Armored Medical Research Laboratory Fort Knox, K^rtucky First Partial Report On PROJECT NO. 21, Determination of the Sources, Magnitude and Costs of Gunnery Errors Project No. 21 24 May 1944 ARLORED LEXICAL RESEARCH LABORATORY Fort Knox, Kentucky Project No, 21 472.1 SHEA 24 May 1944 L. PROJECT; No. 21, Determination of the sources, magnitude and costs of Gunnery errors; First Partial Report. a. Authority: Letter, Office of Surgeon General 24 Larch, 1944 b, Purpose: To obtain quantitative data to serve as a basis for critical evaluation of the capacities, limitations and expectations in firing on the move with the gyrostabilizer. 2. DI3GUSSION a* The ability to maintain effective fire from a moving tank is clearly desirable, provided it can be obtained at a cost which does not out- weigh the advantages gained. In order, therefore, to reach a meaningful conclusion as to the value of a particular method of securing moving fir’s, it is necessary to know its capacities and limitations in terms of quan- titative measurement of the precision of fire which can be maintained. b. The present apparatus for run stabilization is lin'd tad in its capacity in that it provides for a decree of stabilization in elevation only and leaves entirely to the gunner the problem of controlling deflec- tion. It is recognized, therefore, that the effectiveness of moving fire witH this equipment cannot approach that of firing from uhe stationary tanks,’ The lack, heretofore, of any body of basic data relative to its capacities has made it difficult to assess its value and the cost of its employment, c. It may be that the equipment has certain psychological value and ussfullness as a,weapon of opportunity. It is difficult, if not im- possible, however, to obtain factual data upon its value when so employed. If the equipment is accepted for tnis use alone, tnen the basis for accept- ance must be clearly understood and every precaution taken to 'avoid an erroneous idea of its capacities upon which the crew may depend for reduc- tion of enemy targets in given combat situation. In the present study, an attempt has been made to secure the required basid? data upon which to evaluate the equipment, the conditions of test being set up and maintained to produce a highly favorable situation for use of the gyrostabilizer0 As a basis for evaluation, the capacities and limitations of moving fire have been compared with those possessed by stat- ionary fire and firing from the halt of short duration. e. The study included evaluation of the performance of both the 75 ram gun with Ai shot and Hi) and of the cal. 30 coaxial machine pun. Because of the clearly distinct uses of the two weapons, however, the results will be retorted separately, the present report dealing with the 75 ran gun only. f. The test procedures and results are presented in the Appendix. 3. CONCLUSIONS: a. Under highly favorable conditions of operation, the comparative precisions of moving fire with the gyrostabilizer, firing from the halt and firing from the stationary tank at ranges from 200 to 1000 yards were as follows: Type Fire Probability of Hit on Tank Front Target (7 ft. by 7 ft0) 200 yds. $00 yds. 1000 yds. Stationary 99+t 99+* From halt 99+/S 99+$ 88$ Moving, with Gyro • 82$ 46'S 19$ Moving, without Gyro 46$ 18/6 6,5$ b. Above probabilities apply only to operations with a highly skilled crew, excellent mechanical condition of equipment, favorable terrain, range being exactly known, and cOiaplete familiarity with nature of ground and appearance of turret in advance. Under combat conditions, lesser proba- bilities of nits must be anticipated. c. The effectiveness of fire in terms of hits per minute upon a tank front target for equal ranges and equal rates of advance was tv.'ice as great in firing from the halt as in moving fire, and in terms of halted time only, the number of hits per minute at 2000 yards front the halt was greater than at 500 yards when moving with the stabilizer in operation. d. In situations requiring actual destruction of enemy targets no advantage to offset the reduced effectiveness of fire is seen in moving fire with the present stabilizing equipment over firing from the halt, either in terms of reduced vulnerability or greater rate of advance. e. Against selected horizontal targets, the probability of effective hits with ricochet burst H3 in moving fire at 500 yds. varied from 102 to 262 depending upon the sight employed. Chances of hitting within the target area were approximately doubled when firing from the halt. f. The effectiveness of moving fire with present gun stabilization equipment was founu to be seriously limited by the lack of stabilization in the horizontal direction and by the failure to achieve a high degree of vertical stabilization. g, As a consequence of the limited stabilization, the time lag from the instant when the gunner decides to fire until firing actually takes place produces an inevitable error in aim which appears to account for as much as 70% of the dispersion of firec 4, RECOMMENDATIONS; That the data contained in the report be considered in decisions with respect to future use of the present stabilization equipment and in the development of tactical plans which involve firing on the move. Submitted by: T. F. Hatch, Lt.Col., SnC Glasselle S. Lawson, 1st. Lt,, Inf. J0G.Dailey, Capt., FA (Armored School) APPROVED WILLARD MACHLE Colonel, Medical Corps Commanding 2 Incls. #1 - Appendix with Tables 1 thru 8 #2 - Figures 1 thru 16c APPENDIX 1. OBJECTIVES OF STUDY: The function of the gyrostabilizer is to reduce the magnitude of angular travel of the gun sufficiently to permit effective firing on the move0 Improvement is secured ,in vertical movement only, leaving the control of horizontal travel entirely to the gunner. It is evident, therefore, that full advantage has not been taken of the potential value of complete gun stabiliza- tion and the effectiveness of moving fire with present equipment cannot be expected to equal or even approximate that of stationary fire. This fact is recognized but the degree to which it limits the value of moving fire has not been fully evaluated in terms of absolute or relative effectiveness. It has not been possible, therefore,to express quantitatively the results that may be expected from firing on the move or to define the limited conditions under which it could be employed with profit. Clearly, such information is required in order to construct a basic tactical doctrine. It was the purpose of the present study to obtain such fundamental information. In order to secure reasonably comparable data and to determine the maximum usefullness of the equipment, the most favorable circumstances of use were deliberately selected for the tests. To this end, the following conditions were maintained: a. The same highly skilled and experienced crew were employed through- out, They had considerable advance practice in the conduct of the tests. b. The tank, gyrostabilizer, power traverse and other controls were maintained in first-class mechanical condition at all times. c. Gun sights were adjusted as frequently as necessary to insure accuracy of alignment in every test. do The terrain was carefully selected to cause minimum disturbance to the vehicle and to remain substantially constant throughout the study. e, For each test the exact range was known and the crew were well acquainted with the appearance of the target and the nature of the ground over which the tank moved. These favorable test conditions must be kept in mind in considering the results obtained. 2„ EQUIPMiM AMD PROCEDURES: a. Nature of tests.' (1) The relative effectiveness of fire was determined for: (a) Stationary fire. (b) Firing from halt. (c) Loving fire, with and without the gyrostabilizer (2) The ranges employed were as follows: Stationary From Halt # Moving fire with gyro Moving fire without (mean range) gyro (mean range) 200 yds. 200 yds. 500 yds. 500 yds. 500 yds. 500 yds. 1000 ydso 1000 yds. 1000 yds. 1500 yds. 1500 yds. 2000 yds. Firing from the stationary tank and from the halt were done at the specified ranges. The moving fire tests, however, were conducted over zones centered at the specified distances, the zones being IOC, 200, and 300 yds, for mean ranges of 200, 500 and 1000 yds. respectively. All ranges vjere determined by tape measurements. (3) Comparative tests were conduct-d with the periscopic sights M4 (1.44 power) and T8 (six and unit power) and telescopic sight M70 (3 power). The VJ+ periscopic sight was equipped with the M36 telescope having the older type reticle (080438)* whereas the T8 and M?0 sights were provided with the new type. The lenses in the M70 sight were properly adjusted to optimum focus. (4) Relative performance was determined for AP shot and ricochet * burst HE fuse) with the 75 ram gun and cal. 30 ball with the coaxial machine gun. The present report deals only with the results with the 75 mm gun and the performance of the machine gun will be reported separately. b. Equipment and Test Facilities (1) Terrain; The tests were conducted at Rolling Fork Range, Fort Knox, during March, April and May, 1944. The ground was essentially flat farm land, only moderately well drained, A general view of the terrain is shown in Fig, 1. Rain occurred frequently during the period of study so that the soil was saturated with water and was soft. Tank tracks penetrated to a depth of 6 inches and hence made definite but yielding ruts. An effort was made to avoid previous tracks in making a run during moving fire-. This became increasingly difficult as the tests progressed but was kept at a minimum by frequent changing of target position. In general it may be said that the terrain was relatively favorable to stable bank performance insofar as irregularity of ground was concerned. In fact, yielding characteristics of the soil resulted in smoother operation of the gyrostabilizer and traverse than was possible when driving on a smooth gravelled road, as demonstrated by motion picture analysis of the movements of the gun and tank in relation to the target. (2) Tar.rets: The target for AP fire consisted in an approximate front silhouette of a German Mk IV tank, painted CD with a black central area 30M x 4SM. The target was centrally mounted, three feet from the ground, just behind a 30' x 20' vertical net, as shown in Fig. 2. The purpose of the net, which was bahely visible to the gunner, was to permit accurate spotting of shots which missed the target. The elevation of the target above the ground permitted scoring of most shorts. In general, all rounds fired in a given test were accounted for as hits on the target or net. (a) For ricochet HE fire, the target consisted in a 3* x 4* vertical cloth panel, 0,Do in color, and mounted at ground level. Immediately back of it on the ground was laid a 12* x 12' black paper sheet, the purpose of which was to permit a rough assessment of the effectiveness of HE fire in relation to distance' of center of burst from the target area, as indicated by damage to the paper sheet or penetration by fragments0 (3) Tanks: Two production models of the medium tank M4A3 were employed. Both were equipped with M34A1 gun mount, modified gyrostabilizer and oilgear power traverse. One vehicle was equipped with mount and linkage for sight T£. Both tanks were carefully serviced prior to starting the tests and properly maintained thereafter so that day to day results so far as they may be affected by these factors were comparable. c. Conduct of tests. (1) On the stationary fire tests, the tank was located at the desired range, sight adjusted and one or more rounds fired, if necessary, to establish accuracy of alignment. For scoring, 5, 10 and 15 rounds were fired at the three ranges of 500, 1000 and 1500 yds. ho time restrictions were placed upon the gunner since the primary purpose of the tests was to establish a useful baseline of precision of the system—gun, ammunition, tank, sights and gunner. (2) For moving fire the tank was driven with bow hatches closed at approximately 10 mph through the zone in as straight a line as possible. The gunner was instructed to start firing when the tank passed the starting zone flag and to continue until the end zone flag was reached. From practice runs the practical number of rounds that could be fired during the time of passage through uhe zones was established and effort was made to maintain these selected rates of fire during the tests. Owing to irregulari- ties in ground, tank operation, and operation of gun controls, however, it was not possible to maintain the schedule exactly. In general, 40 rounds were fired in a complete test; this required from 6 to 10 trips through the zone, depending upon the sight employed. Tests with moving fire were conducted with the tank operating in two directions—directly toward the target andalong a course 20° to the left of the target.line. (3) Firing from the halt proceeded as follows: The tank traveled at 10 to 20 mph to the center of the zone and came to a halt.. The scheduled number of rounds were then fired, after which the tank proceeded at maximum speed out of the zone. The total time of travel through the zone and the actual halted time were recorded. Four, five and six rounds were fired per trip with the M70, M4 and T8 sights respectively and approximately 20 rounds were fired in a complete test* d. Collection of data. Observations of temperature, humidity and wind velocity were regularly made and the relative visibility and position of the sun in relation to tlie target line recorded. The contrast between the target and background was low and remained essentially constant. The deposition of hits over the target and net area was determined in rela- tion to horizontal and/vertical reference lines so that the dispersion pattern could be described statistically for each test. Similarly, the distribution of centers of airburst from HIS fire, as indicated on the ground, was determined in relation to the center line of fire and position of the target. In certain of the test moving picture records were obtained of the angular movement of the gun in relation to the target. From these records information was obtained respecting the relative stability of the gun at the time of firing and in addition, they provided e quantitative measure of the success with which a * skilled gunner can track the target. Information with reference to the relative role of vertical as compared with horizontal movement (velocity and amplitude) was also provided by these photographic records. Other data collected included measurements of the time lag in firing, including reaction time of the gunner and lag in the firing mechanism0 e. Presentation and analysis of results: The results of all tests, firing from the stationary and moving tank and from the halt, at the several ranges and with the three different sights, are shown in the form of dispersion plots in Figs. 3 to 10 inclusive. The position of each hit with AP shot is indicated by horizontal and vertical coordinates over the 20* x 30* net. In the case of the ricochet HE, the center of effect of each burst on the ground is plotted for both range and deflection with reference to the target position and line of fire. On each graph the mean point of impact (MFI) is also shown. (l) The dispersion patterns were, in each case, subjected to statistical analysis, the horizontal and vertical distributions being treated separately on the assumption (borne out by examination of the data) that the elevation and traverse controls operate independently of each other in deter- mining the overall pattern* The calculations included determination of the mean point of impact (MFI), the standard deviations of the horizontal (Of) and vertical (Oy) dispersions and the area including and probability of hits,* The last two are determined directly from GJ and Gr as and l6*OOi*OV respectively. The use of these statistical parameters of the normal probability curve is justified in view of the good agreement between the observed dispersions and the normal distribution, as demonstrated by the representative case in Fig. 11. The resulting values are tabulated in Tables 1 to 7 inclusive, together with the number of rounds fired and the number of actual hits on the target. From these tabulated data one may determine the * The area on a vertical target is comparable in significance to the dis- tance of two probable errors in range, as commonly employed in artillery evalu- ation, in that there are equal chances that a hit v.ill occur within or outside this area. It is the product of the horizontal and vertical distances about the mean point of impact which include 70.7J» of hits in each direction (0.707 x 0.707 = 0.500). relative effectiveness of fire under the several conditions of operation 3, RESULTS: a0 Stationary fire: The known high accuracy of stationary fire is demon- strated by the results of the present tests, as shown in Figs0 3,4 and 5, and in Table 1. The angular dispersion was roughly constant without regard to range, the standard deviations being Co 22 rails both horizontally and vertically This leads to a 90$ probability of hits* over an area considerably smaller than a tank silhouette0 Even at a range of 1500 yds0 the area of 90$ probabil- ity is only 28 square ftQ as compared with 49 square ftc for the tank front targeto b0 Moving fire: (l) The comparative performance of moving fire with the gyrostabilizer in operation was strikingly different, as shown in Figs07,8 and 9 and in Table 20 In terras of standard deviations, the horizontal and vertical dispersions were increased 7»5 to 17o5 times over those for stationary fire with corres- ponding decrease in effectiveness0 Thus, the area of the 90$ probability of hits at 200 yds. is 69 square ft0 or 40$ greater than a tank front (7*x 7®); at 500 ydSo the 90$ area increases to 193 sq0 ft0 or 4 times the area of the tank target, and at 1000 yds0, the area of 90$ probability is over eleven times greater. In terms of angular dispersion, there was a consistent decrease with range, as illustrated in Figo 120 This is to be expected in view of the re- lative decrease in target size at the longer ranges, with consequent increase in the care with which the gunner selects his aim. The performance when fir- ing from the moving tank traveling 20° to the left of the line of fire did not differ significantly from the results obtained when moving directly toward the target**0 Although the differencies between sights were not highly signifi- cant; the best performance was given by the 6 power T8 periscopic sight.*** (2) The relative effectiveness of moving fire with stabilizer, with the practical certainty of stationary fire) is well expressed in terms of the probabilities of hits on a tank front targetQ According to present tests, these are 82$,A6$ and 19$ at 200, 500 and 1000 yards respectively (see Table 5 and Fig, 13). Thus, to obtain the same probability of hits on the target as in stationary fire it would be necessary to fire 102, 2C2 and 5o3 times as many rounds0 With stationary fire, however, it is possible to aim at selected areas within the target which are relatively the most * All statements in this report in regard to probability of hits are based upon the range being known0 ** Angle fire was investigated because it was felt that it might Improve traverse control, owing to the need for constant adjustment of the deflection in one directionD *** The nature of thee© tests does not permit a complete evaluation of the T8 sight in terms of its most important characteristics since questions of re- lative ease of target identification and use in failing light against camouflaged targets, etce, were not involvedo TABLE 1 Dispersion of Hits in Stationary Fire 75rom Gun - AP Shot No, Rounds Dispersion SIGHT Fired Hit Target °y Area,ft.^ Area,ftS*994$ and 88$ at 200,500 and 1000 yards respectively (See Table 5 and Fig,13). Even at 2000 yards the probability of hit on the tank front target was 6b to 80$, which is roughly equivalent to the chances of a hit at 200 yards with moving fire. Of greater significance, perhaps, is the relatively higher rate of effective fire, i.e0, actual hits per minute. Moving at an approximate rate of 10 mph through the firing zone, it required on the average,45 vsecondSand 68 seconds respectively to travel through the 200 yard and 300 yard zones for the 500 yard and 1000 yard ranges. During these trips the number of rounds fired averaged 4 with the 1570,5 with the 1*4 and 6 with the T8 sights. From these figures and the percentages of hits on the tank front target, the number of bits per minute was calculated. The total time of passage through the zone and the halted time were recorded during the tests of firing from the halto Since the number of rounds fired during each trip was kept constant at 4,5 or 6 for the respective sights, it was possible to calculate, similarly, the number of hits per minute when firing from the halt. The resulting data are presented in Table 6 and Fig. 14« In terms of overall time of passage through the zone, one notes that the effective rate of fire was generally more than twice as high when firing from the halt than from the moving tank and that at ranges of 1500 and 2000 yards, the number of hits per minute was nearly as great as at 500 yards with moving fire.- In terms of halted time only, the difference is many times greater with the result that more effective fire can be maintained from the halt at 2000 yards than * Owing to the sSoft ground, tank speed was limited. This increased time of passage through the zone ana thus decreased the rate of effective fire (hits per minute) in the technic of firing from the halt. TABLE 3 Comparative Dispersions of Hits in Moving Fire - With and without Gyrostabilizer 75mm Gun - AP Shot Gyro Sight . No, of Rounds MPI Fror Cent* fi Target 3r,fto . Dispersion <*» <*> 50% Area sq0 ft. Area 8(J • f t Fired rJSi Net Hit Target Horiz, V 61lv o ft, Mil ft. 1 mu MEAN RANGE - 200 YARDS Wi^h IIK 20 20 13 - 06 4*1,3 2,3 3o84 1.9 3,17 19.0 70o0 Without M4 20 20 a -2,0 ♦0.8 2o33 3.88 40S 8o0 49,0 iaodo With M4 40 40 is -1,6 ♦1,5 4,3 2 0a< • 3»3 202 62,6 226 o0 Without U4 20 15 5 flo2 t*20$ 4,2 2.8C i 9.0* 6o0* 166,0 600.0 * Obtained graphically from plot on probability paper, in absence of exact information on position of 5 misses0 TABLE k Dispersion of Hits in Firing from Halt 75mm Gun - AP Shot Sight No. of Rounds | £PI from Center,. Parget Dispersion rte 9k °y 5056 Area sq.ft. Area sq.fto Fired On Net ■lit Target HoriZo Verto fto Mil fto Mil RANGE - 500 YARDS Ml* 20 20 20 ♦ o3 - o3 1.23 1.31* i*o2 ll*.3 M70 18 18 18 - o5 -1.1* loll; 1.36 7o0 25.0 T8 20 20 20 4* o 7 -lo8 loOO lo29 60U 23 0 3 Aver, ■ 1.13 o7£ lo33 0o9 5.97 20 o87 RANGE - 1000 YARDS M1* 20 20 18 + o? -lo8 loOO 1.29 5*5 20 o0 M70 20 20 19 - oi* - .7 2ol2 1,1*1 13 0 2 1*7.0 T8 -r-— 2h 2i* 21* - ok - .1* 1.90 lo73 li**U 1*9.0 Averc 1.78 o59 1.1*9 .50 llo03 33o66 RANGE - 1$00 YARDS Mi* 20 20 12 *2.5 -1«2 2,1*3 1.87 20o2 73ol M70 20 20 16 0 ~ °5> 2,1*1 lo79 18,0 67,2 T8 2h 21* 20 - o2 - o5 1.87 loi*£ lie 7 1*2,3 Aver0 2o26 ,5o lo72 .38 RANGE « 2000 YARDS M70 20 17 13 ♦loU -lo2 2o8* 2.6* 69.1 258.0 T8 20 20 16 0 ♦lo3 2o0* 2o5* iiOoO 153,0 Aver. 2,1* 0ol*0 2.55 0oi*2 51*0 5 205.5 graphically from plot on probability paper because of positions of extreme hits0 TABLE 5 COMPARATIVE PROBABILITIES OF HITS Stationary Fire, Firing From Halt, Loving Fire With and Without Gyrostabilizer i TYPE FIRE Probability of Hit on Tank Front* at Stated Ranges 200 Yds. 500 Ydse 1000 Yds0 Stationary 99+ % 99+ % 99+ * « From Halt 99+ i 99+ 88* Moving, with Gyro 82% 46/S 19* . Moving, without Gyro 46/o IS* 6.5/^(est) Taken to be 7 ft. x 7 ft. TABLE 6 Comparative Rates of Fire and Kits per Minute Moving Fire with Gyrostabilizer and Firing from Halt RANGE SIGHT RDSo PER .'/IMUTE HITS PER MINUTE Moving From Halt Moving From H alt O £ Halted Total Halted 500 yd M4 5o7 5o5 19.0 202B 5.5 19.0 n M70 5.3 4.3 17o0 1.85 4.3 17.0 it TB Bo0: 6oO 20 o0 3.93 6.0 20.0 IC00 yd uu 4.26 3o7 14o5 Oo57 3.3 13.0 tt M70 3.90 3.1 1101 1 o OB 2.9 10o5 n TB 5.02 4.1 14 oO Oo93 4.1 14.0 1500 yd M4 - 2.5 9o7 - 1.5 5.8 ti M?0 - 2*2 9.7 loB 7.B it TB - 20e 9.6 - 203 Bo0 20D0yd M4 - - - 1 n M70 - 2*2 4.0 - 1.4 2.6 ii TB - 3.7 Bel - 2.9 6.5 at 500 yards from the moving vehicle. This substantial gain in effective fire is accomplished without significant, if indeed any, cost in terms of vulnerability since the time of passage through the zone is increased only 25$ • Firing from the halt appears also to lend itself more suitably to evasive action with consequent decrease in vulnerability. d. Comparative results with ricochet burst HE: The results of tests of moving fire and firing from the halt are shown graphically in Fig. 10 and summarized in Table ?• With 'the M4 sight, the dispersion in range was in good agreement with that anticipated from the vertical dispersion obtained with AF fire. The standard deviation in the latter case was 2.1 mis which, when converted into range for M48 HE (70 yards per mil at 500 yards.) amounts to 147 yards, as compared with 130 yards, actually obtained with HS fire. In the case of the M?0 and T8 sights, however, the dispersion in range was con- siderably better than expected from the A? results. With all three sights the deflection dispersion was approximately equal to that obtained with AF fire, the high majority of burst centers being within 10 ft, of the line of fire. The probability of securing an effective hit on a horizontal target, was low. This results in part from the fact that the center of the burst has to be -Immediately adjacent to the target area to produce damage and emphasizes the need for high accuracy of fire against a selected horizontal or dug-in target which is not attainable with moving fire. Taking as a minimum criterion, the ability to place bursts within + 15 yards of a selected mean point of impact to secure effect, the probabilities in moving fire are 10, 20 and 26% with the 14, M?0 and T8 sights, respectively. 'When firing from the halt, the probabili- ties were increased in these tests to 55$ and 32$ for the M70 and T8 sights0 e. Stability of gun in moving tank: The angular travel of the gun in relation to the target, as recorded for representative periods of 3 to 5 seconds just prior to shooting on the 1000 yard range, is shown in Figs, 15a to 15f, Separate curves are presented for horizontal and vertical movement. They are plotted with constant time and angle scales so that the velocity of travel at any point may be readily determined as the slope of the tangent of the curve. The curves show a marked variability in magnitude and velocity of travel and a complete lack of cyclical regularity and there appears to be no relation between the period or amplitude of the horizontal and vertical movements. The action of the gyrostablTizer in improving vertical stability is demonstrated by the greater regularity and considerably less amplitude in the elevation curves* It is clear, however, that full advantage cannot be taken of this relative stability because of the highly erratic behavior of the horizontal movement. For effective shooting on the move it is evident that three favor- able conditions must occur simultaneously; the angular velocity of the gun must be zero or at a constant minimum rate in both directions and it must course across the target at the instant of firing. In only two of the 12 instances illustrated was the gunner able to select a favorable condition with respect to the angular velocities. It is not known whether or not the gun was so adjusted as to pass the target center simultaneously in these two cases. In all other instances there was considerable angular velocity in one or both directions. TABLE 7 Comparative Dispersions - Ricochet HE Moving Eire with Gyrostabilizer vs Firing from Halt Range - 500 Yds0 TYPE FIRE SIGHT No* Rounds MPI, yds Range Range Dispersion, yds. Probability of burst within*15 yds of MFI7 % Fired Damage Target °y 50* Range 90* Range Moving U4 40 2 4=30 130 176 420 10 Moving M70 20 0 +13 62 84 202 20 From Halt M70 20 4 0 13 17 42 55 Moving T8(6x) 20 0 -20 47 64 150 26 From Halt T8(6x) 20 4 420 31 42 100 32 f, Time lag in firing: Because of the wide variability in velocity and magnitude of travel of the gun and complete lack of similarity between the two curves, it becomes obvious that the time lag between the instant when the gunner decides to shoot and the time of actual firing is an important factor in determining the accuracy of moving fire. Accordingly, approximate measurements of this time lag were made on the gunner and the tank employed in these tests. Technic of measurement was as follows: The gunner was seated in the stationary tank and followed through the sight a lamp bulb 100 ft. distant which was moved about a zone to approxi- mate the magnitude and velocity of movement of the actual target in the field. He kept the gun on this target by means of the hand elevation wheel and power traverse. His signal to fire was the turning on or off of the lamp. This signal started an electric timer which was stopped when the firing pin struck the shell casing, the elapsed time representing the total time lag. In order to eliminate the learning factor the observations were carried out repeatedly during an afternoon and the following morning and afternoon. The overall improvement from one afternoon to the next was not significant. The increase over simple reaction time caused by tracking the target was found as the difference between the total time, as measured above, and the time required to complete the action when the gunner simply watched for the signal without simultaneous tracking0 The mechanical time lag in the firing button and in the solenoid and following mechanical linkage were similarly measured, using appropriate electrical contact switches to mark the beginning and end of the period. The average results from twenty or more measurements for each element are given in Table 8, The total time lag is seen to be approximately one-half second. Because of the artificial nature of the ex- perimental technic this is believed to be a minimum figure. It does not allow, for example, for the disturbance to the gunner in the moving vehicle with consequent necessity for him to keep his eye in the sight and at the same time operate the controls. As an approximate measure, it may be applied to the curves of gun movement, in Figs, 15a to 15f, thus making possible a comparison between the stability of the gun at the instant when the gunner decided to fire and the actual time of firing. The comparative velocities and the degree of gun travel during the one-half second lag period are shown on each curve. Several significant points emerge from study of these curves. It is evident that the stability of the gun as measured by angular velocities was no better at the earlier period. Of greater importance, the distance the gun moved during the lag period varied widely and in a wholly unpredictable manner. This observation is important in view of the statement in the Technical Manual 9-731A that in moving fire the gunner learns to anticipate gun movement and is thus prepared to fire the instant the line of sight comes through the target. From a study of these records one must conclude that this alleged practice is not practi- cal owing to the unpredictable speed of angular travel of the gun. As a matter of fact, careful questioning of the gunner revealed that he simply fired, when the target was properly lined up in the sight without regard to the stability of the gun at that moment and with no allowance for time lag0 The correctness of aim then, was a matter of chance and, according to the records illustrated here, there is a 50-50 probability of the error being TABLE 8 Time Lag in Firing ELEMENT TIME - SECONDS Aver. 90% Range Simple Reaction Time 0.285 0,24 to 0.34 Reaction Time with Tracking 0.407 0.30 to 0.48 Lag in Firing Mechanism 0.104* 0.095 to 0.130 Total Tine Lag 0.511 0.44 to 0o60 * Foot button - 0*042; solenoid and mecnanical 0,062 within or outside an area of 2<>92 x 4.50 mils. Converted to area in square feet at 1000 yards, this equals 119 square feet which may be compared with an average area of 163 square feet for 50% probability of actual hits at 1000 yards, as shown in Table 2. The relative magnitude of these values suggests that a major portion of the error in moving fire with present limited stabilization, which exists in spite of the selection by the gunner of relatively favorable moments for firing, arises from the inherent time lag involved in the process. Reference to Table 8 shows that 8C$ of this elapsed time is chargeable to limitations in rapidity of action of the gunner and of this some 10% is basic reaction timea Improvement of controls might decrease the added reaction time resulting from tracking and better design of the firing mechanism woplld reduce its contribution,, It is doubtful, however, if these would reduce the total by more than 25%* g Comparative stability of gun in relation to terrain It is recognized that the relative stability of the gun during tank movement is influenced by the roughness and irregularity of the ground over which the vehicle is travelling, Because of this, essentially flat terrain was selected for these tests in an effort to secure the most favorable conditions of operation. The degree to which this was achieved id demonstrated by comparing the records of angular movement of the gun during the firing tests (Figs 15 a to 15f), with similar curves (Figs, 16a to 16c) obtained while making a dry run over a prepared gravel surface roadway at Cedar Creek Range, Fort Knox, with the gunner tracking a target some 700 yards distant. The curves for Rolling Fork Range are seen to be smoother and more regular than those for the prepared roadway and demon- strate the somewhat superior ground characteristics,on the area selected for the tests. It may be concluded, therefore, that the results here reported represent performance on highly favorable ground, a condition which will not ordinarily be encountered in combat areas. ko SUMMARY OF RESULTS ; Insofar as the 75 mm'gun is concerned, the results of these tests show that, even under the most favorable conditions, the relative precision of fire on the move decreases rapidly with range and that the cost, in terms of increased ammunition requirements to accomplish an effective result is high, especially in view of the limited amount of ammunition available in the vehiclec It is further demonstrated th-t this excessive cost is largely wasted in view of the evident lack of advantage gained over firing from halt. The superiority of effective fire with the latter technic is clearly shown and, at the same time, there is no evidence of increased vulnerability of the tank to enemy fire or marked decrease in the rate of advance. As a matter of fact, in neither case is it possible to show any real advantage from the standpoint of reduced vulnerability, since the speed of the moving tank was not great enough to effect seriously the precision of an opposing high velocity antitank gun. The limited precision of moving fire is inher- ent in the equipment and must remain so as long as limited stabilization is provided in elevation only. It is clear from the present study that even the degree of vertical stabilization which is now provided cannot be fully utilized so long as the gunner is required to control the highly erratic and rapid horizontal movement of the gun entirely by means of the power traverseo Furthermore, without a high degree of stabilization in both directions, the precision of fire is necessarily limited by the unavoidable time lag between the decision to fire and the instant when firing actually occurs a Project No. 21 General View of Rolling Fork Range, Showing Area Employed in Tests ARMORED MEDICAL RESEARCH LABORATORY FORT KNOX, KY. Figure 1 TANK FRONT SILHOUETTE TARGET AND 20' X 30' NET -2" MESH NET, 20‘ X 30' WITH 5‘ COORDINATES— FIG. 2 tank silhouette TARGET / . FIG. 2 FIG. 3 OBSERVED DISPERSIONS, STATIONARY FIRE AND FIRING FROM HALT M4A3 MED. TANK, 75 MM GUN, AP M72 AMMUNITION RANGE - 500 YARDS STATIONARY FIRE - M 4 HALT AND FIRE-M4 STATIONARY FIRE-M70 HALT AND FIRE -M 70 STATIONARY FIRE-T8(6X) HALT AND FIRE-T8(6X) FIG. 3 FIG. 4 OBSERVED DISPERSIONS, STATIONARY FIRE AND FIRING FROM HALT M4A3 MED. TANK, 75 MM GUN, AP M6I AMMUNITION RANGE -IOOO YARDS FIG. 4 FIG. 5 OBSERVED DISPERSIONS, STATIONARY FIRE AND FIRING FROM HALT M4A3 MED. TANK, 75 MM GUN, AP M6I AMMUNITION RANGE -1500 YARDS FIG. 5 FIG. 6 OBSERVED DISPERSIONS, FIRING FROM HALT M4A3 MED. TANK, 75 MM GUN, AP M6I AMMUNITION RANGE-2000 YARDS FIG. 6 FIG. 7 OBSERVED DISPERSIONS, MOVING FIRE WITH STABILIZER M4A3 MED. TANK, 75 MM GUN, AP M72 AMMUNITION RANGE - 500 YARDS FIG. 7 FIG. 8 OBSERVED DISPERSIONS, MOVING FIRE WITH STABILIZER M4A3 MED. TANK, 75 MM GUN, AP M6I AMMUNITION RANGE -IOOO YARDS FIG. 8 FIG. 9 OBSERVED DISPERSIONS - MOVING FIRE WITH AND WITHOUT STABILIZER M4A3 MED. TANK, 75MM GUN, (M-4 SIGHT) APM72 AMMUNITION FIG. 9 OBSERVED DISPERSIONS - HIGH EXPLOSIVE FIRE MOVING FIRE WITH GYROSTAB1LIZER AND FIRING FROM HALT FIG. 10 RANGE-500 YARDS 40 ROUNDS 20 ROUNDS 20 ROUNDS 20 ROUNDS 20 ROUNDS DEFLECTION SCALE-100 FT = '/g INCH FIG. 10 FIG. II HORIZONTAL AND VERTICAL DISPERSIONS MOVING FIRE WITH GYROSTABILIZER 500 YARDS-T8 (6X) SIGHT (STRAIGHT LINE EQUALS NORMAL PROBABILITY DISTRIBUTION ) LOCATION OF HITS - FROM EXTREME LEFT AND BOTTOM OF NET HORIZONTAL DISTANCE - FEET I HORIZONTAL DISPERSION VERTICAL DISTANCE - FEET VERTICAL DISPERSION PROBABILITY SCALE PERCENT HITS < STATED DISTANCE FROM HORIZONTAL AND VERTICAL REFERENCE LINES FIG. II FIG. 12 DISPERSION OF FIRE IN RELATION TO RANGE COMPARISON OF STATIONARY FIRE, FIRING FROM HALT AND MOVING FIRE WITH GYROSTABILIZER HORIZONTAL AND VERTICAL STANDARD DEVIATION - MILS RANGE-YARDS FIG. 12 FIG. 13 PROBABILITY OF HITS ON TANK FRONT TARGET IN RELATION TO RANGE COMPARISON OF STATIONARY FIRE, FIRING FROM HALT AND MOVING FIRE WITH AND WITHOUT GYROSTABIL1ZER 75 MM GUN, AP SHOT STATIONARY PROBABILITY OF HITS - PERCENT RANGE-YARDS FIG. 13 FIG, 14 EFFECTIVE RATE OF FIRE IN RELATION TO RANGE COMPARISON OF FIRING FROM HALT AND MOVING FIRE WITH STABILIZER 75 MM GUN, AP SHOT RANGE-YARDS FIG. 14 FIG. 15 a ANGULAR TRAVEL OF GUN IN MOVING FIRE WITH GYROSTABILIZER RECORDED MOVEMENT PRECEEDING SHOT-IOOO YD. RANGE -ELEVATION ANGULAR TRAVEL OF GUN IN 'ELEVATION AND DEFLECTION - 10 MM = 2 MILS DEFLECTION ELEVATION DEFLECTION TRAVEL IN i SEC., MILS ANGULAR VELOCITY MIL /SEC TIME PRECEEDING SHOT-SECONDS TIME 'lag' FIG. 15 a FIG. 15 b ANGULAR TRAVEL OF GUN IN MOVING FIRE WITH GYROSTABILIZER RECORDED MOVEMENT PRECEEDING SHOT-IOOO YD, RANGE ELEVATION - ANGULAR TRAVEL OF GUN IN ELEVATION AND DEFLECTION - 10 MM = 2 MILS DEFLECTION ELEVATION DEFLECTION TRAVEL IN - SEC., MILS ANGULAR VELOCITY MIL/SEC TIME PRECEEDING SHOT - SECONDS T|ME_J LAG~^ FIG. 15 b FIG. 15 c ANGULAR TRAVEL OF GUN IN MOVING FIRE WITH GYROSTABILIZER RECORDED MOVEMENT PRECEEDING SHOT-IOOO YD. RANGE ELEVATION ANGULAR TRAVEL OF GUN IN ELEVATION AND DEFLECTION - 10 MM = 2 MILS iDEFLECTION ELEVATION DEFLECTION TRAVEL IN - SEC., MILS ANGULAR VELOCITY MIL/SEC TIME PRECEEDilMG SHOT-SECONDS UTIMEJ LAG FIG. 15 c FIG. 15 d ANGULAR TRAVEL OF GUN IN MOVING FIRE WITH GYROSTABILIZER RECORDED MOVEMENT PRECEEDING SHOT-IOOO YD. RANGE ANGULAR TRAVEL OF GUN IN ELEVATION AND DEFLECTION - 10 MM = 2 MILS ELEVATION DEFLECTION ELEVATION DEFLECTION TRAVEL IN - SEC., MILS ANGULAR VELOCITY MIL/SEC i z TIME PRECEEDING SHOT - SECONDS TIME ’lag" FIG. 15 d FIG. 15 e ANGULAR TRAVEL OF GUN IN MOVING FIRE WITH GYROSTABIL1ZER RECORDED MOVEMENT PRECEEDING SHOT-IOOO YD, RANGE ELEVATION ANGULAR TRAVEL OF GUN IN ELEVATION AND DEFLECTION - 10 MM = 2 MILS DEFLECTION ELEVATION DEFLECTION TRAVEL IN | SEC. MILS ANGULAR VELOCITY MIL / SEC TIME PRECEEDIN6 SHOT-SECONDS TIME_ LAG FIG. 15 e FIG. 15 f ANGULAR TRAVEL OF GUN IN MOVING FIRE WITH GYROSTAB1LIZER RECORDED MOVEMENT PRECEEDING SHOT - IOOO YD. RANGE ELEVATION ANGULAR TRAVEL OF GUN IN ELEVATION AND DEFLECTION - 10 MM = 2 MILS DEFLECTION ELEVATION -DEFLECTION TRAVEL IN - SEC., MILS- ANGULAR VELOCITY MIL/SEC TIME PRECEEDING SHOT - SECONDS TIME_ LAG FIG. 15 f FIG. 16 a ANGULAR TRAVEL OF GUN WITH GYROSTABILIZER RECORDED MOVEMENT ON HARD ROAD SURFACE (DRY RUN) TIME-SECONDS ELEVATION ANGULAR TRAVEL OF GUN IN ELEVATION AND DEFLECTION - 10 MM = 2 MILS DEFLECTION ELEVATION DEFLECTION TIME-SECONDS FIG. 16 a FIG. 16b ANGULAR TRAVEL OF GUN WITH GYROSTAB1LIZER RECORDED MOVEMENT ON HARD ROAD SURFACE (DRY RUN ) TIME-SECONDS ANGULAR TRAVEL OF GUN IN ELEVATION AND DEFLECTION - 10. MM = 2 MILS ELEVATION DEFLECTION ELEVATION DEFLECTION TIME-SECONDS FIG. 16 b FIG. 16c ANGULAR TRAVEL OF GUN WITH GYROSTAB1LIZER RECORDED MOVEMENT ON HARD ROAD SURFACE (DRY RUN) TIME-SECONDS ELEVATION ANGULAR TRAVEL OF GUN IN ELEVATION AND DEFLECTION - 10 M M = 2 MILS DEFLECTION ELEVATION DEFLECTION TIME “SECONDS FIG. 16 c