7/30/2019 M1916 37mm manual FM-23-75

1/164

M H I FM 23-75Copy 2 A- s*( I /I / ,/^tx-

7/30/2019 M1916 37mm manual FM-23-75

2/164

FM 23-75BASIC FIELD MANUAL

37-MM GUN , M1916

Prepared under direction oftheChief of Infantry

UNITED STATESGOVERNMENT PRINTING OFFICE

WASHINGTON : 1940

For Bale by the SuperintendentofDocuments, Washington. D-C.Price25 cents

7/30/2019 M1916 37mm manual FM-23-75

3/164

WARDEPARTMENT,W A S H IN G T O N , April 16,1940.FM 23-75, 37-mm Gun, M1916, is published for the information and guidance of all concerned.

[A. G. 062.11 (10-10-39).]BYORDER OF THE SECRETARY OFWAR: iG. C. MARSHAL,Chief 6j Staff.O FF IC IA L :E . S. ADAMS,Major General,

The AdjutantGeneral.ii

7/30/2019 M1916 37mm manual FM-23-75

4/164

TABLE OP CONTENTS

CH A PT ER 1. M E C H A N I C A L T R A I N I N G : Paragraphs PageSectionI. D escription 1-3 1II. Dismounting and mounting, disassemblingand assembling, operation of thepiece______ 4-6 5III. Care andcleaning_______ 7-10 12IV . Functioning_____________ 11-16 15V. Defects and stoppages 17 17VI. Instruments and accessories. - 18-23 19VII. Ammunition______________ 24-31 31C H A P T E R 2. DR I L L F O R P L A C I N G GUN IN ACTION_ 32-42 34CH A P T E R 3. M A R K S M A N SH IP:Section I. Preliminary instruction.... 43-54 45II.Examnation______________ 55-60 66III. Qualificationcourse, gunner'stest___.____________ 61-73 68IV . Qualification course, expert'stest________._________ 74-78 77V . Targets, ranges, and safety precautions_____________ 79-SO 81C H A P T E R 4. T E C H N IQUE O P F I R E :Section I. Direct laying..____________ 81-83 83II. Indirectlaying____________ 84-92 87III.Overhead fire_____________ 93-98 105IV. Fire control andadjustment.__ 99-105 110V. Firing against moving targets._ 106-112 120VI. Other firingmethods________ 113-117 126VII . Range cards______________118-119 132CH A PT ER 5. FIRIN G A T F IELD T A R G E T S :Section I. General ________________ 120-122 136II. Preparatory exercises.______ 123-126 136III.Firing exercises__________... 127-135 138C H A P T E R 6. A D V I C E T O I N S T R U C T O R S :Section I. General_________________ 136-138 142II. Mechanicaltraining_______139-142 143III. Gundrill________________ 143 144IV. Marksmanship_____________144-145 144V. Firingat fieldtargets________ 146-151 145VI. Instruction on thesand table. 152-153 -148I N D E X . 155

III

7/30/2019 M1916 37mm manual FM-23-75

5/164

FM 23-75BASIC FIELD MANUAL

3T-MM G U M ", M1916(The matter contained herein, together with that in FM 23-95,supersedes sections I to IV , inclusive, TB 420-75, June 15, 1926(including Cl, January 2, 1929); TB 1300-37A , A pril 15, 1933 (including Cl, January 2, 1936); the relevant parts of TE 1320-B, A pril2, 1927; TB 1350-37A , August 1, 1932; chapters one and two, parttwo, Basic Field Manual, volume HI, M ay 2, 1932; part four,Basic Field Manual, volume III, August 1, 1932 (including Cl,

January3, 1938); andsections X IV to XVI I , inclusive, chapter one,Cavalry Field Manual, volume I, January 3, 1938.)CHAPTER 1

MECHANICAL TRAINING ParagraphsSECTION I . Description__________ 1-3II. Dismounting and mounting, disassemblingandassembling, operation of thepiece_ 4-6III. Care and cleaning_____________ 7-10IV. Functioning__________________11-16V . Defects andstoppages_____________ 17VI. Instruments and accessories________ 18-23VII. Ammunition______________ 24-31

SECTION IDESCRIPTION

. CH A R A CTERISTICS.The 37-mm gun, M 1916, is a flattrajectory weapon of the field-gun type which fires high-explosive shells or low-explosive shells that weigh slightlymore than a pound. Five general methods of transportingtheweapon area. Gun and cart attached, drawn by muleor horse.b. Gun and carriage unlimbered, drawnonwheels by thegun squad.c. Gun disassembled into three loads consisting of gun andcradle, tripod, and wheels and axle, the first two loads beingcarried and thewheels and axle being pushed.d. Gun and carriageunlimbered andcarried in atruck.e. Gun and carriage brokendown for pack transport.

7/30/2019 M1916 37mm manual FM-23-75

6/164

2-3 37-MM GUN, M1916. G E N E R A L D A T A .Weight of barrel andcradlegroup______pounds 88Weight oftrails (completetripod mount), aboutdo__ 86Weight of wheelsandaxle__________do_- 167Weight of gun andcarriage, complete____--do__ 342L ength of barrel __ inches.- 29.13L ength of recoil_____do7to10M aximumangle of elevation__________degrees 22A mount of traverse to right_________do____ 22A mount of traverse to left _ -do 16Diameter of wheels.._______inches37.75Over-alllengthof vehicle________do_ 75Over-all width of vehicle, trailsspread do. _ _ _ 57Over-all width of vehicle, trailsclosed_____do__39., 25Oil capacity of cradle-.____-_.pints 2.75Weight of ammunition chest, capacity 16 rounds(empty), approximately________pounds 8Weight of 1 round, HE shell____________do__ 1. 57Weight of 1 round, LEshell_____pounds 1. 44Weight of chest containing 16 rounds HEshelldo__ 33.12Weight of chest containing 16 rounds LE shell_do__31.04Muzzle velocity HE shell_______feetper second 1,276Muzzlevelocity LE shell_________do____ 1,312Rateof fire, maximum (aimed fire)rounds per minute-_ 25. D E S C R I P T I O N . a. Barrel assembly. (See figs. 1 , 2, 3, and4.) The barrel assembly consists of the following principalparts: Barrel; breech ring, which is screwed on the rear endof thebarrel formingarecess for the breechblock; breechblock, whichcloses thechamber for firing and carries the extractormechanism and some of the firing mechanism; jacketand jacketshoe which form the rearsupport for the barrel,the shoe forming also a guide for the barrel during recoil;clip, which formsthe front support andguide for the barrel.

& . Cradle.The cradle is located below and supports thebarrel. It is provided with trunnions and a bracket forattachment to the carriage, and carries abracket on the leftside for attachment of the sight. The recoil cylinder of the

7/30/2019 M1916 37mm manual FM-23-75

7/164

37-MMGUN, M1916 3cradle contains the recoil mechanism. A hole is providedthrough the front cap for filling therecoil cylinder with oil.On the right rear uppersurface of the cradle is the drainplugwhich closes the overflow hole.c. Tripod.The tripod comprises the following principalparts: Two trails, front leg, pintle, pintle socket, elevatingmechanism, and traversing mechanism.(1) Thetrails, right and left, aremade of steel of channeliron sections. Riveted to the front of each trail is a trailhead, and to the rear end a trail spade. A xle stay clampblocks, movable in the mortises formed by the trail reen-forcement plates, are provided to which the axle stays arehooked when thegun ison wheels. A traversing screw bushing for attachment of the traversing screw through whichthis screw passes when the trails are closed is on each trail.A lso on each trail is a lunette swivel through which therammer is placed when the gun is drawn by hand, and asingletree eye which is used for joining the gun to the cart.(2) Inaddition tothedescription given in (1) above whichis common to both trails, on the left trail are two trail bracechain eyebolts for securing the trail brace to the trail. Ontheright trailarethefront andrear shoulder guard brackets,front and rear sponge staff fastenings, and trail brace locking plate. Thefront and rear shoulder guard brackets carrytheshoulder guard when it is not in position forfiring. Thesponge staff fastenings, front and rear, are for carrying thesponge staff. The rearfastening has a plunger and springwhich hold thesponge staff inplace. Thetrainbrace lockingplate holds the trail brace when the trails are spread.(3) Thefront leg is attached to the pintle socket by twofront leg pins. Two elevations in mounting are possiblethrough provision of two different holes for the lower pin.Attached to the lower end of the leg isthe front leg float, anenlarged bearing surface to minimize sinking in wet orloosesoil when firing from the tripod.(4) The pintle socket affords the central connection between tripod and axle by engaging the pintle socket bearing(by means of the stud formed on pintle socket). To italso is attached the front leg. The pintle socket and trailsform a joint, the three parts being joined together by the

7/30/2019 M1916 37mm manual FM-23-75

8/164

3 37-MM GUN, M1916

pintlebushing which passes through them, formngacommonaxis pin.(5) The pintle, or gun mount, is in the formof a yoke, theupper ends beingfitted to receive the cradle trunnions. Thepintle is projected downward fromthe yoke, formng apivotwhich fits into the pintle bushing. Projecting through thepintle bushing, the lower end is tapped to receive the pintleretaining plug which holds it in place. Thefront legshackleis suspended from the pintle retaining plug to which it isfastened by the front leg shackle screw.(6) The elevating mechanism is supported on the rearend of a Y -shaped frame which is secured to the pintleatitsupper andlower ends. The elevating screw passes throughthe elevating screw nut which is threaded to receive it, andit in turn is pivoted in the elevating screw nut bracket. Elevation is secured by turning the elevating screw handwheelattached to theupper end of the elevating screw.

(7) A n elevating screw nut clamping lever is providedbelowtheelevating screw nut to lock the elevating gear in position. A bove thehandwheel is the elevating screw latchhousing which engages theelevating screwlatchcatchbracketon the under side of thecradle.(8) Traversing is accomplished by lateral movementsof theelevating screw and nut bracket and the Y -shaped frame,the front ends of the latter being securely attached to thepintle carrying the cradle and barrel. In rear of the pointwhere the elevating screw nut pivots, the elevating screwnutbracket forms a fork and engages the traversing screw nuthousing. A traversing screw nut threaded to engage thetraversing screw is placed in the traversing screwnut housing, and may be revolved by a traversing handwheel attached to thenut. This turning causes the lateral movementor traverse as the traversing screw is prevented from rotating by the traversing screw lock located in the right traversing screw bearing.d. Axleand wheels.Theaxle has aspindle at each end towhich the wheels are fitted. At its center on the lower sideis the pintle socket bearing into which the socket stud isplaced whenthetripod is attached to the axle. A naxle coupling pin, attached to the axle by a chain to prevent loss,

7/30/2019 M1916 37mm manual FM-23-75

9/164

37-MM GUN, Ml916 3-4passes through ahole in the socket stud, securing the tripodto theaxle. On either side of the pintle socket bearing anaxle stay is attached. These are hooked into the axle stayclamp blocks on the trails and assist in securing the axleto the tripod. The axle lock which is assembled underneaththe pintle socket bearing fits between the flanges of thepintle socket or may be swung out of engagement with it,and is held in the desired position by inserting the axlecouplingpin on theproper sideof the axle lock stop. Whenthegun is supportedon thewheels in firingtheaxle lock mustbe swung out of engagement with the pintle socket (unlocked) . At all other times, and especially during transportation of thegun on wheels, the axle lock should be engagedwith the pintle socket (locked).

S E C T I O N IIDISMOUNTING A ND MOUNTING, DISASSEMBLING A NDASSEMBLING, OPERATION OP THE PIECE. D I S M O U N T I N G A N D M O U N T I N G (see figs. 1, 2, 3, and 4). a.Dismounting.(1) To dismount cradle assembly from pintlewith gun assembled.Cock thegun. Open the breech. Insert rammer through bore from the breech. Press down ontrunnion cap latches and turn trunnion cap wing nuts tothe front. Grasp rammer with the left handand elevatinghandwheel with theright. Press in on elevating screw latchwith forefinger of right hand and separate elevating screwfrom elevatingscrew latch catchbracket by pushing forwardon the elevating handwheel. By use of the rammer liftbarrel andcradle from the mount.(2) To unlock axle lock.Draw the axle couplingpin upward about 1 inch, pull axle lock forward, and replace axlecoupling pin behindtheaxle lock stop.(3) To remove axle andwheels from tripod.Remove gunandcradle fromthemount. Pull out axle coupling pin. Straddle the trails. Unhook axle stays and raise the frontof thetrails slightly. Remove axle and wheels to thefront, separating pintle socketbearing fromthe socketstud. Lower trailsto the ground gently as dropping them may injure the frontlegshackle.

7/30/2019 M1916 37mm manual FM-23-75

10/164

S HO ULDER GU AR D PIN-S H O U L D ER GUARD PIN C H A I

SPONG E ST AFF FA ST ENINGAXLE STAY C LA MP

R EA R SPONGE ST AF F FASTENING -TRAIL B R A C E LO CKING PLATE

i SHOULDER G U A R D

TRUNNIO N CAP HOUSING -FR ONT LEG PIN CHAIN E Y E B O LT-FRONT LEG PIN-CLIP LOC KING NU T-B A R R EL-

SPAD E AN G LETRAIL BRA CE TONGU E

RIGHTLU NETTE PL AT E

LU NE T T ERIGHT T R A I L

T R A V E R SING SC RE WEL E V A T ING HA ND W HEE LBR EECH LO CK LE V E RTR A VE RSING H A N D W H E E L '"

[-TRAVE RS ING SC RE W NU TBREECH LO C K CA P

BREECH RING

FRONT LEG FLOA TCR ADLEFRONT CAP

ST RIKERTRAVER SI NG SCREW JO URNA L BO XTRAVERSIN G SCREW J O U R N A L BOX CA P

TRUNNION HOUSINGWING NU T

L E F T TRAILTRAIL ST R A P FASTENERTRAIL B R A C E C HA IN EYE BO LTTRAIL ST A G E CHAIN END LINK

SRADE AN G LE P LA TE-TRAIL SP AD ESPONG E S T A F F PL U N G E RR E A R S PO NG E S TA FF FA ST E NING

SP ONGE ST A FF PLUNG ER SPRINGSP ONGE ST A FF PLUNG ER NUTLUNETTE

L UN E T T E SWIVELLUNETTE PIN

TRUNNION C AP-JA C K E TAXLE STAY CLAM P TRAIL REINFOR CING PL A TE -

L S I N G LE TR E E EY ESP AD E A NG LE PL A T E

TRAIL SP AD ELU N E T T E PIN C O LL AR

RIG HT TRAILTRAIL BR A CE

-TRAIL BR A C E C HAIN

RA FSD 1246

F I G U R E 1.Flan view, 37-mm. gun and carriage.

7/30/2019 M1916 37mm manual FM-23-75

11/164

BREECH BLOCK LEVERSHOULDER GUA RDSTRIKER SPRING

STRIKER RO D COLLARSTRIKER RO DSTRIKER RO D NUTJACKETJACKET LOCKING NUTCLIP LOCKING NUTCLIPBARREL

BREECH BLOCKSTRIKER

SHOULDER GUARDPISTON CROSSHEAD KEY

SEAR PINSAFETY BOLT BRACKET SCREW

SAFETY BOLT BRACKETSAFETY BOLT

SEAR

TRIGGER CRANK LEVERTRIGGER STOP SCREW

TRIGGE R STOP PINCAP

FRONT "S" LINKFILLING 8 DRAIN PLUG TH ON GFHJJNG a DRAIN PLU G "S" LINKFILUNG PLU G SEAR PLUNGER SPRINGSHOULDER GUARD STOP

ELEVATING SCREW LATCH CATCH BRACKETPIN

STRIKER ROD NUT SET SCREWSHOULDER GUARD PIN CHAINSTRIKER HOUSING EYEBOLTSHOULDER GUARD PLUGSHOULDER GU ARD PIN CHAINSTRIKER GUARD PINSTRIKER HOUSINGSTRIKER HOU SING SCREW

RA FSD 1203

F IGURE 2.Elevation, sideview of gun and cradle, 37-mm gun.

7/30/2019 M1916 37mm manual FM-23-75

12/164

BARR EL-C RAD LE

LO CKING NU 1OC K1NG NUT

PL UGCAP

DEF LE CTIO N DIAL RANGE DIAL TELESCOPIC SIGHTIB REECH BLOCK

SHOULDER GU ARD -

ELEVATING SCREW LAT CH CA TCH BRACKETTRIGGER CRA NK LEVERELEVATING SCREW LATCH SINGLETREE EYEELEVATING SCREW LATCH HOUSING LUNETTE SWIVELELEVATING SCREW HANDWHEEL REAR SPONGE STAFF FASTENING

TRUNNION CAP LATCHTRUNNION CAPSOCKET STUD

PINTLE SOCKET

FRONT LEG PIN

FRONT LEG

'-TRAIL BRACE CHAIN EYEBOLTSPADE ANGLE PLATE

TRAIL SPAD E

LOWER BRACKET STRUT EYEFRONT LEG SHAC KLE FRONT LEG SHACK LEPINTLE RET A INING

F RO NT LE G FL OAT

L E F T TR A IL- T R A IL S T R A P F A S T E N E R J-E L E V A T IN G S C R E W N U T B R A C K E T-L .H . A X L E S T A Y B L O C K-AXLE S T A Y C L A M P E Y E B O LT-E LE VAT ING S C R E W["A X LE S T A Y C L A M PTT RAIL R E I N F O R C IN G P L A T E

FIG URE3.Side elevation,side view, 37-mmgun.

7/30/2019 M1916 37mm manual FM-23-75

13/164

Jacketandclipconnecting plate Jacket shoe, J ocket BreechnnL

Counterrecoilbuffer

Pistonvalve'

SightclompTelescopicsightTelescopicsibracketghtStrikerhousing

Piston headLONGITUDINAL SECTION

THROUGHAXIS OFBOREOR CENTERLINEOF GUN

BreechringBarre-JacketshoeSlideTrunnon

StrikerShoulderguardbrackeTrunnion

Elevatingscrewlatchcatchbracket

SearTriggercrank

Elevatingscrewlatch catch pinPIGUSE 4.Longitudina section, 37-mmgun.

F iringpinV Firing pinspring

cbr

Pistoncrosshead'istoncrosshead

IkeyRear cap

A,B,Carethecounterrecoil springs1,2 arethecounterrecoilspringseparators

PistoncrossheadkeyPistoncrosshead keylatch-Triggercranklever

Elevatingscrewlatchcatch

7/30/2019 M1916 37mm manual FM-23-75

14/164

4-5 37-MM GUN, M1916

(4) To mount gun on tripod, the gun and tripod beingremoved from axle.Straddle and raise front of the trails.Hold thembetween theknees. Withright hand remove frontleg pin from front leg shackle, allowing the front leg tofall. Lock front leg in position by inserting front leg pin inthe upper opening in bronze housing and through the frontleg. Lower tripod to the ground. Unstrap the trail straps.Spread trails and adjust trail brace by inserting trail-bracetongue in the right trail. Place barrel and cradle on trunnion bearings. Adjust latch housing on elevating screw toelevating screw latch catch bracket, and lock the trunnions.Remove rammer. Close the breech. Uncock the gun.(5) To remove wheels fromaxle.Raiseor block up end ofaxle. Pull down onlinchpin ringand turn thewheel until therecess in hub is in line withhead of the linch pin. Removelinchpinandwasher. Lift off thewheel. Replace thewasherand linchpin.(6) To assemble gun and tripod on wheels, the gun beingmounted on tripod.Remove gun and cradle from tripod.Disengage trail brace from right trail and place it on theleft. Pull down on traversing screw lock ring and close thetrails. Strap trails together by means of the trail strap.Straddle and raise front of the trails. Grasp trails betweenthe knees, withdraw front leg pin frompintlesocket, and foldback the front leg. Secure front leg in front leg shackle bymeans of the front leg pin. Insert stud of the pintle socketinto pintle socket bearing, hook axle stays, lock axle lock,and insert axle coupling pin into socket stud. Replace gunand cradle on the mount.& . Mounting.The operation of remounting may be accomplished by reversing the order of dismounting.. D I S A S S E M B L I N G A N D A S S E M B L I N G . ! a. To remove breechblock and extractor frombreech ring.Cock the gun. Pushextractor pin to the right witha finger of left hand. Removeextractor pin to the right. Press in on breechblock lever release pin cap and remove breechblock lever. Place thumb ofright hand in the port of breechblock, and left hand, palmup, under breechblock. Unscrew breechblock by turning itto the left. Lift extractor from its seat.

10

7/30/2019 M1916 37mm manual FM-23-75

15/164

37-MM GTTN , M1916 5-6b. To replace extractor and breechblock in breech ring.

Replace extractorin its seat in breech ring. Cock thegun ifit is not already cocked. Screwbreechblock into breechring.Replace breechblock lever. With left handbelow breechring,raise extractor and with right hand return extractor pinfrom right to left. Uncock the gun.c. To remove bajrrel from cradle. (1) L evel barrel by elevating screw. Cock the gun. Open the breech. Uncockthegun. Press upon piston cross headkeylatchwith thumband index finger of right hand, and remove piston cross headkey to the left. Insert rammer through thebore from thebreech and remove barrel to rear, being careful that thebronze shoes do not become damaged by allowing the rearend of barrel to bear down. To overcome any possibilityof damage to the shoes, it is advisable that two men removethe barrel.(2) To replace thebarrel reverse theorderof dismounting,exercising necessary care to insure the sear being returnedinproper relative position with trigger crank andsafety bolt.d. TO remove striker and strikerspring from) striker housing. (1) Depress muzzle of barrel slightly. Remove pistoncross headkey. Slide barrel to therear about 7 inches. Pushstriker to its complete forward position, loosenstriker rod nutset screw, and unscrewnut from striker rod. Allow spring toexpand slowly andpull outstriker andstriker spring.

(2) Td replacestriker andstriker spring, reverse theorderof dismounting.e. To disassemble breechblock. (1) Remove breechblockfrom breech ring. Remove rocker pin by drawing it towardcenter of theport. Lift out rocker. Placehand over rockerseat and turn the breechblock over, allowing the rockerplunger, firing pin, andfiring-pin spring to drop out.(2) To assemble the breechblock reverse the order of disassembling.. O P E R A T I O N . a. To cock gun.Place palm of the handagainst thestriker andpush it forward quickly until head ofsear engages in cocking notchof striker. Cocking by hand isnecessary only for thefirst round.b. To uncock gun.Close breech if not already closed.Place palm of left hand against striker, press on trigger

11

7/30/2019 M1916 37mm manual FM-23-75

16/164

6-7 37-MM GUN, M1916crank lever with thumb of right hand, and allow striker tocome back gently.c. To open breech.Cock the gun. Rotate breechblock bymoving breechblock lever to the left until itmeets the shoulderwhich limits movement of opening.d. To close breech.Rotate breechblock by moving breechblock lever to the right until it meets the shoulder whichlimits movement of closing. The hand must be kept onthe breechblock lever until the lever comes in close contactwith the shoulder which limits movement of closing in orderto avoid any return movement of thebreechblock.e. To load.Open thebreech. Insert around into chamberby grasping it by the base, placing it in the port in breechblock and pushing it into the chamber with thefingers. Closethebreech./. To unload.Open the breech smartly. Opening of thebreech causes extraction and ejection of the cartridge case.

SECTION IIICARE AN D CLEANING

. C L E A N I N G . a. Bore, chamber, and breech ring.Ordinary cleaning after firing using waste or rags includes thefollowing procedure. Remove breechblock. Thoroughly sluiceand sponge bore and chamber with either hot water and issuesoap, sal soda solution, hot water alone, or in the absence ofthese with cold water. Then with dry waste or rags swabbore and chamber until they are perfectly dry and clean.Finally oil parts lightly, making certain that the oil covers allsurface of thebore. This cleaning should be done as soon aspracticable after firing. If the gun is not to be fired forseveral days a daily inspection should be made to determinewhether further cleaning is necessary. The interior of thebreech ring should be cleaned and then wiped with an oilyrag. If the gun is to be stored for an appreciable period aheavy grease, such as rust-preventive compound (U. S. ArmySpec. No. 2-82B), should be applied as a preservative.b. Breechblock.Remove breechblock from breech ring anddisassemble it. With a dry rag clean dirt and oil from theblock and all parts contained therein. Using light oil, lubri-

12

7/30/2019 M1916 37mm manual FM-23-75

17/164

37-MM GUN, M1916 7-8

cate recesses for firing pin, rocker, and rocker plunger.With an oily rag wipe thebreechblock, leaving athin coatingof oil, especially on threads and face of the block.c. Extractor and sear.Remove extractor and sear fromthe gun, and clean and oil by wiping thoroughly, first witha dry and then with an oily rag. Oil recesses for theextractor pin and sear plunger before replacing these parts.d. Outer surfaces of gun.Clean theouter surfaces, thendry and wipe all exposed metal parts with a lightly oiledrag. Oil interior of the striker housing. Place a drop ofoil in recesses for the striker and the safety bolt.e. Tripod.Clean outersurfaces, including mortises of axlestay clamps and the holes through which the traversing screwpasses. Oil lightly trunnion bearings, pintle bushing, socket,stud, bearings of traversing screw, traversing screw, traversing screw plunger, elevating screw latch housing, elevatingscrew nut, and elevating screw./. Axle and wheels.Using asponge, wash with water toremove dirt and other fouling that gathers during transportation. Oil pintle socket bearing lightly. Grease axlespindles at intervals to suit circumstances, insuring that theyare properly lubricated at all times.g. Guides, jacket shoe, and clip shoe.Remove barrel fromcradle. With a cloth wet with dry-cleaning solvent, cleaninner surfaces of guides and outer surfaces of shoes, thendry the parts. Grease liberally with a heavy oil and reassemble. This will be necessary only in sandy country orunder other unusual circumstances.. S PE C I A L P R E C A U T I O N S D U R I N G U N U S U A L C O N D I T I O N S . a.Cold weather.The gun should be tested frequently byhandmanipulation to insure thatit is functioning properly.o. Gas attack.lidson ammunition chests should be closedand if practicable aheavycoating of thick oil applied to thebore and working parts of the gun. Directly after gas attack the gun should be thoroughly cleaned, usinghot watercontaining a little soda if obtainable. A mmunition shouldbe wiped with an oily rag and fired as soon as tactical conditions permit. A mmunition that has been subjected to gasaction should be inspected very carefully and thoroughlybefore firing.

216513402 13

7/30/2019 M1916 37mm manual FM-23-75

18/164

9-10 37-MM GUN, M19169. P I L L I N G R E C O I L C Y L I N D E R O F C R A D L E . a. The recoil cylinder has a capacity of about 2.75 pints of oil. It mustbe kept properly rilled in accordance with the following instructions, or damage to the gun will probably result. TheOrdnance Department will furnish the proper grade of oilfor recoil cylinders. The following specification is used:Oil, recoil,heavy, U. S. A rmy Spec. No. 2-36C. The substitution of any filler other than that issued by the OrdnanceDepartment is prohibited.6. To fill the recoil cylinder, proceed as follows:(1) By means of the elevating screw depress the muzzleas far as possible.(2) Fill oil gun with oil . (Unscrew cap with muzzle attached, draw piston back to its full extent, fill cylinder, screwon cap with nozzle attached, and with nozzle pointing upward push in piston until oil starts to flow in order to forcetheair out of the oil gun.)(3) Unscrew fillingplug in front end cap of recoil cylinderand screw nozzle end of oil gun into position in its stead.(4) Unscrew drain plug.(5) Introduce oil into recoil cylinder by slowly pushing inpiston of the oil gun, and continue until the oil escapingthrough the drain hole (from which the drain plug wasremoved) no longer carries airbubbles.(6) Holding a finger over the overflow hole to preventrapid escape of oil, unscrew oil gun, and allow about 1spoonful (spoon issued with mess equipment) of oil to escape.(7) Screw both plugs tightly in place.0. P R A C T I C E S To BE A V O ID E D I N U SE A N D O P E R A T I O N O F GUN.a. Snapping trigger mechanism when chamber is empty.b. Pressing trigger crank lever, thebreech not being completely closed.c. Rotating or attempting to rotatebreechblock, gun beinguncocked.d.Putting astrain on the shoulder guard, either in carrying the gun or by leaning on it while getting into or out ofgunner's position on left trail.

e. Putting a strain on elevating handwheel by allowingrear end of cradle to drop, or to rest on it when elevatingscrew is unlatched from elevating screw latch catch bracket14

7/30/2019 M1916 37mm manual FM-23-75

19/164

37-MM GUN, M1916 10-13in removing thegun from the mount. Thematerial ofwhichthe handwheel is made is quite brittle and will not standrough handling.

SECT ION IVFUNCTIONING*

1. A C T I O N O F T R I G G E R A N D S E A R IN FIRING.Downwardpressure on the trigger crank lever causes a rearward motion of the trigger crank. The lower arm of the sear is incontactwith thetrigger crank, hencemoves rearward with it.Thesear being pivoted near its upper portion, this rearwardmovement of the lower arm forces the sear head down outof contactwith thecocking notch of thestriker. This downward movement also compresses the sear spring. Pressureon the trigger crank lever should be released when the gunfires.2. A C T I O N O F F IR ING MECHANISM.The firing mechanismconsists of the striker spring, striker, rocker plunger, rockerandrocker pin, firing pin,andfiring-pin spring. The firingmechanism operates when thestriker is released by the searhead. The compressed striker springdrives thestriker to therear about 1 inchwhere it delivers a sharp blowagainst therocker plunger, theforce of which is transmittedto the rockerand through the rocker to the firing pin. The firing pin isdriven forwardcompressing thefiring-pin spring, andstrikingand igniting the primer of the cartridge.3. A C T I O N O F S A F E T Y BOLT.The safety bolt seated in abracket on the left side of the breech ring engages the lowerarmof the sear. The breechblock cap contacts the rear endof the safety bolt and is notched to permit the safety boltto move to the rearwhen the breech is completely closed.The firing pin is eccentrically mounted to permit it to bebrought inline with the primer of the cartridge only whenthebreech is completely closed. Therefore, the sear canrelease the striker to cause discharge only when the breech iscompletely closed.

"The explanation of functioning begins withthe gun supposedlyloaded and cocked.15

7/30/2019 M1916 37mm manual FM-23-75

20/164

14-15 37-MM GUN, M19164. A C T I O N IN RECOIL. a. A ction of thepowder gases on thebreechblock at the moment of discharge causes the recoilof theunited barrel andbreechblock, driving themrearwardadistanceofabout 8 inches.b. The bronzeshoes attached to thebarrelslide in the steelguides attached to the cradle, compellingproper direction ofrecoil.c. Thefiring-pin spring returns the firing pin, rocker, androcker plunger to position when therocker plunger moves tothe rear away from the striker.d. The sear, a recoiling part, moves away from the striker,anonrecoiling part,permittingthesear headunder theactionof the sear spring to rise behind the cocking notch of thestriker.e. Recoil is resisted, its speed regulated, and movementstopped by action of the recoil mechanismwhich is attachedto the recoiling parts by the piston cross head key. Twoforces resist the movement: The strong counterrecoil springis compressed, and themovement of the piston head is resisted by the oil inthe cradle. The oil follows two courses asIt flowsto the front of the pistonhead:(1) It passes through the hollow portion of the forwardendof the piston rod.(2) It forces thepiston valve open against the resistanceof thepiston-valve spring and flows through theholes in thepiston head.5. A C T I O N O F CotnsrTERRECoiL. a. Recoil being stopped, therecoiling partsare instantly moved forward by pressure of thecompressed counterrecoil spring against the piston head.ft. The piston valve actuated by the piston-valve springcloses the holes in the piston head just before counterrecoilstarts. Therefore the speed of counterrecoil is regulated bytherateatwhich theoil in thecradle flows throughthehollowportion of theforward end of thepiston rod.c. The final movement of the returning parts is graduallystopped and shock to thegun prevented by the action of thecounterrecoil buffer which progressively closes the hollowportion of thepiston rod through which theoil must flow.

1 6

7/30/2019 M1916 37mm manual FM-23-75

21/164

37-MM GUN, M1916 15-17

d. A s the recoiling parts return to battery the sear carriesthe striker forward, compresses the strikerspring,and automatically cocks the gun. To permit this action to occur thethumb mustbe removed from the trigger crank lever as thegun fires.6. E X T R A C T I O N A N D E J E C T I O N O F C A R T R I D G E C A SE .T he extractor seated in the breech ring is pivoted near its lowerend on theextractor pin. When the breech is opened by rotating the breechblocksmartly to the left,the extractor camon the face of the breechblock strikes the heel of the extractor, depresses it, andcauses theupperarmof theextractorto rotateto therear. The upperarmof theextractor engagedin front of the rim of the cartridge case extracts the emptycase and ejects it from the gun.

SECT ION VDEFECTS A ND STOPPAGES7. D E F E C T S A N D STOPPAGES. Defects andstoppages do notoccur with sufficient frequency to warrant a special form ofdrill in remedyingthem. They are listedherein for information. Such instruction will be given the soldier in theirnatureandtheactionnecessary to remedy themas will insurethe most efficient operation of the gun.a. When breech cannot be opened and inspection discloses

that gun is not cocked. (1) Causes. (a) Failure to releasepressure on trigger crank lever whenthegun fires.(& ) Worn or broken sear, or weak sear spring.(2) Action to remedy.Cock the gun. Caution firer to release pressure on trigger crank lever when the gun fires. Ifthegun will not cock, replace defective part.b. When breech cannot be opened and inspection disclosesthat gun is cocked. (1) Causes. (a) Firingpin is engaged. in primer because of a weak or broken firing-pin spring orburred or dirtyrocker mechanism.(& ) Piston cross headkey has notbeen inserted fully withthe result that the safety bolt is not withdrawn from notchin breechblock cap.

17

7/30/2019 M1916 37mm manual FM-23-75

22/164

17 37-MM GUN, M1916(2) Action to remedy. (a) Withdraw safety bolt from

notch in breechblock cap and insert piston cross head keyproperly.(b) Tap with some soft object on the protruding part ofrocker andwork breechblocklever until firing pincomesloose.This failing, insert rammer into bore from muzzle and tapempty cartridge case. If this is noteffective, remove rockerandattemptto withdraw firing pin. A s a last resort, breakoff firing pin by forcing the breech open, replace defectiveparts, and cleanand oil rocker mechanism. If the rockermechanism is burred, smooth carefully with a fine file oremery paper.c. When gun fails to eject empty cartridge case. (1)Causes. (a) Failure to open breech smartly.(b) Defective ammunition.(c) Broken or worn extractor.(d) Dirty chamber.

(2) Action to remedy.(a) Close breech and open smartly.(b) If this isnot effective, remove the empty case with therammer by inserting therammer through the bore from themuzzle; thehandextractor also may be used to remove roundsor empty cartridgecases fromthechamber.(c) Replace extractor if necessary.(d) Clean chamber thoroughly.d. When gun fails to return completely into battery.(i)Causes. (a) Dirty or burred slidesor shoes; lackof grease onslides for shoes.(b) Expansion of oil in recoil cylinder because of overheating.(c) Weak counterrecoil springs.(2) Action to remedy. (a) If necessary to continue firing,pushthe gun forwardinto batteryby hand. When necessityforfire ceases, clean and grease shoes and slides. If burred,smooth them carefully with a fine file or emerypaper.(b) If shoes or slides are not dirty or burred, unscrew filling plug and allow about a spoonful (spoon issued with messequipment) of oil to escape.(c) Should the above remedies be ineffective, the gunshould be returned to theOrdnanceDepartment for repair.

18

7/30/2019 M1916 37mm manual FM-23-75

23/164

37-MM GUN, M1916 18SECTION VI

INSTRUMENTS AND ACCESSORIES8. F I E L D G L A S S , TYPE EE.a. Description. (1) The fieldglass, type EE (fig. 5), is an observation instrument of 6-power with an 8 field of view. It contains a graduated milscale for the measurement of small horizontal and verticalangles. In field glasses of older manufacturean invertedsightleaf scale is also provided for the rapid computation of certainfire data. The field glass complete consists of the glassand its carrying case and neck strap.(2) Thefield glass proper consists of two compact prismatictelescopes pivoted about a common hinge which permits adjustment for interpupillary distances. A scale graduatedevery2 millimeters from 56 to 74 permits the observer rapidly toset the telescope to suit his eye distancewhen thespacingofhis eyes isknown. The eyepiececan be focused independentlyfor each eye by screwing in or out. Each is provided witha diopter scale for rapid setting when the observerknows thecorrection for his eye. The zero graduations indicate thesettings for normal eyes.(3) The left telescope is fitted with a. glass reticle (figs. 6and 7) uponwhich areetched avertical mil scale, ahorizontalmil scale, and on field glasses of older manufacture, a stadiascale graduated similar to thesight leaf graduationon theservice rifle, but inverted.6. Use.The field glass is used for observations and themeasurement of small horizontal andvertical angles in mils.The inverted sight leaf, when provided, is used to pick upauxiliary aiming points in direct laying and to determinetroop safety for overhead fire.

c. Adjustments.(1) Interpupillary distance.To adjustthe glass so that the eyepieces are thesame distance apartas the pupils of the observer's eye, point the glass at the skyandopen or close the hinged joint until the field of viewceases to be two overlapping circles and appears to be onesharply defined circle, then note the reading on the scalewhich indicates the spacing of the observer's eyes. Similarsetting of any other field glass will then accommodate hiseyes.19

7/30/2019 M1916 37mm manual FM-23-75

24/164

FIGURE5FedgatyEE,

7/30/2019 M1916 37mm manual FM-23-75

25/164

F IGURE 6.Reticle on field glasses of older manufacture.

.COSCHAMFER .CIS CHAMFER. AT 45*

.o7ie'.ooio(3 - EO uw .

F IGURE 7.Reticle on field glasses of recent manufacture.21

7/30/2019 M1916 37mm manual FM-23-75

26/164

18-19 37-MM GUN, M1916(2) Focus of eyepieces.Look through the glasses, both

eyes open, at an object several hundred yards away. Placethe hand over the front of one telescope and screw the eyepiece of theother in or out until the object is defined sharply.Repeat this operation for the other eye, then note readingon each diopter scale. Similar reading of any other fieldglass will accommodate the same eye.d. Operation. (1) In using the glass it should be held inboth hands, lightly pressed to the eyes so as to keep therelation with the eyes constant but not so as to transmittremors of the body. The bent thumbs may cover the cornersof the eyes to exclude light except that which enters theglass through the lenses. When possible, it is best to use arest for the glass or to rest the elbows on some solid object.(2) The mil scales are seen when looking through theglass and by superimposing them on any objects, the horizontal and vertical angles between these objects may be read.(3) The inverted sight leaf scale is used to secure rangesettings on sharply defined auxiliary aiming points when thetarget is not clear enough for direct aiming.e. Care.The field glass is a rugged, serviceable instrumentbut it should not be abused or roughly handled. Care shouldbe taken not to scratchor mar the lenses.9. L E N S A T I C C O M P A S S , M O D I F I E D P R I S M A T I C TY PE. a. Description.This compass is an instrument of unusual flexibilityand precision when properly used. Ithasapivoted dialneedle inclosed in a nonmagnetic metal case with a hingedcover and an eyepiece containing a small magnifying lens.The needle dial has inscribed on it two azimuth circles of6,400 mils, one with its zero at the north point for use inreading the face of the compass, the other with its zero atthesouth point for use in reading azimuth through the eyepiece (fig. 8). The least reading of the compass is 20 mils.Owing to the sensitive character of the needle suspension,even this accuracy is difficult to obtain unless the compassrests on a solid support. One outside ring about the baseof the compass is graduated into the cardinal points of thecompass and another as an azimuth circle. The former isuseful for taking bearings and the latter is useful on a mapas a protractor and in setting off azimuth by means of the

22

7/30/2019 M1916 37mm manual FM-23-75

27/164

37-MM GU N, M19I6 19index on a movable ringabout the top. Directions are laidoff by means of the index (pointer) on this movable ring.The indexon themovable ring, the zeropoint on theazimuthcircle on the dial, and the north point of the needle aremarked with radiolite for visibility in the dark. The eyepiece consists of a metal standard supporting a small lensthrough which azimuth may be read directly from the outerdial circle. Vertically above the aperture of the standardis anarrow slit. Verticallyacross the glass face of the compass cover is an etched line in the line of collimationof theinstrument.& . Use. (1) Thechief use of thelensatic compass, modifiedprismatic type, withthegun is themeasurement of magneticazimuths. Itmay also be used as amarching compass.(2) If practicable, the compass should be restedon a levelsurface. However, it can be read accurately when held inthe hands, the ring between thumb and forefinger of onehand, theother fingers closed, with thumband forefinger oftheotherhandgraspingthecompass box and theother fingersclasping the other hand, elbows close to the body or restingon theknees, dependingon theposition of theobserver.(3) The instrument should be held as nearly level aspossible to permit thedial to swing free, otherwise errors inthe readings willresult.c. Operation of compass. (1) To decimate compass.(a)Select some point located on the map from which severalpoints can be seen, the gridY azimuth of which can be determined from the map. M easure the magnetic azimuths(readings from magnetic north) to each of the points andcompute the differences betweenmagnetic azimuthsas measuredby theinstrument and the grid Y azimuth taken fromthemap. Theaverage of these differences will be thedeclination constant for that particular compass. Record the valueof the constant for ready reference. If the compass is to beused inanother locality 6 miles ormore distant, the declinationconstant should again be determined for thenewlocality.(b) In determining the declination constant it is best toselect three points, one of which should be at least 2,000mils from one of theother points.

23

7/30/2019 M1916 37mm manual FM-23-75

28/164

C

EEEE

MAGFNLE

RING

AMHHCRE

N

EDA

EC

LN

CAMP

,N

EDARE

FIGURE8Laccm

mfepsmcty

B

he gets_ 20=17 mils, the angle of site to be applied on thesight.1 2If a map is being used in computing data the angle of sitecan be computed by the mil formula M equals ', inRwhich M is the angle in mils, W is the difference in yardsin elevation between gun and target, andR is therange gun-

97

7/30/2019 M1916 37mm manual FM-23-75

102/164

88-90 37-MM GUN, M1916target. Theangleof site of atarget is a plus, aminus, or azeroangle of site, depending on whether the target is above,below, or on the same level as the gun. Except for computing of very accurate data an angle of site of 5 mils orless is disregarded.9. D E T E R M I N A T I O N O F R A N G E . Range inmost cases is estimated by eye. Itmaybe determined by using a range finderif one is available, or may be determined from amap or byplotting. The more elaborate methods of determining rangeareslow andseldom of use in thefield.0. L A Y I N G GU N F O R E L E V A T ION.The quadrant sight is soconstructed thattheQE of the target is computed mechanically. The procedure of laying the gunis as follows:a. Set angle-of-site dial at the angle of site of target.b. Set range dial with the graduation corresponding torange to the target opposite index on angle-of-site dial.c. Center bubble in level vial by manipulating elevatingmechanismof thecarriage.Discussion.Assume that a target hasan angle of site ofplus 10 mils and is ata rangeof 1,000 yards. The gun mustbe laid with a QE equivalent to 10 mils plus 1,000 yards.When the angle-of-site dial is set at plus 10 mils, its indexis moved to the left. No otherpart of the sight is movedby this setting since the angle-of-site dial is a free movingpart. When the 1,000-yard graduation on the range dial isset opposite the index on the angle-of-site dial, the levelvial is moved through an angle which is the sumof the angleof elevation equivalent to1,000 yards and10 mils. The sumof the two angles in this case is (38 plus 10) 48 mils. Whenthe bubble is centered as described in c above, the barrel iselevated 48 mils above the horizontal. Had the angle ofsite beenminus 10 mils and the angle-of-site dial set accordingly, its index would have moved to the right. When the1,000-yard graduation of the range dial is set opposite theindex of theangle-of-sitedial, the level vial is moved throughanangle of (38 minus 10) 28 mils. When thebubble is centered by manipulating the elevating mechanism the barrelis elevated 28 mils above thehorizontal.

98

7/30/2019 M1916 37mm manual FM-23-75

103/164

37-MM GTTN, M1916 911. M IN IMUM RANGE.a. Definition.Minimumrange istheleast range settingatwhich theprojectilewill clear the maskwhenthe gun is fired from a given position on a target witha given angle of site.b. Practical application.(1) To determine theminimumrange when the gun isfirst put in position the gunner mustexecute the following steps:(a) Set range dial at the range to the mask with angle-of-site dial at zero.

(b) By turning elevating handwheel lay the gun so thatthe horizontal cross line of the collimator just clears thetop of the mask.(c) By turning range dial center bubble.(d) Set angle-of-sitedial at the angle of site of the target.Read minimum range on the range dial opposite index onangle-of-site dial and announce minimum range to the guncommander.(2) The minimum range having been determined to beless than the range to the target, the gun commander thenissueshis fireorder for indirect layingandproceeds to engagethe target. When a target has an angle of site less than 5mils, the angle is disregarded (except when data are veryaccurately computed) because it is extremely difficult foran observer to measureanangle of sitewithin 5 mils withoutinstruments.(3) When changing from one target to another, the gunposition not being changed, no change ismade in the settingof the angle-of-site dial unless there isa differenceof morethan 5 mils between the angles of site of the two targets.When a new target is selected in the same direction as theprevious target and the difference between the anglesof siteis greater than 5 mils, the gunner determines the minimum

rangeas follows:(a) Set angle-of-site dial at thesetting forprevioustarget.(b) Set range dial at minimum range for previous target.(c) Turn angle-of-site dial to the angle of site of newtargetandread minimumrange.Discussion.When 'a mask suchas ahill, wood, or heavybrush intervenes between the gun and target it is necessaryto know whether the gun can fire over the mask and engage99

7/30/2019 M1916 37mm manual FM-23-75

104/164

91 37-MM GTJN, M1916the target. A ssume agun to be firing over a crest so thatthe projectiles will barelyclear thecrest without consideringthe gun as engaging any particular target. The trajectorymay be considered fixed since thepiece is fired witha fixedelevation (the one which barely clears the crest), andtheprojectiles continue their flight beyond the maskuntil theystrikethe ground (fig. 1 4 ). Thepoint at which they willstrike the ground depends on the height of the ground,whetherthe ground rises, falls away, or is level. The slopeof the terrain fixes theslope of the line of site which is expressedby theangleofsite. When aparticular target is engaged, theangle of site to beused is involved in the determination of whether or not amask can be cleared because theangle of site is in reality the elevation of the target withrespecttothegunandinvolves the slopeof theterrain beyondthemask. Itcanthenbe said that thedistance fromthegunto theintersectionof this lowest trajectorywith thelineof siteis theleastrangewhichcanbe used fromthegiven gun positionwith thegiven angleof siteandhavetheprojectileclearthemask. Figure14 , @, and illustrates theeffect whichtheslope of the terrain beyond themask has on this leastrange. If it is -known what elevation is required to clearaparticular mask, then in reality it is knownwhether or notany given elevation willclear themask. Whenindirect layingis employed,thepiece is laidby theapplication of theangle ofsiteand the rangerather than by thedirectapplicationoftheQE. Therefore the elevation required to clear amask shouldbe obtainedinterms of range and angle of site. These twoquantities are dependent on each other for their values inmaking up a given QE. For convenience one of them, theangleof site, is fixed for agiven target. This is done bydeciding touse a certain angle ofsite (the angle of site of thetarget being engaged) and thenproceeding to determine therangewhich coupledwith this angleof sitewill give thepiecetheproper elevation to cause the projectilejust to clear themask. In theoperationof determining this leastrangewhichwillclearamask thepieceis laid so thataroundiffiredwouldjust clear themask (1) (b) above. Then by manipulating thequadrant sight (centeringbubble and setting angle of site)the elevation given thepiece is measured interms of yards

100

7/30/2019 M1916 37mm manual FM-23-75

105/164

Target

Target

FIGURE 14.Minimumrange.101

7/30/2019 M1916 37mm manual FM-23-75

106/164

91-92 37-MM GUN, M1916on therangedial. The reading found on therange dial afterthis operation is what is called the minimum range. If thisrange is less than the range to the targetthetargetcan beengaged. The gun can be given additional elevation abovethatnecessary to clear themask (fig. 14 ). If theminimumrangeis greater thantherangetothetarget thetargetcannotbs engaged (fig. 14 ). The gun cannot be given an elevationbelow thatrequired to clear themaskbecause alowerelevationwill probably cause the shell to burst on the mask. Inthis case it will be necessary to move the gun to a positionwhere the minimumrange will be less thanthe range to thetarget.

c. Precautions during firing.When the minimum rangehas been determined thegun has the least elevation whichwill permit a projectile to clear the mask. It is mandatorythat the gun commander exercise the greatest care that hedoes not order a range setting which is less than the minimum range. If he does order such asetting the gunner willinform him that the range he has ordered is less than theminimumrange.Example.Theminimumrangehasbeendetermined as 650yards. The first round fired with asightsettingof 750 burstsbeyond the target. The gun commander, being intent onbracketing, orders a setting of 550 for thenext round. Thegunner informs him thatthe minimum range is 650. Thegun commander then orders a roundfired with a range setting of 650. If thisround bursts beyond the target it is necessary that the gun be moved to a new position.92. USE O F T E L E S C O P I C S I G H T IN I N D I R E C T L A Y I N G . a. Calculation of firing data.Since the telescopic sight is notequipped with an angle-of-site dial or spirit level theQE isnecessarily calculated by the gun commander. With thequadrant sight thiscalculation is unnecessary as the dataare computed mechanically. To determinetheQE to be usedproceed asfollows: Estimate therange to the target. Referto the range table and determine the angle of elevationwhich corresponds to the estimated range. Measure theangle of site. A dd algebraically the angle of elevation andthe angle of site. The result is the QE in mils. A gain referto the range table anddetermine the range in yards which

102

7/30/2019 M1916 37mm manual FM-23-75

107/164

37-MM GUN, M1916 92

corresponds tothis angle. This is the range to be set offonthe sight when thegunis laid.Examples:No. 1.The range to the target is estimated to be 800yardsand the angle of site is plus 10. The range table showsthe angle of elevation for 800 yards is 28 mils. Inthis caseboth the angle of elevation and the angle of site are positiveangles. A ddtheangleof elevation (plus 28) and theangle ofsite (plus 10). The sum is 38 mils which is the QE in mils.Toconvert this to yardsrefer to the range table which showsthat38 mils is the angle of elevation for 1,000 yards. Whenthegunis laid set off 1,000 on therange dial of thesight.No. 2.A ssume the estimated range to the target to be1,000 yards and the angle of site tobe minus 10. The rangetable shows that the angle of elevation for 1,000 yards is 38mils. Inthis casetheangle of site is anegative angle. Thealgebraic addition of the two angles gives a QE of 28 mils.Therange table shows that 28 mils is the angle of elevationfor 800 yards. When the gun is laid set off 800on therangedial of the sight.

& . Laying gun.The telescopic sight can be used in indirect laying though its use in this manner is purely anemergencymethodandisordinarily resorted toonlywhen thequadrant sight is lost or broken. In using this sight it isnecessary that thehorizontal be determined in order that theQE may be measured therefrom. This result is obtained bymeansof aplumb line, thegun, and astake. Therear faceofthe breechblock cap of the gun forms a right angle withthe axis of the bore. Therefore when the rear face of thebreechblock cap is vertical, the axis of the bore is horizontal.To lay the gunproceed as follows:(1) Lay gun for direction.

(2) Hold aplumb line (whichcan be madeby tyingastonetopiece of string)against therear faceof thebreechblock capand raise or lower barrel by turning elevating handwheeluntil the rear face of the breechblock cap from top tobottom is in contact with the plumb line when the line isvertical. The rear face of the breechblock cap will then bevertical and the barrel will be horizontal.103

7/30/2019 M1916 37mm manual FM-23-75

108/164

92 37-MM GUN, M1916(3) Set range dial at zero. When the sight is at zero

the line of sighting is parallel to the bore. When the sightis at zero and the barrel is horizontal the line of sighting isalso horizontal.(4) Set out an aiming stake in front of the gun in suchposition that it is visible in the field of vision of the sightand slightly to the left of thevertical linewhen the deflectiondial is at zero. Turn deflection dial until the vertical lineis in line with the stake. The stake is set to the left toprevent the projectile striking it. It may be set to the rightbut left is preferable.(5) Mark thestakewherethe lineof sightingasestablishedby the horizontal line of the sight intersects the stake. Thismarks the horizontal.(6) Set off on range dial of the sight the range determinedin the calculation of firing data. Bring the intersection ofthe cross lines on themark on the stake by turning elevatingand traversing handwheels. Since the gun has previouslybeen laid for direction the movement of the traversinghand-wheel is slight, being merely enough to bring the intersectionof the cross lines on the mark on the stake after the rangehas been set off on the range dial.c. Determning least QE which will safely clear mask.After the mark denoting the horizontal has been made onthe stake as described in b (2) above, the least quadrantelevation which will safely clear a mask may be determinedas follows:(1) Set off range to mask on rangedial.(2) Lay the gun by means of the elevating handwheel sothat thehorizontal line of the sight just clears the top of themask.(3) Turn range dial until the horizontal line of the sightis alined on the mark on the stake.(4) Bead range on the range dial. This reading expressesin yards the least quadrant elevation which can be used andhave the projectile clear the mask.

104

7/30/2019 M1916 37mm manual FM-23-75

109/164

37-MM GUN, M1916 93

SECTION inOVERHEAD FIRE

3. GE NERAL. Since it will rarely be possible to firethrough gaps in our own line, much of the support accordedto our troops is of necessity overhead fire; that is, fire directed over theheads of friendly troops. After considerationhas been given to those factors which enter intoall firingand which make it improbable or impossible for all shots tohit the exact spot desired, it is possible to lay down certainrules under which overhead firecanbeemployed withsafety.Conversely, these rules determine when such fire is unsafeand is not to be employed. The factors to be taken intoconsideration to insure that all shots clear the heads offriendly troops are enumerated in order to show howsafetyrules are determined.a. Dispersion of shot group.(1) A ll other factors beingdisregarded, every shot does not followthesame path, due toerrors in elevation of thegun, variations in the manufactureof ammunition and gun, condition of gun, and atmosphericconditions. These variations have been determined by testand thevertical and horizontal dispersion of the cone tabulated for all ranges. In addition to dispersion of the shotgroup whichmaybeclassed as mechanical, it is alsonecessaryto consider the human element; that is, errors made by thegun commander in determning thefollowing:(a) Rangeto target.(b) Range to troops.(c) Vertical interval between gun and target.(d) Vertical intervalbetween gun and troops.(2) If fire is adjusted, errors (a) and (c) are eliminatedand (b) and (d) are greatly reduced since a gage for comparison isavailable in the target itself.b. Safety clearance.To insure safety of friendly troopsit is necessary tohave sufficient clearance between the lowestshot and theground to allow for errors in range estimation,for theheightof themen, for slight inequalities in the surface of the ground, and for an ample margin of safety. Atable has been prepared which takes these factors into consideration and gives for each range minimumclearances of

105

7/30/2019 M1916 37mm manual FM-23-75

110/164

93-94 37-MM GUN, M1916the mean trajectory. For convenience these clearances areexpressed in terms of the angles they subtend at the gunand are known as safety angles. Going a little further andassuming gun, troops, and target to be on thesame straightline, if the angle of elevation of the range to thetroops beadded tothesafetyangle theresultwill be theminimum angleof elevation permissible when the troops are at the rangeindicated. This angle of elevation may be converted to arange in yards which is the least range permissible.4. O V E R H E A D FIRE WITH D I R E C T L A Y I N G. D irect overheadfire is that overhead fire which is delivered by employmentof direct laying. Two distinct situations arise in delivery ofdirect overhead fire. One is where troops are stationary asin adefensiveposition, theother is where troops are advancing as inattack. Each situation requires a different methodto determne whether overhead fire can be delivered and forwhat length of time.a. Troops not advancing.(1) Determne range to friendlytroops.(2) Find this range in column 1 of overhead fire table(par. 98).(3) Find corresponding range on the same line in column3 of overhead fire table. This will be the leastrangeatwhichit is permissible to fire overthe friendly troops inthepositionthey are occupying at the time.b. Troops advancing. (1) Determne range to target.(2) Find this range in column 3 of overhead fire table.(3) Find corresponding range in column 1 of overhead firetable. This will be the range to which friendly troops canadvance safely, and when they reach this range fire mustcease or be lifted.c. Rule of thumb.(1) In cases where fire-control tablesare not accessible the following rule of thumb based on theoverhead fire table may be used:(a) Set range dial at range to the target and lay gun onthetarget.(b) Increasesight setting by 500 yards.(c) Look through the sight and note point where the lineof aim strikes the ground. If this point is ahead of thefriendly troops it is safe tofire.

106

7/30/2019 M1916 37mm manual FM-23-75

111/164

37-MM GUN, M1916 94-95(2) Dueto the fact thatthe greatest range graduation onthetelescopic sight is 2,000 yards, this method is limited inapplicationand should be usedonly in case no fire-controltables are available.5. O V E R H E A D FIRE WITH I N D I R E C T LAY ING.Indirect overhead fire is that overhead fire which is delivered byemployment of indirect laying. As in direct overhead fire separatecalculations are made for troops which are stationary andtroops which areadvancing.a. When troopsare visible to the gunner and are not advancing the following method should beused:(1) Determine range to troops.(2) Set angle-of-site dial at the safety angle for troops atthat range. (Thesafety angle may be found in column 2 ofoverhead fire table.)(3) Set range to troops on range dial against index ofangle-of-sitedial.(4) Layhorizontal lineof thecollimator on thetroopswithsight set as above by means of the elevating and traversingmechanism.(5) Center bubbleby turning the rangedial without changing gun position.(6) Set angle-of-site dial at the angleof siteof the target.(7) Read rangeon the range dial now opposite index ofangle-of-site dial. This will be the least range at which it issafe to fire over the friendly troops. If the target is nearerthan range shownon the range dial it is not safe to fire.It will be seen that this method is similar to theordinarymethodof determiningminimumrange, except thatthesafetyangle is set on theangle-of-site dial before the other operations areperformed.b. When the troops are not visible to the gunner and arenot advancing the following method should be used:(1) Measure angleof site of target.(2) Determine range to target.(3) Calculate QK for target.(4) Measureangle of siteof troops.(5) Determine range to troops.(6) Calculate QE for troops.

107

7/30/2019 M1916 37mm manual FM-23-75

112/164

95-96 37-MM GUN, M1916(7) Subtract QE of troops fromQK of target. If theangulardifference between the two is equal to or greater thanthesafety anglefortroops at that range (see overhead fire table),it is safe to fire. If the angular difference between the two isless thanthe safety angle for troops at that range it is notsafe to fire.c. When troops areadvancing the following method shouldbe used to determinehow far the troopscan advancebeforeit is necessary for thefireto cease or be lifted:(1) Determine range to target.(2) Find this rangein column 3 of overhead fire table.(3) Find corresponding range in column 1 on the sameline. This will be the range towhich troops may safely advance before fire must cease or be lifted when troops areon the line of site and the ground is level or has auniformslope. When a hill or pronounced rise lies between gunand target on the ground over which the troops mustad

vance, the troops will be nearer the trajectory than whenthe ground is level or has a uniform slope from gun totarget. Therefore this rise in the ground is necessarily considered and calculation made to determine whether it willbe safe to fire when troops are on the hill or rise in theground. This is done by the same method as used whentroops are stationary, using the hill or rise as the positionof the troops.6. G E N E R A L RUL ES. The following general rules will beobserved in delivery of overhead fire:a. L aying of gun will be checked carefully by the gunnerbefore firing each round.b. Targetand limit of safety will always be visible to theobserver.c. Fire will cease or be lifted when troops reach the limitof safety.d. When overhead fire is to be delivered from the timetroops begin to advance, it will be determined whether it issafe to fire over them in their starting position. It is thennecessary to determine how far they can advance beforefire must cease or be lifted. Both calculations are necessary.e. Required safety angles mustnot be lessened.

108

7/30/2019 M1916 37mm manual FM-23-75

113/164

37-MM GUN, Ml916 9&-9S

/. When practicable, friendly troops should be informedwhen overhead fire is to be delivered.g. When practicable, depression stops should be used toprevent the muzzle being accidentally lowered below the limitof safety.h. Overhead, fire is prohibited, when troop distance is lessthan 400 yards, unless the difference in elevation of gun andfriendly troops makes it perfectly evident that it is safeto flre.7. DUTIES A N D T R A I N I N G O P GUN COMMANDER. Delivery ofoverhead fire requires the highest degree of exactness andaccuracy and no observer or gunner will be allowed toexecutethis kind of fireunlesshe is instructed thoroughly and is proficient in it. The gun commander is responsible for therules of safety. When direct laying is employed thegun commander will be at thegun position and supervise the gunner'slaying. When indirect laying is employed the gun commander, having determined the firing data, will take suchposition that hewill be able to see theposition of the friendlytroops, the target, and the limit of safety. He will give theorders for opening and ceasing fire. He must understandthoroughly the rules for overhead fire and their applicationsufficiently well to repeat them without reference to writtennotes. He will be given practice in applying these rules toassumed situations. The instructor will conduct the observers receiving instruction in overhead fire to gun positionsfrom which overhead fire is assumed to be delivered againsttargets indicated by the instructor. The instructor willexplain the rules and then require the observers to determinewhether or not it would be safe for the gun to fire if troopswere at different -positions along the line gun-target. Thedetermination of the limit of safety will be checked by theinstructor.8. O V E R H E A D FIRE TABLE.The table given below showsdistances to troop positions, safety angles, and least permissible ranges. It is used as described in this section.

216513408 109

7/30/2019 M1916 37mm manual FM-23-75

114/164

98-100 37-MMGUN, M1916Table for overhead fire, high-explosive shell, Mk. //,. muzzle

velocity 1,276 f/s( 1 )Troopdistance

Yards400500600Y O O800900

(2)Safetyangle

Mils23.522.421.321.322.123.3

(3)Correspondingrange 'Yards925

9751,0501,1251,2251,350

(1)Troopdistance

Yards1,0001,1001,2001,3001,4001,500

(2)Safetyangle

Mils24.926.628.229.831.733.7

(3)Correspondingrange'Yards1,4501,5751,6751,7751,9002,000

i Inevenfigures to thenearest 25 yards abovetheexact range.SECT ION IV

FIRE CONTROL AND ADJUSTMENT9. GENERAL . Fire control is the regulation of fire by thegun commander. Itenableshimto bring fire on adesignatedtarget, toopen,and cease fireat will, to control theexpenditure of ammunition, and to engage new targets. The guncommander controls fire by orders, commands, or signalswhich express the firingdata tobe used. When direct laying is employed he transmits the firing data by voice, ashis position is atorvery nearthe gun position. Wheneverpossible hewill issue the firing data in the formof an oralfire order. Inexceptional cases thegun commander maylaythe gun himself or will give a detailed explanation to thegunner instead of issuing a formal fire order.00. FIRE ORDERS. a. Initial fire orders.(1) Initial fireorders (which contain the data for laying thegun for thefirstround) will contain the information shown below andwill begivenin the following sequence:(a) Typeof shell to be used.(6) Angle of site (in case of indirect laying).(c) Range.(d) Deflection.(.e) Aiming point.

(/) Number of rounds to befired.110

7/30/2019 M1916 37mm manual FM-23-75

115/164

37-MM GtTN, M1916 100

(2) The words "type of shell," "deflection," "range," etc.,are understood and not spoken.Example.Assume that an initial fire order for direct laying is to contain the following data: A high-explosive shellis to be used with a range of 900 yards and a deflection ofzero; theaiming point is the base of asmall pine tree directlyto the front and one round is to be fired. The order wouldbe expressed as follows:HIGH EXPLOSIVE.

900.ZERO.TO Y OUR FRONT, SMALL PINE TREE; BASE OPTREE .ONE ROUND.The deflection will always be announced, even if it is zero.Gunners and their assistants are trained to receive andexecute fire orders in a fixed sequence and any variation oromission will cause delay and confusion. Unnecessary wordsare omitted. The command (so M A N Y ) R O U N D S also indicates that the gun is to be loaded at once and to be firedwhen laid.b. Typical fire order for indirect laying.A ssume that ahigh-explosive shell is to be used, that the target is 15 milsto the right of a natural aiming point which is the left edgeof a lone pine tree to the front (deflection, right 15 mils);that the target has a minus 10 angle of site and a range of1,300 yards; one round is to be fired. The fire order would be:HIGH EXPLOSIVE.MINUS 10.1,300.RIGHT 15.TO Y O U R FRONT, LONE PINE TREE, LEFT EDGE

OF TREE.ONE ROUND.c. Subsequent orders.Subsequent fire orders contain onlythe data which are to be changed and the number of roundsto be fired. To enable the observer to order the proper correction for errors in range he should remember the rangewith which the last round was fired because when orders aregiven orally, and when the signals used render it possible, he111

7/30/2019 M1916 37mm manual FM-23-75

116/164

100-101 37-MM GUN, M1916commands theactual range setting to be set off on the rangedial. It is not necessary for him to remember the last settingof the deflection dial because in making corrections he usesthe last setting as a zero; in other words, he commands thecorrection to be made fromthesetting used for the precedinground.Exam-pie.The firstroundwas fired with thedeflection dialset at left 14 and the range dial set at 1,400; the observerwishes to fire thesecond roundwith a change which will movethe burst 2 mils to theright and ata rangeof 1,200 yards;his fire order is:1,200.RIGHT 2.ONE BOUND.The gunner moves the deflection dial to left 12, therangedial to 1,200, and re-lays the gun. If it is desired to changeonly the range for the third round andthe range desired is1,300 yards, the fireorder is:1,300.ONE BOUND.If it is found that therange and deflectionare correct, theobserver may cause a number of rounds to be fired as, forexample, five. The fire order is:FIVE BOUNDS.01. A R M - A N D - H A N D SIGNALS.a. To shift right (.left).Extend one arm toward the gunner(s) concerned; swing thehandand armhorizontallyinthe direction in which the fireis to be shifted, palmturned in that direction; with the palmof thehand toward thegunner (s), expose one finger for eachmil thefire is to be shifted.b. To increase (decrease) range.Thrust the fist upwardvertically from theshoulder tothe full extent of thearmoncefor each increase of 25 yards; thrust it downward verticallyin the same manner for eachdecrease of 25 yards.c. To fire one round.Extend one armabove the head towardthe gunner for whom the signal is intended. Cut thehand sharply downward.d. To fire five rounds.Extend one arm above the head,hand open; flex the wrist, making a quick, choppy, lateralmovement with the hand. 112

7/30/2019 M1916 37mm manual FM-23-75

117/164

37-MMGUN, Ml916 102-103

02. T Y P E S O P FIRE.Fire isdivided into two types, fire foradjustment and fire for effect. Fire for adjustment is thetype used to bringthe centerof impact onthe target. It isdescribed in paragraphs 104 and 105. Fire for effect is thetypeusedto destroy, immobilize, or neutralizeatarget. It isdeliveredafter firehasbeen adjusted. Thenumber of roundsto be fired to effect the destruction of atarget must be decided by the gun commander. Firing a small number ofrounds in a series is better than firing the entire number ofroundsinagroupas itpermitstheobserver to makeslightadjustments and prevents wild shooting. To order fire foreffectthegun commander commands; (SO MANY ) ROUNDS.The command FIRE F O R E F F E C T is not used.Example.A gun commander decides to use 15 rounds todestroy a target, fire having been adjusted. He commandsF I V E R O U N D S and observes the bursts. He makes any corrections that he deems necessary and again orders F I V ER O U N D S . If satisfied, he again orders F I V E R O U N D S . The threeseries should follow each other without unnecessary pause.As the gun is used against definitely located targets and notto cover areas, traversing, searching, and oblique traversingare not standard classes of fire. There are no fixed commands for these classes of fire which, if desired inunusualcases, canbe orderedby detailedinstructions tothegunner.03. SENSING. a. General.When an observer senses aburst from a roundfired he determnes the deflection error;that is, how manymls the burst is to theright or left of thetarget, and whether it is an "over" or a "short"; that is,whether the burst is beyond or short of the target. Hemaybe able to sense the round for deflection but not for range,in which case another round should be firedwith thedeflection correction appliedand with thesame range as the preceding round. In sensing a round the observer senses firstfor deflection and next for range.b. Observer at gun position.Thebest positionfor the observer is at the gun position. From this position his deflection sensing and the deflectioncorrection to bemade on thesight arethe same. He can also exercise better control overthe gun squad when at the gun position.

113

7/30/2019 M1916 37mm manual FM-23-75

118/164

103 37-MM GUN, M1916c. Observer in front or rear of gun position and on line

gun-target.Next to the gun position the best place for theobserver is in front or rear of the gun position and on the linegun-target. However, from such a position his deflectionsensing is not the same as the deflection to be set off on thegun. If he is in rear of the gun the deflection sensing willbe less than the deflection to be set off on the gun; if he isin front of the gun the deflection sensing will be greater thanthe deflection to be set off on the gun (fig. 15). By practicethe observer'is able to determine the proper allowance tomake. If he is halfway between the gun and target his deflection sensing will be twice the correction to be made onthesight; if the gun is halfway between the observer and thetarget his deflection sensing will be half the correction to bemade on the sight; other distances will give other ratios (fig.17). However, the observer usually will be close enough tothe gun position to obviate the necessity of a correction forthe distance of the observer from the gun.

TARGET

F I G U K E 15. Deflection sensing.d. Observer to flank, to flank and forward, or to flank andrear. (1) In each of these cases there will be an additionalerror due to the fact that the deflection sensing varies as theobserver moves to the right or left; that is, the positions ofthe target and the point of impact with relation to eachother seem to change as the observer changes his position.Example.In figure 16 the observer at A reads the actualdeflection which should be set off on the sight. If he movesto B he sees the burst as if it were directly in line with thetarget. A correction for deflection is apparently unnecessary. If he moves to C he reads a deflection that is muchgreater than the correction to be set off on the sight. Noformula has been devised which is satisfactory for use inthe field.

114

7/30/2019 M1916 37mm manual FM-23-75

119/164

37-MM GUN, M1916 103(2) Upon taking a position off the line gun-target the observer should at once estimate where the line gun-targetlies on the ground and read the deflection from this line tothe bursts. As bursts having errors in range will appearto be to the right or left of the target, the observer shouldalso estimate where a line perpendicular to the line gun-target and passing through the target lies. Having estimatedwhere the line lies on the ground, the observer should consider all bursts between himself and this line to be "shorts,"

and all bursts on the far side of the line as "overs." Anobserver should always endeavor to avoid an observationpost off the line gun-target.IT OF BURST

FIGURE 16.Deflection sensings.

115

7/30/2019 M1916 37mm manual FM-23-75

120/164

104 37-MM GUN, M191604. A D J U S T M E N T F O R RANGE.Two methods are used inadjusting for range known respectively as bracketing andcreeping methods. The bracketing method is used underalmost aU conditions. The creeping method may be usedin overhead fire.a. Bracketing method.(1) The bracketing method is theone usually employed in adjusting fire. In this method thetarget is bracketed between an "over" and a "short." Thetarget is kept between two ranges, one increasing and theother decreasing, until the center of impact is on the target.A target is said to be bracketed when one "short" and one"over" havebeen obtained. Adjustmentof fire by thebracketing method is executed as follows: The range to the target is estimated as accurately as possible and a round isfired with this setting. If the burst is observed to be an"over" the range setting is decreased 200 yards and anotherround fired with this new setting. If this is a "short" thethird round is fired with! a range setting which is the meanor average of the two previous range settings. Subsequentrounds are fired with range settings which are the mean ofthe last "short" and the last "over." If the first burst isa"short" therangesetting is increased 200 yards and anotherround is fired. Subsequent rounds are fired with range settings which are the mean of the last "short" and the last"over." The distance from the target of the "short" or"over" is immaterial and need not be estimated or considered by the observer . After the bracket is obtained the rangeis increased or decreased in steps of 100, 50, and 25 yards,until the center of impact is on the target. If the bracket isnot obtained by the second round, the range setting is againincreased or decreased 200 yards and another round fired.Occasions when the bracket will not be obtained by thesecond round will be rare.Example (fig. 17). The range to the target is estimatedto be 1,100 yards and the first round is fired with this setting. The burst is observed to be a "short." The range setting is increased 200 yards and the next round is fired witha setting of 1,300. The burst is observed to be an "over."The bracket is now established. The range setting for thethird round is the mean of the "short" (1,100) and "over"

116

7/30/2019 M1916 37mm manual FM-23-75

121/164

37-MM GUN, M1916 104

(1,300) and is fired with a settingof 1,200. Thethird round isobserved to be an"over." The fourthround is fired with asettingof 1,150 which is themean of the last "short" (1,100)and the last "over" (1,200). The fourth burst is observed tobe a "short." Therange for the fifth round is 1,175 whichis the mean of the last "short" (1,150) and the last "over"(1,200). Thefifth round bursts on the target. This may beverified by two additional roundsand fire for effect opened, orfire for effect may be opened withoutverifying rounds.

(2) Adjustments of less than 25 yards are used onlywhenmakingavery fine adjustment of fire. A s theprobable errorof thegun is about 25 yards at most combat ranges the dispersion will cover the target. Experience has proved thatthe bracketing method is the quickest, most accurate andeconomical method of adjusting fire. Attempts to estimatethedistancebetween aburst and the target and tobringthenext burst on the target are seldom successful due to theinabilityof observers to estimate accurately the distance between two points on the line gun-target. The bracketingmethod eliminates the necessityof doing this. The observerneed determine merely whether a burst is a "short" or an"over." The methodis applicable to practicallyall situations.Even when firingatatargeton thecrest of ahill the"shorts"can be observed and all unobserved bursts are treated as"overs."T A B O E . T1*51 a

_______________________________ V, 'if ________G U N s g 3 g 55 o ui g o

F IGUEE 17.Bracketing method.b. Creeping method.(1) General.This method is used

when bursts must approach the target from but one direction(fig. 18). It is seldom used except in the adjustment ofoverhead fire when friendly troops are so close to the targetthat the bracketing method would be dangerous. In suchcase the first round is fired with a sight setting which willinsure the burst being beyond thetarget; subsequent roundsare fired with sight settings which will insure that the shelldo not burst shortof thetarget. The creeping method is not117

7/30/2019 M1916 37mm manual FM-23-75

122/164

104 37-MMGUN, M1916thenormal method of adjustingfire and shouldnot beusedwhen the bracketing method can be used with safety. It isslower than thebracketingmethod and usually requires agreater expenditure of ammunition. The highly desirablefeature of thecreepingmethodis its factorof safety in certainsituations, particularly in adjusting overhead fire.

TAQGBT. f A , 5I& a I* ______________________________* wtn * &Gun g g g g gO l O g o

FIGURE18.Creepingmethod.(2) Determnationof initialrangesetting.The determination of the range setting to be used for the first roundis important since itmustburston thedesired sideof the target. It isdetermined in the following manner: An "over"being desired in overhead fire, the observer estimates the

extreme range to the target; that is, he estimatesthat thetarget isnot morethanacertain distance from thegun. Hethenuses a rangesettingwhich is greaterthanthisextremeestimated range.Example.Friendly troopsareclose enoughto the targettorender bracketingunsafe. Theobserverestimatesthat thetargetis 1,000 yardsfromthegunandcertainly notmorethan1,100. Heuses1,100asthebase andadds 100 tomake certain thatthefirst round will burst beyond thetarget. Heordersarange of1,200for thefirst round.(3) Adjustment of fire.The errorofeveryburst must beestimated whenadjusting fireby the creepingmethod. Thefirst roundisfiredwith arangesettingwhich will insure theburstbeingonthedesiredside of thetarget whichin theusualcase, overhead fire, is the far side. The observer estimatesthe amountof theerror inyards and halves it. If the firstburst was an"over" as intended, thehalvederror isdeductedfromtheinitial rangesetting and a round is firedwiththenewrange. Theerror ofthesecondburstis estimated, halved,deducted, ananother round fired. This iscontinueduntil thecenterof impact isonthe targetwhen fireforeffect isopened.If atanytime aburst is obtained on the wrong side of thetarget, thenext round isfiredwithachangeequal tohalf thechange madefor the last observed round.118

7/30/2019 M1916 37mm manual FM-23-75

123/164

37-MM GUN, M1916 104-105

Example.The guncommander isdelivering overheadfire.He estimates that a range setting of 1,350 will insure thefirst burst being beyond the target, and fires a roundwiththatsetting (fig. 18). He estimates thebursttobe 300 yardsbeyond thetarget. Half of this error is 150 yards. He deducts 150 from1,350and fires the next round withasettingof 1,200. Heestimates theburst of thesecondround to be 100yardsbeyond thetarget. Half of thiserror is50. He deducts50 from1,200 and fires the thirdround witha setting of 1,150.He estimates theburst to be 100 yards beyond the target.He deducts 50 from 1,150 and fires the fourth round with asettingof 1,100. Theburst is observed to be a "short" (onthewrong side of the target). The observer makes a changeequal to half the change made for the previousround(whichwas 50) and fires the fifth round witha setting of 1,125. Itburstson thetarget. This isverified by two additional rounds,found to be correct, and fire for effect is opened.05. A D JUSTM ENT F O R D EFL ECT ION . T he observer shouldhave thezeroof thehorizontal mil scale of his glasses trainedon the target before theshell bursts. The deflectionerror issensed at the instant the shell bursts. If this is not donesensing may become difficult owing tothe smoke cloud beingblown toone side or dissipated. Thedeflectionerror assensedis immediately changedtoadeflectioncorrection andgiven tothe gunner in an adjustment order.Examples.No. 1.The burstof a shellis sensedas 14 milsleft of the target. Theobserver orders R I G H T 14, thusmoving thenext burst 14 mils tothe right. The observer orderstheactualcorrection to be maderegardless ofthe reading onthe deflection dial.No. 2.The gunner has made the correction previouslyordered, and thedeflection dial is set at right14. A roundis fired and the observer senses the burst to be 3 mils leftof the target. He orders R I G H T s. The gunner sets the deflection dial at right17, thus giving thegunadditional 3 milsdeflection to the right. Another round is fired and theobserver senses the burst to be 1 mil right of the target.He orders L E F T i and the gunner sets thedeflection dial atright16. The gunner re-lays on theaiming point aftereachchangeof sightsettingby turning theelevatingand traversinghandwheels. 119

7/30/2019 M1916 37mm manual FM-23-75

124/164

106-107 37-MM GUN, M1916SECTION V

FIRING AGAINST MOVING TARGETS06. G E N E R A L . a. Due to the slow andlimited traverseandlack of power topenetrate heavy armor plate, theuse of the37-mm gun, M 1916, againstmoving targets such as heavilyarmored tanks and cars is not contemplated. If necessaryto employ the gun against light armored tanks and cars,themethod shown below may be used.b. The methodsusually employed for firingon point targetsare too slow for this type of fire. Because of the target'sabilityto make changes of direction and speed it isnecessaryfor the observer to make estimates of angular speeds andtoannounce changes of deflection and range which will keepthe fire on the target. The method employed can best bedescribed by outlining thedutiesof the various membersofthe squad duringfiring.07. OBSERVER.The observer has the problem of targetdesignation, range and deflection estimation, fire orders, adjustment, and control of fire. Based on time of flight ofthe high-explosive shell, M k. II, the following time factorsare used for certain key ranges as indicated below:

Key ranges_____(yards) __ 400 800 1,200 1,600Time of flight of shell(seconds) __ 1.1 2.3 3.7 5.2Timefactors______do__ 12 4 5

a. When the target appears theobserver quickly designatesthetarget to thegunner by as simple adesignationaspossible.He then quicklyestimatestherange to the target and observing the target through his glasses reads the angular movement in mils which thetarget makes whilehe is counting thenumber of seconds; that is, time factor for the key rangewhich is nearest his estimated range to the target. Thisangular movement in mils is thengiven in his fire order asrightor left deflection.b. The fire order used forpoint targets has been found tooslow for use against moving targets. The best results have

120

7/30/2019 M1916 37mm manual FM-23-75

125/164

37-MM GUN, M1916 107-108been obtained by using a fire order with the elements in thesequence as follows:TARGET (DESIGNATION).

RANGE.DEFLECTION.Example.A tank appears in the zone of fire of a gun.Theobserver immediately designates the target to thegunnerwho, if necessary, moves the trails of the gun and points thebarrel in thedirection of the tank. In themeantime the ob

server, having estimated the range to the target, is readingthe angularmovementduringatimefactor which correspondsto the estimated range to the target. He reads this movement by alining the zero of his horizontal mil-scale on thetank, then holding the glasses as still as possible counts theproper number of seconds. This is done very quickly andaccuracy improves greatly with practice. A ssume that atank appears in the right of his sector at a range of 900yards and he reads the angular movement during two seconds to be left 12 mils. His fire order would be as follows:TO Y O U R RIGHT FRONT, THAT T A N K .900.LEFT 12.His adjustment order for the second round based on hissensings for the first round includes merely the correctionsindeflectionandrange. Deflectionchanges for thesecondandsucceeding rounds must be based not only on errors in direction as determined from sensing each previous round butalso must be based on changes of direction and speed of thetarget. Proficiency in estimating deflection changes to compensate for cha