery as described in
paragraph 57.
■ 55. Y- Azimuth. — The battery commander commands:
COMPASS (SO MUCH) . The executive does not repeat this
command. He lays the battery with either a prismatic com-
pass or an aiming circle. The instrument should be at least
30 yards from any masses of metal which might deflect the
needle. The steel helmet and other metal objects should be
removed from the vicinity of the instrument.
a. With the prismatic compass . — The executive determines
the compass reading to the target by subtracting the declina-
tion constant of his prismatic compass from the announced
Y-azimuth, adding 6,400 if necessary. He then places him-
self at least 60 yards in rear of the base piece and at a posi-
tion such that the compass reading of the line from his
instrument to the sight of the base piece is approximately
the compass reading determined as above. He holds the
compass to his eye and gives the following command to the
gunner: AIMING POINT, THIS INSTRUMENT, DEFLEC-
TION ZERO, or PLATEAU 0 DRUM 100.
20
FIRING
55—56
The execution of this command lays the piece on the pro-
longation of the line: Executive — base piece. The executive
measures the compass reading of this line by reading to the
sight of the piece. He then determines the difference be-
tween this compass reading and the desired compass reading
and commands a shift of this amount to lay the piece on
the desired azimuth. The remaining pieces are laid parallel
by reciprocal laying on the base piece (par. 58) .
b. With the aiming circle . — The instrument is set up at
least 60 yards from the nearest piece and in such a position
that it is suitable as an aiming point for all pieces. The
executive lays the 0-3,200 line of the aiming circle on tho
announced Y-azimuth as follows:
(1) French aiming circle. — (a) He subtracts the an-
nounced Y-azimuth from the declination constant of the
aiming circle (adding 6,400 to the declination constant if
necessary) .
(b) He sets the remainder on the azimuth and microm-
eter scales of the aiming circle.
(c) He releases the compass needle and centers it with
the lower motion. After clamping the needle, he lays each
piece reciprocally on the aiming circle (par. 57) .
(2) American aiming circle , M1916. — (a) He measures the
magnetic azimuth to the base piece and to this magnetic
azimuth adds the declination constant of his aiming circle.
(b) He subtracts the announced Y-azimuth from this sum
(adding 3,200 if necessary). The result is the firing angle
for the base piece, using the aiming circle as an aiming point.
(c) He commands: AIMING POINT, THIS INSTRUMENT
NO. 1 (base piece), DEFLECTION (SO MUCH) (as deter-
mined in (b) above).
(d) He then sets this announced deflection on his aiming
circle and lays on the base piece.
( e ) He then lays the other pieces reciprocally on the aim-
ing circle (par. 57).
■ 56. Base Angle. — a. The battery commander commands,
for example: BASE ANGLE 1,800. The executive does not
repeat this command.
b, If the orienting line runs through the sight of the base
piece, the executive commands, for example: AIMING
21
56-58
FIRING
POINT, THAT STAKE (or other aiming point on the orient-
ing line), DEFLECTION 1,800. The remaining pieces are
laid parallel to the base piece by any convenient method.
c. If the orienting line does not run through the sight of
the base piece, the executive sets up the aiming circle for
use as an aiming point at a suitable point on the orienting
line, lays the 0-3,200 line of the aiming circle in the proper
direction by setting the base angle (1,800) On the azimuth
scale and laying the instrument along the orienting line with
the lower motion. He then lays each piece reciprocally on
the aiming circle (par. 57).
■ 57. Laying Parallel With Aiming Circle. — The aiming
circle is set up in a position suitable for use as an aiming
point and the 0-3,200 line is established in the proper direc-
tion as described in paragraphs 54, 55 b, and 56. The execu-
tive, by means of the upper motion, directs the instrument
on the sights in turn, determining and announcing the deflec-
tion for each piece from the readings on the aiming circle.
When guns with French sights are being laid with the French
aiming circle, the plateau and drum readings are taken di-
rectly from the aiming circle. With panoramic sights, 3,200
mils must be subtracted from readings which exceed 3,200.
The executive commands, for example: AIMING POINT,
THIS INSTRUMENT, DEFLECTION NO. 1, 3091; NO. 2,
2738; NO. 3, 2369; NO. 4, 2045. When time permits, the
operation is repeated at the command of the executive until
the same readings are obtained on two successive trials.
The executive then commands, for example:
AIMING POINT, AIMING STAKES.
REFER.
Each gunner refers and announces the referred deflection
for his piece.
H 58. Laying Parallel by Reciprocal Laying. — This method
should be considered only an emergency means of forming
a parallel sheaf for use when an aiming circle is not available.
a. The base piece having been laid for direction, the execu-
tive may command, for example: ON NO. 1 LAY PARALLEL.
b. All pieces are brought to the horizontal after setting
site zero (300) , range zero; pieces other than the base piece
22
FIRING
58—61
are traversed to their centers and by shifting trails are
pointed approximately parallel to the base piece. The gun-
ner of the base piece refers in turn to the sights of the
other pieces and announces the deflection reading of each,
for example: “No. 2, 1580; No. 3, 1560; No. 4, 1550.”
c. Each gunner sets as deflection the reading announced
for his piece, and using the sight of the base piece as the
aiming point, lays for direction; the chief of section reports,
“No. (so and so) ready.” When time permits, the operation
is repeated at the command of the executive until the same
readings are obtained on two successive trials.
d . When the pieces have been laid, the executive an-
nounces an aiming point and causes the pieces to be re-
ferred.
■ 59. Laying Parallel by Use of a Common Aiming
Point. — When the pieces are using a common distant aim-
ing point and are in line at regular intervals, the executive
may form a parallel sheaf by means of a deflection and a
deflection difference. The deflection announced is that of
the base piece. The deflection difference is determined by
measuring or estimating the interval between two adjacent
pieces perpendicular to the direction of the aiming point
and dividing by the distance to the aiming point in thousands
of yards. The deflection difference is open if the aiming
point is in front; close, if in rear.
■ 60. Direction Established by One Piece. — After estab-
lishing the direction for the base piece, the battery com-
mander may cause the others to be laid parallel by the com-
mand: ON NO. 1 (or other piece) FORM SHEAF PARAL-
LEL. The executive does not repeat this command. He
forms a parallel sheaf by reciprocal laying; by having the
base piece referred to the aiming circle, laying the aiming
circle reciprocally on the sight of the base piece, and then
laying the remaining pieces parallel with the aiming circle;
or by the use of a common aiming point and a deflection
difference.
■ 61. Deflection Difference. — a. If the battery commander
desires to control distribution directly, following a command
for direction he announces a command for deflection dif-
23
61-62
FIRING
ference; for example: ON NO. 1 (or other piece) OPEN
(CLOSE) (SO MUCH).
b. If the battery commander desires to control distribution
indirectly through the executive, he will give a command for
convergence (par. 62) followed by a deflection difference to
obtain the desired width of sheaf; for example: CONVERGE
AT 3,000, ON NO. 1 OPEN 8.
■ 62. Converging the Sheaf. — a. The command given by
the battery commander is: CONVERGE AT (SO MUCH) .
The executive does not repeat this command. He causes the
sheaf to be formed parallel by any one of the methods de-
scribed in paragraphs 57, 58, and 59. He then determines
the individual corrections to converge Nos. 2, 3, and 4 on No.
1 at the range announced by the battery commander, and
gives the commands necessary to accomplish this conver-
gence. When the pieces are at regular intervals, this may
be effected by a command for deflection difference; for
example: ON NO. 1 CLOSE (SO MUCH).
b. On occupation of position, the executive may prepare a
convergence table as follows: He measures the distance in
yards between pieces, normal to the direction in which he
expects to fire, and, by the mil relation, computes the con-
vergence at ranges which may be fired. He tabulates these
results. The following table is convenient in determining
the individual shifts for convergence ; the values are given in
mils.
Interval from No. 1 (yards)
-ttange
100
90
80
70
60
50
40
30
.
20
10
5
1,500
67
60
53
47
40
33
27
20
13
7
3
2,000
50
45
40
35
30
25
20
15
10
5
3
2,500
40
36
32
28
24
20
16
12
8
4
2
3,000.
33
30
27
23
20
17
13
10
7
3
2
3,500
29
26
23
20
17
14
11
9
6
3
1
4,000
25
23
20
18
15
13
10
8
5
2
1
4,500
22
20
18
16
13
11
9
7
4
2
1
5,000.
20
18
16
14
12
10
8
6
4
2
1
5,500
18
16
15
13
11
9
7
5
4
2
1
6,000
17
15
13
12
10
8
7
5
3
2
1
7,000
14
13
11
10
9
7
6
4
3
1
1
8,000
13
11
10
9
8
6
5
4
3
1
1
9,000
11
10
9
8
7
6
4
3
2
1
1
10,000
10
9
8
7
6
5
4
3
2
1
1
24
FIRING
63-66
■ 63. Angle of Site. — For the 75-mm gun, French, M1897,
the command is: SITE PLUS (MINUS) (SO MUCH), or
SITE ZERO; for other pieces: SITE 305 or (SO MUCH).
The site is not announced when using the gunner’s quadrant,
and, with some types of materiel, when using direct laying.
■ 64. Projectile. — The command for shell is: SHELL MK. I
(or other type designation) ; the use of shrapnel is directed
by the command for corrector setting.
■ 65. Charge. — a. For charges termed normal reduced, or
supercharge, the charge is designated in a fire command
only when other than the normal charge is to be used. In
such case, the command is: REDUCED CHARGE or SUPER-
CHARGE. When a change is to be made from either of the
two above charges to the normal charge, the command is:
NORMAL CHARGE.
b. For numbered charges the command is: CHARGE I or
(SO MUCH) .
■ 66. Fuze. — a. When using shell (except time shell), the
command for the fuze is; FUZE QUICK (DELAY).
b. When using shrapnel (or time shell) , the command for
a corrector setting is: CORRECTOR (SO MUCH); for a
change in the corrector setting: UP (DOWN) (SO MUCH);
for percussion fire: PERCUSSION. When the fuze setter is
graduated for corrector and time, the commands are: COR-
RECTOR (SO MUCH) ; TIME (SO MUCH) , changes being
indicated by a corrector change or a new time setting.
When the battery has both time shell and shrapnel avail-
able, the use of shrapnel is directed by the command shrap-
nel, given before the command corrector (so much) .
c. When using fuze setters graduated for corrector and
range, the fuze range is the same as the range setting unless
otherwise announced. When a fuze range other than the
piece range is to be used, the fuze range is announced thus:
“Fuze range (so much).” When firing with the range drum,
the fuze range is announced whenever it differs from the
piece range. When pieces are laid at an elevation rather
than at a range setting, the fuze range is announced initially;
thereafter, whenever changed.
25
67-68
FIRING
■ 67. Pieces to Fire. — a. To fire the battery, the command
is: BATTERY. To fire one platoon, the command is:
RIGHT (LEFT), indicating the right (left) platoon. To
fire any other combination of pieces, the command is:
NUMBER (S) (SO AND SO). The command fire at will
directs all pieces to fire.
b. When a change in pieces to fire or the method of fire,
or both, is to be made, the commands for both elements are
given. Decreasing or increasing the number of rounds in a
method of fire does not constitute a change of method.
■ 68. Methods of Fire. — The methods of fire are salvo fire,
volley fire, volley fire sweeping, continuous fire, by piece at
my command, fire at will.
a. Salvo fire. — The command is: RIGHT (LEFT) , and in-
dicates the flank from which pieces are to be fired succes-
sively. Fire is opened at the executive’s command fire,
pieces being fired at the command of chiefs of section, in
order from the right (left), at intervals of 2 seconds. The
interval of 2 seconds may be changed by adding at (so
many) seconds. This interval will be used until the method
is changed or another interval announced. The executive
gives the command fire when he sees that the pieces are
ready to fire. If one or more pieces are apparently in error
or are very slow, they are called out and the remaining
pieces fired.
b. Volley fire. — The command is: (SO MANY) ROUNDS.
Fire is opened at the executive’s command fire, given im-
mediately after the range or elevation. Each piece to be
fired fires the specified number of rounds as rapidly as is
consistent with accuracy without regard to other pieces, each
round being fired at the command of the chief of section,
no. (so and so) fire. There are three exceptions to the
above, as follows:
(1) When firing at a moving target with direct laying,
the announcement of the range is the authority to fire; each
piece is fired at the command of the gunner. (See the per-
tinent manual in the FM 6-series for thei Service of the
Piece.)
(2) When safety regulations require personnel to take
cover, the designated pieces fire simultaneously at the execu-
26
FIRING
68
tive’s command, which is given when the pieces are ready to
fire and cover has been taken.
(3) When the battery commander prescribes a time inter-
val during the firing of a single piece; for example, 3 rounds
at 10 seconds. Each round is fired at the executive’s com-
mand.
c. Volley fire , sweeping . — (1) Normal sweeping. — The com-
mand is: (SO MANY) ROUNDS SWEEPING (RIGHT),
(SO MANY) TURNS (MILS). Fire is opened and executed
as prescribed for volley fire, except that after each round
the gunner traverses the piece the number of turns of the
handwheel or the number of mils specified in the command.
The sweep is always to the left unless right is included in
the command. When the last round of the sweep has been
fired, the gunner traverses the piece back to the original
laying.
(2) Cross sweeping. — The command is: (SO MANY)
ROUNDS CROSS SWEEPING, (SO MANY) TURNS (MILS).
The execution is the same as for normal sweeping, except
that even-numbered pieces sweep to the right.
d. Continuous fire . — The command is: CONTINUOUS
FIRE RIGHT (LEFT) AT (SO MANY) SECONDS. If fire
is by a single piece, right (left) is omitted and at so many
seconds may be omitted, in which case the piece is fired as
rapidly as it can be laid accurately. Continuous fire, when
executed by more than one piece, is a succession of salvos,
the pieces being fired consecutively at the interval desig-
nated in the command. The fire is continued until the
method of fire is changed or until the command cease
firing is given. Changes of data are applied so as not to
stop the fire or break its continuity.
e. By piece at my command. — To fire each piece individu-
ally at his command, the battery commander commands:
BY PIECE AT MY COMMAND. When the battery is ready
to fire, the executive reports to the battery commander,
“Battery is ready,” and, when the battery commander’s
command to fire is received, commands, for example: NUM-
BER (SO AND SO) FIRE.
f. Fire at will. — The command is: TARGET (SO AND SO) ,
FIRE AT WILL. This method is used for firing at a target
27
68-71
FIRING
attacking or about to attack the battery. Direct laying is
employed. The laying is as prescribed in the pertinent
manual of the FM 6 -series for the Service of the Piece.
Without further command from the executive or the battery
commander, each piece opens fire at the command of the
chief of section and fires as rapidly as possible until the
command cease firing is given.
■ 69. Holding Fire. — a. If the battery commander does not
desire the pieces to be loaded, he commands: DO NOT
LOAD before announcing the range or elevation. To begin
fire after the command do not load, the battery commander
commands the range or elevation.
b. If the battery commander desires the pieces to be loaded
but the opening of fire to be held, he commands: AT MY
COMMAND before announcing the range or elevation..
The command is not repeated by the executive. When the
pieces are ready to fire, the executive reports, “Battery is
ready.” To begin firing, the battery commander commands:
FIRE, which is repeated by the executive, at my command
continues in effect until a method of fire is announced not
followed by at my command.
■ 70. Gunner’s Quadrant. — The command to use or discon-
tinue using the gunner’s quadrant is announced immediately
before the range or elevation. The command is: QUAD-
RANT or WITHOUT QUADRANT.
■ 71. Range or Elevation. — a. The command for range is
the announcement of the range setting, as, “4,800”; for ele-
vation' the elevation setting, as, “140.6.” When firing more
than one piece and the pieces are laid at different elevations,
and in this case only , the command same elevation may be
used.
b. The command for the executive to fire a series of
ranges in a definite sequence is zone, followed by the range
bound (if other than 100 yards) and the limiting ranges.
For example: ZONE, 4,800, 4,600; or ZONE 200, 2,200, 2,600.
The executive does not repeat the command but gives com-
mands to fire at the following ranges: the first range an-
nounced, and ranges differing by 100 yards or by the amount
of the range bound announced, until the final limiting range
28
FIRING
71-72
is reached; then ranges halfway between those fired in the
reverse order. The ranges fired for the first command given
above are 4,800, 4,700, 4,600, 4,650, 4,750. For zone fire using
elevations, the command must include the elevation bounds
as well as the limiting elevations; in other respects the pro-
cedure is similar. For example: ZONE 6 MILS, (QUAD-
RANT) 148, 160; the elevations fired are 148, 154, 160, 157,
and 151.
c. If it is desired to fire through a zone two or more times,
appropriate commands are repeated as necessary.
d . The command for the range or elevation always is given
in eacli series of fire commands when it is intended that
pieces be loaded and fired.
■ 72. Schedule Fires. — ai Written data for concentrations
and standing barrages usually are sent to the executive by
command sheet. The arrangement of entries on this sheet is
such that the executive can announce his commands in
proper order by reading from it. Frequently, however, the
executive will find it necessary to furnish each chief of sec-
tion written data for each mission to be fired on a time
schedule. Data for a rolling barrage are furnished by the
battery commander on section data sheets to the chiefs of
section, who are individually responsible for announcing data
and giving the commands to fire according to the schedule.
b. The number of rounds to be fired is determined from
the method of fire, zone and range (elevation) commands,
and appropriate entries in the “Remarks" column of the
command sheet. When time limits are shown for missions
other than a rolling barrage, the executive causes the fire to
start at the designated time. These time limits simply re-
quire that the missions be completed within the specified
time without restricting the executive as to the rate of fire.
c. The normal barrage may be started by the piece senti-
nels (par. 22) or at the executive's command barrage. Com-
plete data, including rates of fire and duration, for all stand-
ing barrages should be furnished each chief of section. Suf-
ficient ammunition for several complete barrages is stored
in a place convenient for prompt use. One round is always
kept ready for immediate loading. When not engaged in
firing, the battery is kept laid on its normal barrage. The
177568°— 39 3 29
72-73
FIRING
battery commander should warn the executive by the com-
mand lay on normal barrage when he foresees a lull in fir-
ing during which the barrage may be called for.
■ 73. Determining the Adjusted Compass. — a. If the initial
laying was by compass, the battery commander may order
the executive to “Report the adjusted compass.” In this
case the executive determines the difference between the
deflection of his base piece after adjustment and the deflec-
tion of the base piece which resulted from the initial laying
by compass. He applies this difference, in the proper sense,
to the initial compass and reports the result as the adjusted
compass.
b. If the initial laying was not by compass, or if it is
desired to obtain the adjusted compass by actual measure-
ment, the base piece having been adjusted, the procedure is
as follows:
(1) The battery commander commands: MEASURE THE
ADJUSTED COMPASS.
(2) The aiming circle having been set up so as to be suit-
able as an aiming point for the base piece, with the 0-3,200
line approximately in the direction of fire, the executive
commands: NO. 1 (the base piece), AIMING POINT
THIS INSTRUMENT, MEASURE THE DEFLECTION. The
gunner of the base piece refers to the executive’s instrument
and announces the deflection.
(3) Using the French aiming circle. — The executive lays
reciprocally so that the 0-3,200 line on the aiming circle
is pointed in the direction of the line of fire. He then
measures the clockwise angle to compass north by centering
the needle with the upper motion. This angle subtracted
from the declination constant (plus 6,400 if necessary) gives
the adjusted compass. The executive reports, “Adjusted
compass (so much) .”
(4) Using the American aiming circle , M1916. — The exec-
utive measures the magnetic azimuth to the base piece. He
then subtracts the reading given by the gunner of the base
piece from the magnetic azimuth (adding 3,200 if necessary).
This amount plus the declination constant of the aiming
circle is the adjusted compass. (The quadrant in which the
gun is pointing must be considered, otherwise it would be
30
FIRING
73-74
possible to obtain results 3,200 mils in error when using the
panoramic sight or a multiple of 1,600 mils in error when
using the French sight.)
■ 74. Instrument Direction. — a . To\ record. — (1) Immedi-
ately following registration on the base point (or check
point), the executive on order of ’the battery commander,
lays the 0-3,200 line of his observing instrument which has
been set up close to and behind the base piece on a high
burst above the base point, and thus determines the direc-
tion: Base piece — base point. He then records this direc-
tion as instrument direction , by referring it to any conveni-
ent reference point. He is thus able at any subsequent time
to lay the 0-3,200 line of his instrument in the direction of
the base point, provided he does not move his instrument.
(2) For example, the base piece having been adjusted for
direction, the battery commander may command: RECORD
INSTRUMENT DIRECTION, 4,300.
(3) The executive —
(a) Sets up his observing instrument near the base piece.
(£0 Selects an angle of site and a corrector setting that
will surely give bursts visible through the instrument.
(c) Sets the azimuth and micrometer scales of the instru-
ment at zero.
id) Directs the line of sighting in the direction in which
the burst is expected and elevates the instrument to the
angle of site selected.
(e) Commands, for example:
SITE PLUS 30.
CORRECTOR 35.
NO. 1 ONE ROUND.
4,300.
FIRE.
(/) Turns the vertical hair of the instrument to the burst
with the lower motion, thus placing the 0-3,200 line of the
instrument in the desired direction.
(gr) With the upper motion, directs the line of sighting
on a convenient point and records the reading, for example,
453, so that the 0-3,200 line of the instrument can be laid
in the same direction at any time.
31
74
FIRING
( h ) Reports to the battery commander, “Instrument di-
rection recorded/’
(4) The direction of the reference point should be ma-
terialized by stakes for night use. The position of the in-
strument should be marked by a stake.
(5) When registration is not permitted, the battery com-
mander may direct the executive to establish and record
instrument direction without firing. In this case, the execu-
tive sights his instrument on the base point, if necessary,
lining it in from a crest in front or in rear of the position.
If the base point is not visible from any point near the
position, he lays the instrument in the direction of the base
point by the same means used to lay the piece; for example,
by a base angle announced by the battery commander.
5. Subsequent use of instrument direction.— (1) Schedule-
fire missions subsequently sent the battery include a refer-
ence to the instrument direction; that is, the map shift from
the base point (check point), on which direction was re-
corded, to the right edge of the standard area (target)
upon which fire is to be delivered. Just prior to delivering
a concentration, the executive lays his observing instru-
ment in this new direction and fires an air burst with the
base piece, using the computed deflection. The deviation
of this burst from the vertical hair of the instrument is
noted and the entire battery is then given a deflection cor-
rection of this amount, thus insuring a plane of fire cor-
rected for changed atmospheric conditions and direction
errors of laying.
(2) For example, the battery commander, in sending data
to the executive for a concentration, may command:
INSTRUMENT DIRECTION LEFT 146.
3,800.
BASE DEFLECTION LEFT 150.
ON NO. 1 OPEN 3.
SHELL MK. I.
FUZE QUICK.
BATTERY ONE ROUND.
ZONE 5 MILS.
QUADRANT.
115, 125.
32
FIRING
74
(3) The executive —
( a ) Having established the 0-3,200 line of the instrument
as in a above, places the line of sighting in the direction
ordered by applying the instrument-direction shift to the zero
of the instrument with the upper motion. For the foregoing
command, sets the azimuth and micrometer scales at 6,254
<6,400—146) without disturbing the lower motion.
(b) Selects an angle of site and a corrector setting which
will give bursts visible through his instrument and com-
mands, for example:
BASE DEFLECTION LEFT 150.
ON NO. 1 OPEN 3.
NO. 1 ADJUST.
SITE 340.
CORRECTOR 35.
NO. 1 ONE ROUND.
3,800.
FIRE.
(c) Observes this round seven mils right of the instru-
ment direction and completes the commands for the fire
mission, as follows:
BATTERY ADJUST.
LEFT 7.
SHELL MK. I.
FUZE QUICK.
BATTERY ONE ROUND.
QUADRANT.
115.
FIRE.
120 .
FIRE. (And continues the mission ordered.)
c. To measure an instrument-direction shift . — To deter-
mine the instrument-direction shift to a target on which an
adjustment has just been made, the battery commander
may, when no other method is practicable, direct the execu-
tive to fire a high burst over the target and report the
instrument-direction shift.
33
75—76
FIRING
■ 75. Adjusting Sheaf Parallel With High Bursts. — a.
The base piece having been laid for direction, the battery
commander commands, for example:
ON NO. 1 (the base piece) ADJUST SHEAF PAR-
ALLEL.
4,000.
b. The executive —
(1) Gives the necessary commands to have the other pieces
laid approximately parallel to No. 1.
(2) Sets up his observing instrument and lays the 0-3,200
line approximately in the direction of fire.
(3) Selects an angle of site and a corrector which surely
will give bursts visible through his observing instrument, and
elevates his instrument to the angle of site selected.
(4) Determines the angles subtended by the interval from
the base piece to each of the remaining pieces at the range
given (4,000' yards) .
(5) Commands, for example:
SITE 350 (PLUS 50) (or SO MUCH).
CORRECTOR 35 (or SO MUCH) .
BATTERY BY PIECE AT MY COMMAND.
4,000.
NO. 1 (the base piece) FIRE.
(6) Puts the vertical hair of his instrument (the azimuth
scale of which has been set at zero) on the point of burst of
the base piece and then commands: NO. 2 FIRE.
(7) Turns the upper motion of the instrument and meas-
ures the angle between the points where the first round burst
and the second round burst, and, to correct the error ob-
served (if any), commands: NO. 2 RIGHT (LEFT) (SO
MUCH).
(8) Adjusts the other pieces in a similar manner, causing
the pieces to be fired at intervals appropriate for accurate
observation of deviations, and correcting each piece indi-
vidually.
(9) Reports to the battery commander, “Sheaf adjusted.”
■ 76. Report by Operator of Beginning and Completion of
Fire. — At the first round of a salvo or similar series of fire,
the telephone operator reports to the battery commander,
34
FIRING
76-77
“On the way.” If the rate of fire is slow, he may report
each round, “No. 1 on the way,” “No. 2 on the way,” and so
on. On the completion of the salvo or series, the operator
reports, “Round completed.”
Section VT
EXAMPLES OP FIRE COMMANDS
■ 77. 75-mm Guns With Panoramic Sights. — a. Direct lay-
ing. — (1) Initial commands:
TARGET, THAT COLUMN OP INFANTRY.
DEFLECTION 10.
CORRECTOR 30.
BATTERY ONE ROUND.
2 , 200 .
(2) To change data:
DOWN 5.
TWO ROUNDS.
2,600.
b. Fire at will . — (1) The battery commander (or executive)
commands :
TARGET, THAT CAVALRY.
FIRE AT WILL.
(2) The chiefs of section repeat the above commands.
c. Aiming point and deflection , battery in line at regular
intervals. — (1) For the initial laying of the battery with the
battery commander controlling the distribution directly, to
form an open sheaf and begin fire with one gun, the battery
commander commands:
AIMING POINT, TO THE RIGHT FRONT, THAT
BARE TREE.
DEFLECTION 240.
ON NO. 1 OPEN 7.
SITE 290.
CORRECTOR 35.
NO. 2 ONE ROUND.
4,000.
The executive repeats the above command, and, at the proper
time, adds: FIRE.
35
77
FIRING
(2) To change data after firing a salvo, the battery com-
mander commands:
LEFT 20.
NO. 2 RIGHT 5.
UP 5.
4,200
The executive repeats these commands, adding: FIRE.
d. Compass , registering on a base point. — (1) The battery
commander commands:
COMPASS 1,450.
SHELL MK. I.
FUZE QUICK.
NO. 1 ONE ROUND.
QUADRANT.
200 .
(2) The declination constant of the instrument is, for
example, 200 (or 6,600). The executive sets up the aiming
circle in a position suitable for use as an aiming point by
all pieces, subtracts from the declination constant (6,600)
the announced Y-azimuth (1,450), sets the remainder (5,150)
on the azimuth scale of the aiming circle and centers the
needle with the lower motion. He then lays the battery
reciprocally on the aiming circle (par. 57), commanding, for
example:
AIMING POINT, THIS INSTRUMENT (aiming cir-
cle).
DEFLECTION NO. 1, 800; NO. 2, 400; NO. 3, 2,900;
NO. 4, 2,500.
AIMING POINT, AIMING STAKES.
REFER.
SHELL MK. I.
FUZE QUICK.
NO. 1 ONE ROUND.
QUADRANT.
200 .
FIRE.
(3) On completion of the adjustment of the base piece,
the other pieces having followed the deflection changes, the
battery commander commands:
36
FIRING
77
RIGHT 5.
RECORD BASE DEFLECTION.
(4) The executive repeats these commands and, at the
proper time, reports, “Base deflection recorded.”
e. Base angle , recording base deflection without adjust-
ing , — (1) The battery commander commands:
BASE ANGLE 1,800.
RECORD BASE DEFLECTION.
(2) The executive converts the above commands, thus:
AIMING POINT, THIS INSTRUMENT.
DEFLECTION NO. 1, 1,400; (and so on).
AIMING POINT, AIMING STAKES.
REFER.
RECORD BASE DEFLECTION.
(3) The executive reports, “Base deflection recorded.”
/. Shift from base deflection and zone fire , staggered posi-
tion. — (1) The battery commander, controlling distribution
indirectly through the executive, commands:
BASE DEFLECTION RIGHT 100.
CONVERGE AT 5,000.
ON NO. 1 OPEN 12.
SITE 305.
SHELL MK. I.
FUZE QUICK.
BATTERY TWO ROUNDS SWEEPING, 6 MILS.
ZONE, 4,900, 5,100.
(2) The pieces of the battery are at the following inter-
vals from No. 1: No. 2, 10 yards; No. 3, 35 yards; No. 4, 90
yards.
(3) The executive converts the command of the battery
commander thus (par. 62) :
BASE DEFLECTION RIGHT 100.
NO. 2 RIGHT 2, NO. 3 RIGHT 7, NO. 4 RIGHT 18.
ON NO. 1 OPEN 12.
SITE 305.
SHELL MK. I.
FUZE QUICK.
BATTERY TWO ROUNDS SWEEPING, 6 MILS.
4,900.
FIRE.
37
77-79
FIRING
and continues the fire throughout the zone.
g. Firing a salute . — The battery commander gives the fol-
lowing commands directly to the gun squads:
WITH BLANK AMMUNITION.
21 (OH SO MANY) ROUNDS.
BATTERY BY PIECE AT MY COMMAND.
LOAD.
NO. 1 FIRE.
NO. 2 FIRE.
NO. 3 FIRE.
NO. 4 FIRE.
NO. 1 FIRE.
* * * * *
When the required number of rounds has been fired: CEASE
FIRING.
■ 78. 75 -mm Guns With French Sights. — Using an aim-
ing point and deflection, the battery being in line at reg-
ular intervals, when the battery commander desires to con-
trol distribution directly, he commands:
AIMING POINT, TO LEFT FRONT, THAT
CHIMNEY.
PLATEAU 10, DRUM 105.
ON NO. 1 OPEN 10.
SITE PLUS 5.
SHELL MK. I.
FUZE QUICK.
RIGHT RIGHT.
4,100.
■ 79. 155-mm Howitzers. — a. Having recorded base deflec-
tion, to begin a precision adjustment on a target, the
battery commander commands:
NO. 1 ADJUST.
BASE DEFLECTION LEFT 80.
SHELL MK. I.
CHARGE V.
FUZE DELAY.
NO. 1 ONE ROUND.
QUADRANT.
290.
38
FIRING
79
b. Having completed the previous mission, to begin a
bracket adjustment, the battery commander commands:
BATTERY ADJUST.
BASE DEFLECTION RIGHT 140.
CONVERGE AT 7,500.
SITE 300.
SHELL MK. I.
CHARGE V.
FUZE QUICK.
NO. 2 ONE ROUND.
WITHOUT QUADRANT.
450.
c. To adjust for direction with a high burst and to fire
through a zone.
(1) The battery commander commands:
INSTRUMENT DIRECTION LEFT 95.
TIME 22.
370.
BASE DEFLECTION LEFT 107.
CONVERGE AT 6,000.
ON NO. 1 OPEN 10.
SHELL MK. I.
CHARGE V.
FUZE QUICK.
BATTERY ONE ROUND.
ZONE 7 MILS.
QUADRANT.
313, 327.
(2) The executive sets his observing instrument in the
direction ordered and commands:
BASE DEFLECTION LEFT 107.
ON NO. 1 OPEN 7.
NO. 1 ADJUST.
SITE 350.
CORRECTOR 50.
CHARGE V.
TIME 22.
NO. 1 ONE ROUND.
370.
FIRE.
39
79
FIRING
(3) The executive observes the burst to be 5 mils left of
the vertical hair of his instrument. He then commands:
BATTERY ADJUST.
RIGHT 5.
SHELL MK. I.
CHARGE V.
FUZE QUICK.
BATTERY ONE ROUND.
QUADRANT.
313.
FIRE.
40
80-81
CHAPTER 2
ELEMENTARY BALLISTICS AND DISPERSION, AND
EFFECTS OF PROJECTILES
Paragraphs
Section I. Elementary ballistics and dispersion 80-85
II. Effects of projectiles 86-89
Section I
ELEMENTARY BALLISTICS AND DISPERSION
■ 80. Definitions. — Ballistics treats of the motion of the
projectile and the conditions affecting it. Interior ballistics
deals with the motion of the projectile in the piece; exterior
ballistics with the motion of the projectile after leaving the
piece. Gunnery is the practical application of ballistics so
that the desired effects may be obtained from fire. Gunnery
is divided into two phases: Preparation of fire and conduct
of fire .
■ 81. Exterior Ballistics. — a. The trajectory. — The trajec-
tory is the curve described by the center of gravity of a pro-
jectile in flight.
(1) The origin is the center of the muzzle of the piece.
(2) The level point is the point, on the descending branch
of the trajectory at the same altitude as the origin.
(3) The base of the trajectory is the straight line joining
the origin and the level point.
(4) The plane of fire is the vertical plane containing the
axis of the bore when the piece is laid.
(5) The line of site of a point is the straight line con-
necting the origin with that point.
(6) The plane of site is the plane containing the line of site
and a horizontal line perpendicular to it.
(7) The line of elevation is the axis of the bore prolonged
when the piece is laid.
(8) The angle of fall is the angle between the base of the
trajectory and the tangent to the trajectory at the level
point.
(9) The angle of impact is the angle between the tangent
to the trajectory at the point of impact and the plane tan-
gent to the surface of the ground at that point.
41
81
FIRING
(10) The slope of fall is the tangent of the angle of fall
and is expressed as 1 on 10 (or so much) .
(11) Other elements of the trajectory are indicated in fig-
ure 1.
b. Form of the trajectory (fig. 2). — (1) In a vacuum . — If
there were no air to offer resistance to the projectile, the
form of the trajectory would be determined entirely by the
elevation, the muzzle velocity, and gravity. The form would
be a symmetrical curve (approximately a parabola) ; the
angle of fall would equal the angle of elevation, and the
maximum ordinate would be at a point halfway between the
origin and the level point.
Or igin
Basa
- E —
® Standard trajectory.
Level .point
-n
(5) Time fire.
Figure 1 . — Elements of the trajectory.
42
FIRING
81
(2) Effects of air resistance. — (a) Resistance of the air
tends to retard the projectile from the instant it leaves the
piece. This makes the trajectory a more complex curve than
that in a vacuum; the angle of fall is greater than the angle
of elevation, the maximum ordinate is closer to the level point
than to the origin, and the range is reduced.
(b) Air resistance increases with the velocity, is approxi-
mately proportional to the cross-section of the projectile,
and varies with the shape of the projectile. The retardation
of a projectile depends upon the ratio of air resistance to
mass of projectile; in general, air resistance varies as the
square of the caliber, while mass varies as 'the cube. Ac-
cordingly, retardation is less for large projectiles than for
smaller ones of the same shape.
c. Drift . — The deviation of a projectile from the plane
of fire, caused by air resistance, rotation, and gravity, is
termed drift. The line of fire is the trace of the trajectory on
the ground.
(Note the tremendous decrease in range caused by air resistance.)
Figure 2. — Comparison of a trajectory in a vacuum and one in air.
d. Variations in trajectories. — (1) The trajectory for a
given projectile and piece varies with the muzzle velocity
and with the quadrant elevation. Accordingly, range flexi-
bility increases with the number of different propelling
charges designed for the weapon and the possible variations
in quadrant elevation. A standard trajectory is one ob-
tained with standard conditions of materiel and atmosphere;
that is, conditions adopted as standard in the preparation
of Firing Tables. These conditions are assumed to be as
follows :
(a) Weight of projectile, as given in the appropriate Firing
Table.
(b) Temperature of powder, 70° F,
43
81
FIRING
(c) Air density, that corresponding to 29.53 inches of
mercury at 59° F. at the battery, considered as 100 percent.
(d) Air temperature, 59° F. at the battery.
( e ) No wind.
(2) Variations from the standard conditions given in (1)
above have the following effects on projectiles:
(a) Weight of projectile . — A projectile heavier than stand-
ard causes a decrease in the range for the lower elevations,
but an increase in range for the higher elevations. A pro-
jectile lighter than standard has the opposite effect.
(b) Temperature of powder. — A powder temperature
higher than standard causes an increase in muzzle velocity
and consequently an increase in the range ; a powder temper-
ature lower than standard similarly causes a decrease.
(C) Air density. — Air density above normal (over 100 per-
cent) offers more resistance to the projectile and conse-
quently causes a decrease in the range; air density below
normal similarly causes an increase.
(d) Air temperature (elasticity) . — Air temperature higher
than normal causes an increase in range; lower than nor-
mal, a decrease.
(e) Wind . — A head wind causes a decrease in the range,
a rear wind an increase; a cross wind from the right (left)
forces the projectile to the left (right) ; an oblique wind,
having components both parallel and perpendicular to the
direction of fire, affects both range and deflection.
e. Time fire (fig. 1) . — In firing time-fuzed projectiles which
may be burst in the air by appropriate settings, the point of
burst is the point at which the burst takes place or would
have taken place if not obstructed. The following effects
obtain in time fire:
(1) Making a corresponding change in range settings of
the piece and fuze setter, the corrector and site remaining
constant, results in no change in the height of burst.
(2) By changing only the corrector, the burst is drawn
back or advanced along the trajectory, resulting in a change
in height of burst and burst range.
(3) Changing only the site results in a corresponding rais-
ing or lowering of the burst practically in a vertical line.
44
FIRING
81-82
The burst range is not changed but the height of burst and
trajectory are changed.
(4) By making a change in the corrector and a compen-
sating change in site, the height of burst remains constant.
The trajectory and burst range are changed.
/. Rigidity of the trajectory . — The theory of the rigidity
of the trajectory is the assumption that the trajectory may
be tilted up or down through small vertical angles about the
origin without materially affecting its shape. The flatter
the trajectory, the more nearly is the assumption correct.
The assumption is utilized primarily in bracket fire to cor-
rect for the altitude of the target by applying the angle of
site to the range or elevation, thus tilting the trajectory up
or down about the origin. When using large elevations
with large angles of site, errors may be introduced by this
assumption, and, in carefully prepared fire, elevation cor-
rections should be determined from the complementary an-
gle-of-site tables given in Firing Tables (par. 139 / (6) ) .
Instead of complementary angle-of-site tables, some Firing
Tables have position -effect tables which combine the site and
the complementary angle of site into one range effect.
g. Firing tables . — Information necessary for the practical
handling of trajectories is given in the appropriate Firing
Tables.
B 82. Interior Ballistics. — Accuracy in firing is affected by
the following conditions:
a. Wear of the piece (erosion) , if uniform, reduces muzzle
velocity; if uneven or excessive, it causes variation in muzzle
velocity and inaccuracy in the flight of the projectile. When
the lands are worn, the projectile is given insufficient spin,
and erratic results ensue.
b. Coppering (deposit of copper from the rotating bands
on the surface of the bore) causes inaccuracies, high pres-
sures, and increased erosion.
c. Lack of cleanliness, both with respect to the bore and
the projectile, may cause increased erosion and improper
centering of the projectile.
177568 °— 39 -
■4
45
82-83
FIRING
d. Improper ramming or injuries to the rotating band may
permit the escape of gases around the rotating band, greatly
increasing erosion and causing erratic velocities.
e. Lack of uniformity in the weight of projectiles or pro-
pelling charges will cause nonuniform velocities.
/. Varying lots of powders or variations in powder tem-
perature will result in varying velocities.
■ 83. Dispersion. — a. General . — If a number of rounds were
fired from a piece under conditions as nearly identical as
possible, the points of impact of the projectiles on a hori-
zontal plane would be dispersed about a point called the
center of impact. The following are characteristics of dis-
persion:
(1) Shots are more scattered in range than in direction.
(2) Shots fall in an area, assumed for practical purposes
Center of A.
impact
2 %
25%
7%
2 %
Figure 3. — Dispersion diagram.
to be a rectangle and called the rectangle of dispersion,
whose long axis lies along the line of fire and whose center
is the center of impact.
(3) Shots are grouped more closely toward the center
than toward the edges of the rectangle.
(4) As many shots fall beyond the center of impact as
short thereof, and as many to the right as to the left.
b. Range probable error. — (1) If a line AB (fig. 3) is
drawn through the center of impact perpendicular to the
line of fire, there are as many shots short of the line as
over. If a line CD is drawn parallel to AB so that there are
as many shots beyond CD as there are between CD and AB,
the distance between CD and AB, measured along the line of
fire, is the value of the range probable error, which is the
error that will be exceeded as frequently as it is not ex-
ceeded, This error for any particular weapon is determined
46
FIRING
83-84
by actual firing and is taken as the index of the accuracy
of the piece.
(2) If lines are drawn parallel to AB at intervals of one
probable error, the percentages of shots falling in each sub-
division will be approximately as indicated in figure 3.
(3) Since the range probable error is known, being given
in Firing Tables, the relative position, in range, of the
center of impact and a target lying in the rectangle of dis-
persion may be deduced from the percentage of shots over
or short of the target; that is, X (fig. 3) represents the posi-
tion of the target if 25 percent of the shots are over and
75 percent short; Y , if 10 percent are over and 90 percent
short; Z, if 37 percent are over and 63 percent short.
c. Direction probable error . — Dispersion in direction fol-
lows the same laws as dispersion in range but is much less.
Values are given in Firing Tables.
d. Vertical probable error. — Dispersion in a vertical plane
follows the same laws as dispersion in a horizontal plane.
The vertical probable error is the product of the range
probable error and the tangent of the angle of fall. Values
are given in Firing Tables.
e. Dispersion on slopes. — A positive slope is one which
rises away from the piece. A negative slope is one which
descends away from the piece. Dispersion on a positive slope
is less, on a negative slope more, than that on a horizontal
plane.
/. Height- of -burst probable error . — In time fire, disper-
sion is due to variations in trajectories and in the time of
burning of the fuzes. Distribution follows the law of errors.
The rectangle of dispersion for height of burst is derived
from the vertical projection of the points of burst; for burst
range it is the horizontal projection.
g. Practical application. — The solution of problems, such
as the expenditure of ammunition to obtain a given number
of hits in a certain area and the distribution of shots in an
area, can be obtained by applying the necessary dispersion
scales to the area.
■ 84. Fork. — The fork is a unit of range change used in
conduct of fire. It is the change in elevation necessary to
47
84-85
FIRING
move the center of impact four range probable errors. Its
practical value is a function of the quadrant elevation and is
given in Firing Tables, usually in mils.
■ 85. Probabilities Deduced From the Laws of Disper-
sion. — These probabilities are derived by application of the
laws of dispersion. The following are among the most im-
portant of those on which the principles of conduct of fire
are based:
a. Probability that target is within bracket.
Number of sensings
Probability (%)
At one
At the
One-fork
Two-fork
Four-fork
limit
other
bracket
bracket
bracket
1
1
70
85
92.3
1
2
75
89
96
1
3
76
90
97
2
2
85
94.5
99+
3
3
92.5
98
99+
b. Probability that target is within zone of dispersion of
center of one-fork range bracket. — A one-fork bracket hav-
ing been obtained with one sensing at each limit, the proba-
bility that the target is within the zone of dispersion of
rounds fired at the center of the bracket is 96.8 percent.
This probability is increased as additional verifying sensings
are obtained.
c. Probability that center of impact is within a given dis-
tance of the target.
Number of
sensings
Distance in probable errors
In one
sense
In the
other
One
Two
Three
Four
1
1
54
Probabi
86
lity (%)
98
99+
1
2
51
86
98
99+
1
3
44
80
96
99+
2
2
70
96
99
99+
3
3
99+
i
99+
99+
99+
48
FIRING
86-87
Section II
EFFECTS OF PROJECTILES
■ 86. Penetration. — a. The path of a projectile after strik-
ing the ground depends upon the angle of impact, the nature
of the ground, and the shape, weight, velocity, and rotation
of the projectile. Frequently a projectile is diverted to the
right or left. With angles of impact between 0 and 125 mils,
a projectile usually ricochets, leaving a narrow furrow in
the ground; the angle of ricochet is roughly one and one-
half times the angle of impact. With angles of impact be-
tween 125 and 450 mils, a projectile usually enters the
ground and either remains just below the surface or rico-
chets. With angles of impact between 450 and 700 mils, the
projectile tends to rise in the ground but usually does not
emerge.
b. Penetrations in ordinary compact soil are approximately
as follows:
Caliber
Striking
velocity
Angle of
impact
Penetration
(vertical or
horizontal)
75-mm_
Foot-seconds
730
Mils
800
Feet
4
lOS-mm
800
800
6
155-mm
770
800
7
8-inch_ . .
790
800
9
240-mm
806
800
14
■ 87. HE Shell (fig. 4) . — a. Proper action of fuze and booster
causes the bursting charge to detonate. Incomplete detona-
tion of the bursting charge causes the shell to break into a
few large fragments and is termed a low order burst. A dud
is a shell which has failed to burst.
b. The fragments of a bursting shell are divided, according
to the direction in which projected, into three general groups;
side spray, base spray, and nose spray.
c. The following are characteristics of the effect of shell
bursts: The main effect is from the side spray; effect is small
when the height of burst is above normal; the small depth
covered by fragments requires accurate range adjustment.
49
87-88
FIRING
d. The effect of a shell bursting on ricochet is similar to
that of an air burst, the axis of the shell being inclined
upward. Ricochet fire is used only with the light artillery.
S Pirection of fire.-
Figure 4. — Shell bursts.
e. With a quick fuze, the . shell usually bursts before it
penetrates. At very small angles of impact, the body instead
of the fuze may strike the ground, resulting in a nonbursting
ricochet.
/. Areas covered effectively by fragments from HE shell
are approximately as follows:
Caliber
Effective
Radios of
large effec-
tive frag-
ments
Depth
Width
75-mm
Yards
5
9
9
Yards
30
40
70
, Fards
150
i 300
550
105-mm
155-mm _
■ 88. Shrapnel (fig. 5) . — a. The main effect of a shrapnel is
from the balls; however, the case, which does not rupture,
and the head and fuze are effective. The balls upon being
ejected are contained roughly within a cone, the apex of
which is at the point of burst. The apex angle of the cone
is termed the angle of opening.
b. Against inflammable targets, incendiary effects may be
obtained with low or graze bursts.
50
FIRING
88
Point of
Point of
® Range, 4,000 yards.
Point of
® Range, 6,000 yards.
Figure 5. — Normal bursts, 7 5 -mm shrapnel.
51
89
FIRING
■ 89. Chemical Shell. — a. Fuzes . — Since it is usually desired
to distribute the filler of the shell in air rather than in a
crater, a quick fuze should be used if the shell will not
ricochet. If the angle of impact will give a large proportion
of ricochets, a delay fuze should be used.
b. Smoke . — The type of smoke shell in use is WP, contain-
ing white phosphorus. In addition to its smoke-producing
effect, WP has a marked incendiary effect and inflicts severe
bums on personnel.
52
90-93
CHAPTER 3
PREPARATION OF FIRE
Paragraphs
Section I. General 90-94
II. Preparation of fire with instruments 95-109
III. Firing charts 110-114
IV. Survey operations, plans, and proce-
dure 115-122
V. Preparation of fire from firing charts. _ 123-133
VI. Schedule fires 134-142
Section I
GENERAL
■ 90. Definition. — Preparation of fire is the determination
of firing data. The object of preparation is to obtain the
most accurate data possible under existing conditions.
■ 91. Units of Measure. — The unit of length or distance is
the yard. The unit of angular measure is the mil (m) equal
to 1/6,400 part of the circumference of a circle. Practically a
mil is the angle subtended by one yard at a distance of 1,000
yards. The mil relation is expressed by W—Rxn i where m
is the angular width of the object in mils, W is the width
of the object in yards, and R is the range or distance in
thousands of yards. The mil relation is approximately true
for angles of less than 400 mils.
■ 92. Data Necessary to Open Fire. — The following infor-
mation is necessary to have the battery deliver the desired
fire:
a. Direction.
b. Distribution.
c. Projectile, fuze, and, when necessary, charge.
d . Pieces to fire and method of fire.
e. Site and range, or quadrant elevation.
■ 93. Steps in Preparation. — There are three general steps in
preparation of fire as follows:
a. Determining basic data which are direction, distribu-
tion, site, and range.
53
93-96
FIRING
b. Determining corrections for conditions not standard.
d. Converting basic or corrected data to settings for the
piece.
■ 94. Kinds of Preparation. — Preparation of fire is made
with instruments or from firing charts, depending upon the
time and facilities available for getting basic data and cor-
rections. In either case the preparation is as accurate as
circumstances permit.
Section II
PREPARATION OP FIRE WITH INSTRUMENTS
R 95. General. — Instruments ordiharily are used for the
preparation of data when time is pressing or when other
facilities are lacking. Means available are the battery com-
mander’s telescope, aiming circle, prismatic compass, range
finder, field glasses, and calibrated hand or other object.
Fires with data prepared with instruments must be ob-
served and data corrected as a result of observation.
■ 96. Direction. — Direction is obtained by determining the
firing angle, the T-azimuth of the direction of fire, or the
shift from a known direction. Direction is usually de-
termined from an observation post and converted for use at
the battery. Occasionally, direction may be determined by
actual measurement at the battery.
a. Terms used. — (1) The firing angle is the clockwise hori-
zontal angle from the target to the aiming point, vertex at
the piece. The piece as here used means the base piece
(usually No. 1).
(2) The measured angle is the clockwise horizontal angle,
vertex at the observation post, between the target and the
aiming point, base point, or other datum point. The one ex-
ception to this is in the computation of a shift (par. 100),
in which case the measured angle is the smaller (not neces-
sarily clockwise) angle between the base point and target
as measured at the observation post.
(3) The target offset is the horizontal angle between the
piece and observation post, vertex at the target.
54
FIRING
96-97
(4) The aiming -point offset is the horizontal angle be-
tween the piece and observation post, vertex at the aiming
point.
b. Deflection. — The firing angle, corrected, is converted
to a setting, termed the deflection, to be applied to the
sights. An increase of deflection moves the plane of Are to
the left; a decrease moves it to the right.
(1) Panoramic sight . — If graduated from 0 to 3,200, the
deflection is the firing angle when the latter is less than 3,200;
if greater, it is the firing angle less 3,200. If graduated from
0 to 6,400, the deflection is the firing angle.
(2) French sight. — To convert a firing angle to deflection,
add the deflection constant , 100, to the firing angle ; subtract
the largest multiple of 1,600; the largest even number of
hundreds in the result is the plateau setting; the remainder,
after subtracting this even number of hundred mils, is the
drum setting.
c. Abbreviations and symbols.
M, measured angle.
A t firing angle.
Ty target or target offset.
Py aiming point or aiming-point offset.
Gy piece.
Oy observation post.
OPy distance, in thousands of yards, from O to P.
OGy distance, in yards, from O to G.
r, distance, in thousands of yards, from O to T.
Ry distance, in thousands of yards, from G to T.
■ 97. Determining Direction at the Observation Post. —
a. General. — The principle of each method of determining
direction is to visualize an angle at O whose sides are parallel
to the sides of the direction angle used to lay the piece and
thus equal to it. For example, in figure 6, OT ' is parallel to
GT and OP ' is parallel to GP. It is evident that the target
offset T equals the angle TOT' and the aiming-point offset P
equals the angle POP'. These offsets applied to the angle
TOP (the measured angle M) give the angle T'OP\ which
is equal to the angle TGP (the firing angle A), since their
sides are parallel.
55
97-98
FIRING
Figure 6. — -Determination of direction at O.
b. Determination of offsets (fig. 7) . — The angle OTG is
the target offset T. The line O'G is visualized from G per-
pendicular to OT (or OT extended) . By the mil relation, T
equals O'G divided by O'T/ 1,000. For practical purposes,
OT is used instead of O'T when they do not differ by more
than 500 yards. In such case, T=0'G/r. When the differ-
ence between OT and O'T is more than 500 yards, O'T/ 1,000
is used. The value of O'G usually is estimated. The aiming-
point offset P is determined in like manner.
■ 98. Determining the Firing Angle. — c. General (fig. 6). —
To determine the firing angle, visualize the measured angle
TOP and apply to it the target offset and the aiming-point
offset, away from the piece, either by computation or me-
chanically, so that the sides of the resulting angle T'OP'
will be parallel to the sides of the firing angle TGP. For
computation, the sign of each offset is determined as fol-
56
98
FIRING
lows: If the offset, applied away from the piece, cuts into
the measured angle, it is minus. If the offset, applied away
from the piece, increases the measured angle, it is plus.
If the offset, applied away from the piece, is so large that it
starts inside the measured angle and continues outside of
it, or starts outside and then extends inside the measured
angle, the part within which it starts controls the sign.
b. Examples of determination of the firing angle by com-
putation. — Figure 7 illustrates the four cases.
c. Mechanical computation. — The battery commander’s
telescope or aiming circle may be used to determine the firing
angle by applying the offsets mechanically, as follows:
(1) Set the azimuth and micrometer scales at zero and
lay on the target, using the lower motion.
(2) Determine the size of the target offset. With the
upper motion, turn the index away from the piece by the
amount of the target offset, measuring the amount on the
scales of the instrument. The 0-3,200 line of the instrument
remains on the target.
(3) With the lower motion, turn the vertical hair to the
target. The 0-3,200 line of the instrument now has been
moved away from the piece by the amount of the target off-
set and is parallel to the GT line.
(4) With the upper motion, bring the vertical hair to the
aiming point. This measures the angle T'OP.
(5) Determine the size of the aiming-point offset. With
the upper motion, turn the vertical hair away from the piece
this amount, measuring the amount of movement by the
micrometer scale. The reading of the scale is now the
firing angle A.
d . Rapid plotting . — The determination of the firing angle
and the range by rapid plotting is particularly appropriate
when the target offset or aiming-point offset is so large that
use of the mil relation is not sufficiently accurate (that is,
when the offset is greater than 400 mils) . It consists of
drawing a diagram to scale and measuring therefrom the
firing angle and the range.
e. O as an aiming point (fig. 8), — (1) If an instrument at
the observation post is used as an aiming point, M is the
58
FIRING
98—99
clockwise angle from the target to the piece. It is corrected
by T and the result is increased by 3,200 mils if the piece
is on the right, or decreased by 3,200 mils if the piece is on
the left.
Figure 8. — Calculation of the firing angle with O as aiming point.
(2) When all of the pieces are visible through the instru-
ment at O, the deflection may be determined for each in
turn. When this condition does not exist, the executive’s
instrument or a single piece may be laid by the instrument
at O. The remaining pieces are laid reciprocally on the exec-
utive’s instrument or on the sight of the directing piece.
■ 99. Determining Direction by Y- Azimuth. — a. Terms
used. — Compass north is the north direction indicated by a
compass. Y -north or grid north is the north direction of a
y-grid of a map or grid. Y-azimuth of a line is the clock-
wise angle, measured at any point on the line, from y-north
to the line. A compass north seldom coincides with mag-
netic north because of errors of individual compasses. All
compasses should be calibrated with reference to a control
line, usually y-north. The y-azimuth of the north direction
indicated by a compass is the declination constant of the
59
99
FIRING
compass. When the declination constant is applied to a
compass reading, the result is the Y-azimuth of the direction.
b. Use of the prismatic compass (fig. 9.) — The method of
determining the Y-azimuth of the line of fire, using a pris-
matic compass at O, is as follows:
(1) Take the compass reading of the target from O.
(2) Add the declination constant of the instrument, thus
obtaining the Y-azimuth of the target from O. (If the sum
is greater than 6,400, 6,400 is subtracted.)
Compass reading of T= 1250 m
Declination constant = 190 m
Y-azimuth of T from 0 = 1250+ 190 = 1440 m
T — = 286 in
o . 5
Y-azimuth of T from G~ 1440 — 286 = 1154 m
Figure 9. — Determining y-azimuth with the prismatic compass.
(3) Apply the target offset away from the piece; the result
is the Y-azimuth of the GT line. The compass reading
with declination constant added is the clockwise angle from
Y-north to the target and, in determining signs of offsets,
is considered the measured angle. When using a compass,
the measured angle always fcUls to the left of the OT line .
If the target offset cuts into this angle (piece on the right
of the line OT, or OT extended), the offset is minus ; if the
60
FIRING
99-101
target offset falls outside this angle (piece on the left), the
target offset is plus.
c. Use of the aiming circle. — (1) Set the declination con-
stant on the azimuth and micrometer scales.
(2) With the lower motion, center the magnetic needle,
the final movement being with the slow motion. The
0-3200 line is now on F-north.
(3) Clamp the needle. With the upper motion, turn the
vertical hair to the target. This measures the F-azimuth
of the target from O.
(4) Determine the target offset. Apply this to the F-
azimuth found in (3) above. This is done mechanically as
follows : with the upper motion, turn the vertical hair away
from the piece by the amount of the offset, measuring the
amount of movement by the micrometer scale. The reading
is the F-azimuth of the GT line.
■ 100. Determining Direction by Shifts From a Known
Direction (fig. 10). — a. Computation. — If base deflection
(par. 52) has been recorded on the base point, the initial
direction for a target is usually determined as a shift from
base deflection. The computation of the shift is similar to
the computation of a firing angle, considering the base point
as the aiming point. The angle of a shift is measured from
the base point to T; it is right if the target is to the right of
the point, left if the target is to the left of the point. The
signs of the offsets are determined as in paragraph 98 a, the
measured shift being considered the measured angle. If the
combined offsets are greater than the shift and the sign is
minus , the shift is in the opposite direction from the meas-
ured shift.
b. Rapid plotting. — Shifts may be plotted as in determin-
ing the firing angle (par. 98 d) .
■ 101. Direct Methods of Determining Direction. — a. Di-
rect measurement. — If the target can be seen from the posi-
tion of the piece, the firing angle may be measured with the
sight or with an instrument set up adjacent thereto.
b. Lining in. — If the target can be seen from a position in
rear of the piece, the piece may be laid for direction by lin-
ing the axis of the tube on the target by eye.
177568 °— 39 -
-5
61
101-102
FIRING
c. Laying on an airplane . — Direction for a target may be
given by laying a piece or an instrument at the battery posi-
tion on an airplane which signals when it is on the GT line.
The airplane may signal when it is on the GT line extended
to the rear of the battery. The piece may be laid by setting
the deflection scale so that the line of sighting is parallel to
the axis of the bore, and traversing the piece to place the
vertical hair on the airplane; otherwise, the piece is laid in
a known direction and the shift to the airplane is measured
by the sight. When an instrument is used, the same pro-
cedure is followed, the piece being laid reciprocally on the
instrument.
e/p*
Figure 10. — Shifts.
d. Air burst . — A round is fired in the general direction of
the target at a range which will not endanger friendly troops
and at a site and correcter to give a visible air burst. When
the burst is seen, its deviation from the target is measured
at the observation post and the direction of the piece is cor-
rected accordingly.
■ 102. Distribution. — a. Terms used. — (1) A sheaf consists
of the planes of fire of two or more pieces of a battery, con-
sidered as a group.
62
FIRING
102
(2) A parallel sheaf is one in which the planes of fire are
parallel.
(3) An open sheaf is one effectively covering a maximum of
front without sweeping.
(4) A converged sheaf is one in which the planes of fire
are converged at the points of burst.
(5) A crossed sheaf is one in which the planes of fire con-
verge at a point short of the points of burst, the bursts ap-
pearing in reverse positions from the pieces firing.
(6) Deflection difference ( DD ) is a uniform change in the
deflection of adjacent pieces to obtain a desired width of
sheaf.
b. Parallel sheaf . — The executive usually is charged with
the formation of a parallel sheaf. Upon occupation of posi-
tion, he lays the battery parallel in the direction indicated by
the battery commander or, in the absence of specific instruc-
tions, in the general direction of fire. When the initial
direction is given by compass or by base angle (par. 124) , the
pieces are laid by the aiming circle or other instrument and a
parallel sheaf is formed directly; when given by use of an
aiming point, the executive may form a parallel sheaf as
explained above or by determining a deflection difference.
When the battery commander desires a parallel sheaf formed
by firing, he commands: ON NO. 1 ADJUST SHEAF PAR-
ALLEL (par. 75) followed by the range at which it is desired
to adjust the sheaf. When the battery commander desires
a parallel sheaf formed without firing, he commands: ON
NO. 1 FORM SHEAF PARALLEL (par. 60).
c. Converged sheaf . — The battery commander usually con-
verges the sheaf prior to opening it to fit the target or
adjusting point. This is accomplished by the command:
CONVERGE AT (SUCH RANGE) ; the range announced is
the multiple of 500 nearest the initial range. When the
initial direction is given by means which do not give a
parallel sheaf directly (aiming point and deflection), the
executive must first form the sheaf parallel before converging
it. The sheaf is converged by the executive on No. 1 (par.
62).
d. Fire without sweeping. — (1) The interval between the
bursts of adjacent pieces is one third the desired width of
63
102
FIRING
the sheaf. Hence, the deflection difference for a target
which can be covered without sweeping is, from a converged
sheaf, 1/3 W/R, where W is the width of the target in yards.
(2) The front of an open sheaf equals four times the effec-
tive width of a single burst; the width of the sheaf (distance
between flank bursts) is three times the width of a single
burst as shown in the table below:
Projectile
Effective
width of a
single burst
Width of
open sheaf
Front covered
by open
sheaf
75-mm
Yards
30
40
70
Yards
90
120
210
Yards
120
160
280
105-mm
155-mm .
e. Sweeping fire . — When a target is too wide to be covered
effectively with an open sheaf, a wider sheaf is used ' and
each piece is traversed a definite amount after each round,
usually to the left, until the front is covered. This is termed
sweeping fire, of which there are two kinds; normal sweeping
and cross sweeping. The data necessary are distribution;
number of rounds sweeping; amount of sweep or traverse
after each round.
(1) Normal sweeping. — (a) Distribution. — For normal
sweeping, No. 1 is laid on the right of the target. The
total front to be covered equals the width of the target plus
the effective width of a single burst. Each piece covers one
fourth of the total front. The deflection difference to obtain
the necessary distribution from a converged sheaf is open
1/4 F/R, where F is the total front covered.
(b) Number of rounds sweeping. — The number of rounds
sweeping is equal to the front to be covered by each piece
(one fourth of the total front) divided by the effective width
of a single burst. Fractional rounds are taken as whole
rounds.
(c) Amount of sweep . — The amount of sweep is the effec-
tive width of a single burst converted to mils at the piece-
target range. For materiel equipped with the panoramic
sight, the amount of sweep is announced in mils. For the
64
FIRING
102
75-mm gun, M1897, with French sight, the amount of sweep
is announced in turns of the handwheel to the nearest whole
number, each turn traversing the piece 1.8 mils.
id) Rapid computation of distribution for standard
areas. — Usually the width of the target or target area is
assigned as a multiple of 100 yards (par. 137) . In order
quickly to determine the deflection difference from a con-
verged sheaf and, in the case of sweeping fire, the number of
rounds sweeping and the amount of sweep, the following
procedure is used:
75-m vi and 105-mm materiel
Deflection difference: Open 30 JR from a converged sheaf
for each 100 yards of target width.
Number of rounds: Number of rounds equals number of
100 yards of target width.
Amount of sweep: 30 JR mils. For the 75-mm gun with
French sight, the number of turns is 17 JR.
155-mm materiel
Deflection difference: Same as for 75-mm or 105-mm
materiel.
Number of rounds: Battery one round for 100- and 200-
yard widths; two rounds sweeping for 300- and 400-yard
widths.
Amount of sweep: 60 /R mils.
(2) Cross sweeping. — (a) In cross sweeping, the line of
fire of No. 1 is placed on the right of the target; those of
Nos. 2 and 3 on the middle; and that of No. 4 on the left.
Nos. 1 and 3 sweep to the left; Nos. 2 and 4 sweep to the
right. Each piece covers half the entire width of the area.
In this manner each platoon covers half the target width
with the superimposed fire of two pieces.
(b) Cross sweeping is used in prolonged fire when it is
desired to rest the pieces in turn, leaving the front covered by
fire. It is not used for wide fronts because of the wide trav-
erse required of each piece and the possibility of large gaps
in the front covered by fire; it is not used when five or more
65
102-104
FIRING
rounds sweeping are necessary to cover the target. Cross
sweeping usually is used only for the rolling barrage.
/. Shifting fire. — When the width of the target is too great
to be covered with an open sheaf and sweeping fire is not to
be used, the target should be attacked by a succession of
open sheafs.
■ 103. Site. — a. Computation. — From O measure the site
(plus or minus) of the target and of the piece and calculate
the difference in altitude, in yards, between target and piece.
Convert this difference into mils of site. The site is plus
if the target is above the piece, minus if below.
h. Setting. — (1) French 75-mm gun. — The site is an-
nounced as plus or minus , zero being horizontal. The least
Setting is 5 mils.
(2) Other materiel. — On all other materiel, the horizontal
site setting is marked 300. A site below horizontal is sub-
tracted from 300, one above is added. The least setting is
one mil.
■ 104. Projectile, Charge, and Fuze. — The type of projec-
tile, the charge, and the fuze are determined by the effect
desired.
a. Projectile. — For destruction and for fire against person-
nel with cover, high- explosive shell is used. For fire against
personnel in the open, shrapnel or high-explosive shell is
used. Shrapnel is less effective at long ranges; for the
75-mm gun, high- explosive shell is preferable to shrapnel at
ranges greater than 4,000 yards.
b. Charge . — (1) Howitzer . — The charge is determined
largely by the angle of impact desired. The charge selected
should be such that the target range is not more than
three-fourths the maximum range for the charge. If sev-
eral charges are suitable, the smaller charge produces less
wear and gives a greater angle of impact and greater frag-
mentation effect; the larger charge usually gives the smaller
dispersion. In precision fire for destruction, the charge
giving the greatest accuracy (least dispersion) usually is used.
(2) Gun. — The lowest charge consistent with the mission
is used; this may often be reduced charge. In guns having
66
FIRING
104-107
supercharge, it is used only when necessary to obtain greater
range or accuracy.
c. Fuze . — (1) Impact . — For action against personnel, the
quick fuze usually is used. When firing at ranges at which
ricochets occur, the delay fuze should be used (par. 87).
In fire for destruction, the quick fuze is used where frag-
ment or blast effect is desired; the delay fuze when pene-
tration is necessary.
(2) Time . — A corrector setting giving an equal number of
airs and grazes is desired for adjustment. The height of
burst depends upon site as well as corrector setting, and
both must be determined accurately in order to be effective.
The corrector for the first firing must be estimated. Cold
weather requires a corrector higher than standard; warm
weather, a corrector lower than standard. When a cor-
rector giving the proper height of burst for adjustment has
been determined, it should be used to start later adjustments.
■ 105. Pieces to Fire. — Precision fire habitually and bracket
fire occasionally are started with one piece. However, in
bracket fire when the data are accurate, when the target is
fleeting, or when observation is difficult, it is advantageous
to start fire with the battery.
■ 106. Method of Fire. — a. If fire is opened with a single
piece, the method of fire usually is one round. When the
battery or platoon is fired during adjustment, the method
of fire usually is by salvo. When the target is moving rap-
idly, or is capable of extremely rapid movement, it may be
desirable to adjust with battery (or platoon) volleys.
b. In fire for effect, the method of fire usually is by volley
or volley fire sweeping. In some cases, continuous fire may
be employed.
■ 107. Range. — a. Determination . — Range is determined by
the most accurate means available. When the range is de-
termined from the observation post, any difference between
r and R must be considered.
b. Range settings . — Range scales are designed to give the
elevation for a definite projectile and charge; hence, settings
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107-110
FIRING
for other combinations of projectiles and charges must be
determined from the Firing Tables.
c. Elevation settings. — When the gunner’s quadrant or ele-
vation scale is used, the elevation corresponding to the range
is obtained from the Firing Tables and to this is applied the
site.
E 108. Units of Announcement. — If data are prepared very
accurately, the settings so computed may be used. Usually,
it is sufficiently accurate to announce initial data in the fol-
lowing units: deflection or compass, to the nearest 10 mils;
convergence, to the nearest 500 yards; deflection difference,
to the nearest mil; site, to the nearest 5 mils; corrector, to
the nearest five points; range, to the nearest 100 yards; and
elevation, to the nearest 10 mils.
■ 109. Minimum Elevation. — To determine the minimum
elevation before a position is occupied by the pieces, the pro-
cedure is as follows:
a. Measure the site of the mask from the position to be
occupied, using an aiming circle or other instrument.
b. Add thereto the elevation for the piece — mask range for
the available ammunition having the lowest muzzle velocity.
c. Add two forks at the piece — mask range.
d. If the mask is occupied by friendly troops, add the num-
ber of mils subtended by 5 yards at the piece — mask range.
Section III
FIRING CHARTS
■ 110. Description. — a. A firing chart is a diagram, accu-
rately constructed to a known scale, showing the relative po-
sitions of batteries, base points, base lines, check points,
targets, and other data pertaining to the preparation of fire
(par. 124) . It usually is constructed on a grid sheet but may
be on a map, if available, or map substitute (air photo) .
b. Subject to restrictions imposed by higher authority, the
battalion commander prescribes the firing chart to be used
by his battalion. The firing chart used by the batteries for
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FIRING
110-111
the preparation of firing data must be a duplicate of the
one on which fire missions are assigned by the battalion.
c. This section discusses the characteristics of the several
types of firing charts. The operations by which a firing
chart is built up are considered in section IV. The battalion
observed-fire chart is described in chapter 5.
■ 111 . Maps and Grids (AR 100-15 and TM 2180-5). — If an
accurate map or map substitute of suitable scale is available,
it is used for the firing chart. If suitable maps are lacking,
as will usually be the case, composites, mosaics, or provi-
sional fire-control data sheets may be used to build up
firing charts. Single vertical air photographs may be used
alone or in conjunction with maps or charts.
a. Grid systems. — When a map with a standard grid is
not available, a grid system may be improvised. A point is
arbitrarily assigned coordinates and a definite direction is
arbitrarily assigned a Y-azimuth. The grid system of each
subordinate unit must conform to this system.
b. Coordinates. — The distance of any point east of the
zero Y-line is the X coordinate and the distance north of
the zero X-line is the Y coordinate. In writing coordinates,
the X coordinate is written first and the whole inclosed in
parentheses. Thus, to the nearest yard (204.729-186.684) ;
to the nearest 10 yards (204.73-186.68) ; to the nearest 100
yards (204.7-186.7). It is seldom necessary to give more
than two digits to the left of the decimal for each coordi-
nate; for example, (04.729-86.684). If the point is fixed
within an area 10,000 yards square, only one digit need be
given before the decimal. Thus the above coordinates would
be (4.729-6.684); to the nearest 100 yards, (4.7— 6.7) . If a
large number of points are being designated by abbreviated
coordinates, the decimals and dash may be omitted, thus
(4767).
c. Measurements. — (1) Angles. — Measurements of angles
on a map or chart are made with a protractor.
(2) Y-azimuth. — The Y-azimuth of a line may be meas-
ured at any point where this line crosses a Y-line or X-line.
(3) Distances. — Distances are measured by accurate
scales, graduated in yards.
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111-112
FIRING
d. Computation of basic data from coordinates . — When a
map has been distorted or when two points are on different
sheets of the map, or when extreme accuracy is desired, it
is advantageous to determine the direction and range by
trigonometric calculation.
■ 112. Air Photos. — Air photos for field artillery use are
generally plain verticals, mosaics, or obliques. Plain ver-
ticals and mosaics are used in the construction of firing
charts. Obliques are used principally in designation of tar-
gets of opportunity and in maneuvering observed fires; they
may be used to transfer data to the firing chart by means of
restitution.
a. Scale . — The scale of the plain verticals and mosaics
must be determined. On the margin of the photo can be
found the focal length of the camera and the height of the
plane when the picture was taken. The representative frac-
tion equals the focal length divided by the height of the
plane. This scale is only approximate. A more accurate
method is to compare photo distances with corresponding
ground distances. This establishes a ratio between photo
distances and ground distances, and the true ground distance
may be found from a photo distance by the use of this ratio.
b. Gridding. — (1) A grid may be transposed from a grid-
ded photo to another photo on which the same terrain ap-
pears by noting the relation of the grid lines to terrain fea-
tures. The same method may be used in transposing the
grid from a map to a photo with varying degrees of accuracy.
(2) To transfer a grid from a map or control sheet to a
photo, the following procedure is usual (fig. 11) :
(a) Select on the photo three we 11 -distributed points, such
as A, B, and C, which appear on the map or whose coordi-
nates are known. The scale of the photo is then determined
as described above.
(b) From the map, A is found to be 190 yards south of
X-grid line 81, for example. About A on the photo strike
an arc northward with radius of 190 yards to the scale of the
photo.
(c) Repeat this for B, the radius here being 400 yards in
the same direction.
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FIRING
112
id) With a straightedge, draw the 81 Jt-grid line tan-
gent to the two arcs. Draw the remaining .X-grid lines
parallel and 1,000 yards apart to the scale of the photo.
64 55 56
(e) In a similar manner, construct the Y-grid lines,
c. Restitution . — Restitution is the process of determining
map, or chart, locations of features appearing on air photos.
The following are suitable methods:
(1) Tracing -paver method. — (a) This is analogous to trac-
ing-paper resection. It is suitable for determining the loca-
tion of a few points, preferably located near the center of the
photo.
(b) Identify on the photo at least three points (prefer-
ably five) that appear on the chart. Mark these points and
the point to be located, on the tracing paper. This is done
most readily by tacking the photo over the tracing paper and
pricking through each point. On the tracing paper, draw
rays from the point whose location is desired to each of the
known points. Place the tracing paper on the chart so that
the ray to each of the known points passes through the
71
112
FIRING
chart location of the corresponding point. The point whose
location is desired is then in its true relative position to the
known points, and it is located on the cfiart by pricking
through its position on the tracing paper on to the chart.
(2) Grid method . — This method is suitable for transfer-
ring a mass of detail. Three or more well -distributed points
about the margin of the area to be transferred are selected
on the photo and identified on the chart. The points are
joined by straight lines on both the photo and the chart to
form homologous figures. The opposite sides of these two
figures are divided into the same number of equal parts, and,
by joining the points of division, the two areas (photo and
chart) are subdivided into the same number of small homolo-
gous figures. Locations then are transferred by inspection,
the detail appearing in each figure of the photo being trans-
ferred to the corresponding figure of the chart.
(3) Intersection method (fig. 12) . — ( a ) Two well -separated
points whose chart locations are known are identified on the
photo. The line joining them is taken as a base. The loca-
tion of a point is determined as follows: On the photo, draw
lines from the point to the ends of the base; on the chart,
using the corresponding base, draw back rays making the
same base angles as on the photo; the intersection of these
rays is the chart location of the point.
(b) When several points are to be transferred, the same
procedure can be followed graphically. Stack together the
photo and two sheets of tracing paper, with the photo on
top; fasten these down securely with thumbtacks. With a
sharp needle, prick through the two ends of the selected
base line ( ab , fig. 12) and each of the several targets, such as
Ti, Tz, and T 3 . Remove the photo; on the upper tracing
paper draw the rays, ab, aT 1} aT z , aTz. On the lower tracing
paper draw the rays ba, bT lf bT 2 , bT 3 . Place both sheets of
tracing paper on the firing chart so that point a on the upper
sheet is over a on the chart, and b on the lower sheet is over
b on the chart. Orient the upper sheet by means of the
ray ab, and the lower sheet by means of ba. Prick through
the intersections of corresponding rays; for example, the in-
tersection of rays aTi and bT r . This process locates the tar-
gets on the chart.
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FIRING
112-113
Doth sheets superimposed on chart
Figure 12. — Intersection method of restitution.
(c) For accurate results, known points must be located
accurately and angles of intersection must be greater than
500 mils. Serious errors may result if the direction line join-
ing the photo images selected as control points is in error
due to distortion.
■ 113. Use of Single Vertical as a Firing Chart. — In ex-
ceptional cases, a firing chart may be constructed on a single
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113-116
FIRING
vertical air photo showing the target area. The problem is
one of locating the gun position with respect to the photo.
To accomplish this, either two points on the photo or one
point on the photo and a direction must be identified and
the scale of the photo must be known.
■ 114. Use of Mosaic as a Firing Chart. — The mosaic is
used as a firing chart in the same general manner as is a
fire-control map. Angular measurements are relatively ac-
curate. The scale of the mosaic must be determined and
mosaic distances converted to true ranges by use of the
factor, true distance/mosaic measurement, determined as in
paragraph 112 a. Altitudes must be determined by com-
parison with a contoured map or by use of an instrument.
Locations of points often may be determined by inspection.
Registration on selected points is desirable. In the absence
of registration, a true distance to some point in the target
area must be determined. These considerations are treated
more completely in section IV.
Section IV
SURVEY OPERATIONS, PLANS, AND PROCEDURE
■ 115. Purpose of and Necessity for Survey. — a. The pur-
pose of artillery survey is to gather topographic data of the
proper character and in the proper amount to enable bat-
talion and higher headquarters to assign targets, and bat-
teries to compute firing data.
b. Regardless of the type of map available, field artillery
units must be trained to build up firing charts of a scale and
accuracy comparable to a 1:20,000 fire-control map. Survey
is the only means of effecting this,
■ 116. Primary Data To Be Obtained. — The primary data
to be determined and plotted on the firing chart are some or
all of the following:
a. An initial point, which serves as an origin (starting
point) of the survey operations.
b. An orienting line, defined in paragraph 124 e.
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FIRING
116-118
c. One or more place marks which are points whose co-
ordinates and altitudes are known. These points are used
as origins for battery survey work.
d. Observation posts, base point or points, check points,
and other points for reference and control.
e. Targets. The accurate location and plotting of targets
is a continuing process, to the end that eventually the chart
shows the locations of all known targets of importance in the
area which it embraces.
/. Battery positions. These may be located directly by the
battalion survey operations or, more usually, determined by
the various battery surveys and their coordinates reported.
g. A declinating station, defined in paragraph 120 c (7).
■ 117. Declinating. — a. Plane' table. — Magnetic objects such
as steel helmets and pistols should be removed from the
vicinity of the instrument. Orient the plane table (par. 118) .
Attach the declinator and turn it until the needle points to
the index. Draw a fine line along the edge of the declinator.
Repeat at least three times. The mean of the lines is the
proper position of the declinator.
b. Aiming circle. — Set up the aiming circle over a point
from which several points of known Y-azimuth can be seen
(par. 120 c (7) ) . These points should lie in different quarters
of the compass. Level the instrument carefully. Set the
scale at zero and center the needle. With the upper motion,
turn successively to the known points and record the read-
ings. Check by continuing around to the first point read,
and if the readings on this point differ by more than one
mil, the measurements are discarded and the readings are
made again. Subtract the compass reading to each of the
points from its known Y-azimuth. The average of the differ-
ences is the declination constant (par. 99) of the instrument.
■ 118. Orientation. — a. Methods. — A plane table may be
oriented by means of a declinated instrument (declinator or
aiming circle) or by means of a known line.
(1) By declinated instrument. — (a) Declinator. — Rotate
the declinated plane table until the compass needle is opposite
its index. Lock the table and verify by checking the position
of the needle.
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118
FIRING
(b) Aiming circle. — If a distant visible point is plotted on
the table, read the T-azimuth of the distant point with a
decimated aiming circle. Through the plotted point draw a
line whose direction is the T-azimuth read. Lay the alidade
along this line, rotate the table until the alidade is alined
on the distant point, and lock the table. Check to see that
the board is not oriented 3,200 mils 'from the true direction.
(2) By a known line. — (a) Table at one end of the line . —
Place the alidade along the plotted line and rotate the table
until the alidade is alined on the far point. Clamp the table
and verify the sighting. Check as in (1) (b) above.
(b) Table on a line joining two known points. — Place the
alidade along the plotted line and orient the table by eye.
Rotate the table until the line of lighting is on the proper
point, clamp the table, and verify. Without disturbing the
board, reverse the alidade and sight on the other known
point. If the line of sighting falls exactly on the point, the
table is oriented; if not, either the sighting was improperly
done or the table is not on the line. Make the necessary cor-
rections and repeat the operation.
(3) By a three-point resection. — Resection (b (4) below)
is primarily an orientation of the table.
b. Location of points. — Points may be located horizontally
by inspection, traverse, intersection, resection, from an air
photo, or by a combination of any of the above methods.
Points may be located vertically by contours or by calcula-
tion from the angle .of site.
(1) Inspection. — A map or air photo may show the de-
sired point, or a feature very close to it, from which the
point may be located by eye.
(2) Traverse . — (a) Procedure. — The board is set up and
oriented at a known station. A ray is drawn through the
plotted station toward the next station. Orientation is nor-
mally either by back sight or by needle. In making a needle
traverse, it is necessary to occupy only every other station.
The back-sight method of orientation is more accurate; the
alidade is placed, reversed, upon the ray drawn from the
previous point to the occupied station and the board rotated
until the previous point is sighted on. Distances are de-
termined by pacing, stadia, or taping. Taping is the most
76
FIRING
118
accurate. When taping on slopes, care must be taken that
the tape is held level while measurements are being made.
(b) Instillment traverse . — This is a traverse in which the
angles between legs are measured with an angle -measuring
instrument.
(3) Intersection . — When two or more known points can be
occupied, a distant point may be located by setting up and
orienting the board at each known point and drawing rays
to the point to be located. The intersection of the rays is
the position of the desired point. The known points must
be chosen so that the angle between the rays is not less than
500 mils. Accuracy of the work should be checked by sights
from a third known point, if possible.
(4) Resection . — Resection is the location of the occupied
station by means of rays drawn from other points located on
the chart or map. Angles of intersection should not be less
than 500 mils. In a three-point resection, except by the
back-azimuth method, the known points and the occupied
station must not lie on the circumference of the same cir-
cle; the farther the occupied point is from the circumference
the greater the accuracy. When the resection is complete,
the location of the occupied point should be checked by
sighting on a known point not used in the original operation.
(a) Three-point resection, triangle -of -error method . — Set
up and level the board and orient it as accurately as pos-
sible. Sight on each of three distant plotted points, draw-
ing a ray from the plotted position of each. If these rays
intersect in a point, the orientation is correct, and the inter-
section of the rays, p, is the correct location of the occupied
point, P. If the intersections of the rays form a triangle,
the orientation is faulty and a better orientation is necessary.
In this case, a trial location of p may be obtained by esti-
mating, or sketching in, two circles as shown in figure 13 © .
In this figure, one circle is constructed to pass through a
(the plotted position of the distant point A) , b (the plotted
position of the distant point B ) , and ab (the intersection of
the rays through a and b) . Similarly, the second circle is
constructed to pass through b, c, and be. A circle through a,
c, and ac can be used in place of either of the two drawn.
The intersection of the circles gives an approximate location
177568 °— 39 -
-6
77
118
FIRING
of p. The board is reoriented by laying the alidade along
the line from p to the most distant point and sighting that
point. A new set of rays is drawn. If these rays intersect
in a point, the location of p is correct. If a second triangle
is formed, corresponding vertices of this and the original
triangle are joined, and the intersection of these lines will
give a fairly close location for p (fig. 13 © and ©) ,
Figure 13. — Solution of the triangle of error.
(b) Three-po?,nt resection, tracing -paper method ,
1. With plane table . — Attach a sheet' of transparent
paper to the table, orient the board roughly, and
clamp. Through an estimated location of p,
sight on A , B, and C successively and draw rays,
disregarding a, b, and c. Place the transparent
paper over the map or chart and move the former
until the appropriate rays pass through a, b, and
c. The point p is now over its true position and
may be marked by pricking through the tracing
paper. The use of five instead of three points is
more accurate.
78
FIRING
118-119
2. With instrument . — The angles between the distant
points may be measured with an aiming circle or
other angle -measuring instrument and plotted on
transparent paper. This is not as accurate as
direct sighting, since to the errors of the instru-
ment those of plotting are added.
(c) BacJc-azimuth method . — This method requires an
accurately decimated angle -measuring instrument and three
distant visible points located on the map or chart. The back
azimuth of a given line is the azimuth plus 3,200 mils. Set
up a declinated instrument at the point to be located and
measure the Y-azimuth of each of the three distant points.
Add 3,200 mils to each Y-azimuth and through each plotted
point draw a ray having its proper back azimuth. The inter-
section of the rays will be the location of the station P. This
is the only method that can be used when P is on the circum-
ference of a circle passing through A, B } and C.
■ 119. Trigonometric Methods. — a. General . — When time
and equipment are available and when other conditions war-
rant the degree of accuracy sought, survey locations in bat-
talion and higher units should be obtained by instrument
readings and computation rather than by graphical methods.
Either a transit or an aiming circle may be used. The com-
putation may be with logarithm tables or with the slide rule.
To avoid gross errors, the following checks should be incor-
porated in every survey:
(1) All traverses should be closed.
(2) When establishing vertical control, the mean of fore-
sight and backsight readings should be used when possible.
(3) When using a transit to obtain the distance to a far
point, two triangles having a common side, which is the
distance desired, should be established and solved for the
common side. The two results should not vary more than
0.5 percent (5 yards per thousand) . The bases of the tri-
angles should be of such length and direction that the angle
subtended by each at the inaccessible point will be at least 50
mils (3°).
(4) When using an aiming circle to obtain the distance
to a far point, one triangle ordinarily is solved. The base
79