MCWP 3-16.3 FM 6-50 TTP for the Field Artillery Cannon Gunnery - page 5

 

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MCWP 3-16.3 FM 6-50 TTP for the Field Artillery Cannon Gunnery - page 5

 

 

FM 6-50, MCWP 3-1.6.23

c. Unit. Any military element whose structure is prescribed by competent authority, such as a table of organization

and equipment; specifically, part of an organization (AAP-6).

d. Unit’s Military Equipment and Supplies. This includes unit facilities and installations, civilian equipment and supplies

used by allied forces but excludes medical equipment and supplies.

e. Pollution (pollute). Destroy the purity of or sanctity of; make foul or filthy; contaminate or defile (man’s environment).

DETAILS OF THE AGREEMENT.
4. Priorities.  The priorities and the extent of the denial of military equipment and supplies must be decided by the commander

ordering it, taking into account the their potential value to the enemy. Some examples could be:

a. As a high priority:

(1)
(2)
(3)
(4)
(5)
(6)
(7)

Classified equipment, materials and documents.
Petroleum, oil and lubricants.

Sophisticated weapons systems or electronic equipment.
Heavy weapons and associated ammunition.
Communications equipment.
Ferrying and bridging equipment.
Air, sea and land transport.

b. As a second priority: Any other military stores, military equipments and supplies or military facilities which may

be of use to the enemy.

5. Implementation of the Denial. Instructions for the denial of an item of military equipment or of supplies should

included in the appropriate national support publication in sufficient detail to enable their direct use to be denied to

enemy and also to prevent the enemy from making use of them after cannibalization between similar equipments.

be 

an

3-20

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FM 6-50, MCWP 3-1.6.23

3-23. EMERGENCY ALARMS

OF HAZARD OR ATTACK

The BC must ensure that emergency alarms of hazard or

attack are provided in the unit SOPs. The applicable details

to be included in the SOPs have been extracted from

STANAG 2047 and are shown below.

EXTRACT

STANAG 2047 (Edition 6)

EMERGENCY ALARMS OF HAZARD OR ATTACK (NBC AND AIR ATTACK ONLY)

Audible and visual alarm signals must be given by means which cannot easily be confused with other

sounds or sights encountered in combat. The alarm signals will be given in all cases as soon as an attack

or the presence of a hazard is detected. The alarm signals will be repeated throughout the unit area by all

who hear or see the original alarm signal since most available alarm signals are generally limited in range.

Additionally, audible and visual alarm signals should normally be supplemented by simultaneous use of

radio, telephone, and public address systems.

DETAILS OF THE AGREEMENT
3. It is unlikely that personnel can understand and react quickly and correctly to more than two alarm

signals. The following hazards require fast and correct reaction: use or presence of chemical or biological

agents, and an imminent air attack or nuclear operation. Therefore, alarm signals for these two hazards

are mandatory (see Note (1)). In the case of radiological contamination, a delay in personnel taking cover

may be acceptable.
Note (l): No reference is made to ground attack in order to reduce to a minimum the number of signals.

Signals for ground attack, if deemed necessary, remain the prerogative of field commands.

4. The spoken word (vocal alarm signals) remains the most effective means of informing troops in an

emergency.
5. Visual alarm signals are included to supplement the audible alarm signals under conditions when audible

signals may be lost due to other noises or to replace audible signals when the tactical situation does not

permit the use of sound:

a. Reliance should not be placed on visual alarm signals during the hours of darkness or in conditions

of poor light.

b. Visual alarm signals should be used when purely audible signals may be lost due to other noise.

c. Visual signals should be used to warn those personnel arriving at a particular location of an imminent

hazard.

d. Apart from the audio-visual signals detailed at paragraph 2, Note 2 of Annex A, normal signal

flares are excluded from use as a color alarm signal for NBC and air attack.

e. Visual signals need not be used by mobile forces.

6. The actual form of a visual signal and method of display are left to the discretion of the local commander.

Only the color at Annex A is mandatory. However, to aid recognition, it is recommended that the red

signal preferably be square and the black signal preferably be triangular.

3-21

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FM 6-50, MCWP 3-1.6.23

7. The alarm signals listed in this agreement are primarily intended to serve as alarms of enemy action.

They may be used, however, in an emergency when friendly action could produce similar effects on its

own forces.
8. Conflict with civil regulations. Alarm signals for use by NATO forces operating on land are in Annex

A. There are some differences between the alarm signals prescribed herein and some national civil defense

alarm signals. These differences are considered minor for air attack. Reservations are indicated by each

nation where nations or local regulations prohibit NATO Forces operating in their territory for sounding

alarm signals in exercises and/or alarm signals incompatible with the public warning system in wartime.

Pratice alarm signals.

9.

In those case where nations or local regulations preclude sounding alarm signals

during exercises, local commanders should negotiate with local authorities to obtain authorization to sound

alarm signals periodically. In the absence of agreement, small alarm devices emitting sounds similar to

the prescribed audible alarm signals and having limited range should be used during exercises to keep

personnel familiar with the audible alarm signals.
IMPLENTATION OF THE AGREEMENT

10. This STANAG is implemented when the necessary orders/instructions have been issued, directing

forces concerned, to put the content of this agreement into effect.

ANNEX A TO STANAG 2047 (Edition 6)

EMERGENCY ALARMS AND WARNING SIGNALS

The following are emergency alarms and warning signs for NATO Forces operating on land. In respect of the audible alarm

signal, one or more of the signals listed below should be used.

TYPE OF HAZARD

VISUAL WARNING SIGN

AUDIBLE ALARM SIGNAL

la. Imminent Air Attack.

1b. Red. Preferably square in shape.

1c(1) Unbroken warbling siren for one

minute.
(2) Succession of long blasts on vehicle

horns, whistles, bugles or other wind

instruments in a ratio of 31; approximately

3 seconds on and 1 second off.
(3) Vocal “Air Attack” or corresponding

national term where only one nation is

involved. TYPE OF HAZARD VISUAL

WARNING SIGN AUDIBLE ALARM

SIGNAL

3-22

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FM 6-50, MCWP 3-1.6.23

TYPE OF HAZARD

VISUAL WARNING SIGN

AUDIBLE ALARM SIGNAL

2a. Imminent arrival of, or presence of,

2b(1) Black. Preferably triangular in

2c(1) Interrupted warbling sound on a

chemical or biological agents or

shape.

siren.

radiological hazards.

(2) Donning respirators and taking

(2) Succession of short signals on vehicle

protective action followed by such hand

or other horns by beating metal or other

signals as may be prescribed in local

objects in a ratio of 1:1; approximately 1

instructions. (See Notes 1,2, and 3.)

second off.
(3) Vocal “Gas, gas, gas” or

corresponding national term where only

one nation is involved.

3a. All Clear.

3b. Removal of appropriate warning

3c(1) Vocal “all dear (s-type of

signal.

attack)” or corresponding national term

when only one nation is involved.

(2) If used, a steady siren note for one

minute or a sustained blast on a vehicle

horn, whistle, bugle or other wind

instrument to indicate absence of all NBC

and air attack hazards.

NOTES:

1. Automatic alarms for the early and rapid detection of biological and chemical agents and radiological

hazards may complement the devices referred to previously.

2. A special audio-visual pyrotechnic signal producing a whistle sound and a yellow, red, yellow display

of lights may be used. The combination of colors should be produced as near simultaneously as possible.

3. Wearing respiratory protection in the presence of radiological hazards is not mandatory but will be

decided by the local commander.

3-24. BOMBING, SHELLING,

ROCKETING, MORTARING,

AND LOCATION REPORTS

The BC must ensure that his unit SOPs provide guidance

concerning bombing, shelling, rocketing, mortaring, and

location reports including the format to be used when

preparing these reports must also be included. Guidance

for the commander is provided in FM 6-121, in Appendix

J of this manual, and in STANAG 2934, Chapter 13.

3-23

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FM 6-50, MCWP 3-1.6.23

EXTRACT FROM STANAG 2934 (Edition 1) Chapter 13, Annex A

FORMAT FOR BOMBING, SHELLING, ROCKETING, MORTARING, AND

SECTION I:
A. UNIT OF

LOCATION REPORTS

BOMREP, SHELREP, ROCKREP, MORTREP (indicate which)
ORIGIN. Use current call sign, address group or code name.

B. POSITION OF OBSERVER. Grid reference preferred - encoded if this discloses the location of a headquarters or

important observation post.
C. DIRECTION (FLASH, SOUND OR GROOVE) AND ANGLE OF FALL/DESCENT (omit for aircraft). Grid bearing

of flash, sound or groove of shell (state which) in mils, unless otherwise specified. The angle of fall or descent may be

determined by placing a stickhod in the fuze tunnel and measuring in mils, unless otherwise specified, the angle formed by

the stick/rod in relation to the horizontal plane.
D. TIME FROM.
E. TIME TO.
F. AREA BOMBED, SHELLED, ROCKETED, OR MORTARED.

1. Location to be sent as:

a. Grid reference (clear reference is to be used)

OR

b. Grid bearing to impact point in mils, unless otherwise specified and distance in meters from observer. This information

must be encoded if paragraph B is encoded (when this method is used, maximum accuracy possible is essential).

2. Dimensions of the area bombed, shelled, rocketed, or mortared to be given by:

a. The radius (in meters)

OR

b. The length and width (in meters)

G. NUMBER AND NATURE OF GUNS, MORTARS, ROCKET LAUNCHERS, AIRCRAFT OR

OF DELIVERY.
H. NATURE OF FIRE. Adjustment, fire for effect, harassing, etc. (may be omitted for aircraft).

OTHER METHODS

I. NUMBER, TYPE AND CALIBER (state whether measured or assumed) OF SHELLS, ROCKETS (OR MISSILES),

BOMBS, ETC.
J. TIME OF FLASH TO BANG (omit for aircraft).
K. DAMAGE (encode if required).

L. REMARKS. (for additional information on Sections I, II, or III).
SECTION II: LOCATION REPORT
M. SERIAL NUMBER.
N. TARGET NUMBER.

by the locating units.

3-24

Each location which is produced by a locating unit is given a serial number.
If the weapon/activity has previously been given a target number, it will be entered in this column

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FM 6-50, MCWP 3-1.6.23

P. POSITION OF TARGET. The grid reference or grid bearing and distance of the located weapon/activity.
Q. ACCURACY. The accuracy to which the weapon/activity has been located. CEP in meters and the means of location

if possible.

R.
S.

A: CEP is 50 meters or better.
B: CEP between 50 meters and 100 meters.
C: CEP between 100 and 150 meters.
D: CEP between 150 and 200 meters.
E: CEP between 200 meters and 300 meters, and
I: CEP worse than 300 meters.

TIME OF LOCATION. The actual time the location was made.

TARGET DESCRIPTION. Including dimensions if possible:

1. Radius of target in meters

OR

2. Target length and width in meters (attitude if possible).

SECTION III: COUNTERFIRE ACTION
T. TIME FIRED. Against enemy target.
U. FIRED BY.

.

V. NUMBER OF ROUNDS-TYPE OF FUZE AND PROJECTILES.

3-25

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FM 6-50, MCWP 3-1.6.23

CHAPTER 4

LAYING THE BATTERY, MEASURING, AND REPORTING

Section I

THE AIMING CIRCLE

4-1. DESCRIPTION OF

THE AIMING CIRCLE

The M2A2 aiming circle is the primary means of orienting

the cannon battery or laying weapons on the azimuth of

fire. This section presents information that should be the

starting point for any training program on the aiming circle.

The aiming circle components are discussed below.
a. Telescope. 

The telescope is a four-power, fixed focus

optical instrument with a reticle pattern like the one shown

in Figure 4-1.

Note: 

Some aiming circles may not be equipped with

the P-2 reticle pattern (national stock number [NSN]

1240-01-1 52-8516) which is used to perform the

POIARIS 2 method of hasty survey.

modification can be made at direct support

maintenance. Verify the expiration date in the lower

right hand corner of the P-2 reticle pattern. If it has

expired, turn in the aiming circle to direct support (DS)

maintenance for repair.

b. Reflector. 

The reflector (Figure 4-2, page 4-2) is a

plastic signal post mounted on top of the telescope. It is

used as an aiming point for other instruments sighting on

the aiming circle.

c. Elevation Knob. 

The elevation knob (Figure 4-3, page

4-2) is used to raise and lower the telescope line of sight.

It is also used to measure vertical angles. (See paragraph

4-26.)

(1) Elevation scale. Each graduation on the elevation

scale (Figure 4-3) represents 100 mils. The scale is numbered

at 100-mil intervals. The black numbers 0 to 1100 indicate

elevation (+). The red numbers 0 to 400 indicate depression

(-).

(2) Elevation micrometer scale. Each graduation on

the elevation micrometer scale (Figure 4-3) represents 1 mil.

The scale is numbered at 10-mil intervals. The black numbers

0 to 100 indicate elevation (+). The red numbers 0 to 100

indicate depression (-).

d. Magnetic Compass. 

The magnetic compass is located

in the main housing (Figure 4-3). For rough centering, the

magnetic needle may be seen through the windows on top

of the body assembly. A small glass magnifier (Figure 4-3)

and reticle with three vertical lines are at one end of the

recess. These aid in aligning the end of the magnetic needle.
e. Leveling Vials. 

There are two tubular leveling vials

and one circular leveling vial (Figure 4-2) on the aiming

circle. One tubular leveling vial (on the left side of the

elbow telescope) is used in leveling the telescope so that

the operator can measure vertical angles. The other tubular

leveling vial (located on the left side of the main housing)

or the circular leveling vial (fisheye bubble) is used in leveling

the aiming circle for measuring horizontal angles. When

the tubular leveling vials are not in use, the protective covers

should be closed to prevent damage.

f. Azimuth and Azimuth Micrometer Scales.

(1) The azimuth scale (Figure 4-3) is located below the

magnetic compass housing. It is graduated in 100-mil

increments from 0 to 6,400 mils and is numbered every 200

mils. The portion of the azimuth scale from 3,200 mils

through 6,400 mils has a second 0-3200 scale numbered in

red from the black 32 through the large black 0 on the

azimuth scale.

4-1

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FM 6-50, MCWP 3-1.6.23

Note:

Also located on the azimuth scale is an

imaginary line called the 0-3200 line. This line starts

at the black O and goes through the black 32 on this

scale. This is the line we orient on the azimuth of fire

during the laying process.

(2) On the azimuth scale, the red numbers 0 to 3200

indicate azimuth. The lower row of graduations parallels

the 3,200- to 6,400-mil upper row of graduations. This

permits the aiming circle to be used with other instruments

that have scales labeled from 0 to 3,200 mils. The red

numbers are used only in the following instances:

(a) You are reading red numbers to an M12-series sight,

and you are measuring a deflection.

(b) You are checking the lay of one aiming circle with

a second circle. The operator of only one of the two circles will

see red. He can read red to preclude having to add or subtract

3200 to or from the reading.

(3) The azimuth micrometer (Figure 4-3) is located on

the azimuth knob on the lower right side of the magnetic

needle housing. It is graduated in 1-mil increments from

0 to 100 mils and is numbered every 10 mils. Azimuth

micrometer can be read to an accuracy of 0.5 mils.
g. Upper (Recording) Motion. 

The upper motion allows

the operator to place values on the azimuth scale and azimuth

micrometer by means of the azimuth knob (Figure 4-3). The

values are read on the azimuth scale index, which is located

below the magnetic needle magnifier. The upper motion

of the instrument has both a fast motion and a slow motion.

Pulling back on the azimuth knob enables fast motion.

Rotation of the azimuth knob produces slow motion.

Horizontal angles are read in two parts--the thousands and

hundreds of mils are read from the azimuth scale, and the

tens and units of mils are read from the azimuth micrometer.
h. Lower (Nonrecording) Motion. 

The lower motion is

controlled by the orienting knobs (Figure 4-2). It is used

to orient the 0-3200 line of the aiming circle without changing

the values on the upper motion. Lateral movement of one

orienting knob enables fast movement of the lower motion

of the aiming circle. The two orienting knobs should be

used at the same time for slow movement of the lower motion.

Caps are provided for covering the orienting knobs to prevent

unintentional use of the lower motion.
i. Leveling Screws. 

The three leveling screws (Figures

4-2 and 4-3) are used to level the aiming circle. These

screws are on a spring plate located below the orienting

knobs and above the baseplate assembly.

j. Base Plate Assembly. 

The base plate assembly (Figure

4-3) serves as the base of the instrument when it is mounted

on the tripod and also serves as the base of the carrying

case. It is a flat circular plate to which the instrument is

attached by means of the spring plate. An instrument-fixing

screw is threaded into a socket on the underside of the base

plate assembly to attach the instrument to the tripod. The

socket is kept clean and free of obstructions by a spring-loaded

cover that remains closed when the instrument is not attached

to the tripod. The base plate is fitted with a rubber gasket

4-2

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FM 6-50, MCWP 3-1.6.23

that forms a watertight seal when the cover is latched to

the baseplate.

k. Notation Pad. 

A rectangular notation pad (Figure 4-2)

on the baseplate is used for recording the declination constant,

date of declination, and initials of the person performing

the declination.
l. Filter. 

The filter (Figure 4-3) is a lens, which is placed

over the eyepiece for protection against the sun’s rays. It

is stored on the side of the telescope body. It is held in

place by a spring-loaded ball.
m. Compass Needle Locking Lever. 

When the locking

lever (Figure 4-2) is in a vertical position, the needle is

locked. When the lever is turned either right or left to the

horizontal position, the needle is unlocked. To preclude

damage to the magnetic needle, this lever should be returned

to the locked position gently.

CAUTION

The needle must be locked when not in use.

4-2. SETTING UP THE AIMING CIRCLE

a. 

To setup the aiming circle (Figure 4-4), do the following

actions:

(1) Unstrap the legs of the tripod, loosen the leg clamp

thumbscrews, and extend the legs to the desired length.

Tighten the leg clamp thumbscrews.

(2) Place the tripod over the point to be occupied. One

tripod leg should be pointing in the approximate direction

of sighting, and the leg with the night-light mount should

be to the operator’s left. Attach the plumb bob to the hook

under the instrument-fixing screw assembly. The plumb

bob should be within a l-inch radius of the station marker.

(3) Firmly embed the tripod legs. Make sure the tripod

head is approximately level when the legs are embedded.

Then remove the tripod head cover.

(4) Pull back the spring-loaded cover on the base of

the baseplate and place the aiming circle on the tripod.

Loosely screw the instrument-fixing screw assembly into

the base plate.

(5) Center the plumb bob over the orienting station by

moving the base plate of the aiming circle.

(6) Tighten the instrument-fixing screw into the

baseplate of the aiming circle.

CAUTION

Be careful not to exert excessive pressure when you

are tightening the instrument-fixing screw. The slotted

arm may bend and damage the tripod head.

(7) Remove the aiming circle head cover, and hang it

on the tripod head cover or a leg clamp thumbscrew to

prevent damage.

(8) Install the night lighting device accessory case if

necessary.

b. 

Some common malpractice are as follows:

Not clearing the area of magnetic attractions

weapons, steel helmets, and eyeglasses.

such as

4-3.

Failure to set up the tripod so that one leg points in

the direction of the sighting. This puts one more tripod

leg in the instrument operator’s way as he moves around

and increases the chance that he will kick a leg and

knock the aiming circle off level.

LEVELING THE AIMING CIRCLE

There are two methods of leveling the aiming circle for

normal use. Either the circular leveling vial or the tubular

leveling vial (Figure 4-5) can be used.

4-3

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FM 6-50, MCWP 3-1.6.23

a. 

The preferred method is to level the aiming circle by

using the circular leveling vial (fisheye bubble) as follows:

(1) Loosen the leveling screws approximately halfway.
(2) Rotate the head of the aiming circle until the circular

leveling vial is over the leveling screw adjacent to the notation

pad.

(3) Using the thumb and forefinger of each hand, turn

the other two leveling screws in opposite directions. The

bubble will move in the same direction as the left thumb.

Note: 

This is known as the left thumb rule.

(4) When the bubble moves on line with the fisheye,

center the bubble by using only the third leveling screw.

Rotate the head over each of the other two screws. If more

than half the bubble moves out of the center ring, relevel

the instrument. If the bubble cannot be centered, use the

technique discussed in b below. Then turn the instrument

in for repair as soon as possible.
b. 

Level the aiming circle by using the tubular leveling

vial as follows:

(1) Loosen the three leveling screws (approximately

halfway) to permit the instrument to be leveled. Rotate the

instrument until the axis of the tubular leveling vial is parallel

to any two of the three leveling screws. Center the bubble

by using these two leveling screws. Grasp a screw between

the thumb and forefinger of each hand. Turn the screws

simultaneously so that your thumbs move either toward each

other or away from each other. This movement tightens

one screw as it loosens the other. The bubble always moves

in the same direction as the left thumb.

(2) Rotate the instrument 1,600 mils,

bubble by turning the third leveling screw.

4-4

(3) Rotate the instrument back to the first position, and

relevel the bubble if necessary.

(4) Repeat these steps until the bubble remains centered

in both positions.

(5) Rotate the instrument 3,200 mils from the first

position. If the bubble remains centered in this position,

rotate the instrument 3,200 mils from the second position.

If the bubble remains centered in this position, rotate the

instrument throughout 6,400 mils. If the bubble remains

centered, the instrument is level. If the bubble does not

remain centered when the instrument is rotated 3,200 mils

from the first position, the leveling vial is out of adjustment.

To compensate, using the same leveling screws that were

used to place the instrument in the first position, move the

bubble halfway back to the center of the leveling vial. Rotate

the instrument 3,200 mils from the second position; and

using the other leveling screw, move the bubble halfway

back to the center of the level vial. The instrument is now

level, and the bubble should come to rest in its vial at the

same off-center position (within one graduation) regardless

of the direction in which the instrument is pointed. If the

leveling vial is out of adjustment, the instrument should be

turned in for repair at the first opportunity.

(6) The plumb bob normally remains attached to the

aiming circle until the firing unit is laid.

4-4. TAKING DOWN THE

AIMING CIRCLE

Take down the aiming circle as follows:
a. 

Elevate the telescope to about 300 mils.

b. 

Ensure that the magnetic needle is locked.

c. 

Cover the tubular leveling vials. Be sure the M51

instrument light is turned off and secured in its case.
d. 

Ensure the caps of the orienting knobs are closed.

e. 

Place the azimuth knob over the notation pad.

f. 

Turn the leveling screws counterclockwise until the

screws are to their lower stops. Then loosen each leveling

screw knob one-quarter turn.
g. 

Place the carrying case cover over the aiming circle,

and latch the cover locks.
h. 

Unscrew the instrument-fixing screw, and remove the

instrument from the tripod.
i. 

Replace the tripod head cover.

j. 

Retract and collapse the tripod legs, and tighten the

thumbscrews.

k. 

Strap the tripod legs together.

and center the

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FM 6-50, MCWP 3-1.6.23

4-5. DECLINATING THE AIMING CIRCLE

a. 

The aiming circle must be declinated when any of the

following situations exist:

After an electrical storm.
Anytime the instrument has received a severe shock;

for example, if it is dropped from the bed of a truck

to the ground. The magnetic needle is a delicately

balanced mechanism, and any shock may cause a

significant change in the declination constant.
Anytime the aiming circle is moved outside a 25-mile

radius from the area in which it was last declinated.

Because of local magnetic attractions, any move of

the aiming circle may result in an appreciable change

in the relationship of grid north and magnetic north

as measured by the instrument.

A minimum of once every 30 days to determine if

any changes in the declination have occurred because

of the annual shift of magnetic north or because of

accidents involving the instrument that may not have

been reported. If a radical change is observed, the

instrument should be declinated again within a few

days to determine if the observed change is a real

change in the characteristics of the instrument.

When the instrument is first received.
Anytime the instrument is returned from ordnance

repair.

b. 

The aiming circle must be declinated in an area free

from magnetic attractions. Azimuths must be known to two

or more azimuth marks, preferably in opposite directions.

These azimuth marks should be a minimum distance of 300

meters, preferably 1,000 meters.
c. 

Declinate the aiming circle as follows:

(1) Set up the aiming circle, and level it.
(2) With the upper (recording) motion, set the known

azimuth to the azimuth marker.

(3) With the lower nonrecording motion, sight on the

azimuth marker that corresponds to the azimuth set with

the upper motion. (See Figure 4-6.)

Note: 

At this time, the 0-3200 line will be aligned

with grid north.

(4) Release the magnetic needle. With the upper

motion, float and center the magnetic needle. (See Figure

4-7, page 4-6.)

(5) Read the declination constant directly from the

azimuth scales (to the nearest 0.5 mil).

(6) Using a second azimuth, repeat the above steps.

(If a second azimuth marker is not available, use the first

marker again.)

(7) Compare the two declination constants determined.

If they agree within 2 mils, determine the mean. Express

it to the nearest whole mil by using artillery expression.

On the notation pad, record the mean (four-digit number),

the date, and the initials of the individual performing the

declination.

4-5

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FM 6-50, MCWP 3-1.6.23

Note: 

If the two values differ by more than 2 mils,

repeat the entire process.

d. 

A declination station maybe established by simultaneous

observation, hasty astro, observation of Polaris, or

circumpolar observation. (See Chapter 5.)
e. 

Declination can be performed by scaling a grid azimuth

to two distant points. The following procedures are used:

(1) Place the aiming circle over the selected point and

level it.

(2) Select two distant points on a map. Scale the

direction to each from the occupied point.

(3) Using the direction scaled from the map, declinate

the aiming circle by the procedures previously discussed.

(4) Compare the two values determined. They must

agree within 10 mils.

(5) If the values determined agree within 10 mils,

determine the mean; record it on the notation pad. If the

values do not agree within 10 mils, repeat the entire procedure.

Note: 

A declination constant determined by

simultaneous observation or from a map should be

verified as soon as possible.

4-6. CARE AND HANDLING

OF THE AIMING CIRCLE

a. 

Protect the aiming circle from shock.

b. 

Keep the instrument clean and dry.

c. 

Clean the lens with an optical lens cleaning brush and

lens tissue only.
d. 

Keep the magnetic needle locked anytime it is not in

use.
e. 

Keep the aiming circle head cover over the aiming circle

head.
f. 

Cover all tubular leveling vials.

g. 

Rotate the azimuth knob until it is over the notation

pad before trying to replace the head cover.

Section II

PRECISION LIGHTWEIGHT GPS RECEIVER (PLGR)

4-7. GLOBAL POSITIONING

SYSTEM DESCRIPTION

Global positioning system (GPS) is a space-based navigation

system which provides worldwide, continuous, all weather,

three-dimensional position information. The GPS system

consists of the following three primary components:

The satellite constellation. Ensures worldwide coverage

with a minimum of four satellites within electronic line

of sight to any point on the earth.
A master control station and five monitoring stations.

These provide ground-based support for the satellites.

The GPS receivers. These receivers provide the operator

with navigational and location data.

Currently, the primary receiver being issued to ground forces

is the AN/PSN-11, precision lightweight GPS receiver

(PLGR). The PLGR can provide location information

precise enough for use by cannon artillery. For detailed

information on the GPS/PLGR operation, maintenance, and

additional equipment, refer to TM 11-5825-291-13. Major

components of the PLGR are shown in Figure 4-8.

4-8. FA SURVEY APPLICATIONS

The PLGR can be used to determine the grid location of

the orienting station. Individual howitzer locations can also

be determined, but individual PLGR-derived positions are

not on common survey control. The following actions must

be taken to ensure accuracy when using the PLGR as an

artillery positioning device:
a. Verify PLGR Setup.

(1) Crypto. The proper crypto keys must be loaded

before the PLGR will function using the precise positioning

system (PPS). The PPS must be used to achieve the necessary

accuracy and to avoid enemy electronic warfare measures.

If the crypto variable is not loaded, the PLGR cannot

be used to establish artillery positions.

4-6

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FM 6-60, MCWP 3-1.6.23

(2) Datum. Map datum should be the same as the

(4) Elevation. Mean sea level is the preferred selection

operational datum being used by all other maneuver, fire

since most military maps use it as the basis for the elevation

support and target acquisition units. If the same datum is

scale.

not used, significant position errors are possible.

(3) Coordinates.

The UTM coordinate format is

(5) Units of measurement. Meters is the preferred

preferred since it is the standard used by survey and most

selection since most military maps refer to distance and

fire control systems.

elevation in meters.

4-7

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FM 6-50, MCWP 3-1.6.23

(6) Almanac data. Almanac data must be 1 day old.

If almanac data are not 1 day old, there are possible satellite

vehicle or timing errors not noted by the PLGR.

b. Figure of Merit (FOM). 

FOM is an accuracy estimation

of the data displayed by the PLGR which ranges from one

through nine. FOM 1 is the best accuracy estimation

displayed by the system, and FOM 9 is the worst. For

artillery positioning, only coordinates determined with a FOM

1 will be considered for use.

c. Mode of Operation. The PLGR offers the choices of

FIX, CONTINUOUS, 

or AVERAGING  as modes of

operation. The AVERAGING mode yields the most

accurate data and is preferred when determining a position

for indirect fire weapons.
d. Verify Position.

Position verification, to check for

unacceptable errors, must always be done prior to firing.

The following are possible methods of verifying a PLGR-

derived grid coordinate:

(1) Always use two persons to check the PLGR data.
(2) Use two different PLGRs to independently determine

the position data.

(3) Use resection or graphic resection if identifiable

points are visible.

(4) Conduct a map spot of the location. A map spot

is the minimum acceptable verification and should be used

in conjunction with the other available means.

WARNING

Azimuth determined with the PLGR is for navigation

only The PLGR azimuth is not accurate enough

for use in establishing directional control and

should never be used for that purpose. Tests show

that the PLGR-determined azimuth maybe in error

by as much as 200 mils.

4-9. GPS LIMITATIONS AND

CONSIDERATIONS

a. 

GPS receivers rely on electronic line of sight with the

satellites. The PLGR must be able to acquire at least four

satellites before a three dimensional position can be

determined.

Dense foliage, buildings, mountains, and

canyons will mask GPS signal and cause the receiver to

fail. All GPS receivers automatically try to track satellites

to a position as low as 10° above the level horizon. Each

receiver has a function which displays the direction and

vertical angle to each of the satellites being tracked. Use

this display to determine if signal masking is what is causing

the system to fail. When a satellite signal is masked, the

operator can either reorient the PLGR antenna or move to

another location to improve signal reception.

b. 

Multipath distortion (reflected signals) may occur if the

receivers antenna is tilted away from a satellite. This causes

a reflected signal to be received which has more power than

the direct signal.

Coordinates determined under these

conditions can be off by as much as several hundred meters.

To correct this problem, reorient the receiver antenna to a

position that eliminates the distortion.

c. 

As with all aspects of artillery operations, personnel must

be properly trained in the safe operation of equipment. The

PLGR will provide accurate location data only if it is operated

in strict accordance with the procedures outlined in the

technical manual. Battalions and batteries must ensure that

training and testing on GPS operations are part of their safety

certification program.

Specifically, all battery level

leadership must be able to identify, and properly correct

when needed, the setup functions of the PLGR. These

personnel must also be proficient in map reading and hasty

survey techniques needed to conduct an independent

verification check of the PLGR-derived position.

SECTION III

GUN LAYING AND POSITIONING SYSTEM

4-10. DESCRIPTION OF THE GUN

control, and allow the operator to transfer directional control

LAYING AND POSITIONING SYSTEM

to the individual howitzers using standard laying commands.

Additionally, the GLPS eye-safe laser range finder eliminates

The gun laying and positioning system (GLPS) supplements

the need to measure subtense to determine the distance to

the M2A2 aiming circle, and will be the primary instrument

the howitzer.

used to orient howitzers in cannon units not equiped with

Paladins. When used in conjunction with the PLGR, the

The system is man-portable and tripod-mounted. It can be

GLPS will determine grid location, establish directional

emplaced and used much the same as the M2A2 aiming

4-6

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FM 6-50, MCWP 3-1.6.23

circle, but without the need for external survey support.

Technical data on GLPS capabilities are located in Table

4-1, and the major components of the system are shown in

Figure 4-9. Battery leadership must be proficient in the

setup and orientation procedures for the GLPS as listed in

the equipment operator’s manual. An independent check

of the GLPS orientation must be made before using it to

lay the howitzers.

4-9

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FM 6-50, MCWP 3-1.6.23

Section IV

THE M2 COMPASS

4-11. DESCRIPTION

OF THE M2 COMPASS

The M2 compass (Figure 4-10) is the alternate instrument

for orienting, or laying cannons. The unmounted magnetic

compass is a multipurpose instrument used to obtain angle

of site and azimuth readings. The components of the M2

compass are discussed below.
a. Azimuth Scale. 

The azimuth scale is numbered every

200 mils from 0 to 6400. The scale is graduated every 20

mils and can be read to an accuracy of 10 mils.
b. Sights. 

The compass has front and rear leaf sights and

a mirror in the cover for sighting and reading angles.
c. Levels. 

The compass is equipped with a circular level

for leveling the instrument before the azimuth values are

read. A tubular level is used with the elevation scale to

measure angles of site.
d. Angle-of-Site Mechanism. 

Rotation of the level lever

causes the elevation level and the elevation scale index to

rotate as a unit. The index clamps against the bottom piece

to keep the mechanism from moving unless it is actuated

by the level lever.
e. Magnetic Needle and Lifting Mechanism. 

The

magnetic needle (the white end of the needle) shows a

magnetic north direction for orienting purposes. The needle

is delicately balanced and jewel-mounted, on a pivot, to

rotate freely. The magnetic needle reading is taken when

the bubble is centered in the circular level. The lifting

mechanism includes a needle-lifting (locking) pin and a

needle lifting lever. The lower end of the pin engages the

lever. The upper end projects slightly above the body of

the compass to engage the cover when it is closed. Thus,

it automatically lifts the needle from its pivot and holds it

firmly against the glass window.
f. Azimuth Scale Adjuster Assembly. 

The azimuth scale

adjuster assembly rotates the azimuth scale to introduce the

declination constant. Two teeth at the adjuster engage teeth

on the underside of the azimuth scale. Thus, turning the

adjuster with a screwdriver rotates the azimuth scale

approximately 1,800 mils. The scale is read against a fixed

index under the rear sight hinge.

4-12. DECLINATING THE M2 COMPASS

a. 

The procedure for declinating the M2 compass from a

surveyed declination station free from magnetic attractions

is as follows:

(1) Set the M2 compass on an aiming circle tripod over

the orienting station, and center the circular level.

(2) Sight in on the known, surveyed azimuth marker.
(3) Using the azimuth adjuster scale, rotate the azimuth

scale until it indicates the same as the known surveyed

azimuth.

(4) Recheck sight picture and azimuth to the known

point. Once the sight picture is correct, and the azimuth

reading is the same as the surveyed data, the M2 is declinated.

4-10

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