Army Artillery Firing Report

8/9/2019 Army Artillery Firing Report

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THE GENERAL SERVICE SCHOOL

LIBRARY

THE COMMAND AND GENERAL STAFF COLLEGE

LIBRARY

Call Number L 0-111-2,7Acc~soin Ymter 11147

CGSC Form 154 (Rev) 22 Oct 52Army-CGSC-p5-1707-28 Feb 55-M-2M

99-G. S. Schs., Fort Leavenworth-8.15-27-25M


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ARTILLERY FIRINGLectures to The Staff and Line ClassesGeneral Service Schools, Fort 'Leavenworth, Kansas,

October ,1919

BY

Major L. J. McNair , F. A.

9,LL Wp

Line Class:

Staff Class:

T. T. 30, October 10.T. T. 41, October 16.T. T. 54, October 23,T. T. 26, October 10.T. T. 50, October 27.

T. T. 62, November 5.

The Army Service Schools PressFort Leavenworth, Kansas

1919

%

3 ~a


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ContentsSubject Par.

GENERAL --------------------------------------- 1-3PART I. Preparation of fire ----------------------- 4-41

Defined ---------------------------------------- 4Mechanism of laying --------------------------- 5Methods of laying. Direct. Indirect ------------- 6

Laying for direction. Deflection ------------------- 7Deflection graduation of sights ----------------- 8

Laying for elevation --------------------------- 9-20Systems. Independent line of sight. Direct laying -10-15Indirect laying. Site------------------------16-17Elevation scale graduation ---------------------- 18Quadrant laying ------------------------------ 19Data needed to lay the piece-------------------- 20

Finding th e deflection-------------------------21-31Description, direct and indirect laying. Methods -_ 21On the ground, without map or compass -- _--------22Reciprocal laying ----------------------------- 23Means for measuring angles --------------------- 24On the ground, without map, but with compass.-- 25By th e map, but without compass----------------26By the map, with compass---------------------- 27Conversion of angles into deflection-------------- 28Deflection difference------------------------29-30Application of various methods------------------31

Finding th e site---------------------------------- 32Finding the range------------------------------- 33Finding th e elevation-------------------------34-36

Range Tables --------------------------------- 34Use of tables to find elevation-------------------- 35Time fire. Data for. Corrector__---------------36

Summary of firing data. Refinements of the prepar-ation of fire-------------------------------37-41Summary of firing data------------------------- 37Nature of refinements possible------------------38-39Atmospheric and ballistic corrections------------ 40General --------------------------------------- 41

PART II. Firing -------------------------------- 42-67Dispersion-----------------------------------42-46

Law of dispersion. Probable error------------43-44Effect of dispersion---------------------------- 45

3


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-4-Subject Par.

Safe distances from points of fall --------------- 46Fire for adjustment ----------------------------47-57Defined -------------------------------------- 47Observation------------------------------------- 48

Methods of adjustment------------------------ 49Adjustment by measured deviations --------------- 50Adjustment by bracketing---------------------51-54Bracket adjustment ---------------------------- 55Adjustment of time fire ------------------------- 56Method of fire during adjustment. Salvo -------- 57

Fire for effect --------------------------------8-60Classes. Precision, zone, systematic. Volleys__- 58Use of datum or registration point --------------- 59Use of witness point --------------------------- 60

Special shell ---------------------------- 61Effect of fire------------------------------------ 62Clearing the crest ----------------------------- 6-65

Elevation form ulas------------------- -------- 66Reaching a reverse slope ------------------------ 67

PART III. Special auxiliaries --------------------- 68-78Aerial observation----------------------------68-72

Balloon-------------------------------------- 68Airplane ---------------- 6------------------9-72

Advantages. Disadvantages ------------------- 69Communication ------------------------------- 70Signals ------------------------------------- 71Method -------------------------------------- - 72Sound ranging-------------------------------73-75Apparatus ---------------------------------- 73Method -------------------------------------- 74Possibilities------------------------------- 7

Flash ranging ----------------------------------- 76High burst ranging ----------------------------- 77-78


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Artillery FiringGeneral1. Artillery firing has changed as a result of thewar. Contrary however to the general belief, thechanges are not in the nature of discarding the old,but adding to it, developing and refining it, whentime and the situation permit. The accomplishedartilleryman of today must have a much larger tech-nical repertoire than formerly. For example, cor-rections for atmospheric conditions have greatlydeveloped, although applicable only under certainconditions. Again, when detailed maps of the plandirecteur type are available, the newly developed ar-tillery topography affords highly important advan-tages.On the other hand, the older, cruder methods inuse before the war are still sound, still necessary,and cannot be neglected without dangerously impair-ing fighting efficiency.

2. It is the aim and duty of the artilery to de-liver effective fire when and where needed.The problem of delivering effective fire on agiven point at a given time is largely one of tech-nique.To insure that the given point and time meetthe needs of the infantry and the situation in generalis a tacticalproblem; in fact, it is the essence of ar-tillery tactics.

3. This discussion of artillery firing will be con-fined wholly to technique, and will include the fol-lowing:

(a) repar ti fMetos i ;

r 5


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--6--Finding th e deflection.Complete firing data.

(b)- Firing:Dispersion.Fire for adjustment.Fire for effect.Effect of fire.Clearing a crest.Reaching a reverse slope.(c) The special auxiliaries of:Aerial observation.Sound ranging.Flash ranging.High burst ranging.

PART IPreparation of Fire

4. The preparation of fire is finding the firingdata, which are defined to be "the information andcommands necessary to enable the gun squads toaccomplish the orderly, rapid and accurate service ofthe pieces."

Therefore 'before one can intelligently proceedwith the preparation of fire, it is necessary to under-stand the mechanism of laying a piece of artilleryand how it is served.

5. Mechanism of laying. The object of layingis to give the piece such an elevation (or depression)in a vertical plane and such direction that the pro-jectile will reach the target.

Formerly the elevation and direction were mat-ters of guesswork and skill on the part of the gun-.ner; with modern artillery the cannoneer executescommands mechanically by means of laying instru-ments. The cannoneer must have a certain degreeof skill and dexterity, but responsibility for suc-cessful results rests mainly with those determiningthe data announced to the cannoneers.

6. Kinds. of laying. Laying is direct and in-direct.


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-7-For direct laying the piece is sighted for direc-

tion and elevation on the target itself which must bevisible to the gunner.For indirect laying the piece is given directionby sighting on any convenient designated point (aim-

ing point), and elevation by a quadrant or level.The cannoneers do not see or know the target of ne-cessity.Indirect laying is easily the predominatingmethod. It has a number of advantages.The pieces can fire effectively from concealedand protected positions. An aiming point is dis-

tinct and definite; the target is generally vague andindefinite. Indirect laying is thus possible whendirect laying would either be ijipossible or very dif-ficult. Indirect laying affords decided advantagesof collective control and eliminates difficulties of tar-get designation. It operates to place the brain workof firing on the officer and makes the soldier's workmore purely mechanical.

Direct laying is, however, decidedly superior formoving targets.7. Laying for direction. This operation is thesame for either direct or indirect laying. A deflec-

tion must be announced, which is the horizontal an-gle to be set on the sight in order that the piece whenlaid will give shots correct in direction.The gunner, the cannoneer on the left of the

trail near the breech, sets the sight at the deflectionordered and traverses the piece till the line of sightis on the aiming point or target for direction.

Laying for direction is not difficult, althougherrors in sight setting occur occasionally, and accur-acy in sight setting must be insisted upon andchecked.


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-8-8. Deflection graduationof sights. Sights are

graduated so that all deflections from 0 to 6400 milsmay be set. Unfortunately, however, among the va-rious materiels now in our service, there is not uni-formity in the method of graduating the deflectionscale. The angular unit is generally the mil,*and all except the British howitzers are graduatedclockwise; but in the matter of numbering the scaleand its origin, there are the following principalsystems:

Figure 1 is the old U. S. system, 0 to 6400 mils,with the gun axis at 0, that is, when the sight is setat 0 deflection, its axis is parallel to the gun axis.The limb is graduated in hundreds of mils; singlemils are set by means of a micrometer graduatedfrom 0 to 100 mils.

Figure 2 is the system of the French 75 gun nowin our service. It is difficult to understand how theminds who conceived this remarkable weapon couldalso conceive so clumsy a system of deflection gradua-tion; there is no defense for it. The gun axis is at100. The circle is divided into four quadrants grad-uated alike. Each quadrant is divided into eightsubdivisions of 200 mils each, called plateaux, andnumbered successively 0, 2, 4, 6, 8, 10, 12, 14. Thus"Plateau 2" means any one of the four identicalsubdivisions between 200 mils and 400 mils. A mi-crometer subdivides the plateaux; it reads from 0 to200 mils. Readings on the micrometer are referredto as "Drum, so and so." A complete deflection

*It is asumed that the student is familiar with the miland its properties; if not, see par. 14 of the War Departmentmanual "Artillery Firing," or other texts in which th e mat-te r is discussed. 1 mil=3.375 minutes, 33/8 minutes; 18 mils(more exactly, 17,778) =1 degree.

The sight of the British 8-inch and 9.2-inch howitzersis graduated in degrees and minutes, one-half clockwise andthe other half counter clockwise; the sight of th e 155 Fillouxgun (French) is graduated in decigrades.


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* 1Breech100' on limb 0-100 on Micrometer

fig 1.OLD U.S.

must therefore be expressed in two units, thus, "Pla-teau 4, Drum 175"; while in other systems one num-ber is sufficient, thus, 1435.

Figure 3 is the system of the 155-mm. Schneiderhowitzer used in our division artilery. The gun axis


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y G

Breech

200'5 on Iimb-0200 on MicrometerFig 2

75 FRENCH GUNis at 1000, that is, the 0 of the sight scale is 1000mils to the left front. The graduation is from 0 to6400. The limb is graduated in hundreds, and themicrometer from 0 to 100. No real advantage isderived from the position of the origin of graduation;


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''pTHE C!"~N(a~fr

I00'5 on i imb; 0-100 on Micrometer

155 SCHNEIDER HOWITZERon the other hand, it causes considerable incon-venience.

Figure 4 is the new U. S. system. The gunaxis is at 0. The scale is in tw o halves, each grad-


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1 l Breech100'5 on iimb-0-100 onMicrometer

Fi9 4.NEW U. 5.uated from .0 to 3200. This is advantageous in re-ciprocal laying (par. 23). The limb is graduated inhundreds, and the micrometer from 0 to 100.


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-13-9. Laying for elevation. This operation is dif-

ferent for the methods of direct and indirect lay-ing. But in both cases a range setting or elevationis announced to give the bore an elevation corres-ponding to the range of the target.

5i, 5.SCHEME OF LAYING FOR

155 m.m. HOWITZ E RRANGE

10. Systems of laying for elevation. Two typi-cal systems of laying for elevation are shown inFigures 5 and 6. Figure 5 is essentially that of the155 howitzer and is the simpler. , Figure 6 is thatof the 75 gun and embodies the so-called independentline of sight.


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-14--11. In Figure 5, K is an optical sight for ac-curate laying. It is mounted on a shank R curved

to a circumference having the trunnion w as a center.The sight and shank, K and R, slide up and down ina seat B fastened to the cradle. The sight shank isgraduated for range. The graduation for a par-ticular range is so placed that when the shank isset at this graduation, the sight axis makes a verti-cal angle with the gun axis equal to the elevation cor-responding to the given range. S. is the elevatingscrew fixed at the lower end of the trail of the car-riage and at the upper end of the cradle. It is oper-ated by a handwheel and suitable gears M.

12. If now any desired range be set on theshank R, and the piece then elevated by means ofthe elevating system S and M until the line of sightis at the height of the target, the operation will re-sult in the piece being elevated above the target byan amount corresponding to the range. In otherwords, the piece will be laid for range (or elevation).

This case is direct laying (par. 6), and is thesimplest.It will be noted that as soon as the range is an-nounced, the operations of setting this range andelevating the piece the proper amount are simple andeasily performed by the gunner, a corporal.

13. As thus described, laying for elevation orrange involves two operations, i. e.:(a) Setting the range on the sight shank.(b) Sighting on the target.

With this system, these operations must be per-formed successively and practically by one man.Moreover a change of range after the first shot in-volves a complete repetition of the process.In view of these facts, the French introduced theindependent line of sight shown in Figure 6. A sub-


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-15-cradle or rocker is placed between the cradle andtrail-a mechanical complication, it is true. Thelower end of the elevating screw S is mounted, noton the trail as in Figure 5, but on the rocker. This

ri. 6.INDEPENDENT LINE OF

75 m.. FRENCH GUNMODEL 1897

SIG HT

screw is operated by a cannoneer on the right of thepiece, No. 1. The rocker can be elevated by the gun-ner on the left of the piece through the pinioh H.The piece can therefore be elevated by either thegunner or No. 1, but in different ways.

A range scale R moves when the piece is movedwith respect to the rocker, and thus indicates ranges


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-16-of the piece with respect to the rocker. The sight Kis fixed to the rocker so that when the range scalereads 0, the line of sight is parallel to the bore ofthe piece.

14. When a range is- announced, No. 1 (on theright) turns Ml and S till R indicates this range. Atthe same time, before or after, the gunner (on theleft) turns H, thus moving the whole, system, till theline of sight is on the target. This constitutes lay-ing for range, the same result as in par. 12, but ob-tained in a different manner.

15. The advantage of this system is in generaltwo-fold:

(a) The two phases of laying for elevation, de-scribed in par. 13 as successive, are made simul-taneous and apportioned to two, instead of one,cannoneers. This saves time.

(b) Changes of range do not entail relaying.No. 1 merely changes the range setting by meansof M and S; the gunner does nothing. This isimportant as the gunner is also concerned withthe deflection and is busy (par. 7). In otherwords, the sight is constantly available to thegunner for sighting purposes, and is independentof changes of range.

16. Indirect laying (par. 6). When the targetcannot be seen, the elevation must be given by thebubble, which refers it to the horizontal. Exceptwhen the target is on the same level as the piece,

L

P TS //

Fig. 7.INFLUENCE QF SITE ITH INDIRECT LAYING.


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-17-'this involves a correction of the elevation for rangeto make it correct with respect to the target.

Thus, in Figure 7, GH is a horizontal throughthe piece, and T is a target more elevated than thepiece. The angular difference of level at the piecebetween the target and the piece is called the site. Inthe figure, the site is TGH.

If direct laying were used, an elevation E wouldreach the target; but if used with indirect layingwithout correction for site, the' shot would fall shortby PT. If the elevation for indirect laying were in-creased by the site S, the piece would have the sameelevation above the target as for direct laying, andwould be correctly laid.

The site is + (plus) when the target is abovethe piece, and - (minus) when the. target is below-the piece. With this convention, the elevation for in-direct laying (quadrant elevation) is the elevationfor .the range with the site added algebraically.

Example :The piece is on contour 520, the target elevation is 610

feet. Map range, 3700 yards. Elevation for range only,621'. What is the elevation for indirect laying?

Solution :The target is 610-520=90 feet=30 yards above th epiece. The site is+, and equal to

30-mils, or 8 mils, or 27'3.7

The elevation required is therefore 621+27'=648' .17. -W ith the sighting systems shown in Figures

5 and 6, the site is announced as such separately fromthe range (except in quadrant laying, par. 18), andis combined automatically by the mechanism. Theoperation of indirect laying is as follows:

For Figure 5, the announced range is set on thesight shank R as for direct laying. The site an-nounced is set on the scale r. -The piece. is then


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-18-elevated till the bubble of r is centered, which laysthe piece for elevation. This operation is performedentirely by the gunner on the left side of the piece.

For Figure 6, the gunner sets the site on r andat once centers the bubble of r by moving H. No. 1on the right turns M and S till R indicates the rangeannounced. The two cannoneers wo rk independ-ently.

18. Elevation scale graduation. The scale usedin laying for elevation are graduated either in rangeor in angular units.

Those graduated in range are in meters, * thishaving been adopted for service in Europe.. The 75gun is so graduated.

The scales graduated in angular units vary.The 155 howitzer is graduated in twentieths (of adegree); the 155 Filloux gun (G. P. F.) and theBritish howitzers in degrees and minutes. The m ilhas been adopted for future angular graduations.

19. Quadrant laying. The methods of layingfor elevation indirectly just described (pars. 16 and17), while simple and mechanical, involve mechan-isms with joints which become worn. For very ac-curate work, where speed is not essential, laying forelevation is by gun ner 's quad rant .

The quadrant is a frame carrying a pivoted armwhich can be set at any useful elevation. This armcarries a bubble. The instrument is held by hand onthe tube of the piece, so that the play of auxiliaryparts is eliminated. The elevation set is the quad-rant elevation (par. 16).

*Increase meters 10% to obtain yards. Thus 1200meters= 1200 +120=1320 yards (1312, more exactly). De-crease yards 10% to obtain meters. Thus 1312 yards=1312-131=1181 meters (1200, exactly).


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-19-20. It is thus seen that the cannoneers, in order

to lay the piece, need the following data:(a) Deflection,and for direct laying(b) Range,or for indirect laying(b) Site,(c) Range,or for quadrantindirect laying(b) Quadrant elevation, which includes site.The practical finding of these data constitutethe major portion of the preparation of fire, and willbe considered first.

FINDING THE DEFLECTION21. For direct laying, the deflection is thatwhich, for the particular piece, corresponds to theaxis of the bore (par. 8). For the 75 gun, thiswould be Plateau 0, Drum 100. Strictly speaking,it would be necessary to correct for the drift, thevalues of which are given in the range tables. Across wind is usally allowed for, as is also any con-

siderable cross movement of the target. Direct lay-ing is generally hurriedly prepared, however, and re-finements are not often practicabe, so that thecorrections are made as a result of the observation ofthe first shots.

For indirect laying, the deflection determina-tion is more difficult. The ideal method would be toset an instrument at the gun position and measurethe angle from the target clockwise to the aimingpoint. This direction and origin of measurementmust become a fixed habit; otherwise errors andconfusion are almost inevitable. The angle thusmeasured, when modified for peculiarities of sightgraduation (par. 8), is the deflection.

Practically, the problem is not as simple as this,since the target ordinarily cannot be seen from theposition of the piece.


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,1tualbir:k"+2 L i U U,. U-Yb4

-20-A number of the principal methods of finding

the deflection will be explained, as follows:(a) On the ground, without map or compass.(b) On the ground, without map, but with compass.(c) By the map, but without compass.(d) By the map, with compass.

In all cases; the problem is to measure the de-flection at a point other than the piece, where thetarget can be seen, or from a map, and transmit thismeasurement to the piece in a form which can beused to lay the piece for direction.

TI

G'G

P

Fig. 8.


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-21-22. ' (a) On the ground, without map dr com-

pass. Two cases arise, (A) a distant point P isused as an aiming point, and (B) the battery com-mander's instrument B is used as an aiming point.

For (A), TGP, as indicated in Figure 8, isthe angle sought, T being the target and G the piece.

For (B), the angle TGB is sought.Since these angles cannot be measured directly,

recourse must be had to indirect methods. The bat-tery commander's post is' probably the nearestpoint from which the target and the aimingpoint or piece can be seen. But even 'from here, ifthe angles TBP and TBG' be measured, they are in-correct due to the displacement of B and G.

Measurements made from B can be -utilized, how-ever. Draw BT ' parallel to GT, BP ' parallel-to GP,and BG' in prolongation of GB. Then, for case (A),T'BP' is exactly the angle sought, since its sides areparallel to those of TGP. Similarly for case (B),T'BG' is the angle sought. This is called the paral-lel method. Another is called the parallax method,but is less simple'and will not be discussed.

Although simple in principle, the parallel meth-od presents some difficulty practically, because thereis nothing on the, ground to establish the parallelsBT ' and BP'. If time is important they must beestimated by eye. This can be done with surprisingaccuracy after a little practice. If more time isavailable, the angular offset at B of T' from T and ofP' from P can be calculated more or less accuratelydepending on the speed necessary. For example, theoffset T'BT in mils is roughly BG in yards dividedby BT in thousands of yards. In the case ofP'BP,BG is rather oblique for good calculations; a bettervalue would be BG" divided by BP in thousands,where BG" is perpendicular to the bisector of the an-gle BPG. When an instrument is available, the ac-


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-22-curacy of the method depends almost wholly on thetime and care used to find the offsets T'BT and P'BP.

Case (A) is restated: An instrument (which isgraduated clockwise) is set up at B and oriented, noton T but on T' so that BT' is parallel to GT. Withoutdisturbing the orientation, it is pointed, not on P, buton P' so that BP' is parallel to GP. The instrumentreading is then the angle sought..

23. Reciprocal laying. For case (B), however,the offset of the aiming point is eliminated. Theinstrument oriented and pointed on T' as before isthen pointed on G, instead of on G' estimated.

The angle T'BG thus obtained is not the anglesought but differs from it by exactly 3200 mils. IfT'BG is less than 3200, 3200 is added to it; if T'BG isgreater than 3200, 3200 is subtracted from it. Thecorrectness of this rule can readily be verified byinspection of Figure 8. This method, where thebattery commander "lays" on the piece as an aimingpoint and the piece on the battery commander, iscalled reciprocal laying. The term' is perhaps morecorrectly applied to two pieces, one of which is laidin the desired direction and is used by the abovemethod to assist in laying the other piece parallel toitself.

It was seen above that the method involves acalculation, causing occasional errors and delay. Thisis eliminated in the graduation of the sights of the75 gun and the laAtest American models (Figures 2and 4, par. 8). The angle-measuring instrumentis graduated in the same manner as the sight. Witheither of the sights named, no conversion of the anglemeasured at B is necessary; the angle is announcedas read. The correctness of this statement is bestestablished by considering actual values with a dia-gram such as Figure 8.


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-23-24. Measurements on the ground as in the pre-

ceding paragraph are preferably made by instru-ment, such as the aiming circle, scissors telescope, etc.When instruments are not available, the determina-tion is still possible, but naturally with much less ac-curacy. The means used would be handbreadths,the B. C. ruler, the field glass, and the like.

25. (b) On the ground, without map, but withconpass. This requires an aiming circle (par. 517,Manual of Artillery Firing), but as this instrumentis very portable, it may be considered as nearly al-ways available. The aiming circle is similar intype to the transit, but is smaller, less elaborate,and less accurate. It measures horizontal and ver-tical angle in mils, and can be oriented in any de-sired direction. The telescope and compass are bothmounted on the upper limb.It will be noted that the method described inpars. 22-24 requires a point B from which the targetcan be seen, as well as the piece or an aiming point.This is not always possible. The compass furnishesa solution in case the previous method cannot beused. The method of using the compass is simplyan extension of the method of par. 22.

The aiming circle is set up at a point from whichthe target can be seen, as near as possible to thepiece; and oriented on a line parallel to the linepiece-target (par. 22).

This places the 0 of the scale in a position forthe measurement of -deflections (par. 21).Without disturbing the orientation, the telescopeand compass are turned until the compass needle isopposite its index. This index is on the telescopeaxis, so that the telescope is pointing to the magneticnorth. The angle has then been measured from the


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-24-target to a fictitious aiming point, i. e., the magneticnorth.

The angle thus measured is then transmitted toa similar instrument near the piece and from whichthe piece can be seen; or the instrument can be movedto this position. The latter is better if time permits,for compasses have individualities. The instrumentsetting is -left unchanged; it is only necessary toplace the needle opposite its index by turning bothupper and lower limbs. The instrument is thenoriented the same as previously. From this pointthe method is exactly the same as that of par. 22.The -telescope is turned on an aiming point or thepiece, whichever method is selected, and the readingis the same as the angle T'BP' or T'BG in Figure 8,par. 22.

26. (c) By the map, but without compass. Asimple method is that indicated in par. 21. Thepiece, target and aiming point are located accurate-ly on the map. The angle at the piece from the tar-get clockwise to the aiming point is then measuredwith the protractor.

A more practicable and more general, and inmost cases more accurate, method is the following,used on stabilized fronts: A line is materializedon the ground and carefully surveyed as to directionexpressed in true azimuth. The direction is thenplotted on the map, as well as the position of the tar-get and piece. The angle between the line of fire(piece-target) and the line on the ground (orientingline) is then measured. clockwise from the line offire.by means of the protractor.

The aiming circle or similar instrument is thenset up on the orienting line at any point where thepiece can be seen. The angle read from the map isthen set and the aiming circle pointed on the orient-


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-25-ing line by turning the entire instrument. Thisplaces the zero of the horizontal scale in a directionparallel to the desired line of fire. The telescopeand upper limb can then be pointed on a distant aim-ing point or on the piece as expedient and the de-flection found as in par. 22-23.

27. (d) By the map, with compass. This meth-od is much the same as (b), par .25.It is necessary to know the declination constantof the compass of the aiming circle used. 'This isthe setting such that when applied and the entireaiming point turned till the needle is opposite its in-dex, the zero of the scale will be pointed at the truenorth. In other words, it is the setting which willpermit orientation on the true north by means of theneedle.

Begin by setting up the aiming circle at anypoint from which the piece can be seen and orientingit on the true north in the manner described. Markthe true north on the ground by setting the upperlimb at 0, sighting through the telescope and settinga stake on the vertical hair.Plot the piece and target on the map, and with

the protractor measure the angle at the piece fromthe target clockwise to. the grid or true north. Setthis angle on the aiming circle and turn the wholetill the telescope is on the stake marking the truenorth. The aiming circle is then oriented in a di-rection parallel to the line of fire, and the angle tothe piece or aiming point can be read with his orien-tation, in the same manner as for (a), par. 22.28. Conversion of angle read into deflection. Theangle at the piece measured clockwise from thetarget to the aiming point, discussed in the forego-ing paragraphs,must be converted to the sight grad-uations, unless the instrument used has a second


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-26-scale which makes the conversion automaticaly. Thisis true of the French aiming circle for the 75 gunand of the new American aiming circle for th e "New.U. S." scale shown in Figure 4, par. 8.

If the aiming circle makes no conversion, thefollowing methods are applicable:

75 gun. Add 100 to the angle read (see Figure2, par. 8) ; subtract as many quadrants of 1600 milsas possible. The remainder is converted into pla-teau and drum by inspection, thus:

Angle read on aiming circle, 2975.2975+ 100-3075.3075-1600= 1475or Plateau,14, Drum 75

Or the angle read is 435435+100=535or Plateau, 4, Drum 135

155 howitzer. Add 1000 to the angle read (Fig-ure 3, par. 8) ; if the sum is greater than 6400, sub-tract this amount, thus:

Angle read is 5800.5800+1000=68006800-6400= 400

New U. S. (Figure 4, par. 8). Subtract 3200from the angle read if it is greater than 3200.

29. Deflection difference. Thus far only a singlepiece has been considered, but the battery com-mander has ordinarily to find the deflection forthe four pieces of his battery. In Figure 9 thepieces G1, G2, G3, and G4 are laid with parallel linesof fire (parallel fire), by means of a common aimingpoint P. The deflections are d 1 , etc., as indicated.G2 P 1 , G 3 P 1 and G 4P 1 are all parallel to G 1P. Similar-ly G 3P2 and G 4P. are parallel to G 9 P,, and G 4P8 isparallel to G 8 P. It will thus be seen that the deflec-tions decrease successively from the right (1stpiece) to the left (4th piece). d 2 is less than d 1 bythe angle P 1G9 P, or G 9 PG 1 , or roughly 1 platoon front


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-27--L'?7es f bre

P

DEFLECTION OIFFERENCE

G2G1 divided by the distance to the aiming pointG1P, or 20GAP (in thousands)Also d3 is less than d2, and d4 than d3, by the sameamount.


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-28-In other words, if the pieces be equally spaced,

the deflection of the adjacent pieces for parallel firediffers by a constant amount called the deflectiondifference. The deflection difference is announcedas such with respect to a certain piece, usually theright, for which the deflection determination wasmade. A command might be, for example, "Pla-teau 8, Drum 135; on No. 1, close 5." All pieces setthe deflection P1. 8, Dr. 135. Closemeans to decreasethe deflection, swinging the line of fire nearer toNo. 1. Accordingly No. 2 decreases its deflection5, No. 3 twice 5 or 10, and No. 4 three times 5 or 15.

30. For nearby aiming points the deflection dif-ference is so large that it would introduce seriouserrors to assume it constant for all pieces. For thisreason nearby aiming points are not used (nearerthan 1000 yards). In case distant aiming points arenot available, reciprocal laying (par. 23) must beused. In this case, a deflection is read and an-nounced for each piece, or it may be read for onepiece and the others laid parallel to it by laying onthe sight of the laid piece (par. 23).

31. The applicability of the various methodsof finding the deflection depends on the situation andalso on the facilities at hand particularly the mapsand instruments.

For rapid work, such as the hasty occupation ofposition and immediate opening of fire, (a) on theground, without map or compass, is ordinarily themost suitable method (par. 22). The use of an aim-ing point is more rapid than reciprocal laying, butfrequently the ground is such that a suitable aimingpoint cannot be found. Reciprocal laying is very sat-isfactory.

Method (c) (par. 26) is the most precise andsatisfactory method developed for a highly organ-


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-29--ized stabilized sector, carefully surveyed. If a goodmap and time are available, it can be used even whenthe terrain is not so well organized beforehand.

The compass method (d) (par. 27) is a fair sub-stitute for (c) when the ground is not organized forthe use of the latter.

In connection with the use of maps there is al-ways a considerable amount of topographical workto be done for accurate work unless the m ap and thedata pertaining to it are very complete. This makesan abundance of t ime essential.

FINDING THE SITE32. The site is necessary for indirect laying (par.

16). It m ay be determined:(a) By direct measurement.(b) By indirect measurement and calculation.(c) From the map.

An estimation of site, unless comparative, is gen-erally worthless. It is better to use 0 than pure es-timation, unless the site is so considerable that itssign at least is reasonably certain.

St

Bh, _ _ gSy

B'Fag.I.

SITE DETERMINATION


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-30-(a) Direct measurement . An aiming circle is

set up sufficiently near the piece to be considered asa t the piece for practical purposes. The site is thenmeasured directly by the portion of the instrumentused for vertical angles.

(b) Indirect measurement and calculation. InFigure 10, B is the observation point where the tar-get T and the piece G are visible. But T is not visi-ble from G.

The figure is one enclosed by 5 faces; the sidefaces are vertical, as well as th e lines BB' and TT';the face GB'T' is horizontal. Construct BBh parallelto B'T', and BBh ' parallel to B'G.

The angle TGT' is the one desired but it cannotbe measured directly. The best solution ordinarilypossible, and a general one, is to find the differencein elevation between G and T, T'T, and divide thisby the distance GT' or GT. TT' is made up of BB'+BhT'.

BB'=Sg (measurable) X GB (in thousands).Similarly BhT St (measureable) XBT (in

thousands).GT must either be estimated, or be determined byplane table, calculation, or similar means.

Example: St=+25 mils BT4000 yardsSg=-10 mils GB= 800 yardsGB makes an angle of 450 with the line of fire GT.

Required: The site SSolution: BB' = 8 yards BhT = 100 yardsTT'=108 yardsGB projected on GT is about 800 x.7=560 yardsBT projected on GT is substantially 4000 yeards.

108Therefore GT=4560 yards and S =-=24 mils4.56And, since T is higher than G, the sign is +, orS= +24 mils.

Careful attention must be paid to the signs ofSt and Sy; BB' and BhT will not always be added asin this case.


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-31-(c) From the map. This is simple, provided

the map is contoured or otherwise provided with el-evations. The difference in elevation between thepiece and the target is read from the map, togetherwith the range. The site can then be computed asin the preceding case.

FINDING THE RANGE33. Three methods are used:

(a) The map,(b) Range finder,(c) Estimation,in the order of general accuracy.

The map is ordinarily more accurate than therange finder, their relative accuracy depending onthe quality and scale of the map, assuming that therange finder is well handled. The accuracy of a maprange can frequently be increased by topographicaloperations to locate accurately the target and thepiece; time is an important factor in such work.

The service range finder in the hands of a rea-sonably trained officer or soldier is some four timesmore accurate than estimation. Its probable errorfor artillery ranges up to about 5000 yards is 90yards. The range finder is in most cases more rapidthan the map. It is the only reliable means of effect-ively attacking a rapidly moving target which is vis-ible only a short time.

FINDING THE ELEVATION34. As seen in par. 11 and those following, some

systems of sights have scales so graduated that therange may be set directly on the sight in either di-rect or indirect laying. In the latter case, the site isset separately.

Such graduations, however, are strictly correctfor but one ammunition, and during the war there


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-32-were as many as 20 kinds of ammunition issued forthe 75 gun at one time.* So that even though thesight be graduated in range, it is-often necessary touse tables showing the proper setting for a givenrange for the ammunition to be used. Such tablesare called range tables or firing tables. When thesight is not graduated in range, range tables are in-dispensable.

The range tables give considerably more datathan the elevation corresponding to a given range,some being more as of interest or for study thanpractical utility.

The drift is the movement of the projectie outof its initial plane of fire due to the rifling, gravity,and the air resistance. It is to the right for right-handed rifling.

The angle or slope of fall is sometimes necessary,for example as in par. 67.The probable error is discussed under Firing

(par. 43).35. When the range has been found (par. 33),

the use of the tables to find the range setting or el-evation is best explained by the following examples:

((a) The range has been determined as 1600meters. What range should be announced for the 75gun, using shell with direct laying?

In the range tables, opposite the range 1600, isfound the required value, 1400. The range scale wasgraduated for the French shrapnel; the shell is amore efficient form ballistically and has a highermuzzle velocity.

(b) The range has been determined as 7300 me-ters, and the site as +24 mils. What data should

*Due either to form or weight of projectile or fuse,necessitating different tables.


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-33-be announced in order to lay the 155 howitzer forelevation by means of the sight mounting?

Since there is no stated condition to m ake thisinadvisable, the smallest possible charge will be used.Charge 1 will theoretically reach this range but con-ditions might well give a short with the maximumelevation ; therefore Charge 0 is chosen. The re-quired data are then: Charge 0; Site, +24; Eleva-tion, 481 twentieths.

(c) The range has been determined as 6800 me-ters and the site as -5 mils. What data should beannounced in order to lay the 15 gun for elevationby the sight mounting, using shell?

A reference to the table shows that this rangeis off the scale of ranges, but a range setting is givenwith a notation in the column, "Site + 100., Thismeans that the range setting may be used if the siteis raised 100 mils, which has the, effect of increasingthe elevation sufficiently to make up the deficiency inthe range scale. Therefore the required data are:Shell; Site, +95; Range, 450.

(d) The range has been determined as 4600 me-ters and the site as +14 mils. What data should beannounced in order to lay the 75 gun for elevation bymeans of the gunner's quadrant (par. 19), usingshell ?

The elevation for 4600 meters is 803'14

14 mils = - = 47' (dividing by .3 is substantially the same as.3multiplying by 3.375, footnote, par. 8). Therefore8'3'+47'-8'50' is the quadrant elevation. The datarequired are then: Shell; Quadrant, 8050'.

36. Time fire. Time fire is with projectiles,either shell or shrapnel, equipped with time fuses setto give bursts in air before the projectile strikes. Inthis case, an additional element of the firing data is


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-34-necessary, the fuse setting. This may be the tabulartime of flight given in the range tables, or a specialcolumn of fuse settings m ay be included in the tables.

It ordinarily hapens, however, that the tabularsettings are incorrect due to atmospheric conditionsor other causes. This necessitates a correction ofthe tabular values each time a new range is used,for if the tabular values are incorrect for one range,they are incorrect for other ranges. The gradua-tions are in range to avoid the range tables. Therange announcement serves both for the sight andthe fuse setter. If the bursts are not correct, therange setting is not changed; but instead the correc-tion is made on an auxiliary scale, called the cor-rector or correctorscale. In this way the correctiononce made is applied automatically thereafter regard-less of range. The range tables or drill regulationsgive a tabular corrector which is ordinarily used tostart firing in the absence of more accurate data as tothe correct value for the particular conditions.

SUMMARY OF FIRING DATA. REFINEMENTS OFTHE PREPARATION OF FIRE

37. Summary of firing data.-From he preced-ing discussion, the firing data and the methods of ob-taining them m ay be summarized as follows:

Aiming point: Distinct, definite and distant point,or an instrument near th e pieces. Used to layfor direction with indirect laving.

Deflection: (par. 21 et seq.) : Setting of sight to beused to give correct direction; necessary in bothdirect and indirect laying.

Deflection difference (par. 29): Correction ap-plied with indirect laying to make the deflectionapplicable to the pieces other than th e one forwhich it was determined.

Site (par. 32): The angular height of th e targetfrom th e piece, used with indirect .laying; an-nounced and set separately from the elevation, orincluded in th e announced elevation, accordingto materiel and method.


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-35-Projectile, charge, fuse: Generally speaking, mat-ters of selection rather than determination; must

be specified however.Fuse setting (par. 36) Necessary in time fireonly.Method of fire (pars. 57 and 58, b) : Discussedlater.Range or elevation (par. 33 et seq.) : Range oftarget determined in various ways; range tablesthen used to give the proper range or elevationsetting to be announced.38. Refinements of the preparationof fire. Re-

ference has already been made in several instancesin the foregoing discussion to particulars in whichthe preparation of fire could be refined if time andfacilities permitted, such as:

The use of accurate maps for deflection and range.Topographical operations to secure more accuratedata as to deflection, site and range.Care and minuteness of instrumental measurements;calculations; entering into deflection, site andrange.The advantage of so doing is evident: the effectdesired is produced more rapidly and more surely,as the accurate preparation eliminates a part of theadjustment during firing. This shortening of thefire for adjustment renders our artillery less exposedto neutralization or destruction before accomplishingits mission.39. In addition the war gave great impetus tothe practical application in the field of refinementsin the following respects:

(a) Those related to peculiarities and irregularitiesof the pieces and ammunition which affect thefire, such as, weight and form of projectile,variation in powder charge, wear of the boreand its effect on velocity.(b) Atmospheric conditions, such as, the density orweight of air, temperature and its effect on theair and powder, wind.All of these matters had been studied beforethe war, but their practical application had been lim-ited to the coast artillery. Their wide applicationin the war was possible on account of the elaborate


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-36-organization and equipment of the front. Their ap-plication in the future will depend on the recurrenceof comparable conditions.

Refinements of this character had the greatesttactical importance in the, surprise attacks on theWestern front in 1918. In fact, during the winter1917-1918, the Germans radically revised their ar-tillery technique along these lines in order to permittheir great offensive of 1918. The French had theirsystem perfected upon our arrival in Europe in 1917,the process having been started immediately upon theorganization of th e Western front.

40. No detailed explanation of corrections forthe elements enumerated is possible here; they arecovered in the service firing tables and in the Manualof Artillery Firing.

It is of importance, however, that the combatarms with which artillery works appreciate in a gen-eral way the disturbing elements affecting artilleryfire. Those here considered are distinct from disper-sion discussed later (par. 42).

Values are tabulated below for 75 shell atranges of 5,000 and 10,000 meters, for the variouselements stated.

Range-Meters5,000 1,000

1.5 inches of barometer change, due eitherto temperature or pressure, will change th eactual range, in meters, by 144 ' 367

10 meters/sec., or 33 ft/sec., change inthe muzzle velocity of the piece will changethe actual range, in meters, by 93 134

A wind up or down the range of 22 milesper hour will cause a variation from the tabu-lar range, in meters, of 88 322

A variation of 1 lb. 10 oz. in th e weight ofprojectile will cause a variation in the range,in meters, of 40 132

365 955(NOTE: These values are for a concrete case, and are

strictly correct only for this case.)


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-37-If a combination of such influences should occur,as is possible, in such a way that their results wouldbe cumulative, it can be seen that the point of fall ofprojectiles would be changed by 365 meters for therange of 5,000 meters and 955 meters for the range10,000 meters.The dominating element in the above figures istemperature, and it is appreciated that large varia-

tions in this element are possible even in a few hours.It is possible to correct at least partially for suchconditions, provided the necessary meteorlogical andother data are available. This may or may not be thecase.41. In general, it may be concluded that the pre-paration of artillery fire requires a period of timevarying from a minute to hours and days, dependingon the situation. The artilleryman's art consistsnot only of a familiarity with all methods, but of asensibe appreciation of what methods are applicableand appropriate in a given situation, and what resultscan be expected.


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PART IIFiring

DISPERSION42. In the preparation of fire, it is believed thatsufficient details were given to bring out the unavoid-able approximations and the many uncertain ele-ments entering into the problem, and make it evident

that the preparation of fire must in the general casebe imperfect. Imperfections are not confined to thepreparation of fire, but enter into the firing itself,notably because of dispersion.

Dispersion is the scattering of shots intended tostrike or burst in the same place. Shots fired withthe same data and ammunition should strike in thesame place, but it is well known that such is neverthe case.

43. Law of dispersion. It has been conclusivelyestablished that the points of fall of a very largenumber of supposedly like shots will always begrouped according to a fixed law, called the law oferrors. The law can be applied to a particular caseand all desired details calculated, when a character-istic value, called the probable error, is known. Ex-planation of the law of dispersion by what is some-times called the 25-16-7-2 rule is sufficient for thisdiscussion.

The supposedly like shots group themselvesabout a center, or center of impact. Consider theposition of the shots only in range. One-half areshort and one-half over. Their distribution is shownin Figure 11. The parallel lines are equi-spacedand one probable error apart. The middle line passesthrough the center of impact. With the space di-vided in this manner, the percentages of a very large

39


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-40-number of shots which would fallvarious spaces are those shown.

Center

for range in the

Figure 11.These values are not strictly accurate, but are

sufficiently so for practical purposes. The principalinaccuracy is in the outer or 2% spaces. The shotsare not actually confined to the limits "4" shown, butthe proportion outside is very small (7/io of 1% forboth sides of the center). Two per cent includes allshots not included in the other spaces.

The spaces are subdivisible with fair accuracy,thus: 50% of the shots are within 1 probable error ofthe center; within what limits would 70% be in-cluded? 70-50=20% are in the 16% spaces, 10%in each. By proportion, which is not strictly correct,the 10% would occupy 19%6 of the 16% space; or 70%of the shots would be within 1s/s probable errors ofthe center.

The same process applies to dispersion in direc-tion.

2% 37%

216%

125/Q

025%

116%

27%

32 %

4


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-41-* 44. Probableerror. The values of the probableerrors for the different projectiles and ranges are

given in the range tables. These values are a mea-sure of the accuracy of the piece. The values given,however, are those of the proving ground, with veryfavorable conditions. For this reason, it is custom-ary to increase the tabular probable errors by 50%in using them practically.It should be remarked that the probable error indeflection is very small as compared with that inrange, and that the probable error, in both rangeand deflection, increases rapidly as the range in-creases.45. Dispersion is a practical factor in severalrespects:

(a) It makes hits less frequent.(b) It prevents our infantry from receiving the fullmeasure of protection from artillery fire, becausethe fire on the objective of attack must cease orlift when they are still some distance away; orif the infantry approach too close, they suffercasualties from our artillery fire.(c) It greatly increases the difficulty of conductingartillery fire.46. It is generally taken that infantry cannotapproach more closely than the following distancesto the center of impact of fire of the 75 gun, in thedirection of range, that is, when the fire is over theirheads:

H. E. shell or time shrapnel, depending on the range,150 to 200 meters.Time shell, ' 200 to 250 meters.This takes into consideration the dispersion ofthe trajectory, the effective radius of the fragments,and, in time fire, the dispersion of the fuse in time

of burning.If the fire is enfilade, these distances may be re-duced to about 75 meters. If the ground slopes


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-42-downward from us toward the enemy, they must beincreased.

FIRE FOR ADJUSTMENT47. It is eminently desirable to correct whatever

inaccuracies occur in the preparation of fire, duringthe firing itself. This is in general possible if the fir-ing can be observed, and the period of the firing de-voted to this correction is called fire for adjustment.When the adjustment has been completed as far ascircumstances permit, fire for effect is or may be un-dertaken. If observation is not possible, fire for ef-fect is delivered from the outset, but with diminishedeffectiveness due to lack of adjustment. No amountof careful preparationof fire can entirely eliminatethe necessity of fire for adjustment, nor yield thesame effectiveness.

48. Observation, on which fire adjustment de-pends, is viewing the bursts or strike of the projec-tiles in order to determine their location with respectto the target. Observation is of two broad classes,aerial and terrestrial. The former is discussed later(par. 68).Terrestrial observation is classified, according tothe position of the observer with respect to the lineof fire, as: axial,when the observer is on or near theline of fire; forward,when he is materially in advanceof the pieces; lateral,when he is to one flank. Com-bined observation is the use of more than one obser-ver at considerably separated points; this method,when well organized, enables the shots to be locatedwith respect to the target in both range and direction.A single observer near the line of fire observesfor direction by noting the angular deviation of theshot from the target. A command to the battery"Left (or right) (so much)," stating the deviationobserved, will correct the direction of the shot rea-


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-43-sonably closely. He cannot, however, measure direct-ly the distance of the shot from the target in range.If, however, the smoke of the burst obscures the tar-get, he knows the burst is short; if the smoke brings.the target into relief, he knows the shot is over.49. The two classes of observation:

Combined, which locates the shot in both directionand range,and the single-observer forms, which locate definite-ly only in direction, and short or over in range,control and determine the two methods of fire foradjustment, i. e.:(a) Adjustment by measured deviations.(b)' Adjustment by bracketing.50. Adjustment by measured deviations. Thesecond shot is corrected by the amount the first shotdeviates from the target and should thus hit the tar-

get; in general, it does not, and is corrected by one-half the deviation. The third shot is corrected byone-third its deviation; and so on till the adjustmentis sufficiently refined. This gives due weight to allof the shots fired and should insure a steady approachto the target. Unfortunately, however, the informa-tion as to the position of the shot essential to thismethod'is rarely available, and its application is lim-ited principally to highly organized fronts. It shouldbe noted that dispersion makes its influence felt inthis method by protracting and complicating theprocess.

51. Adjustment by bracketing. This is themethod in general use. The fire is opened at therange determined. The direction is corrected bythe measured deviation. If the observation forrange is "short," the range is increased; if "over,"the range is decreased. The amount of the rangechange depends on the accuracy of the initial deter-mination; if we were very confident of its accurcy;about 100 meters would be sufficient; but if the ini-


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-44-tial range was estimated and rather long, 400 metersrange change would be advisable. One or more shotsare observed at this altered range, and if still inthe same sense as the first range, the range is againchanged the same amount. Finally, a range will befound which gives shots in the opposite sense. Therewill thus be two ranges, differing by 100, 200, or 400meters, or by an equivalent amount in elevation,one range giving observations short and the othergiving observations over. These two ranges or ele-vations constitute what is called a "bracket." Thesize of the bracket is generally stated, thus, "a 100-meter bracket has been obtained."

52. It would seem that a bracket based on cor-rectly observed shots would make it certain thatthe target lay within its limiting ranges. Thiswould be true but for one factor-dispersion. If oneshot is observed at say the short limit of the bracket,a reference to Figure 11 will show that the shot maybe one at the short limit of the dispersion. In thiscase, although the particular shot is short, the rangemay.really be over, which raises doubt as to the cor-rectness of the bracket.

For this reason, it is good practice to verify abracket, before finally accepting it, by securing atleast two observations at each limit.53. After obtaining the first bracket the processof range adjustment is continued by firing at the

mid-range of the bracket. When this range hasbeen observed, a new bracket results of one-halfthe size of the former one.' This process is con-tinued until a bracket is obtained of a size equal tosix tabular errors, approximately 100 to 200 meters,generally nearer the former value. Firing at themid-range of this bracket will almost surely giveboth shorts and overs for the same range. Based


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-45-on the proportions of shorts and overs, small changesof elevation are made until substantially equal pro-portions of shorts and overs are obtained. Thisconstitutes what is known as a precision adjustment,used for the destructionof a target such as a batteryor trench.54. It frequently happens that, during the earlystages of bracketing, a range gives both shorts andovers. The bracketing ceases in this case, and firingat.this range is continued, if a precision adjustmentis sought.55. ~Bracket adjustment. Frequently the tar-get is of indefinite extent in range, so that therewould be no object in a precision adjustment onsome one point of it; or again, the time available maybe too short to permit a precision adjustment, forsuch firing takes time; or the target may be suscep-tible of movement or in slow movement. In such cases,the bracketing process is cut short with a bracket ofabout 200 meters, sometimes more or less, depend-ing on the conditions. Fire for effect must thencover all of the bracket in order to be sure of reach-ing the target; and this method is followed (par.58-b).. Such an abbreviated or rough adjustmentis called a bracket adjustment.56. Adjustment of time fire. Time fire may bewith either shrapnel or shell. The adjustment oftime shrapnel consists essentially of a. bracket ad-justment for range the same as though the fire werepercussion, followed or accompanied by an adjust-ment of the fuse so that the projectile will burst inair at the proper height. This height depends onthe weapon: For the 75 gun, the best height ofburst in fire for effect is 3 mils above the target, butthe trajectory passing through the target.

With time shell fire, the object is to place theburst vertically above the target, at a linear height


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-46-of about 20 meters. The methods are somewhatdifferent from those used with time shrapnel.

57. Method of fire during adjustment. Theusual method of fire during adjustment is the salvo,and generally by the entire battery. A salvo is thesuccessive discharge of the pieces at regular inter-val from one flank of the battery to the other. Theinterval is about three seconds. The object of theinterval between shots is to permit the observationof individual shots, in order that all possible informa-tion may be derived from them. Salvos may beplatoon or battery, depending on whether two orfour pieces are used.

FIRE FOR EFFECT58. Fire for effect is of three classes, depending

on the extent of the preceding adjustment:(a) That based on a precision adjustment (par.53), called precision fire for effect. This is simplya continuation of the last stages of adjustment.Successive salvos are fired at the range or elevation

determined in adjustment. Firing is continued un-til the desired effect is obtained or until a large ac-cumulation of observations gives definite indicationthat the range is incorrect. In the latter case,which would generally be due to changed atmospher-ic conditions, a suitable change in elevation is madeand the firing continued.

(b) That based on a bracket adjustment, calledzone fire for effect (par. 55). The entire depth ofthe bracket is searched, in bounds of 25 to 50 metersfor shell and 100 meters for time shrapnel. If am-munition is available, a shell should be fired every10 meters in deflection for the 75 gun and every20 meters for the 155 howitzer . The method ofcovering the area depends, however, on the time and


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-47-ammunition available and the importance of the tar-get.

The method of fire used may be battery volleys,in which each piece fires rapidly a prescribed num-ber of rounds with fixed data, but without regardto the other pieces; or zone fire, in which each piecefires rapidly and independently through an entireseries of different firing data. Zone fire is some-what more rapid than volleys, but the fire is not aswell in hand and is apt to become erratic unless thebattery is extremely well trained.(c) That based merely on the preparation offire, without previous adjustment, called systematicfire for effect. The method is the same as for zonefire for effect, except that the depth and widthsearched must in the general case be greater thanwith the bracket adjustment, in order surely to coverthe errors in the firing data. It was this methodwhich was used so extensively in the great surpriseattacks on the Western front, since the considera-tion of secrecy prevented practically all preliminaryfire for adjustment.

This method particularly, and (b) to a lesserextent, are extravagant in ammunition, and rela-tively ineffective. The lack of concentrated effectmust be offset by increasing the amount of artilleryfiring on a given locality; the rate of fire is limitedby the resistance of the mat6riel.Precision adjustment (a) is the only methodwhich can be relied upon for considerable destruc-tion. Methods (b) and (c) cause more or less de-struction, but are principally effective in neutral-izing, that is, causing the enemy to take cover, andkeeping down or stopping his fire.59. Adjusted fire can be delivered on a targetwithout adjustment on that target itself, particular-ly when good maps are available. A prominent


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-48-point, called the datum or registrationpoint, is se-lected in the vicinity of the target, and a precisionadjustment made upon it. The fire is then shiftedto the target by measuring the difference in databetween the datum point and the target, either fromthe map or on the ground. The use of a datumpoint may be necessitated either because observa-tion on the target is not possible or because the tar-get has not yet appeared. Registration is an effect-ive method of preparing to attack prospective tar-gets quickly, but it may reveal prematurely the pres-ence of the artillery.

60. Another case special to a highly organizedsector is the use of a witness point. An adjustmentmay be secured on a target by special means, suchas flash or sound ranging, aerial observation, ex-ceptional atmospheric conditions, etc., but it maynot be possible or desirable to fire for effect atthe time, or it may be necessary to repeat the firefor effect at some other time, when conditions wouldbe changed and the same facilities for adjustmentwould not be available. It is therefore necessaryto "record" the adjustment on the ground in sucha manner that it can be utilized later when de-sired. This is done by means of a nearby pointcalled the witness point, of the same character asthe datum point but used differently. Immediatelyafter the adjustment on the target, a precision ad-justment is made on the witness point. The differ-ence in the firing data on the target and the witnesspoint are compared and recorded. When later itis necessary to fire on the-same target, but observa-tion on it is not possible, an adjustment is made onthe witness point, the previous differences in datafor the target applied to the new adjustment, andfire for effect delivered on the target. It is essen-tial that the first firing on the witness point be de-


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-49=

livered immediately before or after the adjustmenton the target, to eliminate discrepancies due tochanged atmospheric conditions.

SPECIAL SHELL61. In addition to the principal projectiles, theH.E. shell and the shrapnel, there are a number ofspecial shell, notably the gas shell and the smokeshell, as well as the thermite, the star or illuminating,

and the incendiary shell. There is nothing special inthe methods of firing these projectiles. They areordinarily constructed so as to give the same trajec-tory as the shell, thus enabling the necessary ad-justments to be made with shell. This is generallyadvisable in order to avoid betraying the intention ofusing the special shell before it can be used effec-tively.The kinds of special shell, their effects, and thequantities to be fired to produce the desired effectare covered in other lectures and in special regula-tions.

EFFECT OF FIRE62. Before the lade war, the data on the effect offire was largely experimental, and thus limited; orcalculated, considering the effect of the individualprojectile and the dispersion as measured by. theprobable error.In service however there are so many conditionsentering into the effect produced that pre-war datahave been largely discarded in favor of the large

mass of practical data accumulated during the war.Some few data are given here, from Frenchsources:

Destruction of batteries:By 75 gun, 500 to 800 rounds.By 155 howitzer, 300 to 400 rounds.By 155 gun, 400 to 600 rounds.


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-50-By 8 or 9 inch calibers, 200 to 300 rounds.By 12-inch, or similar calibers, 100 to 200 rounds.

For each weapon, it is assumed that the protec-tion of the battery attacked is such that it can besuccessfully attacked by the particular weapon.

Wire cutting :75 gun, a breach 25 meters wide in a band of wire15 to 20 meters deep, 600 to 800 rounds at

mid-range and 1,000 to 1,200 rounds at longrannge, fired by one battery.155 howitzer, same breach, 200 to 300 rounds.

Destruction of trenches:75 gun, not effective, except to a certain extent

when the trench can be enfiladed.155 howitzer, 80 to 100 rounds for each point

selected for destruction.CLEARING THE CREST. REACHING A REVERSE

SLOPE63. Clearing the crest. In paragraph 7 it isstated that protection and concealment are advan-

tages of indirect laying; in fact, they are the princi-pal ones. The amount of protection afforded by aridge behind which artillery is emplaced dependsprincipally on the steepness of the slope in front ofthe position, the steeper the slope the better the pro-tection. But if the slope is too steep, firing will biimpossible because projectile will not clear the crest.It is evident that the crest can be cleared for a longrange or a large site when it would not be cleared fora short range or small site.

A number of methods are used to determinewhether a crest can be cleared under given condi-tions, but this discussion will be limited to a singlemethod.

64. In paragraph 16 it is shown that the quad-rant elevation used for indirect laying is the eleva-tion for the range increased algebraically by thesite. If St is the site of the target, Ert is the eleva-


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-51-tion for range of the target, Eqt is the quadrant ele-vation for the target, then

E qtErt + StThese values can be readily found in a given

case by the methods already explained (see par. 37),and have no reference to clearing the crest.

Now suppose it were the intention to fire, not atthe target, but at the crest itself. If the elevationfor the range from piece to crest is Ere, S, is the siteof the crest measured from the position of the piecein the same manner as for the target, and Eqc is thequadrant elevation sought,-then we have as for thetarget

Eq-E rc+ScEscc

Ert

Eqc 5\c Eqgs

Fig. 12.CLEARING THE .CREST.

These elements are shown in Figure 12. It isevident that if the elevation for firing on the targetis greater than that for firing on the crest, the crestwill be cleared.

The addition of the elevation for the range ofthe crest and the site of the crest will always be anarithmetical one, since from its nature the crest willbe above the pieces and its site plus (+). The site of


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-52--the target, however, must be carefully considered asto sign.

The following examples illustrate the methodstated:

1. Site of target,-12 mils; range of target,3,400 meters. The pieces are in position 600 metersbehind a crest whose site is 70 mils. Can the crestbe cleared with 75 shrapnel fire? With shell fire?

Shrapnel . The elevation for the range of thetarget is, by the range tables, 60 11'. The site of thetarget, in mils, is 12/.3=40', minus.

The quadrant elevation is then 6 11'-40'=531'.

The elevation for the range of the crest is 42'.The site of the crest is 70 X 3.375=236'z--3' 56'.

The quadrant elevation of the crest is the30 56'+42'=4 38'.

The quadrant elevation for the target is thengreater than for the crest, so that the crest will becleared.

Shell. E 0 t=4 35'-40'=3 55k.This is less than the quadrant elevation of the

crest, so that shell cannot be fired at the given range.2. A certain battery position has been tenta-

tively selected from the map, on the eastern slope ofSentinel Hill, on the 900-foot contour. What is theminimum range which could be used with 75 shell,firing west over the hill? Assume the site of thetarget as 0 and the height of the treees on the hill as20 feet.

Judged from the contours, the shoulder on theslope is about on the 1,000-foot contour. The dis-tance between the 900 and 1,000-foot contours is200 yards, or 600 feet. The vertical interval, in-cluding the trees is 120 feet. The slope Qf the"crest" is then 120/600=20%20X4/7=11.43, or the slope is 110 26'


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-53-In addition it is well to allow 30' clearance to

cover inaccuracy and irregularities on the hill. Theelevation for the range of the crest is about 10'. Thepermissible quadrant elevation is then

110 26'+40'=12 26'Since the site of the target is 0, this is the per-missible elevation for the range of the target, or therequired minimum range is 6,400 meters.65. With the pieces in position the elevationwhich will clear the crest can be measured with thelaying instrument directly. Allowance must be madehowever, for the drop of the projectile between thepieces and the mask, if this distance is considerable.66. Elevation formulas. It is sometimes foundconvenient to make use of formulas which give theelevation for a given range without the use of rangetables. A number are given below, but no formulaof this kind is accurate for all ranges, unless it isvery complex.In problems to clear the crest, a clearance of 30'should be allowed in the case of the 75 gun and 1o forthe 155 howitzer to cover inaccuracy in the formulaas well as for other uncertain factors.


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-54-E is the elevation in degrees; R is the range in

thousands of meters.75 gun. Shrapnel. R (R+4)E =

4Shell. R (R5)

6155 howitzer. Shell Charge Elevation Limit ofrange.Approx.

00 R (R+5) - 90004

0 R (R+6) 80004

1 R (R+6) 70003

2 R (R+5) 60002

3 R (R+2) 50004 R (R+4) 40005 R (R+6) 3000

67. Reaching a reverse slope. Ground protectedfrom hostile fire by a covering crest can be reached ifthe angle of fall of the fire directed upon it is suffi-ciently great.. The vulnerability of terrain to firein this manner may be determined by comparing thereverse slope with the slope of fall of the trajectory.The latter is given in the range tables, but may alsobe determined by means of the empirical formulasgiven in par. 66 for the elevation. The angle of fallmay be taken as one-half greater than the elevation.The slope of terrain may be determined from the mapfor this purpose in the same manner as in problem 2,par. 64. Or the scale of map distances may be used.


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PART IIISpecial Auxiliaries

AERIAL OBSERVATION68. Aerial observation is of two kinds, balloon

and airplane. The methods of balloon observationare essentially those used on the ground. Communi-cation is normally by telephone, connection beinggiven direct to the battery firing.

69. Airplaneobservation. Airplane observationof fire has the advantage of vertical observation,which is of great value not only in the observationof fire but also in the location of targets. In terres-trial observation, the deviation laterally only can bemeasured; that in range can only be determined asshort or over. With vertical observation, the devia-tion of the shot both laterally and in range can bemeasured, at least as far as the position of the obser-ver is concerned.

The disadvantages of airplane observation offire are in communication with the ground, in themovement of the plane, the obstruction of vision forvarious reasons, and the operations of hostile planes.In addition, a high degree of co-operation betweenthe artillery and the airplane is necessary and is diffi-cult of attainment.

70. Communication between the airplane andthe ground is now by radio; it was at first by visualsignals, and indications point to the use of radio tele-phone for the future. Communication between theground and the airplane is ordinarily by panel signalsdisplayed on the ground, but some airplanes are nowequipped with facilities for receiving radio, in whichcase reciprocal radio communication is possible.

55


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-56-71. The present official manual covering the

method of procedure is "Aerial Observation for Ar-tillery," A. E. F. No. 80, Revised, with changes.

Communication is by code for the sake of bre-vity; messages can rarely be spelled out. In theground panels, there are conventional combinationsto represent the various necessary phrases, such as,the method of fire, "battery is ready to fire," "bat-tery has fired," "repeat," "acknowledged," etc.

The radio signals from the airplane to the groundare combinations of letters and numerals to designatetargets, start and interrupt the fire, and to reportthe results of shots, particularly as to the deviationsfrom the target in range and direction.

The observer can estimate distances in connec-tion with the burst of shots by comparison withknown distances between prominent objects; or hemay have a photograph of the target with the mapgrid to scale on it. When the shots are close to thetarget (about 100 meters in range or 10 meters indirection), the observer reports only the sense, asshort or over, right or left.

72. The methods of adjustment and fire for ef-fect are those described in connection with terres-trial observation (par. 47 et seq.). Adjustment bymeasured deviations can sometimes be used, when theobserver can estimate deviations with great accur-acy (par. 50).

The preparation of fire must be as accurate aspossible. In addition, if the battery has opportunityto adjust partially, the first shots are less apt to belost by the aerial observer and the adjustment willbe abbreviated. The preliminary adjustment mightbe a shift of fire from datum point (par. 59), balloonobservation, or other means.


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-57-The method of fire is mostly by battery salvo;but may be by volley if the shots are difficult to see;or by single piece, to simplify.In the early stages of adjustment each salvo isfired at the signal "Fire" of the observer. Duringfire for effect, the firing may be continuous or in longseries, the observer reporting on the fire in generalterms at intervals, unless the fire is so erroneous asto demand an interruption.

Airplane observation at night is possible, underspecial conditions.SOUND RANGING

73. Sound ranging is a valuable auxiliary in ar-tillery work in two ways: to locate hostile batteries,and to locate the strike of our own projectiles in firefor adjustment.The system is a development of the war, the mat-ter having been actively pushed by all of the warringnations during the stabilized period up to the Spring

of 1918.Six stations are selected and accurately surveyedon the are of a circle whose center, in general terms,is about where the sound to be located is expected to

originate. The stations are from 1200 to 1700 metersapart; the arc of stations should be from 1500 to 6000meters behind the front line.At each station is installed a microphone con-nected electrically to a central station. Here thereis an apparatus consisting essentially of a movingpicture film on which shadows are cast by suitabledevices as follows: first, a continuous longitudinalline for each microphone; second, transverse linesevery hundreth of a second. affording a scale for timemeasurements. When a microphone is disturbedby a sound its particular line on the film shows zig-zag instead of straight. The central station is loca-ted in a well protected spot usually well behind the


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-58-lines. There is also a control station, which mustbe in advance of all microphones. Its function isas follows: The apparatus in the central stationcannot operate continuously as it moves too rapid-ly and must be read occasionally. It is so arrangedthat it can be started and stopped electrically fromthe control station. Thus, when the. operator atthe control station hears a sound which he considersdesirable to locate, he starts the instrument in thecentral station; because of the location of thecontrol station, the sound has not yet reached themicrophones. After the sound has ceased, theoperator stops the apparatus, and the readings canbe taken.

74. Depending on the origin of the sound, itwill be recorded at the central station for the dif-ferent microphones at different times. Nothing willbe known directly as to the direction of the sound,but the instrument makes it possible to read foreach pair of adjacent stations, the difference in thetime of arrival of the sound at the two stations.Knowing the velocity of sound, the difference in dis-tanceof the origin of the sound from the two stationsmay be found. Mathematically, this determines ahyperbola somewhere on which the origin of sound islocated. Practically the asymtote of this hyperbolamay be substituted for the hyperbola itself; and sincethe asymtote is a straight line, the solution is simpli-fied. In this manner, the direction of the sound isdetermined, not for each microphone as is oftenbelieved, but for each pair of microphones. For sixmicrophones then, there would be five direction linesfound, whose mean intersection locates the sound.

75. Not only can the sound be located, butby means of the characteristics of the film recordof the microphone disturbance, the nature of the


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-59-sound recorded can be determined, such as the cal-iber of the piece firing, whether it is a gun or ahowitzer, and even the exact type.Sound ranging has its limitations. Duringheavy firing, the records are so confused that de-terminations are impossible; 5 rounds per secondsis stated as a limit in this connection. Atmosphericconditions materially affect its operation, nec-essitate corrections, and in some cases prevent re-liable determinations. An example of the latteris a wind blowing perpendicular to the line of micro-phones and toward the source of sound. On theother hand, fog and night do not interfere as inthe case of visual systems.A well trained section will be able to reportthe coordinates of a hostile battery in from 3 to5 minutes after the firing.The accuracy is variable. Under favorableconditions, the error should be within 50 metersup to 8000 meters range; and in all practicablecases, it should not exceed 150 meters. When ob-servations on the same position for a long periodof time are possible, extreme accuracy is attainedby averaging the results.

FLASH RANGING76. This system is in principle the locationof the flashes of hostile batteries or of our own

projectile bursts by means of angular observationsfrom the extremities of known base lines. Usual-ly four observation posts work together, thusgiving two check readings. The posts are accurate-ly located and equipped with special instruments.A source of difficulty is the identification andsimultaneous reading of the same flash from widelyseparated points. This is facilitated by means ofa light system. The posts are connected with a


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-60-central station by telephone and by light signals.When an observer sees a flash, he sets his instru-ment. accurately on it and at the same time pressesa key which lights his lamp in the central station.If the lamps of all or sufficient observers light atthe same instant, the central operator can assumethe observers see the same flash, and he telephonesthem to read and report.The readings are set on a plotting board, andthe result reported by telephone.In 1918, much progress was made by our flashranging sections in following moving operationsand obtaining useful results, which is far moredifficult than operations on a stabilized front.

HIGH BURST RANGING77. This is a phase of the work of the flash

ranging sections. It is used under the followingconditions: A target' cannot be seen, except per-haps by aerial observation which we will say is notavailable; but the location of the target on the mapis accurately known. This might often be the case,as bridges, buildings, road crossings, railroads, etc.The firing data is prepared as accurately as. pos-sible from the map. A series of 10 or 12 shots isthen fired at data so calculated as to give air burstssurely high enough to be visible, but with the tra-jectory directed as accurately as possible on the tar-get. The bursts are observed and located horizontallyand vertically by the flash ranging sections. Thecenter of the group is then calculated, and by meansof charts, the point of fall of the trajectory pro-longed through the center can be determined.

Unless the trajectory thus found is consider-ably in error with respect to the target, fire for ef-fect can be undertaken, by searching an area about


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-61-the calculated trajectory. Under conditions inEurope, it was stated that the accuracy of the methodwas sufficient to permit the searching of an area assmall as six probable errors in range. Precisionfire cannot be executed by this method.

78. High burst ranging may be used in the samemanner as a witness point (par. 60). For example,an airplane adjustment may have been made on atarget. To record this adjustment for subsequentuse without the necessity of readjusting by airplane,the high burst method is resorted to immediatelyafter the first adjustment. When it is later desiredto resume the fire, a series of high bursts is fired,observed, and the results compared as to trajectorywith the 'former ones. The difference determinesa correction which will put the fire again on the in-visible target.


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ABRIDGED ARTILLERYRANGE TABLES

FOR USE AT

GENERAL SERVICE SCHOOLSFORT LEAVENWORTH, KANSAS

1. 75 mm. Gun.(a) American shrapnel.(b) H. E. steel shell, Model 1917, RY fuse

(French).

2. 155 mm. Howitzer.Long H. E. steel shell, Model 1914, short fuses.

ChargeChargeChargeChargeChargeChargeCharge

00012345

October, 1919Ft. Leavenworth, Kan .Army Service Schools Press


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-3-CHARACTERISTICS OF VARIOUS KINDS OF

AMMUNITIONDivision Artillery

75 Gun and 155 Howitzer

Kind of projectile, fuse

American shrapnelFrench shrapnel -------E. E. shell, normal chargeLong fuse --------Short fuse ---------Reduced chargeShort fuse ----------AL semi-steel shellLong fuse Charge 00._Steel shell, Mod. 1917*.-Semi-steel shell, Mod.1918* --------------Steel AL R/2 shell______

Shrapnel, Charge 00_.Charge 0_.Charge 1__Charge 2__Charge 3__Charge 4__Charge 5__

Long shell (O.A.)Short Charge 00..fuse Charge 0..Charge 5__Long fuse Charge 00--Charge 0.Charge 5--

Semi-steel shell (F.A.)Short fuse Charge 00..Charge 0..'Charge 5_.Long fuse Charge 00..Charge 0..Charge 5__

30' Elevation

oycel

?r G w w U2

75 GUN17551755

17801800

1130

92509700

77008400

6500

16.4 1720 11400 890 9513.7 1900 11100 840 97

14.6 1820 10700 840 9317.6 1660 11200 880 87

155 HOWITZER

89.5

95.

95.5

96.0

96.5

144013501160940830740680

1420131066514201310665

1475136068014751360680

40' Elevation10800 865 12210200 835 1158300 800 1067000 730 1125800 685 1004800 615 1004050 580 93

1040097003950

1015095003800

1225011400425011950112004150

NOTE: In al l cases the iSS charges are 7 in numher: 00, 0, 1, 2, 3, 4, 5.NOTE: In all cases th e 155 charges*Average for various fuses.

are 7 in number : 00, 0, 1, 2, 3, 4, 5.


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-4-75 GUN

American Shrapnel 21-sec. Combination Fuse.Probable Error

d a a 0 a55 55 r o d+ cd b4 b0 a 03 o- C a

Documents

Army Artillery Firing Report