Copy 3

DEPARTMENT OF THE ARMY FIELD MANUAL

105-mm HOWITZERM52 SELF-PROPELLED

DEPARTMENT OF THE ARMY * DECEMBER 1956AGO 2790C-Nov

FM 6-77

FIELD MANUAL I DEPARTMENT OF THE ARMYNo. 6-77 WASHINGTON 25, D. C., 11 December 1956

105-mm HOWITZER M52, SELF-PROPELLED

Paragraphs Page

CHAPTER 1. INTRODUCTION--_________. 1-4 4

2. ORGANIZATION ______-___ 5, 6 8

3. SECTION DRILLSection I. General _________--------- _ 7, 8 10

II. Preliminary commands and 9-14 11formation.

CHAPTER 4. PREPARING HOWITZERFOR FIRING ANDTRAVELING

Section I. Preparations for firing-______ 15, 16 19II. Preparations for traveling___ 17, 18 20

CHAPTER 5. DUTIES IN FIRING,INDIRECT LAYING

Section I. General --_--_____--------- 19, 20 21II. Duties of chief of section_---- 21-36 22

III. Duties of gunner ____---_-- _ 37-46 28IV. Duties of cannoneers and

driver. 47-73 35

CHAPTER 6. FIRING BY DIRECTLAYING

Section I. Technique of fire____________ 74-82 44

AGO 2790C 1

Paragraphs Page

Section II. Duties of chief of section____ 83-91 53III. Duties of remainder of sec- 92-97 56

tion.

CHAPTER 7. TECHNIQUES AND SITU- 98-108 59ATIONS THAT REQUIREATTENTION

8. BORESIGHTING ANDBASIC PERIODICTESTS

Section I. General _____________------ 109, 110 70II. Boresighting __________----. 111-115 71

III. Basic periodic tests --------- 116-126 80CHAPTER 9. MAINTENANCE AND 127-131 85

INSPECTIONS10. DECONTAMINATION OF 132-135 88

EQUIPMENT11. DESTRUCTION OF EQUIP- 136-139 91

MENT12. SAFETY PRECAUTIONS__ 140-143 9313. TRAINING

Section I. General _____________------ 144-147 96II. Minimum training schedule___ 148-150 98

CHAPTER 14. TESTS FOR QUALIFICA-TION OF GUNNERS

Section I. General ________________-__ 151-158 102II. Test, direct laying, direct fire 159-163 105

telescope.III. Test, indirect firing, deflection 164-168 107

only.IV. Test, displacement correction_ 169-173 111V. Test, measuring deflection____ 174-178 113

VI. Test, laying for elevation, ele- 179-183 115vation counter.

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Paragraphs Page

Section VII. Test, laying for elevation, 184-188 116gunner's quadrant.

VIII. Test, measuring elevation____ 189-193 117IX. Test, measuring site to mask__ 194-198 118X. Tests and adjustment of 199-206 120

sighting and fire controlequipment.

XI. Test for materiel ______----- 204-208 123

APPENDIX REFERENCES -------.--. .------- 126

INDEX________ ------------------- ------- ------- 130

AGO 2790C 3

CHAPTER 1INTRODUCTION

1. Purpose and ScopeThis manual is a guide to assist commanders in

developing the sections of 105-mm howitzer M52,self-propelled, firing batteries into efficient smooth-working teams that have a sense of discipline whichwill impel them to operate effectively under thestress of battle. This manual prescribes individualduties and section drills, inspection and maintenancedrills, and tests and adjustments for sighting and firecontrol equipment, and provides instructions for thedecontamination and destruction of equipment.2. Definitions and Terms

a. Section. Tables of organization and equipmentprescribe the personnel and equipment comprisingeach section of a battery (figs. 1 and 2). In thismanual the term section is often used to designateonly the personnel required to serve one piece and itsequipment.

b. Front. The front of a section is the direction inwhich the muzzle of the howitzer points.

c. Right (Left). The direction right (left) is theright (left) of one facing the front.

d. In Battery. A howitzer is said to be in batterywhen the recoiling parts are in the normal firingposition.

4 AGO 2790C

Figure 1. 105-mm howitzer M52, self-propelled,and section personnel.

3. Description of EquipmentTo avoid accidents caused by exceeding the capa-

bilities and limitations of the motor carriage, allmembers of the section should be familiar with theperformance charcteristics shown in figure 3. Forfurther details pertaining to full-track vehicle capa-bilities and combat driving, see TM 21-306.4. References

Publications pertaining to the 105-mm howitzerM52, self-propelled, and auxiliary equipment, cov-ering related matters which are not discussed in de-tail in this manual, are listed in the appendix.

AGO 2790C 5

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TURNING RADIUS, PIVOT ROAD CLEARANCE 19sa"

SPEED 25 MPH SRIDGE CLASS30 TON

FORDING TRENCHDEEPTH 48'/TL

- LE = i330_

Figure S. 105-mm howitzer M52, self-propelledperformance characteristics.

AGO 2790C 7

CHAPTER 2ORGANIZATION

5. Composition of Sectiona. The section consists of section personnel, a 105-

mm howitzer M52, self-propelled, and auxiliaryequipment (fig. 1).

b. The personnel of the howitzer section are-(1) A chief of section (CS).(2) A gunner (G).(3) An assistant gunner (No. 1).(4) Four cannoneers, numbered from 2

through 5.(5) A motor carriage driver (D).

c. Section equipment is listed in appropriate SNLand TOE 6-317R.

6. General Duties of Personnela. Chief of Section. The chief of section is the

noncommissioned officer in command of the sectionand, as such, is responsible to the battery executivefor-

(1) Training and efficiency of personnel.(2) Performance of duties listed under section

drill, duties in firing, tests and adjustmentof sighting and fire control equipment, andinspection and maintenance of all section

8 AGO 2790C

equipment including the performance ofscheduled preventive maintenance serviceon motor carriage.

(3) Observance of safety precautions.(4) Preparation of field fortifications for pro-

tection of equipment, ammunition, andpersonnel.

(5) Camouflage discipline; local security; andchemical, biological, and radiologicalsecurity discipline.

(6) Maintenance of the weapon record book.(7) Police of the section area.

b. Gunner. The gunner is the assistant to thesection chief in carrying out the duties specified in aabove. The gunner's specific duties are prescribed inthe appropriate chapters of this manual.

c. Cannoneers. Cannoneers perform duties aslisted in this manual and any other duties that thechief of section prescribes.

d. Driver. The driver's primary duty is drivingthe motor carriage (TM 21-306) and performingpreventive maintenance on the vehicle. He also per-forms such other duties as prescribed by this man-ual, by TM 9-717A, or as may be assigned by thechief of section. These duties can include substitut-ing for any member of the section in firing.

AGO 2790C 9

CHAPTER 3SECTION DRILL

Section I. GENERAL

7. ObjectiveThe objective of section drill is the attainment of

efficiency: maximum precision coupled with highspeed.8. Instructions

a. Adherence to the drills prescribed is necessaryto develop maximum efficiency and to prevent injuryto personnel and damage to equipment. Section drillmust be conducted in silence except for commandsand reports. The section must be drilled until re-actions to commands are automatic, rapid, andefficient.

b. Errors are corrected immediately. Each mem-ber of the section must be impressed with the im-portance of reporting promptly to the chief of sec-tion any errors discovered before or after the com-mand to fire has been given. The chief of sectionwill report errors immediately to the executive.

c. Battery officers supervise the drill to insure thatinstructions are carried out and that maximumefficiency is obtained.

d. Personnel should be rotated during training sothat each member of the section can perform all the

t0 AGO 2790C

duties within the section. In addition, battery over-head personnel not assigned specific duties duringdrill periods should be trained in the fundamentalsof section drill in order that they will be capable offunctioning efficiently with a howitzer section if re-quired.

Section II. PRELIMINARY COMMANDS AND FORMATIONS9. To Form Section

a. To Fall In. The chief of section takes his post.On the command of execution the section forms in asingle rank at close interval, centered on and facingthe chief of section at a distance of 3 paces (fig. 4).Higher numbered cannoneers, if present, form inorder between No. 5 and the driver. The chief ofsection may indicate in his preparatory commandthe place and direction in which the section is toform. At the first formation for drill or exercisethe caution, "As section (s) ," precedes the command.The commands are FALL IN, or 1. IN FRONT(REAR) OF YOUR PIECE(S), 2. FALL IN, or 1. ONTHE ROAD FACING THE PARK, 2. FALL IN. Execu-tion is as follows: The section moves at double timeand forms at close interval, at attention, guidingon the gunner (fig. 4).

b. To Call Off. The section being in formation,the command is CALL OFF. At the command, allpersonnel in ranks, except the gunner, execute eyesright. The section then calls off in sequence, "Gun-ner," "1," "'2," "3," "4," "5," "Driver." As eachman calls out his designation he turns his headsmartly to the front.

AGO 2790C 11

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12 AGO 2790C

10. Posts of SectionThe command is 1. CANNONEERS, 2. POSTS. The

command is general and is applicable whether thesection is in or out of ranks, at a halt, or marching.All movements are executed at double time and areterminated at the position of attention. Highernumbered cannoneers, if present, take posts as pre-scribed by the chief of section.

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AGO 2790C 13

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AGO 2790(] 1

a. Dismounted. The section moves to posts asshown in figure 5. All personnel are 2 feet outsidethe tracks and facing to the front.

b. Prepared for Action. The piece having beenprepared for action, posts are taken as shown infigure 6.

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AGO 2790

c. Mounted, Not Prepared for Action. The sectionmoves to posts as shown in figure 7. Nos. 3, 4, and 5ride in another designated vehicle.

11. To Change PostsTo acquaint the members of the section with all

duties and to lend variety to drill, posts should bechanged frequently. The section being in formation,the commands are 1. CHANGE POSTS, 2. MARCH, or1. SECTION CHANGE POSTS, 2. MARCH.

a. At the command 1. CHANGE POSTS, 2. MARCH,all number cannoneers except No. 5 (or the highestnumbered cannoneer) take two left steps, taking theposition of the next higher numbered cannoneer. No.5 moves at double time in rear of the section to thepost of No. 1. All other members of the section standfast.

b. At the command 1. SECTION CHANGE POSTS, 2.MARCH, the driver (or the leftmost man) movesat double time in rear of the section to the post of thegunner. The gunner and all the other men in linetake two left steps as in a above.

12. To MountThe commands are 1. PREPARE TO MOUNT, 2.

MOUNT, or MOUNT.a. At the preparatory command, the section

moves at double time to positions shown in figure5. At the command of execution, all personnelmount. All personnel, except Nos. 3, 4, and 5, hastento positions as shown in figure 7. Nos. 3, 4, and 5do not mount the motor carriage. They move at

16 AGO 2790C

double time to the vicinity of a designated vehicleand mount it at the command of the driver.

b. If any members of the section are to remaindismounted, their designation is announced with thecaution, "Stand fast" given between the preparatorycommand and the command of execution. For ex-ample: 1. PREPARE TO MOUNT, "Driver stand fast,"2. MOUNT.

c. If the command is MOUNT, the section exe-cutes, without pausing, all that has been prescribedfor the command 1. PREPARE TO MOUNT, 2. MOUNT.

13. To Dismount

The commands are 1. PREPARE TO DISMOUNT, 2.DISMOUNT, or DISMOUNT.

a. At the preparatory command, all members ofthe section mounted in the motor carriage placethemselves in a position from which they may dis-mount easily. At the command of execution, mem-bers of the section dismount in inverse order ofmounting and quickly take posts as shown in figure5.

b. At the command DISMOUNT, the sectionexecutes without pausing all that has been pre-scribed for the command 1. PREPARE TO DISMOUNT,2. DISMOUNT.

14. To Fall Outa. At Drill. When it is desired to give the per-

sonnel a rest from drill or relieve them temporarilyfrom a formation or post, the command FALL OUTAGO 2790C 17

is given. The command may be given at any timeand means that the section is to remain in thevicinity of the drill area.

b. When Firing. When firing has been suspendedtemporarily, but it is desired to have the section re-main in the vicinity of the motor carriage, thecommand FALL OUT is given. Men stand clearof the piece to insure that settings and laying re-main undisturbed. During these periods the chiefof section may direct the men to improve the posi-tion, to replenish ammunition, or to do other neces-sary work.

18 AGO 2790C

CHAPTER 4PREPARING HOWITZER FOR FIRING AND

TRAVELING

Section I. PREPARATIONS FOR FIRING-i5. General

The howitzers of a battery will ordinarily be putinto position individually under the direction of theexecutive and chiefs of section. A stake should bedriven into the ground at a point where the centerof each carriage is to be placed. Another stakeshould be placed in the direction of fire 50 to 100yards from the first stake, so that the driver of themotor carriage can point the tube at the far stake ashe drives the vehicle into position over the firststake. Each vehicle is halted at its proper place bythe chief of section. Hand signals for guiding thevehicle are found in FM 21-60 and FM 25-10 andare discussed in paragraph 108, this manual.16. To Prepare for Action

a. The motor carriage being in position or ap-proaching it, the command is PREPARE FOR AC-TION. Duties of individuals are given in table I.Each man takes his post (fig. 6) upon completion ofhis duties.

b. The howitzer normally will be partially pre-pared for action before reaching the firing position.

AGO 2790C 19

The duties of the cannoneers in preparing for ac-tion are the same whether the howitzer is movingor halted, but only such operations as are practicableare carried out while moving. Immediately afterthe howitzer is established in position, preparationfor action is completed without further command.

c. If PREPARE FOR ACTION has not been or-dered before the howitzer is established in position,the command is habitually given by the chief ofsection as soon as the vehicle is halted in position. Ifpreparation for action is not desired, the caution,"Do not prepare for action" must be given.

Section II. PREPARATIONS FOR TRAVELING17. March Order

To prepare to resume travel, the command isMARCH ORDER. Duties of individuals are listedin table II. Each man takes his post (fig. 7) uponcompletion of his duties.18. To Resume Firing in Another Position

a. If firing is to be resumed shortly in anotherposition in which the howitzer must be immediatelyready to fire, the command MARCH ORDER is notgiven. When a displacement is ordered, only thoseoperations necessary for the movement of the motorcarriage and the security of equipment are per-formed.

b. If the command MARCH ORDER is givenwhile the equipment is partially prepared for travelas described in a above, the remaining operationspertaining to march order are completed.

20 AGO 2790C

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CHAPTER 5DUTIES IN FIRING, INDIRECT LAYING

Section I. GENERAL

19. InstructionsThe general instructions in paragraphs 7 and 8

on the conduct of section drill apply equally to sec-tion drill in duties in firing by indirect laying. Forduties of the battery executive, see FM 6-40 andFM 6-140.20. Duties of Individuals

(table III)In general, the duties of individuals in the section

in indirect fire are as follows:a. The chief of section supervises and commands

his section and is responsible that all duties of thesection are performed properly, all commands exe-cuted, and all safety precautions observed.

b. The gunner sets the commanded elevation anddeflection, lays the piece, and refers the piece.

c. No. 1 opens the breech, loads the piece, andfires the piece.

d. No. 2 receives prepared rounds from No. 3and passes them to No. 1.

e. No. 3 fuzes projectiles and sets fuzes.AGO 2790C 21

f. No. 4 prepares charges.g. No. 5 removes ammunition from containers.h. The driver shifts carriage as directed by the

chief of section and assists No. 5 in removing am-munition from containers.

Section II. DUTIES OF CHIEF OF SECTION

21. List of Duties(Detailed description of duties, pars. 22-36.)

a. Indicates the aiming point to the gunner.b. Measures the site to the mask.c. Follows fire commands.d. Indicates when the piece is ready to fire.e. Gives the command to fire.f. Lays the piece for elevation when the gunner's

quadrant is used.g. Reports errors and other unusual incidents of

firing to the executive.h. Conducts prearranged fires.i. Records basic data.j. Observes and checks frequently the functioning

of the materiel.k. Assigns duties when firing with reduced per-

sonnel.1. Verifies the adjustment of the fire control

equipment.m. Checks, before they are replaced in their con-

tainers, all rounds not fired which have been pre-pared for firing.

22 AGO 2790C

n. Controls the movement of the motor carriage.o. Supervises use of ammunition.

22. Indicates Aiming Point to GunnerWhen an aiming point is designated by the exe-

cutive, the chief of section insures that he hasproperly identified the point in question. The chiefof section then indicates it to the gunner. If thereis any possibility of misunderstanding, the chief ofsection will turn the panoramic telescope until thehorizontal and vertical cross hairs are on the pointdesignated.

23. Measures Site to MaskThe command is MEASURE THE SITE TO

THE MASK. The chief of section, looking throughthe bore, directs the gunner in placing the tube insuch a position that the lowest element of the borejust clears the crest at its highest point in the prob-able field of fire. The gunner then turns the eleva-tion counter knob in the appropriate direction untilthe three elevation verniers line up. The chief ofsection reads the elevation from elevation counterand reports to the executive, "Sir, No. (so-and-so),site (so much) ."24. Follows Fire Commands

The chief of section follows fire commands. Herepeats the commands as required.25. Indicates When Piece' is Ready to Fire

When the executive can see arm signals made bythe chief of section, the chief of section will extend

AGO 2790C 23

his right arm vertically upward as a signal that thepiece is ready to fire. He gives the signal as soon asthe gunner calls, "Ready." When arm signals can-not be seen, the chief of section reports orally tothe executive, "Sir, No. (so-and-so) ready."26. Gives Command to Fire

When No. 1 can see arm signals made by thechief of section, the chief of section will give thecommand to fire by dropping his right arm sharplyto his side. When his arm signals cannot be seen, hecommands orally, FIRE or NO. (SO-AND-SO),FIRE. The chief of section will not give the signalor command to fire until all cannoneers are in theirproper places.27. Lays Piece for Elevation When Gunner's Quadrant is

Useda. The command QUADRANT (SO MUCH) in-

dicates that the gunner's quadrant is to be used. Inlaying for elevation, the gunner's quadrant is em-ployed only when the elevation counter is inoperativeor known to be inaccurate. The gunner's quadrantmay be specified for use with assault fire or on cer-tain destruction missions.

b. Quadrant 361.8, for example, is set on the gun-ner's quadrant as follows: The upper edge of theindex plate is set opposite the 360 mark of the grad-uated arc on the quadrant frame, and the micro-meter on the index arm is turned to read 1.8. Caremust be taken to use the same side of the quadrantin setting both the index plate and the micrometerknob.

24 AGO 2790C

c. The announced quadrant having been set onthe gunner's quadrant, the piece loaded, and thebreechlock closed, the gunner's quadrant is set onthe quadrant seat on top of the breech. The wordsline of fire must be at the bottom of the quadrantwith the arrow pointing toward the muzzle. Thechief of section must be sure to use the arrowwhich appears on the same side of the quadrant asthe scale which he is using. He stands squarelyopposite the side of the quadrant and holds it firmlyon the quadrant seat, parallel to the axis of the bore.It is important that he take the same position andhold the quadrant in the same manner for eachsubsequent setting, so that in each case he will viewthe quadrant bubble from the same angle.

d. The chief of section then directs the gunnerto elevate or depress the tube until the bubble is cen-tered, being careful that the last motion is in thedirection in which it is more difficult to turn thehandwheel. He cautions the gunner when the bubbleis approaching the center, in order that the final cen-tering may be performed accurately.

e. Special and calibration corrections will beadded algebraically at the battery fire directioncenter and commanded as NO. (SO-AND-SO),QUADRANT (SO MUCH).28. Reports Errors and Other Unusual Incidents of Firing

to ExecutiveIf, for any reason, the piece cannot be fired, the

chief of section promptly reports that fact to theexecutive and the reasons therefor; for example,

AGO 2790C 25

"Sir, No. (so-and-so) out, misfire." Whenever it isdiscovered that the piece has been fired with anerror in laying, the chief of section reports that factat once; for example, "Sir, No. (so-and-so) fired 40mils right." Whenever the gunner reports that theaiming posts are out of alinement with the sight andthat the misalinement is due to the displacement ofthe carriage, the chief of section reports that fact tothe executive and requests permission to realinethem. Likewise, he promptly reports other unusualincidents that affect the service of the piece.

29. Conducts Prearranged FiresWhenever the execution of prearranged fires is

ordered, the chief of section conducts the fire of hissection in conformity with the prescribed data.

30. Records Basic DataThe chief of section records data of a semi-

permanent nature in a notebook. This data includessuch information as minimum elevation; aimingpoints used and their deflections; prearranged fireswhen section data sheets are not furnished; safetylimits in elevation and deflection; number of roundsfired, with the date and hour; and calibration andspecial corrections when appropriate.

31. Observes and Checks Frequently Functioning ofMateriel

The chief of section closely observes the function-ing of all parts of the materiel during firing. Beforethe piece is fired, he makes sure that the recoil me-chanism contains the proper amount of oil; there-

26 AGO 2790C

after, he carefully observes the functioning of therecoil system. He promptly reports to the executiveany evidence of malfunctioning (TM 9-717A). Ifthe piece returns to battery with a shock, an over-supply of recoil oil is indicated; if the piece over-recoils or does not return to battery, an insufficientamount of recoil oil is indicated. Whenever theamount of reserve oil is less than that prescribed,the index on the indicator rod of the replenisher willindicate "fill."

32. Assigns Duties When Firing With Reduced PersonnelWhenever the number of personnel serving the

howitzer is temporarily reduced to below that indi-cated in this manual, the chief of section makes suchredistribution of duties as will best facilitate theservice of the piece. Loss of cadremen, various de-tails, and casualties will necessitate the sectionsoperating with a reduced number of personnel to theextent that it is almost normal for section membersto double up on duties. Around-the-clock firing re-quires the chief of section to divide the section intoshifts to provide for relief.

33. Verifies Adjustment of Fire Control EquipmentSee TM 9-324A for detailed instructions on test-

ing and adjusting sighting and fire control equip-ment.

34. Checks, Before They are Replaced in Their Containers,All Rounds Not Fired Which Have Been Preparedfor Firing

The chief of section personally checks all rounds

AGO 2790( 27

not fired that have been prepared for firing beforethey are replaced in their containers, to see that allseven powder increments are present in proper con-dition, that they are assembled in proper numericalorder, and that they are of the same lot number. Healso checks to see that the lot number on the projec-tile and cartridge case corresponds to the lot numberon the container.

35. Controls Movement of Motor CarriageWhen it is necessary to move the motor carriage,

the chief of section instructs the driver to start theengine. He then controls the displacement of themotor carriage by voice, interphone, or hand signals.

36. Supervises Use of AmmunitionThe chief of section supervises control and use of

proper lot numbers of ammunition as directed bythe battery executive.

Section III. DUTIES OF GUNNER

37. List of Duties(Detailed description of duties, pars. 38-46.)

a. Centers the level bubbles on the panoramictelescope mount.

b. Lays the piece for direction.c. Alines the aiming posts, assisted by No. 5.d. Lays the piece for elevation.e. Sets a common deflection to a common aiming

point after the piece has been laid.

28 AGO 2790C

f. Sets or changes the deflection.g. Signals and/or calls "Ready."h. Refers the piece.i. Makes corrections for aiming post displace-

ment.

38. Centers Level Bubbles on Panoramic Telescope Mount(fig. 8)

The gunner centers the level bubbles on the tele-scope mount by operating the leveling knobs as partof preparing the sight for action. Once the bubblesare leveled, it should not be necessary to make fur-ther adjustments during firing. However, the levelof the mount is verified before calling "Ready."39. Lays Piece for Direction

(fig. 9)The piece being in position, tube in center of tra-

verse, and not laid for direction, the executive com-mands NO. (SO-AND-SO) ADJUST, AIMING.POINT THIS INSTRUMENT. After the gunnerhas reported "Sir, No. (so-and-so) aiming pointidentified," the executive commands NO. (SO-AND-SO) DEFLECTION (SO MUCH). The gunnersets the commanded deflection on the coarse azi-muth scale, as viewed through the window, and themicrometer scale. He then directs the driver tomove the motor carriage until the vertical line ofthe sight reticle is approximately on the executive'saiming circle. The gunner then traverses the tubeuntil the vertical line of sight is exactly on the exe-cutive's aiming circle. He checks to insure that the

AGO 2790C 29

E~~~~~LEVAflON ~ ~

i I LEVELINGELEVATIM "MOCHAN

LEVEUNGEL^ 0 0 P _ PRV ADJUSTINGN

' iFigure 8. Telescope mount T179.

bubbles are level and announces, "Sir, No. (so-and-so) ready for recheck." As additional deflectionsare announced by the executive, he sets them on thecoarse azimuth and the micrometer scales and tra-verses the tube so that the vertical line of sight is on

30 AGO 2790C

COARSE AZIMUTHSCALE

AZIMUtH

RESET KNOB 8

Figure 9. Panoramic telescope T149E1.

the aiming circle. When the executive announces"No. (so-and-so) is laid," the tube is oriented andshould not be traversed except on order of the exe-cutive.

40. Alines Aiming Posts, Assisted by No. 5The piece having been laid as in paragraph 39,

the executive may command AIMING POINT,AIMING POSTS, DEFLECTION 800, REFER.At this command the gunner sets 8 on the coarseazimuth scale and 0 on the micrometer scale and,with hand signals, directs No. 5 in the alinement ofthe aiming posts with the vertical line of the sightreticle. If, because of the nature of the terrain, theaiming posts cannot be set out at deflection 800, the

AGO 2790C 31

gunner turns the azimuth micrometer knob untilthe coarse azimuth and micrometer scales are onanother even-hundred-mil graduation. He alines theaiming posts at this new deflection. The chief ofsection reports the altered deflection to the exe-cutive "Sir, No. (so-and-so) 800 in canyon (or otherreason), laid on deflection 700." The executive willthen command NO. (SO-AND-SO) LAID, RESETCOUNTER TO 3200. The gunner resets azimuthcounter to 3200. All subsequent deflection changesmust be set on the azimuth counter. The tube isoriented and should not be traversed except on orderof the executive.41. Lays Piece for Elevation

(fig. 10)The gunner sets the announced elevation on the

elevation counter, then clamps the elevation countersetting knob in position with the clamping knob. Hethen elevates or depresses the tube in the directionindicated by the arrows in the elevation vernier untilthe indexes in the elevation vernier are alined. Finaladjustment will be made in the direction of increas-ing resistance.42. Sets Common Deflection to Common Aiming Point After

Piece Has Been LaidThe battery having been laid, the executive may

command AIMING POINT, CHURCH STEEPLE,REFER. At this command, without moving thetube, each gunner turns his sight to the aimingpoint designated and reports the deflection to theexecutive. The executive then commands, COM-

32 AGO 2790C

' RIGHT

() WRONGFigure 10. Alining elevation vernier indexes.

AGO 2790C 33

MON DEFLECTION 3200. At this command eachgunner pushes in on the azimuth counter reset knoband rotates it until 3200 is read on the scale of theazimuth counter. All subsequent deflection changesmust be set on azimuth counter. He makes a finalcheck to verify that the line of sight is still on theaiming point.

43. Sets or Changes Deflection

The command is DEFLECTION (SO MUCH).If, for example, the command is DEFLECTION3300, the gunner rotates the azimuth knob in theappropriate direction until 3300 is read on the azi-muth counter. The gunner then traverses the pieceuntil the vertical hair of the reticle is on the leftedge of the aiming posts or on a designated aimingpoint. Final motion for traversing is from left toright.

44. Signals and/or Calls "Ready"

After the piece has been loaded and laid both indirection and elevation and is ready to fire, the gun-ner will call and/or signal "Ready," by shouting orby raising his right arm, to signify that the pieceis ready to fire.

45. Refers Piece

The command from the executive is AIMINGPOINT THIS INSTRUMENT (OR OTHERPOINT), REFER. Without disturbing the layingof the piece, the gunner turns only the sight until,with bubbles level, the vertical cross hair of the

34 AGO 2790C

reticle is on the point designated. He then reportsthe deflection, as read from the coarse azimuth andthe micrometer scales, to the executive, "Sir, No.(so-and-so) deflection (so much)."46. Makes Corrections for Aiming Post Displacement

For details of correcting for aiming post displace-ment, see paragraph 101.

Section IV. DUTIES OF CANNONEERS AND DRIVER47. No. 1, List of Duties

(Detailed description of duties, pars. 48-53.)a. Opens the breech prior to firing the first round.b. Wipes the bore dry prior to firing the first

round, assisted by No. 2.c. Loads the piece.d. Fires the piece.e. Throws expended cartridge cases out the left

side of the turret.f. Closes the breech at the completion of firing.

48. Opens Breech Prior to Firing First RoundNo. 1 grasps the breech operating handle with his

right hand and releases the breech operating handlecatch. He then pushes down on the handle until thebreechblock locks in position.49. Wipes Bore Dry Prior to Firing First Round

Before firing the first round, No. 1, assisted byNo. 2, thoroughly dries the bore and chamber to in-sure that no oil or water is present.

AGO 2790C 35

50. Loads Piece

No. 1 grasps the round with his right hand at thebase of the cartridge case and his left hand in frontof the rotating band. He then faces the breech and,after an elevation has been announced, inserts theround in the breech and pushes it home with hisright fist and announces "Set." It is extremely im-portant that he use his fist, to guard against gettinghis fingers crushed by the closing breechblock. No. 1will be particularly careful to avoid striking the fuzeagainst any portion of the howitzer. A round to beloaded will be held well out of the path of the recoiluntil the tube is again in battery.

51. Fires Piece

At the command FIRE by the chief of section,No. 1 grasps the lanyard and pulls it to the rear, be-ing careful to stay out of the path of recoil.

52. Throws Expended Cartridge Cases Out Left Side ofTurret

After the piece has been fired, No. 1 recovers theexpended cartridge case and throws it out the ex-pended ammunition hatch located on the left side ofthe turret.

53. Closes Breech at Completion of FiringAfter firing is completed or when directed by the

chief of section, No. 1 closes the breech by trippingthe extractors with the base of an expended cart-ridge case or other appropriate materiel. The ex-tractors should never be tripped by hand because of

36 AGO 2790C

the possibility of the hand being crushed by theclosing breechblock.

54. No. 2, List of Duties(Detailed description of duties, pars. 55 and

56.)a. Passes prepared rounds to No. 1.b. Inspects and insures that fuze setting is cor-

rect.

55. Passes Prepared Rounds to No. 1No. 2 receives prepared rounds from No. 3 and

passes them to No. 1. He positions himself duringfiring on the door of the ammunition stowage com-partment. As he passes the round to No. 1, hechecks to make sure that there are no nicks or burrson the rotating band. He hands the round to No. 1in such a position that No. 1 may readily receive itas prescribed in paragraph 50.

56. Inspects and Insures That Fuze Setting Is CorrectNo. 2 checks the prepared round as he passes it to

insure that the fuze setting commanded is actuallyset on the projectile.57. No. 3, List of Duties

(Detailed description of duties, pars. 58-61.)a. Fuzes projectiles or changes fuze.b. Sets the fuze setter M26 or M28.c. Sets fuzes.d. Passes prepared round to No. 2.

AGO 2790C 37

58. Fuzes Projectiles or Changes FuzeNo. 3 removes the fuze or closing plug from the

projectile; removes (or replaces) the supplementarycharge, if necessary; and screws in the designatedfuze. In assembling fuzes to, or removing fuzesfrom projectiles, only the authorized fuze wrenchshould be used. Variable time (VT) fuzes should bescrewed in by hand and tightened with fuze wrenchM18, using only manual force. Do not hammer onthe wrench or use an extension handle. On fuzes soequipped, No. 3 removes the safety pull wire fromthe fuze.

59. Sets Fuze Setter M26 or M28No. 3 releases the time scale clamping screw

marked "T" and, grasping the handle, turns thebody until the index on the body is opposite the an-nounced time on the time scale. He then locks thetime scale clamping screw, being careful not to dis-turb the setting. For accuracy, he looks squarelyat the scales and indexes in the same manner eachtime.

60. Sets Fuzesa. Selective Superquick and Delay Fuzes. When

fuze quick is commanded, No. 3 will verify thesuperquick setting. (The slot on the setting sleeveshould be alined with the letters SQ.) When fuzedelay is commanded, No. 3 will turn the settingsleeve until the slot is alined with the word DELAY.

b. Combination Time and Superquick Fuzes. Thecombination time and superquick fuze may be set

38 AGO 2790C

for time action. After fuzing the projectile, No. 3removes the safety pull wire from the fuze. Forpercussion action, the command is FUZE QUICK.For time fuzes, No. 3 verifies that the S on the set-ting ring is alined with the index on the fixed ring;if not, he sets it at S.

c. Setting Time Fuzes.(1) Using fuze setter M26 or M28. After

making the announced setting on the fuzesetter M26 or M28, No. 3 carefully placesthe setter over the fuze and turns the set-ter in the direction of increasing readingsuntil the notch on the time ring of thefuze engages the stop on the setting ringof the fuze setter. He places the handle inthe most convenient position, pushes downon the fuze setter until the notch fully en-gages the stop, and continues to turn it inthe direction of increasing readings untilthe pawl in the adjusting ring assemblydrops into the notch of the fixed fuze ring.This action prevents further turning andindicates that the fuze is set. He thenlifts the fuze setter from the fuze andmakes a visual check to see if the fuze isproperly set. If the fuze is not properlyset, he sets the fuze to S by turning thesetter in the direction of increasing read-ings and then resets the fuze.

(2) Using fuze setter M14 or M27. Fuze set-ters M14 and M27 are wrench-type set-ters in which the time scale on the fuze

AGO 2790C 39

is used in setting the fuze. With M500-series fuzes, No. 3 engages the key of thefuze setter in the notch on the setting ringof the fuze and rotates the lower cap in thedirection of increasing readings until theannounced time setting is opposite the in-dex mark on the fuze.

d. VT Fuzes. The older type VT fuzes (M97)operate and function in such a manner as to requireno setting by personnel. The new type VT fuzes(M513-series) have a time setting ring and areset by using the fuze setter M28 in the same man-ner as the M54-series time fuzes are set by usingthe fuze setter M26. However, if the fuze setterM28 is not available, the wrench-type fuze setteris used to set the new type VT fuzes. VT fuzes ofcertain lots are issued with a wax coating on theplastic ogive. This wax coating is necessary for theproper functioning of the fuze and should not be re-moved. VT fuzes should be used as issued; that is,with the wax coating on the ogive, if so issued, orwithout a wax coating, if so issued.

61. Passes Prepared Round to No. 2No. 3 positions himself on the ground as near as

possible to the rear of the turret. After No. 3 com-pletes the setting of the fuze, he passes the preparedround to No. 2.

62. No. 4, List of Duties(Detailed description of duties, pars. 63-65.)

a. Prepares charges.

40 AGO 2790C

b. Replaces increments in the cartridge case be-fore rounds are replaced in the container.

c. Assists No. 5 and driver in replacing ammuni-tion in containers as directed by chief of section.

63. Prepares Charges

The fire command will include the designation ofthe charge. No. 4 verifies the number of incrementsand removes those increments numbered higherthan the charge designated. He then replaces theremaining increments in the cartridge case in theiroriginal numerical order. After No. 4 has preparedthe charge, he fits the projectile in the cartridgecase. Care is taken to prevent damage to the lip ofthe cartridge case.

64. Replaces Increments in Cartridge Case Before RoundsAre Replaced in Container

Under the personal supervision of the chief of sec-tion, No. 4 replaces increments in cartridge casesfor all ammunition prepared for firing, but not fired.He checks carefully to see that all seven incrementsare present, in the proper condition, assembled inthe proper numerical order, and of the proper lotnumber.

65. Assists No. 5 and Driver in Replacing Ammunition inContainers as Directed by Chief of Section

See paragraph 69 for details of replacing am-munition in containers.

AGO 2790C 41

66. No. 5, List of Duties(Detailed description of duties, pars. 67-70.)

a. Sets out aiming posts.b. Removes ammunition from containers.c. Replaces unused ammunition in containers.d. Assists No. 4 in preparing charges as directed

by the chief of section.67. Sets Out Aiming Posts

No. 5 sets out the aiming posts as described inparagraph 100.68. Removes Ammuniton from Containers

No. 5 removes the taped end from the cartridgecase portion of the ammunition container and tiltsthe container so that the cartridge case can be takenby No. 4 or the driver when available. He then re-verses the ends of the container and repeats theprocess so that the projectile is received by No. 4 orthe driver when available.69. Replaces Unused Ammunition in Containers

Under the personal supervision of the chief ofsection and assisted by No. 4 or the driver as avail-able, No. 5 replaces unused ammunition in contain-ers. He checks carefully to insure that the lot num-ber on the projectile and cartridge case correspondsto the lot number on the container. He insures thatthe ammunition is in good condition and complete.70. Assists No. 4 in Preparing Charges as Directed by

Chief of SectionSee paragraph 63 for details of preparing

charges.

42 AGO 2790C

71. Driver, List of Duties(Detailed description of duties, pars. 72 and

73.)a. Moves the motor carriage if large deflection

shifts are necessary.b. Assists No. 5 in handling ammunition and per-

forms such other duties as directed by the chief ofsection.

72. Moves Motor Carriage if Large Deflection Shifts AreNecessary

At the direction of the chief of section, the drivershifts the motor carriage to permit a large deflectionshift to fall within the on-carriage traverse limits.

73. Assists No. 5 in Handling AmmunitionWhen No. 5 is unable to keep up with the am-

munition requirements, the chief of section may di-rect the driver to assist in the handling of ammuni-tion. See paragraphs 68 and 69 for details ofhandling ammunition.

AGO 2790C 43

CHAPTER 6FIRING BY DIRECT LAYING

Section 1. TECHNIQUE OF FIRE74. General

a. Firing by direct laying is a technique that de-mands special training. The section must operateas an independent unit. Targets taken under fire bythe section in direct laying are usually capable of re-turning fire on the section at pointblank range;therefore, speed and accuracy are extremely im-portant in direct laying missions.

b. For additional information on firing by directlaying, see FM 6-140.75. Preparation of Range Card

a. The chief of section is responsible for defensein his assigned sector and should be prepared to fireon targets in other sectors.

b. As soon as possible after occupation of posi-tion, the chief of section measures or estimates theranges to critical points in likely avenues of ap-proach for enemy tanks and vehicles. For quickreference, he prepares a range card (fig. 11) uponwhich he notes these ranges.

c. If there are no prominent terrain features,stakes may be driven into the ground at critical

44 AGO 2190C

. \TEE

0 0 s 9Ot OUSEBRIUSH 600

900N-. //ORCHARD

tt BARN

Figure 11. Range card for direct laying.

points for reference. As time permits, the rangecard should be improved by replacing estimatedranges with more accurate ranges obtained by fir-ing, pacing, taping, vehicular speedometer readings,map measurements, or survey.76. Field of Fire

The sector of fire for the howitzer should, if pos-sible, be cleared of all obstructions that might en-danger battery personnel when the howitzer is firedor that might hinder observation. Care should betaken not to disclose the location of the position.77. Priority of Targets

Targets for firing by direct laying usually consistof tanks, vehicles, and personnel threatening thebattery. Personnel will seldom present themselves

AGO 2790C 45

as a clearly defined target. Normally, attacking in-fantry, using all available cover, reveal themselvesonly fleetingly. Fire should be conducted on the areacontaining the attackers rather than on individuals.Tanks usually attack in groups and may be accom-panied by infantry. First priority is given to attackof targets within the assigned sector of the howitzerand second priority to targets in other sectors.Priority within the assigned zone is given to-

a. Tanks at short ranges, threatening to overrunthe position.

b. Hull down stationary tanks covering the ad-vance of other tanks.

78. Ammunition and Fuzesa. General. For close-in fires, a variety of fuzes

and shells are available. When high explosive shellsare used, charge 7 is habitually used for speed, easein adjustment, imparting forward motion to frag-ments, and more effective fuze action. The flattrajectory resulting from use of charge 7, coupledwith dug-in howitzers, may make extremely close-in fire impossible owing to projectiles skipping with-out detonating on impact. At ranges of 200 to 400yards, fuzes may fail to function on hard, flatground; however, preparation of sectors of fire willremedy this situation. The terrain may be preparedfor direct fire by placing mounds of sandbags, dirt,or logs in the sector of fire. When direct fire isplaced on these points as they are approached by anattacking force, the necessity for adjusting fire isreduced.

46 AGO 2790C

b. Ammunition. Ammunition may be high ex-plosive (HE), high explosive antitank (HEAT), orwhite phosphorus (WP). HEAT is designed for,and is highly effective in, antitank and antivehiclefires. HE is ideally suited for antipersonnel fire andis effective against vehicles and tanks. WP may beused to set immobile tanks and vehicles on fire, torestrict defiles, and to produce casualties. However,consideration must be given to the effect of the re-sulting smoke screen on the defense of the howitzerposition.

c. Fuzes. HEAT projectiles contain base detonat.ing fuzes. WP projectiles are fuzed with a super-quick-delay fuze. HE projectiles may be fuzed withsuperquick-delay or time fuzes.

(1) Fuze quick is the most desirable fuze touse with HE shell on close-in targets. It ishighly effective and, since no fuze settingis required, is much faster to use.

(2) The time required to set the fuze and toadjust the point of impact for maximumricochet effect makes fuze delay less desir-able than fuze quick for close-in targets.When fuze delay is used to gain ricocheteffect, the point of impact is adjusted from10 to 30 yards in front of the target. Ifless than 50 percent of the bursts arericochet, the fuze should be changed toquick.

(3) Fuze time is the least desirable fuze forclose-in targets. At short fuze settings,variations in timing action give wide range

AGO 2790C 47

dispersion of bursts. Hence, this fuzeshould be used only for ranges of morethan 1,000 yards. The areas covered effec-tively by air and ricochet bursts are sim-ilar.

79. TrajectoriesTrajectory characteristics change with the type

of ammunition and the charge fired. The followingtrajectory characteristics govern the conduct of fireby direct laying:

a. Ranges from 0 to 400 Yards Using HEAT orRanges from 0 to 600 Yards Using HE, Charge 7.Within range limits of 0 to 400 yards using HEATor 0 to 600 yards using HE, charge 7, the trajectorywill be flat enough to prevent an 8-foot high tankfrom passing safely under it. If fields of fire andterrain allow, the upper range limits for the am-munition and charge used are the ideal at which toopen fire by direct laying. Direct fire can then beconducted over the maximum time without missesif deflection is correct. Also, there is less risk ofobscuring the target with the smoke from a shortburst.

b. Ranges from 400 to 700 Yards Using HEATor Ranges from 600 to 1,000 Yards Using HE,Charge 7. Range limits of 400 to 700 yards usingHEAT or 600 to 1,000 yards using HE, charge 7include the zone in which the trajectory is suffi-ciently flat to permit direct estimation of rangewithout actually bracketing the target. Assuminglittle dispersion, if a hit is obtained at the bottom of

48 AGO 2790C

an 8-foot high tank firing at the upper range limit,700 yards, for example, with HEAT, a 100-yardrange increase will result in a round that will justbrush the top of the tank. During adjustment withinthis zone, range changes should seldom be more than100 yards, and frequently range changes of 50 yardswill be sufficient. The upper limits mentioned hereinare the greatest ranges at which direct fire shouldbe opened unless tactical conditions require other-wise. A trained crew should obtain a hit by thesecond shot.

c. Ranges from 700 to 1,300 Yards Using HEATor Ranges from 1,000 to 1,800 Yards Using HE,Charge 7. The zone of 700 to 1,300 yards usingHEAT or 1,000 to 1,800 yards using HE, charge 7includes the ranges at which hits by direct fire areonly reasonably possible. Bracket methods are nor-mally used to obtain adjustment in this zone. Thereis more dispersion in this zone, and direct fire shouldnot be opened at these ranges unless surprise is notimportant.

d. Ranges Over 1,300 Yards Using HEAT orRanges Over 1,800 Yards Using HE, Charge 7. Atranges over 1,300 yards using HEAT or over 1,800yards using HE, charge 7, firing by direct laying isnot advisable against moving targets. Dispersion isthe controlling factor. Ranges must be known ac-curately or determined by bracketing. At theseranges the slope of fall of the projectile becomes sogreat that a hit on a moving target is very difficultto obtain.

AGO 2790C 49

80. Vertical Displacement Table

Vertical displacement is the change in the pointof burst (up or down) between two rounds firedwith different range settings at an upright target.Table IV shows the vertical displacement for a100-yard range change at various ranges, firingshell HEAT and shell HE, charge 7. The use ofvertical displacement in direct fire is explained inFM 6-140.

50 AGO 2790C

e o oco o ~o o o- o o o oq o oto oo

L aqgq' aaV H i la m 10 L1:: Ims slaos 4 C o1 oi C,5 -4 in 6 ~o - 0 0 C d r vh '7uaruaaeldsla o il N r lee bt ;OOH0

a: o070 O)L $,:~~~~~~~~~~o

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13~~~~~~~~~~~~~~~~~-

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AGO 2790C3 51

C C= C000D

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52.AGO 2790C

p.-

81. Direct Laying, Using Telescope T150E1The telescope T150E1 is normally the only sight-

ing instrument used for direct laying. Paragraphs83 through 97 apply to use of the telescope T150E1only. The reticle pattern of the telescope is correctwhen using shell, HEAT. The cross in the patternrepresents zero range and deflection for boresight-ing the broken vertical line in the vertical center ofthe reticle. The broken lines below the cross repre-sent 400-, 800-, 1,200-, 1,600-, 2,000-, and 2,400-yard ranges. Each horizontal line in the reticlerepresents a deflection of 5 mils. A cant correctionknob and leveling vial are provided on the elbowsection of the telescope which permits correctionfor up to 15 of cant.82. Direct Laying, Using Panoramic Telescope T149E1

The panoramic telescope T149E1 is used for di-rect laying in case of emergency only. Direct layingwith the panoramic telescope T149E1 is muchslower and less accurate than with the telescopeT150E1. For a detailed discussion of the use of thepanoramic telescope T149E1 in direct laying, seeTM 9-717A.

Section II. DUTIES OF CHIEF OF SECTION83. List of Duties

(Detailed description of duties, pars. 84-91.)a. Conducts the fire of his howitzer.b. Alerts his section.c. Identifies or selects the target.

AGO 27900 53

d. Selects the charge, fuze, and projectile.e. Determines the direction of movement of the

target.f. Determines the lead in mils.g. Gives the command for range.h. Gives subsequent commands based on observed

effect.84. Conducts Fire of His Howitzer

The chief of section conducts the fire of his how-itzer when the executive officer commands TARGET(IDENTIFICATION), FIRE AT WILL, or simplyFIRE AT WILL.

85. Alerts His SectionThe command to alert the section is 1. CANNON-

EERS, 2. POSTS. At the command, members ofthe section move to their posts to be ready for theinitial fire command. If the target is outside themaximum traverse of the howitzer, the alert is fol-lowed by the necessary signals to the driver to getthe carriage pointed in the approximate directionof the target.86. Identifies or Selects Target

If the executive officer designates an object as thetarget, the chief of section must identify the targetcorrectly. If the target is a group of tanks or otherobjects, the chief of section selects the target whichis the greatest threat to his own position or theposition of the supported troops. He repeats theidentification to his section, using the minimum

54 AGO 2790C

number of words, such as TANK or INFANTRY(OR OTHER TARGET).87. Selects Charge, Fuze, and Projectile

The chief of section commands the appropriateitems in sequence, such as SHELL HE, CHARGE 7,FUZE ____, or SHELL HEAT. He selects thecharge, fuze, and projectile in accordance with para-graph 78.

88. Determines Direction of Movement of TargetThe chief of section determines the direction of

movement of the target and commands TRAVERSERIGHT (LEFT), STEADY-ON. While givingthese commands he looks along the tube or throughthe periscope M15A1.

89. Determines Lead in Mils

The amount of lead in mils for moving targets isdetermined by considering the speed of the target,the range, the course, and the ammunition beingfired. Figure 12 shows approximate initial leadsthat should be used for various target speeds andcourses in firing HEAT and HE, charge 7. Theinitial command for lead is LEAD (SO MUCH).During adjustment the lead is changed by the com-mand RIGHT (LEFT) (SO MUCH).90. Gives Command for Range

The command is RANGE (SO MUCH). Therange commanded by the chief of section is thatrange to be set on the sight reticle. During the ad-

AGO 2790C 55

LEAD (MILS)SPEED Target traveling perpen- Target traveling 45

dicular to line of fire to line of fireHEAT Charge 7 HEAT Charge 7

Slow (0-1OMPH) 5 5 5 5Medium (10-20 MPH) 20 15 1 5 10Fast (aover 20 MPH) 30 25 20 20

Figure 12. Approximate leads.

justment of fire, range is corrected by the commandADD (DROP) (SO MUCH).91. Gives Subsequent Commands Based on Observed

EffectThe chief of section observes each round and

gives the necessary commands for changes in leadand range to adjust the burst to the target.

Section III. DUTIES OF REMAINDER OF SECTION92. Gunner, List of Duties

(Detailed description of certain duties, pars.93-95.)

a. Corrects for cant of the howitzer.b. Lays on the target with the announced lead

and range.c. Tracks the target.d. Commands FIRE.e. Follows subsequent commands.

93. Corrects for Cant of HowitzerThe gunner checks the leveling vial on the elbow

section of the telescope and rotates the cant cor-

'56 AGO 27900

rector knob until the bubble is centered. This opera-tion corrects for up to 150 of cant.

94. Lays on Target with Announced Lead and Range andTracks Target

The lead and range are measured on the horizon-tal reticle scale of the telescope. The cross in thereticle pattern represents zero range and deflection.The horizontal lines below the cross represent 400-,800-, 1,200-, 1,600-, 2,000-, and 2,400-yard ranges.Each segment and space represents 5 mils of de-flection. The gunner then tracks the target by usingthe traverse and elevating handwheels, keeping theproper sight picture on the center of the target.See figure 13 for proper sight picture.

95. Commands FireAfter No. 1 has called "Set," the gunner com-

mands FIRE, when ready.

96. No. 1

The duties of No. 1 during direct fire are to openthe breech on the first round, to load the howitzer,to call "Set" when the howitzer is loaded, and tofire the howitzer at the gunner's command FIRE.

97. Remainder of SectionThe remaining cannoneers perform their duties

as prescribed for firing by indirect laying.

AGO 2790C 57

10-- M

- - I- --16 - - I - - 16

24 - - i - - 24

7633305

Figure 1S. Gunner's sight picture, telescope T150EI,shell HEAT (lead 15 mils, range 800 yards).

58 AGO 2790C

CHAPTER 7TECHNIQUES AND SITUATIONS THAT

REQUIRE ATTENTION

98. Precision in Laying

a. Sighting and laying instruments, fuze setters,and elevating and traversing mechanisms must beproperly operated to reduce the effects of lost mo-tion. For uniformity and accuracy, the last motionin setting instruments and in laying should be in thedirection prescribed in this manual. To insure ac-curate laying, personnel who lay the howitzer mustbe required to verify the laying after the breechhas been closed.

b. The line of sight when setting and reading ascale or centering a bubble must be at a right angleto the scale or level vial to prevent parallax errors.Bubbles must be centered exactly.

c. For uniformity and accuracy in laying on aim-ing posts, the vertical cross hair in the reticle of thepanoramic telescope must be alined with the leftedges of the aiming posts.99. Aiming Points

a. General. After the howitzer has been laid ini-tially for direction, it is referred to the aiming postsand usually to one or more distant aiming points.An aiming point must have a sharply defined point

AGO 2790C 59

or vertical line which is clearly visible from thehowitzer so that the vertical cross hair of the pano-ramic telescope can be alined on exactly the sameplace each time the howitzer is relaid.

b. Distant Aiming Point. A distant aiming pointis one at sufficient distance (at least 2,000 yards)so that normal displacements of the howitzer infiring or traverse will not cause a horizontal angularchange in direction (with the same settings on theazimuth scales) of more than one-half mil. Theexecutive officer usually designates the distant aim-ing point or points to be used.

100. Aiming Postsa. Two aiming posts are used for each howitzer.

Each aiming post is equipped with a light for useat night. The most desirable distance from thehowitzer to the far aiming post is 100 yards, con-sidering accuracy of laying, visibility, and ability tocontrol the aiming post lights. First, the far aimingpost is set up and alined. The near aiming post isthen set up and alined halfway between the faraiming post and the howitzer. The vertical crosshair of the panoramic telescope must be on the leftedge of the aiming posts for proper alinement. Toinsure equal spacing of aiming posts, the distanceto both the near and the far aiming post shouldbe paced by the same man. If ground conditionsmake pacing inaccurate, the distance from the how-itzer to the aiming posts may be measured by usingthe panoramic telescope and the aiming post asmeasuring devices (d below).60 AGO 2790C

b. For night use, the aiming post lights shouldbe adjusted so that the far light will appear severalfeet above the near light. On flat terrain this maybe accomplished by using only the lower half of thenear aiming post. The two lights placed in this waywill establish a vertical line for laying the howitzer.

c. Since the panoramic telescope is mounted atconsiderable distance from the center of rotation ofthe top carriage, large changes in deflection willcause misalinement of the aiming posts.

d. To measure the distance from howitzer to aim-ing posts, the stadia method may be employed byusing the panoramic telescope and the aiming postas measuring devices. No. 5 cannoneer, in settingout the aiming posts, holds the upper section of oneof the aiming posts in a horizontal position, perpen-dicular to the line of sighting. The gunner measuresthe length of this section in mils on the horizontalcross hair of the panoramic telescope. For example,the upper section of the aiming post is 41/2 feet longand measures 15 mils when it is 100 yards from thehowitzer. The proper location for the near aimingpost, in this case, would be at the point at whichthe 41/2-foot section measures 30 mils. In manycases, the ideal spacing of 50 and 100 yards cannotbe obtained, but the aiming posts will be properlyspaced when the near aiming post is set at a pointwhere one section of the aiming post (41/2 ft) heldhorizontally measures twice the number of mils onthe horizontal cross hair that it measured at thefar aiming post location. This measurement may beperformed at night by attaching the night lighting

AGO 2790C 61

devices on the ends of one section of an aiming postand holding it horizontally.

101. Correction for Displacement of Aiming PostsWhen the gunner notes that the vertical cross

hair of the panoramic telescope is displaced fromthe line formed by the two aiming posts (or aimingpost lights), he lays the howitzer so that the faraiming post (light) appears exactly midway be-tween the near aiming post (light) and the verticalcross hair (fig. 14). If the displacement is due totraversing the howitzer, the gunner continues to layas described above. If the displacement is due toprogressive shifting of the carriage from shock offiring or other cause, the gunner will notify the chiefof section, who, at the first lull in firing, will notifythe executive and request permission to realine theaiming posts. To realine, the howitzer is laid withthe far aiming post midway between the near aim-ing post and the vertical cross hair (fig. 14). Thefar aiming post is moved into alinement with thevertical cross hair of the telescope and then the nearaiming post is alined. If terrain conditions make itimpossible to move 1 of the 2 aiming posts, thehowitzer is laid for direction and both aiming postsare alined to the right rear of the howitzer at thecommanded deflection.

102. Testing Targeta. If the regular testing target or a visible dis-

tant aiming point is not available, a testing targetmay be improvised either by drafting the aiming

62 AGO 2790C

FAR AIMING POST FAR AIMING POST

NEAR AIMING POST PT

LEFT RIGHTDISPLACEMENT DISPLACEMENT

Figure 14. Gunner's sight picture of aiming posts in properrelationship when correcting for displacement.

diagrams to the correct measurements (TM 9-324A) or by the following technique:

(1) Carefully boresight the howitzer on a dis-tant aiming point.

(2) Place a flat piece of masonite, wallboard,or similar material covered with a sheetof weather-resistant paper 50 yards infront of the howitzer so that its face isperpendicular to the line of sight throughthe tube. To render the testing targetstable, the target may be fastened to astand constructed for that purpose.

(3) Without disturbing the relationship of thetelescopes to the tube, mark on the paperthe centers of the lines of sight throughthe telescopes and the tube.

AGO 2790C 63

(4) From the centers marked, construct aim-ing diagrams such as those found on stand-ard testing targets.

b. For use in either leveling or canting the test-ing target, a mil scale may be drawn at the bottom ofthe target. A small nail at the top marks the centerfrom which the arc was drawn and provides a hookfrom which to suspend the plumb line (fig. 15).

c. Vertical reference lines may be drawn throughthe centers of each of the diagrams (fig. 15). Theselines may be used when the trunnions cannot beleveled by setting the testing target with the cantangle of the howitzer. The target is tilted until theline of sight through the tube tracks the tube refer-ence line when the tube is elevated or depressed.Then, the panoramic telescope should be adjustedso that its vertical cross hair tracks between theappropriate reference lines when the tube is elevatedor depressed.

103. Cease FiringThe command CEASE FIRING is normally given

to the howitzer section by the chief of section, butin emergencies anyone present may give the com-mand. At this command, regardless of its source,firing will cease immediately. If the howitzer isloaded, the chief of section will report that fact tothe executive. The executive acknowledges this an-nouncement by saying "No. (so-and-so) loaded."If CEASE FIRING came from the fire directioncenter, firing is resumed at the announcement of theelevation. If CEASE FIRING came from within

64 AGO 2790C

PANORAMIC TELESCOPE- / IIT149E1

43-43/64 IN-20 IN -

TELESCOPET150EI

4 IN

105-MM HOWITZER-_T96E1

8-3/4 IN

MIL SCALE(Not to Scole)

Figure 15. Vertical reference lines and mil scaledrawn on testing target.

AGO 27900 6

the firing battery, the executive will investigate thecondition that caused the command to be given.When the condition is corrected, firing is resumedat the executive's announcement of the elevation.

104. Changes in Data During Firinga. If a change in firing data is made before the

howitzer is loaded, the corrected data is announced.The new data is then set off and firing is resumedat the announcement of the elevation.

b. If a change in firing data is made after thehowitzer is loaded, the command CEASE FIRINGis given. If no change in fuze setting is required,or if the howitzer is loaded with percussion-fuzedshell, the new data is set off and firing is resumedat the announcement of the elevation. If the how-itzer is loaded with time-fuzed shell and the datarequires a change in fuze setting, the chief of sectionwill suspend firing and that fact will be reported tothe executive; for example, "No. 2 loaded, time (somuch)." The howitzer will not be unloaded unlessdirected by the executive. In continuous fire,changes in data are so applied as not to stop the fireor break its continuity.

105. To Unload Piecea. A complete round, once loaded, should always

be fired in preference to being unloaded, but militarynecessity may dictate otherwise.

b. When the command UNLOAD is given, No. 1opens the breech slowly; No. 2, standing at thebreech, receives the ejected round or cartridge case.

06 AGO 2790C

c. Should the extractor fail to extract the com-plete round, the staff and unloading rammer (head)is used. Unloading will be done only under the im-mediate supervision of an officer. The officer in-spects the recess in the head of the rammer toassure that it is free from obstructions. No. 1 theninserts the rammer in the bore until the head in-closes the fuze and comes into contact with theprojectile. He pushes and, if necessary, taps therammer staff slightly or operates the spring-oper-ated rammer until the round is dislodged. He thenpushes the round out of the breech and No. 2 re-ceives it.

d. If the cartridge case is extracted but not theprojectile, No. 1 fills the chamber with waste andcloses the breechblock. He dislodges the projectileas in c above. No. 2 then opens the breech, removesthe waste, and receives the projectile as No. 1pushes it to the rear.

e. For further information on unloading, see FM6-140 and TM 9-324A.

f. In case of a misfire, the instruction in para-graph 142 will be followed.

106. Care of Ammunitiona. To insure uniform results in firing, to prolong

the life of the tube, and to avoid accidents, caremust be exercised in the storage and handling ofammunition at the battery. Provisions of TM 9-1900 applicable to field service should be followedcarefully. In the field, conditions existing in each

AGO 2790C 67

position will determine the amount of time, labor,and materials required to store and preserve theammunition adequately. If the position is to beoccupied for only a few hours, a tarpaulin spreadon the ground may be sufficient; for longer periodsof time, more elaborate facilities should be provided.

b. Ammunition must be protected from damage.When ammunition is received, it should be sortedinto lots and placed in the best available storage.Powder temperature should be kept as uniform aspossible. Ammunition data cards should be keptuntil after all ammunition for that lot is expended.Ammunition should be left in containers until itsearly use is expected. Protection should be providedagainst moisture, dirt, direct rays of sun and, as faras practicable, artillery fire and bombing. Protec-tion from weather, dirt, and sun may be obtainedby the use of tarpaulins below and above ammuni-tion and dunnage between the layers. Projectilesstacked in the open should be raised off the groundby at least 6 inches. If drainage is not good, ditchesshould be dug around the stacks. A liberal use ofdunnage should be made between layers, and cover-ing tarpaulins should be raised at least 6 inchesfrom the stack to insure adequate ventilation. Eachstack should contain not more than 75 rounds andshould be not more than 4 layers high. Stacks shouldbe at least 10 yards apart.

c. For further information on care of ammuni-tion, see FM 6-140, TM 9-324A, TM 9-1900, andTM 9-1901.

68 AGO 2790C

107. Section Data BoardWhen positions are occupied for more than a few

hours, data boards may be used by each section forrecording such items as deflections to aiming points,calibration corrections when appropriate, minimumelevations, data for barrages and counterprepara-tions, and other data which may be needed quickly.If such information assumes a standard pattern,the section may paint a form on the inside of thehull and chalk in the various items of informationin the appropriate spaces.

108. Hand SignalsStandard hand signals are used to indicate to the

driver the proper movement of the motor carriage.Dismounted signals are given facing the driver andare as illustrated in FM 21-60 and FM 25-10.

AGO 2790C 69

CHAPTER 8BORESIGHTING AND BASIC PERIODIC TESTS

Section I. GENERAL109. Purpose and Scope

The purpose of this chapter is to outline the pro-cedures for boresighting and for making basic peri-odic tests of on-carriage fire control equipment. Theprocedures covered will include only those that maybe accomplished at battery level.

110. EquipmentThe equipment listed in a through d below is

needed for performing boresighting and periodictests.

a. Boresights. Front and rear boresights or im-provised substitutes are necessary for boresightingand testing. If boresights are not available, crosshairs may be fastened on the muzzle and the firingpin hole in the breechblock bushing may be used asa rear sighting guide by removing the firing lockfrom the closed breechblock.

b. Testing Target. A testing target (par. 102) orsuitable substitute is needed for both boresightingand testing. If the testing target is not available,a clearly defined aiming point 2,000 yards or morefrom the gun may be used for boresighting.

70 AGO 2790C

c. Tools. The section equipment includes all thenecessary tools for boresighting and testing. Caremust be taken in using the screwdrivers andwrenches to insure that damage to fastenings doesnot result through carelessness or the use of inap-propriate tools.

d. Plumb Line. Although not essential for bore-sighting, it is necessary that a plumb line be usedin the basic periodic test in order to obtain maxi-mum accuracy. The farther from the gun that theplumb line is placed, the longer the line must be.To keep a long plumb line taut it may be necessaryto add weight to the line. Wrenches or rocks maybe used. The tendency of the weight to swing maybe decreased by placing a bucket containing wateror other liquid under the plumb line so that theplumb bob is partially immersed in the liquid. Aplumb line strung from a building or tree is desir-able and should be used if possible. Units in gar-rison may find it convenient to rig a plumb line ona building. The line may then be nailed in placeso that it can be used permanently.

Section II. BORESIGHTING

111. Generala. Description. Boresighting consists of alining

the line of sight through on-carriage fire controlinstruments parallel to the line of sight through thecenter of the tube. Boresighting is conducted bysection personnel before firing and during lulls infiring.

AGO 2790C 71

b. Methods. The three general methods of bore-sighting the weapon are the-

(1) Testing target method.(2) Distant aiming point method.(3) Standard angle method.

c. Leveling. Prior to starting the tests, the how-itzer should be placed in the center of traverse. Thevehicle should be placed upon ground as level aspossible, since no means are provided on the car-riage for cross-leveling the trunnions. The groundmay be built up under one track to assist in approxi-mately leveling the trunnions. There should be nomore than 20 mils of cant in the trunnions duringany boresighting operation.112. Conditions

The on-carriage sighting equipment of the weaponis in correct adjustment and "boresighted" whenthe conditions in a through d below exist.

a. Mounts and instruments are securely attachedand there is no binding or excessive backlash be-tween the gears.

b. The lines of sight of on-carriage sightingequipment are parallel to the axis of the bore.

c. All scales and indexes read zero.d. All bubbles are leveled.

113. Testing Target Methoda. General. It is essential that the proper testing

target be used for the weapon being boresighted.If a testing target is not available, a substitute may

72 AGO 2790C

be constructed as explained in paragraph 102. Thetesting target method consists of boresighting byusing the aiming diagrams on the testing target asaiming points. The steps to be followed are as fol-lows:

(1) Trunnions. Although it is not absolutelynecessary to level the trunnions for bore-sighting, it is advisable to do so wheneverpossible. Accurate results can be obtainedmore readily if the trunnions are level,because then a corresponding tilt does nothave to be introduced in the mounts andtesting target. In no case should there bemore than 20 mils cant.

(2) Tube. Level the tube by using the gunner'squadrant on the leveling plates of thebreech ring. Make certain that the shoeson the gunner's quadrant are positionedbetween the engraved lines on the levelingplates.

(3) Boresights. Open the breech and insertthe breech boresight in the chamber. At-tach the muzzle boresight, stretching linencords across witness marks on the muzzleand securing the ends by placing a straparound the end of the muzzle over thecords.

(4) Panoramic telescope mount level. The levelof the locating plate is checked by insuringthat the bubbles in the leveling segmentlevel vials and the leveling mechanism levelvials are accurately centered.

AGO 2790C 73

b. Elevation Counter. To make the elevationcounter reading agree with the tube elevation, placethe gunner's quadrant on the breech pads and, byelevating or depressing, bring the tube to 0 eleva-tion. Rotate the elevation counter setting knob untilthe elevation vernier indexes are alined. If thecounter reading does not agree with the gunner'squadrant reading within plus or minus one-half mil,zero the elevation counter, loosen the lock setscrewin the side of the bellcrank (fig. 16) and, with a% 2-inch hex setscrew wrench, turn the bellcrankadjusting screw until the elevation vernier indexesare alined. Tighten the lock setscrew while makingcertain that the adjustment does not change.

Note. Some T179 mounts will have a setscrew or cap-screw on top of the bellcrank adjusting screw. This screwmust be removed before the bellcrank adjustment can bemade.

c. Testing Target Alinement. Place the testingtarget at least 50 yards in front of the howitzerwith the face of the target perpendicular to the lineof sight through the tube. Position the target sothat the bore diagram is alined with the boresight.While elevating and depressing the tube, tilt thetarget until the intersection of the muzzle boresightcords tracks between the vertical reference lines onthe bore diagram without deviation. Fix the targetin this position. Elevate or depress the tube to alinethe intersection of the muzzle boresight cords withthe center of the bore diagram.

d. Panoramic Telescope Alinement. Rotate theelevation and azimuth knob until the horizontal and

74 AGO 2790C

E f

Figure 16. Bellerank adjustment.

vertical lines of the reticle pattern are alined withthe horizontal and vertical lines respectively on thepanoramic telescope diagram on the testing target.The coarse azimuth scale and the micrometer scaleof the panoramic telescope should now read 0; ifthey do not, loosen the locking screws on themicrometer scale and slip the micrometer scale to 0.Then tighten the locking screws, being careful notto disturb the setting of the telescope or scales.

e. Direct Fire Telescope Alinement. After pro-cedures prescribed in c above are performed, rotatethe cant correction knob to level the cant correction

AGO 2790C 75

level vial. Unlock the boresight knob locking levers.Rotate the azimuth and elevation boresight knobsuntil the cross hairs at zero range on the reticlepattern are alined with the center of the direct firetelescope diagram on the testing target. If thecross hairs of the telescope cannot be brought intocoincidence with the lines on the aiming diagram byusing the boresight knobs, notify ordnance main-tenance personnel.114. Distant Aiming Point Method

The distant aiming point method of boresightingconsists of alining the lines of sight of on-carriagefire control equipment and the line of sight throughthe axis of the tube on a common point at least2,000 yards away from the howitzer. A distant aim-ing point may be used if a testing target is notavailable or if its use is impractical. The stepsprescribed for the testing target method apply ex-cept that both the boresights and the optical sightsare alined on the same point instead of on separatediagrams of a testing target. Accurate leveling ofthe trunnions is unnecessary.

115. Standard Angle Methoda. General. Conditions may exist when the bore-

sighting methods previously described are imprac-tical. Under such circumstances, the howitzer maybe boresighted by referring to a selected point onthe muzzle. The deflection and elevation anglesnecessary to refer the line of sight of the panoramictelescope to the selected point on the muzzle arereferred to as the standard angles. Once the stand-

76 AGO 2790C

ard horizontal and vertical angles are determined,they may be used for quick boresighting when moreprecise methods cannot be used. Correction of mis-alinement as a result of this test should be verifiedby a more accurate method at the earliest oppor-tunity. In using the standard angle method of bore-sighting, be sure that the position of the recoilingparts with respect to the nonrecoiling parts is thesame as when the standard angles are determined.

b. Preliminary Operations. The ideal time to de-termine the standard angles for later use is afterperforming basic periodic tests when the trunnionsare level (par. 111c) and the panoramic telescopemount is known to be in correct alinement (par.113d). The procedure for determining standardangles is as outlined in (1) through (8) below.

(1) With the tube in battery, scribe lines inthe paint to mark the normal position ofthe parts that move in recoil with respectto the parts which do not move in recoil.

(2) Boresight the howitzer by using a testingtarget.

(3) With adhesive tape, fasten a bright com-mon pin in the right horizontal witnessmark at the muzzle of the tube. Allowthe pin to project to the right of themuzzle (fig. 17).

(4) Fasten the telescope parallax shield in placeover the eyepiece.

(5) By turning the azimuth micrometer scaleand elevating or depressing the tube as

AGO 2790C 77

50 50

111 l Il 11111 I lllllllllllII

PIN

Figure 17. Sight picture of projecting pin.

78 AGO 270DC

necessary, place the horizontal cross hairsof the panoramic sight on the metal pinin the right horizontal witness mark ofthe tube.

(6) Verify that the sight mount is level andthat the intersection of the horizontal andvertical cross hairs of the panoramic tele-scope are exactly on the junction of thepin with the muzzle.

(7) Read and record the deflection from thepanoramic telescope, estimating to thenearest one-fourth mil. This is the stand-ard azimuth angle for the howitzer tested.

(8) With the gunner's quadrant seated on thequadrant seats, measure and record theelevation of the tube to the nearest one-fourth mil. This is the standard elevationangle for the howitzer tested.

c. Performance of Standard Angle Method. Oncethe standard angles have been determined and re-corded, the steps in performing the standard anglemethod of boresighting are as outlined in (1)through (5) below.

(1) Verify that the parts that move in recoilare in the same position with respect tothe nonrecoiling parts as they were whenthe standard angles were determined.

(2) Fasten a pin in the right horizontal wit-ness mark of the muzzle so that the pinprojects out to the right of the muzzle.

(3) Place the parallax shield on the eyepiece ofthe telescope.

AGO 2790C 79

(4) Set off the standard elevation and azimuthangles (b(6) and (8) above).

(5) If the intersection of the cross hairs of thepanoramic telescope is not exactly on thejunction of the pin and the muzzle, thesight is out of adjustment. If the azimuthangle is in error, it may be corrected bybattery personnel by slipping the azimuthmicrometer scale. If the elevation angleis in error by more than one-half mil,bellcrank adjustment (par. 113b) must beperformed.

Section III. BASIC PERIODIC TESTS

116. GeneralBasic periodic tests are performed by the section

under the supervision of the battery executive andthe artillery mechanic. These tests are performedat the discretion of the unit commander. Suggestedtimes for performance of the tests are once eachyear if the howitzer is used only for nonfiring train-ing; once every 3 months if the howitzer is fired;as soon as possible after intensive use, accidents,or traversing extremely rough terrain; and when-ever the howitzer fires inaccurately for no readilyapparent reason. The tests reveal whether or notthe on-carriage sighting equipment, the gunner'squadrant, and the fuze setter are in correct adjust-ment. Preparation for the tests includes-

a. Boresighting the howitzer.

so80 AGO 2790C

b. Placing the motor carriage on a site that isas near level as possible.

c. Preparing parallax shields for the panoramictelescope T149E1 and telescope T150E1 for it willbe necessary to eliminate parallax in viewing aplumb line or testing target at close range. Theshield should be the same diameter as the eyepiecelens housing. The shield should be made of stiffcardboard or brass shim stock and should have avertical and horizontal centered slot l/16-inch wideby 1/4 -inch long. The shield should be placed infront of the eyepiece with the slot in the verticalposition.

d. Establishing a suitable plumb line for thetests (par. 110d).117. Test of Cross-Level Setting, Telescope Mount T179

For test of cross-level setting, telescope mountT179, see TM 9-324A.118. Test of Longitudinal-Level Setting, Telescope Mount

T179For test of longitudinal-level setting, telescope

mount T179, see TM 9-324A.119. Test of Elevation Counter Synchronization

With the gunner's quadrant placed on the breechpads, take elevation readings at 0, 225, 625, 1,025,and 1,155 mils, and if the elevation counter andthe gunner's quadrant do not agree within 1/2 milat 0 elevation and 1 mil at each of the other read-ings, the synchronization adjustment must be madeby qualified ordnance maintenance personnel.

AGO 2790C 81

120. Test of Plumb of Reticles in Telescopes T149E1 andT150E1

For test of plumb reticles T149E1 and T150E1,see paragraph 87c(6), TM 9-324A.121. Test of Gunner's Quadrant

The gunner's quadrant must be in proper adjust-ment before conducting tests and adjustments ofother sighting and fire control equipment. Inspectthe shoes of the gunner's quadrant for dirt, nicks,or burs. Similarly, inspect the leveling plates on theupper surface of the breech ring. Dirt, nicks, or burson these surfaces will cause the instrument to give in-accurate readings. For detailed testing of the gun-ner's quadrant, see paragraphs 122 through 124.

122. End-For-End Test, Gunner's Quadranta. Set both the index arm and the micrometer

scale of the gunner's quadrant at zero, making surethat the auxiliary indexes match.

b. Place the quadrant on the leveling plates ofthe breech ring with the "line of fire" arrow on thequadrant pointing toward the muzzle and centerthe quadrant bubble by turning the elevating hand-wheel.

c. Reverse the quadrant on the leveling plates(turn it end-for-end). If the bubble recenters, thequadrant is in a