MCWP 3-16.3 FM 6-50 TTP for the Field Artillery Cannon Gunnery - page 16

 

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MCWP 3-16.3 FM 6-50 TTP for the Field Artillery Cannon Gunnery - page 16

 

 

FM 6-50, MCWP 3-1.6.23

APPENDIX J

CRATER ANALYSIS AND REPORTING

J-1. CRATER ANALYSIS TEAM

Although greater reliance should be placed on reports from

trained teams, all personnel should know how to analyze

craters and make the proper report. Since crater analysis

teams are not authorized by TOE, each unit (including units

normally located in rear areas) should select and train at

least one team of two or three members. To adequately

support their maneuver unit, fire support personnel must

know how to analyze and report crater information.

J-2. EQUIPMENT
Three elements—direction, dimensions, and curvature—must

be measured for crater analysis. The equipment used by

the crater analysis team should consist of the following items:

Declinated aiming circle (or M2 compass), stakes, and

communications wire used to obtain the direction from

the crater to the weapon that fired the projectile.
A curvature template (Figure J-1) to measure the

curvature of the fragment to determine the caliber of

the shell. The template can be constructed of heavy

cardboard, acetate, wood, or other appropriate material.
Defense Intelligence Agency Projectile Fragment

Identification

Guide (DST-1160G-029-85) for

measuring fragment dimensions.

J-3. SHELL CRATER ANALYSIS
a. 

The projectiles direction of flight can be determined with

reasonable accuracy from its crater of ricochet furrow. By

accurately locating the crater and determining the direction

of flight, it is possible to obtain the azimuth of a ray that

will pass through or near the enemy position. While it is

possible to determine the direction to a battery from one

crater or ricochet furrow, the battery may be located by

plotting the intersection of the average azimuths from at

least three widely separated groups of craters.

b. 

In crater analysis, differences in angle of fall, projectile

burst patterns, directions of flight, and time fuze settings

will help to distinguish between enemy batteries firing on

a given area.

Note: 

Refer to FM 3-100 for guidance on friendly

troop safety from the effects of craters contaminated

with chemical agents. Refer to STANAG 2002 in FM

3-100 for guidance in marking craters containing

chemical, biological, or radiological contamination.

J-1

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FM 6-50, MCWP 3-1.6.23

J-4. VALUE OF ANALYSIS

By analyzing shell craters, it is possible to do the following:

Verify as confined locations, suspected locations that

have been obtained by other means.
Confirm the presence of enemy artillery and obtain an

approximate direction to it.
Detect the presence of new types of enemy weapons,

new calibers, or new ammunition manufacturing

methods.

J-5. INSPECTION OF SHELLED AREAS

Shelled areas are inspected as soon as possible. Craters

that are exposed to the elements or are abused by personnel

deteriorate rapidly thereby losing their value as a source of

information.

J-6. SURVEY OF CRATER LOCATION

Areas must be located accurately enough for plotting on

charts, maps, or aerial photographs. Deliberate survey is

not essential; hasty survey techniques or map spotting

usually will suffice. Direction can be determined by use

of an aiming circle or a compass.

J-7. DETERMINATION OF DIRECTION

a. Pattern. 

A clear pattern produced on the ground by

the detonating shell indicates the direction from which the

shell came.

b. Factors Affecting Pattern.

Because of terrain

irregularities and soil conditions, typical shell crater patterns

are the exception, not the rule. Side spray marks are a

principal part of the pattern caused by fragmentation. There

is much less effect from nose spray. Base spray is negligible

from gun and howitzer projectiles but is appreciable from

mortars. The width, angle, and density of the side spray

pattern vary with the projectile, the angle of impact, the

type of fuze, terminal velocity of the projectile, and soil

composition. In determining direction, the following are

considered:

The effect of stones, vegetation, stumps, and roots in

the path of the projectiles.
Variations in density and type of soil.
The slope of the terrain at the point of impact.

From any group, only the most clearly defined and typical

craters are used.
c. Marks on Vegetation and Other Objects. 

The direction

from which a round was fired is often indicated by the marks

made as it passes through trees, snow, and walls. The possible

deflection of the shell upon impact with these objects must

be considered. Evidence of such deflection should not be

overlooked.
d. Drift and Wind Effects. 

Drift and lateral wind effects

do not materially change the direction of the axis of the

shell during flight.
e. Ricochet Furrows. 

Often when an artillery round with

a delay fuze is fired at low angle, it bounces or ricochets

from the surface of the earth. In doing so, it creates a groove,

called a ricochet furrow, which is an extension of the plane

of fire. Care must be taken, however, to determine that the

shell was not deflected before or while making the furrow.

J-8. CRATER ANALYSIS
The first step in crater analysis is to locate a usable crater

for determining the direction to the hostile weapon. The

crater should be clearly defined on the ground and should

be reasonably fresh. Since the crater is the beginning point

for plotting the direction to the enemy weapon, the grid

coordinates of the crater should be determined as an eight-

digit grid, or as precisely as time and method used will

allow. The direction to the firing weapon must be determined

by one of the methods described in the following paragraphs.

Shell fragments and fuzes must be collected for use in

identifying the type, caliber, and country that manufactured

the weapon and/or projectile.

J-9. LOW-ANGLE FUZE QUICK

CRATERS (ARTILLERY)

The detonation of a projectile causes an inner crater. The

burst and momentum of the shell carry the effect forward

and to the sides, forming an arrow which points to the rear

(toward the weapon from which the round was fired). The

fuze continues along the line of flight, creating a fuze furrow.

There are two methods of obtaining a direction to a hostile

weapon from this type of crater. The best results are obtained

by determining a mean, or average, of several directions

obtained by using both methods.
a. Fuze Furrow and Center-of-Crater Method. 

In this

method, stakes are placed in the center of crater and in the

fuze furrow. Then the direction is measured to the hostile

weapon. (See Figure J-2.) A variation of this method is to

place a stake where the shell entered the ground instead of

J-2

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FM 6-50, MCWP 3-1.6.23

the fuze furrow and determine the direction in the same

manner. This method is rarely possible, however, since

indications of the point of entry are usually destroyed by

the explosion of the shell. The five steps of this method

are as follows:

Place a stake in the center of the crater.

Place a second stake in the fuze furrow at the point

where the fuze was blown forward to the front of the

crater.
Setup direction-measuring instrument in line with the

stakes and away from fragments.

Orient the instrument.

Measure the direction to the hostile weapon.

b. Side-Spray Method. 

Another method to measure the

direction to a hostile weapon is to bisect the angle formed

by the lines of side spray. (Figure J-3.) The seven steps in

the side spray method are as follows:

Place a stake in the center of the crater.

Place two stakes, one at the end of each line of side

spray, equidistant from the center stake.
Hold a length of communications wire (or another

appropriate field-expedient means) to each side spray

stake, and strike an arc forward of the fuze furrow.
Place a stake where these arcs intersect.

Set up a direction-measuring instrument in line with

the center stake and the stake at the intersection of

the arcs.

Orient the instrument.
Measure the direction to the firing weapon.

J-10. LOW-ANGLE FUZE DELAY

CRATERS (ARTILLERY)

There are two types of fuze delay craters: ricochet and

mine action.
a. Ricochet. 

The projectile enters the ground in line

following the trajectory and continues in a straight line for

a few feet, causing a ricochet furrow. The projectile normally

deflects upward and, at the same time, it changes direction

usually to the right as the result of the spin, or rotation, of

the projectile. The effect of the airburst can be noted on

the ground. Directions obtained from ricochet craters are

considered to be the most reliable. The five steps to determine

direction from a ricochet furrow (Figure J-4) are as follows:

Clean out the furrow.
Place stakes at each end of a usable straight section

of the furrow.

Set up a direction-measuring instrument

the stakes and away from fragments.
Orient the instrument.
Measure the direction to the weapon.

in line with

J-3

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FM 6-50, MCWP 3-1.6.23

b. Mine Action. 

This occurs when a shell burst beneath

the ground. Occasionally, such a burst will leave a furrow

which can be analyzed in the same manner as the ricochet

furrow. A mine action crater which does not have furrow

cannot be used to determine the direction to the weapon.

J-11. HIGH-ANGLE SHELL

CRATERS (MORTARS)

In a typical mortar crater, the turf at the forward edge (the

direction away from the hostile mortar) is undercut. The

rear edge of the crater is shorn of vegetation and grooved

by splinters. When fresh, the crater is covered with loose

earth, which must be carefully removed to disclose the firm,

burnt inner crater. The ground surrounding the crater is

streaked by splinter grooves that radiate from the point of

detonation. The ends of the splinter grooves on the rearward

side are on an approximately straight line. This line is

perpendicular to the line of flight if the crater is on level

ground or on a slope with contours perpendicular to the

plane of fire. A fuze tunnel is caused by the fuze burying

itself at the bottom of the inner crater in front of the point

of detonation. Three methods may be used to determine

direction from a mortar shell crater-the main axis, splinter

groove, and fuze tunnel methods.

a. Main Axis Method.

The four steps to determine

direction by the main axis method (Figure J-5) areas follows:

Lay a stake along the main axis of the crater, dividing

the crater into symmetrical halves. The stake points

in the direction of the mortar.

Set up a direction-measuring instrument in line with

the stake and away from fragments.
Orient the instrument.
Measure the direction to the weapon.

b. Splinter Groove Method. 

The five steps to determine

direction by the splinter groove method (Figure J-6) are as

follows:

Lay a stake along the ends of the splinter grooves

that extend from the crater.
Lay a second stake perpendicular to the first stake

through the axis of the fuze tunnel.
Set up a direction-measuring instrument in line with

the second stake and away from fragments.
Orient the instrument.
Measure the direction to the weapon.

c. Fuze Tunnel Method. 

The four steps to determine

direction by the fuze tunnel method (Figure J-7) are as

follows:

Place a stake in the fuze tunnel.
Set up a direction-measuring instrument in line with

the stake and away from fragments.
Orient the instrument.

Measure the direction to the weapon.

Note: 

If the angle of fall is too great (a 90° angle), the

fuze tunnel method cannot be used.

J-4

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FM 6-50, MCWP 3-1.6.23

J-12. ROCKET CRATERS
A crater resulting from a rocket impacting with a low or

medium angle of fall is analyzed in the same manner as an

artillery crater resulting from a projectile armed with fuze

quick. However, if the rocket impacts with a high angle

of fall, the crater is analyzed in the same manner as a crater

resulting from a mortar round. The tail fins, rocket motor,

body, and other parts of the rocket, may be used to determine

the caliber and type of rocket fired.

J-5

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FM 6-50, MCWP 3-1.6.23

J-13. SHELL FRAGMENT ANALYSIS

c. Rotating Bands and Band Seats. 

(See Figure J-9.) A

shell may be identified as to caliber, type and nation of

A weapon may be identified as to type and caliber from

origin from the following:

shell fragments found in the shell crater. Dimensions of

the parts as well as of the complete shell, vary according

to the caliber and type of shell. A typical shell is shown

in Figure J-8.
a. Duds and Low-Order Bursts. 

The most logical means

of identifying the caliber of a projectile is to inspect a dud

of that caliber. However, since a dud may not always be

Pattern or rifling imprints.
Width, number, and size of rotating bands.
Dimensions and pattern of keying or knurling on the

band seat.
Dimensions and pattern of keying and knurling

impressed on the rotating band.

available (or, if available, may be too dangerous to handle),

a low-order burst is the next best means of identification.

When the explosive filler is incompletely detonated, a

low-order burst occurs and large shell fragments result. Such

Note: 

Spin-stabilized artillery projectiles require a

rotating band and band seat.

large pieces can be used to identify thread count, curvature,

d. Tail Fins. 

A mortar may be identified from the tail

wall thickness, and other information not obtainable on

tin (Figures J-9 and J-10). Often, tail fins are found in the

smaller fragments. (See Figures J-1 and J-8.)

fuze tunnel of the crater. A mortar that is not fin-stabilized

b. High-Order Burst. 

A high-order burst normally results

may be identified from the pieces of the projectile on which

in small, deformed fragments. These fragments are useless

the rifling is imprinted.

for identification purposes unless they include a section of

e. Fuzes. 

Since the same type of fuze may be used with

either the rotating band or the rotating band seat. Fragments

several different calibers or types of projectiles, it is

of either of these sections positively identify the shell, since

impossible to establish the type and caliber of a weapon by

each shell has its own distinctive rotating band markings.

this means.

J-6

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FM 6-50, MCWP 3-1.6.23

Note: 

With the exception of the rotating bands and

band seats or the tail fins, different types of shells

may be identical in one dimension (such as wall

thickness) but seldom will be alike in two or more

dimensions. Therefore, it is necessary to obtain two

or more measurements to make a positive

identification.

J-7

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FM 6-50, MCWP 3-1.6.23

J - 8

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FM 6-50, MCWP 3-1.6.23

J-9

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FM 6-50, MCWP 3-1.6.23

J-14. SHELLING REPORTS

The division artillery (div arty) is responsible for counterfire.

Therefore, bombing reports (BOMBREPs), shelling reports

(SHELREPs), and mortar reports (MORTREPs) should be

forwarded as quickly as possible to the div arty tactical

operations center (TOC) through either fire direction or fire

support channels. If a report is received by a DS battalion

and that battalion decides to attack, the report of action taken

and a damage assessment, if available, should be forwarded

to the div arty TOC when the action is completed.

a. Contents. 

To provide a standard method of rendering

reports on enemy bombing, shelling, and mortaring within

the NATO forces operating on land, and the United States

armed forces and certain other NATO armed forces, have

concurred in the provisions of STANAG 2008. Refer to

STANAG 2103 as implemented in FM 3-100 (in conjunction

with STANAG 2008), for guidance in reporting the type of

attack.

b. Artillery Counterfire Information Form.

The

information obtained from a crater should be forwarded by

the most rapid means available—the ATI;SHR followed up

with DA Form 2185-R (Artillery Counterfire Information)

(ACIF) (Figure J-11). Regardless of how little information

has been obtained, do not hesitate to forward it. Fragmentary

or incomplete information (a radio or telephone report) is

often valuable in supplementing or confirming existing

information. This radio or telephone report may be followed

by a written report (DA Form 2185-R).

Note: 

A reproducible copy of DA Form 2185-R is

located at the back of this manual.

c. Fragments. 

Any usable fragments obtained from crater

analysis should be tagged (shoe tag) and sent to the battalion

S2. As a minimum, the tag should indicate the following:

The location of the hostile weapon.
The direction to the hostile weapon.

The date-time group of the shelling.

Mortor, artillery, or rocket, if known.

EXAMPLE

The information in the following situation is illustrated on the

completed DA Form 2185-R (Figure J-11). You are the

executive officer of Battery A, 1st Battalion, 3d Field Artillery.

Your cell sign is A3F22, which is located at grid 39288415.

At 0545 hours, the enemy shelled your position for 2 minutes

with a total of eight rounds of HE shells. The tempo and

pattern of bursts suggest an enemy four-gun battery. Your

battery commander believes that the enemy’s intent was

harassment. Your SHELREP team determined the direction

to the enemy battery to be 4,810 mils. They also located a

fragment which included a portion of the rotating band seat.

The shell has been identified as an enemy 122-mm howitzer

projectile.

The four blanks above SECTION I of DA Form 2185-R are

not completed by the SHELREP team. They are filled in by

the receiving agency, for example, the battalion S2

section.
Items B and K or SECTION I are encoded for security

reasons. The current call sign or code name for the unit is

used in item A. Item B is not applicable when this form is

used for crater analysis.
SECTIONS II and III are completed by the target production

section of the div arty TOC.
The information contained in a SHELREP is forwarded by

the DS artillery S2 to the targeting cell at div arty. He plots

(on a SHELREP overlay) the location of the crater and a

line representing the direction measured to the weapon. He

compares the information with that received from other

sources and attempts to locate enemy weapons from the

intersections of direction lines to weapons of the same

caliber.

J-10

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FM 6-50, MCWP 3-1.6.23

J-11

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FM 6-50, MCWP 3-1.6.23

APPENDIX K

MINIMUM QUADRANT ELEVATION RAPID FIRE TABLES

K-1. DESCRIPTION OF THE TABLES

a. 

These rapid fire tables include all the elements of the

platoon leader’s (XO’s) minimum QE discussed in Chapter

6 except Angle 1 (site to crest). Separate tables are included

for each weapon-fuze-propellant combination. The value

listed for elevation in all tables is the sum of the TFT elevation,

two forks, Angle 2, and the comp site factor for the vertical

angle of site for +300 mils angle of site. The tables are

valid only when the sum of Angle 1 and Angle 2 (appropriate

vertical clearance) is 300 mils or less. If the sum is greater

than 300 mils, you must compute the data as shown in Chapter

6. To expedite the process of determining angle 2, Table

K-1 is provided.

b. 

The time listed in the armed VT fuze tables (M513,

M514, M728, M732) includes the TFT time of flight plus

5.5 seconds expressed to the next higher whole second

(minimum safe time) for each listed range. When the time

set on the VT fuze is equal to or greater than the time listed

in the table, the platoon leader’s (XO’s) minimum quadrant

elevation for fuzes other than VT is used (unarmed VT).

Note: 

All M557, M564 tables are used for unarmed

VT fuzes. Use information in the EL column of the VT

tables only when firing less than min safe time.

K-2. USE OF THE RAPID FIRE TABLES

a. 

Add Angle 1 and Angle 2. Sum must be 300 mils or

less to use rapid firing tables (Tables K-2 through K-16).
b. 

Enter the table at the piece-to-crest range and determine

the elevation for the appropriate charge(s).

c. 

Add Angle 1 and elevation obtained from appropriate

table. The sum is the minimum quadrant elevation.
d. 

There are restrictions on the use of the VT fuze when

firing certain charges on some weapon systems. These areas

are boxed on the tables by shading. For the specific

restrictions, refer to the weapon operator’s manual and/or

TM 43-0001-28.
e. 

The TI column in the rapid fire tables is the same as

minimum safe time (MST).

f. 

Fuze M732 has the same performance characteristics as

fuze M728.

Note: Always 

compute the XO’s minimum QE for all

howitzers, and select the largest value as the platoon

leader’s or battery XO’s minimum QE.

K-1

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FM 6-50, MCWP 3-1.6.23

APPENDIX L

GUN DISPLAY UNIT

L-1. DESCRIPTION

The gun display unit links the howitzer into the BCS. At

each gun, the GDU displays firing data and fire commands

from the BCS and transmits the status of the gun to the

BCS throughout the fire mission. The GDU consists of a

section chief’s assembly (SCA), the case assembly (CA),

and two gun assemblies. The section chief receives his fire

commands on the SCA. At the same time, the deflection

and quadrant elevation are displayed on the gunner’s and

assistant gunner’s gun assemblies, respectively. Wire, the

AN/PRC 68, or the AN/PRC 126 radio, is used for

communication with the BCS.

L-2. SECTION CHIEF’S ASSEMBLY

a. 

The SCA (Figure L-1) gives the section chief a display

of firing data and commands to fire. The SCA can be

connected to the case assembly and to a headset.

b. 

The following data can be displayed on the SCA:

Mission.
Special instructions.
Shell.

Powder lot.

Charge.
Fuze.

Fuze setting.
Fire commands.
Deflection.
Quadrant elevation.

FFE data.

L-1

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FM 6-50, MCWP 3-1.6.23

c. 

The keyboard allows selection of piece data, sending

status to the BCS, and self test. The controls, indicators,

and connectors (Figure L-2) are discussed below.

(1) The panel control is used to vary the lighting intensity

of keys and legends. It has ON and OFF positions.

(2) The display control is used to vary the brightness

of the display window data.

(3) The display window shows red letters and numbers

of firing data and command bars. DNL, AMC, and FIRE

bars are not lit except during fire missions.

(4) The MSN MOF/1 key is pressed to show the section

. .

. .

number and mission number in the display window.

(5) The SP INST/2 key is pressed to display special

instructions of azimuth, high angle, or gunner’s quadrant or

to enter the section number in the display window.

(6) The SH/3 key is pressed to show the shell to be

used in adjustment or to enter the section number in the

display window.

(7) The LOT/4 key is pressed to show the projectile

and powder lot or to enter the section number in the display

window.

(8) The CHG/5 is pressed to show the charge to fire

or to enter the section number in the display window.

(9) The FZ/6 key is pressed to show the to to be

used in adjustment or to enter the section number in the

display window.

(10) The FZ SET/7 key is pressed to show the fuze

setting or to enter the section number in the display window.

(11) The DF/8 key is pressed to show the deflection

or to enter the section number in the display window.

(12) The QE/9 key is pressed to show the quadrant

elevation in adjustment or to enter the section number in

the display window.

(13) The FFE SH key is pressed to show the FFE shell

data in the display window.

(14) The FFE LOT/0 key is pressed to show the FFE

lot data or to enter the section number in the display window.

(15) The FFE RDS key is pressed to show the number

of FFE rounds in the display window.

(16) The FFE FZ key is pressed to show the FFE fuze

data in the display window.

(17) The READY key is pressed to lock in the section

number and is pressed when the piece is ready. The ready

message is sent to the BCS.

(18) The SHOT/RC key is pressed once after the first

round is fired. It causes SHOT to show in the display window

and sends the SHOT message to the BCS. It is pressed

again when the last round is fired. This causes RC (rounds

complete) to show in the display window and sends the

ROUNDS COMPLETE message to the BCS.

Note: 

In one round FFE missions and during the

adjustment phase, the section chief must ensure that

he presses the SHOT/RC key twice after firing or he

may not receive data for the next adjustment/mission.

L-2

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FM 6-50, MCWP 3-1.6.23

(19) The SELF TEST key is pressed to start the GDU

d. 

There are connectors for the SCA, power, and data.

self-diagnostic test.

e. 

Binding posts allow for the connection of the following:

(20) The CYCLE key is pressed to acknowledge to the

FDC the receipt of a message. It silences the alarm and

Quadrant elevation gun assembly.

causes the gun number and mission number or updated firing

Deflection gun assembly.

data to show in the display window. The SCA window

goes blank 15 seconds after the last key is pressed. Pressing

LCU (labeled BCU on the case assembly).

the CYCLE key causes the display to reappear.

Auxiliary power.

L-3. CASE ASSEMBLY

f. 

The controls, indicators, and connections (Figure L-4)

are discussed below.

a. 

The case assembly (Figure L-3) provides circuits for

data reception and transmission and for power conversion

(1) The POWER connector allows power connection

required for GDU operation.

between the case assembly and the radio.

b. 

In the battery compartment are the active battery and a

(2) The DEF 1, DEF 2, and DEF 3 binding posts allow

spare battery.

connection of field wire between the case assembly and the

power, ground, and signal binding post, respectivelv, on the

c. 

The power supply unit provides power and data circuits.

deflection gun assembly.

L-3

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FM 6-50, MCWP 3-1.6.23

(3) The QE 1, QE 2, and QE 3 binding posts allow

connection of field wire between the case assembly and the

power, ground, and signal binding posts respectively on the

quadrant elevation gun assembly.

(4) The AUDIO connector allows signal connection

between the case assembly and the radio.

(5) The BCU binding posts allow signal connection

between the case assembly and the BCS (through the wire

line adapter).

(6) The 28V AUX POWER binding post allows

connection to an external 28 volt power source.

(7) The GND connector allows connection to earth

ground.

(8) The alarm gives an audible alert to the operator

when the GDU is receiving a message.

(9) The ALARM control is used to vary the volume

of the audible alarm. (To increase the volume, turn the

control clockwise.)

(10) The POWER ON-OFF switch is used to give

(11) When placed in the NORMAL position, the

NORMAL-BITE switch allows digital communications

between the BCS and the GDU. In the BITE position, it

completes the BITE circuit.

(12) The SCA connector allows signal connections

between the case assembly and the SCA.

L-4. GUN ASSEMBLY

a. 

The gun assembly (Figure L-5) provides instant

identification of required deflection to the gunner or elevation

to the assistant gunner.

b. 

The display window shows quadrant elevation or

deflection information. The tenths digit shows on the QE

display only when the special instruction of GUNNER’S

QUADRANT is received.
c. 

Three binding posts allow connection to the case

assembly as follows:

(1) The TERM 1 binding post is used to connect field

wire between the gun assembly and the power binding post

primary power to the case assembly.

on the case assembly.

L-4

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