Armored Medical Research Laboratory Fort Knox, Kelkituc^v Third Partial Report On PROJECT NO, 37 - STUDY OP ERRORS IN FIELD ARTILLERY PRACTICE SUBJECT: ANALYSIS OF REQUIREMENTS FOR ELIMINATING ERRORS IN LAYING GUNS IN ELEVATION Project Ko, 37 6 April 1945 ARMORED MEDICAL RESEARCH LABORATORY Fort Knox, Kentucky Projects AMRL No. 37; NDRC, SOS-11 File 413.74-4 6 April 1945 THIRD PARTIAL REPORT ON STUDY OF ERRORS IN FIELD ARTILLERY PRACTICE 1. PROJECT: No, 37, Study of Errors in Field Artillery Practice, Third Partial Report; Subjects Analysis of Requirements for Eliminating Errors in Laying Guns in Elevatione a, Authority: Ltr. AGF, 413.68 (R) (8 Apr. 1944) GNRQT-10/78261 dated 8 April 1944. b0 Purpose: To investigate sources of personnel errors in laying the gun in elevation and to recommend improvements in instrument design to minimize chances of error from this source in artillery practice. 20 DISCUSSION: a. In the First Partial Report of this Study (18 Sept, 1944) reports of frequency of errors at the battery showed that among troops in advanced train- ing from 12 to 20$ of the errors were in laying the guns in elevation, Of these errors, the most common were 100 fk in magnitude, but others ranging from 5 to 98 jd were also observed or reported. Errors in elevation were commonly referred to in conference with experienced artillery officers and it was evident that they stood out in the minds of these officers because of the actual or potentially more serious consequences from errors in range than in deflection„ Increasing demands for close artillery support to ground troops in combat has also placed greater emphasis upon errors from this source. These observations and reports clearly indicate the need for improvement in the technic of laying in elevation to reduce the chances of error. b. An analysis of the present form of instruments employed for elevation setting shows that they are basically similar to the panoramic sight and possess the same inherent weaknesses from the standpoint of potential error in use. Laboratory and field studies of the present panoramic sight (See Second Partial Report, 22 March 1945) have emphasized certain clear-cut causes of error in reading, and studies of a modified instrument have indicated the possibility of eliminating these difficulties for the most part, through the application of new principles in design. These principles are equally applicable to elevation-setting instruments and form the basis of the recommendations presented below. c, A more complete discussion of the problem is presented in Appendix I and the essential principles of design of improved instruments are considered in Appendix II. 1 3. CONCLUSIONS; a. Field observations and reports indicate the need for improvement in design of instruments employed in laying guns in elevation in order to reduce the occurrences of errors from this source. b. Analysis of present instruments shows that they possess the same inherent weaknesses from the standpoint of errors in use as are found in the panoramic telescope and that the same principles of design may be employed to give improved function. c. Increasing use of time fire indicates the need for more universal provision of separate means for setting artillery pieces in elevation and for adjusting angle of site0 d. Examination of fire control equipment on present artillery pieces reveals wide variation in the characteristics, method of mounting and of use of the instruments for control of elevation. Development of a few standard instru- ments of proper design would greatly lessen problems in training, supply and field use. e. Leveling vials on the instruments have the limiting lines painted on the glass, Many of the lines have become indistinguishable, primarily because the paint has been chipped or worn out of the grooves. 4. RBCOMESKDATIGNSt a. Provide separate means for laying guns for elevation and angle of site on all artillery pieces which employ time fire. b. Provide elevation and angle of site indicating instruments of direct- reading types, as outlined in Appendix XI, wherein the entire angular value is obtained as a continuous number read from left to right and requiring minimum interpolation on the scale. c. Improve gunner's quadrant. Ml, as outlined in Appendix II, d. In any program for future developments in artillery materiel, that consideration be given to maximum possible standardization of fire control equip- ment so as to reduce the number and variety of instruments for laying guns in elevation. e, Provide leveling vials with the red lines permanently fused into the glass. 5. ACKNOWLEDGEMENT This project is a joint undertaking with RDRC and the field tests reported herein were jointly conducted with the staff of KDRC, Project SOS-11, Dr, John P. Nafe, Director, 2 Prepared by: Theodore Fo Hatch, Lt0 Col,, SnC, AHRL Frederick S, Brackett, Lt„ Col0, SnC, AMRL Steven M0 Horvath, Captain, SnC, AMRL APPROVED BY WILLARD MACHLE Colonel, Medical Corps Commanding 3 Incls: #1 - Appendix I #2 - Appendix II #3 - Figures 1 and 2 3 APPENDIX I lo Improvement in elevation-setting instruments. Field observations and reports (See Project No* 37, First Partial Report, 18 September 1944) indicated that errors in gun laying occur in elevation as well as in deflection and for the same basic reasons, namely, displacement of the coarse and fine scales and lack of certain relation between the two, sparse numbering of scales, etc, The frequency of errors in elevation sotting of the piece is definitely lower, however, than is the case in laying in deflection,, There are a number of reasons for this, of which the most important is the fact that elevation commands are given throughout adjust- ment as complete values and only changes in angle of site are commanded in terms of shifts. Another reason for fewer errors in elevation setting is the smaller magnitude of changes in adjustment as compared with deflection shifts. Despite the lower frequency of errors, however, improvement of instruments to insure even fewer mistakes is desirable, especially when it is recalled that an elevation error on the negative side may endanger friendly troops. The increasing emphasis upon close artillery support for advancing troops correspondingly increases the demand for maximum accuracy of laying in elevation. a. Analysis of the sources and magnitude of errors in reading and setting values on the panoramic sight (See Project No, 37, Second Partial Report, 22 March 1945) reveals certain correctable weaknesses in instrument design: (1) Coarse and micrometer scales displaced from each other and in a direction opposite to the order of reading, i.e., with the hundreds value obtained from a scale on the right; (2) coarse scale continuously moving with reference to the index mark so that for high micrometer readings the index appears to coincide with the next higher hundreds value, thus leading to the well-known 100 error; (3) errors in interpolation on micrometer scale, arising from the fact that the scale is numbered at only 10 intervals; (4) insufficient fineness and clarity of engraving, lead- ing to confusion in scale reading. These sources of error apply equally to the elevation quadrant and the same approach is required in correcting and improving instrument design. Specifically, it is recommended that the hundreds and micrometer scales be brought together so that the complete elevation setting is read from left to right as one continuous number. The units and tens portion of the scale must be enlarged so that every second value, at least, can be numbered, thus minimizing the necessity for scale interpolation. The size and clarity of the numbers and lines must be such as to insure maximum ease of reading. The instrument must also be rugged and capable of withstanding the severity of field use. Proposed designs incorporating these specifications are presented in Appendix II« bo The final adjustment of the piece is accomplished by means of leveling vials. In a large number of levels seen on the guns, the red paint employed to emphasize the etched lines on the vials had been chipped or worn off. As a con- sequence, leveling was not being accurately accomplished. The errors resulting were of small magnitude, but are of considerable importance in time fire and in the close support of infantry. This deficiency can be readily corrected by fusing the marking material into the lines of the glass vial. Incl* #1 1 20 Separation of angle of site and elevation* The ra£id advances in the development and use of time-fire technic has emphasized the need for independent setting of elevation and angle of site© Such independent adjustments are found at the present time only on the light field pieces (75 mb and 105 mm howitzers, 76 mm and 3" AT guns) and on the 1918 models of the 155 mm gun and howitzer,, The modem medium and heavy artillery (4i% 155 mm, 8" and 240 mm) are not provided with this feature* As a consequence, it becomes necessary, in the case of time- fire, for FDC personnel to maintain continuous records of the separate elements (elevation and site) of the total elevation command and to apply corrections properly to these two elements in the course of computations in fire adjustment in order to determine the correct quadrant elevation commands to be sent to the battery0 In contrast, when separate commands are given for elevation and angle of site such repeated separation and combination of figures is not necessary with consequent lesser confusion* Experience in the course of study of artil- lery errors indicates that all unnecessary confusion in procedures, computations, etc*, should be reduced to a minimum in order to minimize frequency of errors* For this reason it is recommended that on all field artillery weapons which employ time-fire, provisions be made for separate setting cf. elevatiob ana angle of site0 3o Variation in elevation instruments„ The characteristics of the various types of elevation setting instruments provided with present day field artillery pieces are shown in Table 1* For the thirteen weapons listed there are eight different kinds of instruments* In five out of the thirteen cases, the elevation setting scales are incorporated in the telescope mount whereas the remaining eight are provided with separate direction and elevation instruments on opposite sides of the weapon* For seven weapons (75 and 105 mm pieces and 1918 model 155 ■» gun and howitzer) separate setting of angle of site is provided* Only the light artillery pieces are equipped with range drums and in modem practice these are not commonly used* In two cases (155 nan gun 111 and 8* howitzer Ml) no elevation scale is provided and complete dependence is placed upon the gun- nery's quadranto In practice the gunner*s quadrant is also commonly used in laying the 4o5w gun and the 155 mm howitzer Ml despite the fact that an elevation scale is incorporated in the telescope mount of these weapons* This practice arises in part frern the awkwardness of one-man laying which was evidently intended in the original design since the elevation scale and panoramic telescope have a common mount* This difficulty is most conveniently obviated by having the eleva- tion set in advance on a separate instrument (gunner’s quadrant) which can bs quickly positioned for laying in elevation after the gunner has completed the deflection setting* ae It is recognized that there are structural and operational dif- ferences between weapons which make it necessary to employ a variety of in- struments for laying in elevation, A consideration of these difference* is outside the scope of the present project* From the standpoint of causation of errors in field artillery practice, however, it is desirable to reduce to a minimum the number of different types of Instruments employed and to provide in every instrument those basic features of design which insure maximum ease and certainty of reading and setting* It is therefore recommended that in the con- sideration of changes in design of elevation and angle of site instruments, as proposed in Appendix II, concurrent consideration be given to the standardization Inclc A 2 of methods of employment of these instruments and their attachment to the various weaponsa It may be possible* for example, to provide one basic instrument for all light artillery and another for the medium and heavy weapons, thus simplifying supply, interchangeability of parts, development of training aids, training of gun crews, and shifting of gun crews in the field0 It would appear desirable, also, to establish a definite policy with regard to separation or combination of de- flection and elevation setting instruments so that proper provisions can be made for convenient access to the instruments in laying for elevation and direction0 Inclo #1 3 TABLE 1 CHARACTERISTICS OF ELEVATION-SETTING INSTRUMENTS FOR FIELD ARTILLERY WEAPONS Weapon Carriage Elev0 Setting Instrument Part of Tel0Mount Elevo Scale Range, Mila tenge Drum Provided Separate Angle of Site Scale 75 nan How0 MIAI MS Mto#Tel0 >M3 Yes 0-800 Yes Yes 75 mm How0 MIAI K3A3 Quad0Range M3 No 0-800 Yes Yes 75 mm Gun 111897 M2A3 QuadoRange M4 No 0-1200 Yes Yea 105 mm How0 M2AI M2A2 Quad qRange M4 No 0-1200 Yes Yes 105 mm How„ M3 M3M3AI Quad, Range M8 No 0-800 Yea Yes 4o5n Gun MI MIAI Mt0,Telo ,M25* Yes 0-1100 No No 155 mm Kow0 MI MIAI Mto,Telo,M25* Yes 0-1100 No No 155 mm How. M191S M1918A3 St.,Quad0,Ml916AI Yes 0-1600 N® Yes 155 mm Gun MI MI Mt0,Quad,,MI No Gunner1a Quad, No No 155 mm Gun M19I8MI M3 St,Quad0,Ml91SAI Yes i 0-1600 No Yes 8" How. MI MI Mto*Quad0,MI No I Uses Quad, No No 8n Gun MI M2 Quad0,Eley0 ,MI No -200-1200 No No 240 mm Hew. MI i Quad0*Elev0,MI No -200-1200 No No * Provided with attached base for quadrant Incl. #3 k APPENDIX II 10 Design requirements for elevation and angle of site IndicatorBo a0 The following characteristics of scale design have been demonstrated as essential for maximum certainty of correct setting and reading fire-control instruments: (1) Direct reading of total angular value from left to righto (2) Positive relation between coarse and fine scales with the sharpest possible transition zone for the coarse scale value when the micrometer completes its rotation and starts over again with the next higher coarae-scale valueg (3) Maximum uee of numbers so as to require the least possible interpolation on scales0 (4) Maximum clarity and readibllity of instrument-requiring numbers of adequate size, sharpness and accuracy of engraving0 (5) Rugged construction with a minimum of moving parts, accessibility for maintenance, inepectdon and adjustment* bo Unlike the panoramic telescope, the elevation and angle of site in- struments require no provisions for rapid motion\ this simplifies construction since the micrometer worn is never disengaged from the coarse gear* Design re- quirements are further simplified by the limited range of tube travel 4h elevation0 For angle of site, a total scale reading of 600 is sufficient and 1200 on the elevation scale includes the range of elevation provided by the gun carriageo Co A micrometer drum with spiral edge operating in conjunction with a secondary dial carrying the hundreds values provides a simple and compact means of meeting the essential operating characteristics outlined above0 Specifically, it provides a reading of the total value of the angle setting at one position, with the coarse and fine scale values always in correct relation to each other, the transition zone being less than 1 on the micrometer scale when the coarse scale value shifts from one hundreds value to the next higher value* Continuous number- ing of the hundreds and alternate numbering of the units reduces the interpolation to a minimum*, This principle of design has been applied with success to the panoramic telescope (Second Partial Report, Project 37, 22 March 1945) and may be employed with equal facility on the elevation quadrant* The essential features of design are indicated in Pig* 1, which shows the layout for application on ths right-hand aide of the elevation quadrant but it is also equally applicable with suitable modification for use on the left=hand sideQ d0 Ths design also shows two piovable index marks on both the coarse and fine scales* These are simply suggested as possible additions, if desired, for example, to indicate minimum safe elevation and to aid in making shifts in Inclo #2 1 angle of eite during- fire adjustment. eQ No specific application of the instrument to any of the present elevation quadrants is shown* owing to the wide variety of instruments now employed* Taking the Quadrant, Range, K4, as an illustration, hew ever, the angle of site instrument could be directly installed, with only minor changes, in place of the present micrometer dial and the instrument for indicating elevation might be sub- stituted for the range drum, thus putting the two devices on opposite sides of the quadrant to avoid confusion. The two coarse scales and the elevation micrometer on the present quadrant would be removedo It is felt that the application of these instruments to elevation quadrants presents no difficulty and that appropri- ate designs can be readily worked out0 f0 Another design which meets the requirements for certainty of reading is the continuous spiral, sanewhat larger in diameter than the spiral which is now employed to indicate range on certain elevation quadrants, This design gives the angular setting at one position and is read from left to right as a total value. The relation of the hundreds to the tens and unit values is always correct and there is no transition zone whatsoever; the only scale interpolation is 1 between the alternately numbered units graduations and there are no moving parts which in any way limit or alter the accuracy of reading. Another advantage of this design is that much of the scale is always visible; thus, one gets a visual sense of the position of the setting in relation to the whole scale which aids materially in the rapid setting of the desired elevation. Owing to the limited capacity of only 600 required of the angle of site indicator, the continuous spiral could be employed in a very compact, rugged instrument. To provide for the elevation capacity of 1200 j(f, however, would necessitate an instrument 7-8 inches in length. The simplicity, absence of accurate moving parts and ruggedness of construction are the chief advantages of an instrument of this type. 2o Design of gunner9s quadrant.. a. The gunner®s quadrant is commonly referred to as a primary test instrument for adjusting fire control instruments into proper relation to the gun tube and for checking instrument scales„ Its employment for direct laying of the gun in elevation during firing is temed an emergency use. As a test instrument, there is very little interest in the gunner’s quadrant from the stand- point of the present study since its limited employment would present few opportu- nities, if any, for contributing to the human errors in firing. Except for the reported wear on the gear teeth, there is no criticism of this instrument with respect to its accuracy. Contrary to the foregoing stated function of the gunner’s quadrant, however, it is new commonly employed for actual laying of the larger artillery pieces in elevation and its possible contributions to errors in artillery practice is, therefore of interest*. In passing, it is suggested * The principal reasons for its use as a field instrument with the heavier artillery are that it can be set to l/5 ?( and by interpolation to 1/10 and can be removed from the gun before firing to avoid shock. It thus provides more accurate laying in elevation, provided the gun is level. Xnclo #2 2 that the relatively fragile design and construction of the quadrant is more in keeping with its function, :as a test instrument than as a practical field instrument*, If it is to be continued in field use, a more rugged design should be adopted and means for cross-leveling provided, in addition to improving the scale design to minimize errors in setting and readings In the meantime con- sideration should be given to certain minor improvements in the present gunner8s quadrant ISlo 3o Improvement in gunner*a Ml a0 Like the panoramic sight and elevation quadrant, the gunner8e quadrant suffers from the use of displaced scales and sparse numbering of the scale graduations (Pig0 2)<> Unlike the other instruments, the coarse scale does not change with rotation of the micrometer0 However, one single turn of the latter is exactly equal to 10 which is the magnitude of the finest coarse scale graduation» Thus, & 10 error may be easily made when the micrometer is in its zero position unless one makes certain that the true micrometer reading is either zero or 10o This is determined by noting the position of a fine index mark on the micrometer bar relative to a similar index on the adjoining part0 Only when these two marks coincide is the micrometer reading zero, at which time the coarse scale position gives the correct angular settingo When the two index lines are apart and the micrometer at zero, the correct micrometer reading is 10 and the true angular setting is therefore 10 j/L greater than the coarse scale value0 The resulting 10 error is most commonly referred to in criticism of the gunner8s quadrant„ In order to eliminate it, the pitch of the micrometer screw should be increased slightly vso that 10 equals something less them one complete turn, and a stop provided to prevent turning more than 10 Since both sides of the quadrant are utilized to give a total capacity of 1600 mils, it is necessary to provide two separate sets of gradu- ations (0 to 9o8 |0 as well as numbers on the micrometer for use with the two coarse scales0 These are offset vertically and suitable masks provided to in- sure reading the correct scale in each case0 Thus, the zero position will have only one value—zero—and the coarse and fine scales readings will always bear a correct relation to each other0 Another suggested modification is the addition of a mask over the coarse scale to indicate more clearly the correct reading and to minimize the confusion from otherwise extensive scale interpolation,. These modifications are indicated in Figure 20 Inclo #2 3 FIG. 1 PROPOSED INDICATOR FOR ELEVATION AND FOR ANGLE OF SIGHT ARMORED MEDICAL RESEARCH LABORATORY FORT KNOX} KENTUCKY Notes: ® Design shows right-hand mounting on Quadrant instrument plan can be reversed for /eft~hand mounting (2) Gear ratio for auxiliary hundreds dial - /• ZO Lr. Cou, E S. Brackett SCALE DOUBLE SIZE DATE MARCH Z~? 1945 Micrcmeier Scale (Unrolled view) Note Gap from 9.6 to 0 FIG. 2 GUNNER’S QUADRANT, With proposed Inclo #3