Armored Medical, Research Laboratory Fof^t Krsiox^ Kentucky Report On ANALYSIS OF PHYSIOLOGICAL CHARACTERISTICS OF T9E1 TANK INFORMATION COPY n copies have,been forwarded t * .Req': r „vS Section, A GF for approval and ' u 27 March 1944 ARMORED MEDICAL RESEARCH LABORATORY Fort Knox, Kentucky 470.6-1 SPMEA 27 March 1944 Report On ANALYSIS OF PHYSIOLOGICAL CHARACTERISTICS GFJW-^ANK 1. PURPOSE: a. To evaluate the present model of tank T9E1 with respect to its physiological characteristics and limitations, including: space for crew, seat design and location in relation to vision devices and controls, design and location of hatchways, lighting, ventilation, placement of sights and vision devices and characteristics and limitation of the vision facilities, b. To indicate the nature and magnitude of the corrections which are necessary to insure effective use of the vehicle by the crew from the standpoint of physiological requirements. 2» DISCUSSION: a. The T9E1 tank is a small vehicle of low tonnage, designed for transport by air and to be used primarily in combat engagements of short duration and high intensity. It must be highly mobile and quick-acting. The crew must be able to function with maximum efficiency and without inter- ference. In this tank these considerations are more important than the question of fatigue or of loss efficiency from prolonged operation, b. Owing to the weight limitations imposed by air transport, the tank is limited in size to such a degree that the crew are seriously re- stricted in movement and large men are unable to perform crew functions quickly and easily. It is impossible to enlarge the vehicle sufficiently to insure adequate space for all personnel regardless of size because of the weight limitation. The only alternative is to improve the vehicle as much as possible and then limit the selection of crews to men small enough to fit into the tank. The recommendations presented below are based upon this fundamental limitation which allows for the selection of men from the small- est 36^ of available personnel. c. Analysis of size limitations and detailed discussion of the various alterations and corrections which are recommended are presented in the Appendix. 3. CONCLUSIONS: a. Because of the size restrictions imposed it is necessary to select small men as crew members. 1 bo Even with these limitations in crew size, certain alterations in design are necessary for effective crew functions. c. Head room in the driver's compartment is not sufficient to accommodate even the shortest men. d. The driver's seat is poorly located with respect to periscope and controls and unnecessary interference is imposed by location of certain other equipment. e. Driver's hatch is not of sufficient size to allow passage and the hatch adjusting mechanism causes interference if passage is attempted. The present access to the bow compartment through the turret is not alto- gether satisfactory. f. Clearance between the 37 mm gun and side walls of the turret is sufficient only for the smaller 35% of available personnel. g. Leg room in the turret and bow are so restricted that only men of limited size can fit into the vehicle without assuming awkward and re- stricting positions. h. Vision devices and gun sights have seriously restricted fields of view. This is in sharp contrast to the needs of this vehicle for maximum field of view to insure the most rapid functiono i. General vision and characteristics of the periscopic gun sight can be greatly improved without major alterations in the vehicle or adding seriously to its weight0 je The ventilation through the crew compartment, with the engine idling, is sufficient to control gun fumes. ko This tank does not lend itself to use of positive-pressure ventilation for gas protection and individual protection must be employed. 1. A number of miscellaneous items of stowage and disposition of equipment require improvement. 4. RECOMMENDATIONS: I. LIMITATION IN CREW SIZE ao That crew members for the T9 tank be selected with regard to size according to the following measurements: Maximum % Population Available (1) Standing height 69" 36 (2) Erect sitting height 36" (min.-34") 36 (3) Shoulder width 17^" 35 (4) Weight 165 lbs. 2 Iio SEATS a. General. (1) If the crew members are to be seated in the tank during landing, the seats must be designed to withstand, with occupants, the de- celeration which takes placeo Airplane type seats together with suitable safety harness are indicated. If, however, the crew will not enter the tank until after the airplane has landed conventional seats will be ade- quate, subject to the following recommendations. b. Bow Seat. (1) Provide driver's seat of bucket type, mounted in a fixed position 30n below the center line of the periscope window. (2) Remove present back rest and provide removable back rest attached by telescoping joint to seat and capable of being raised 10-11 inches from seat. (3) Locate driver's seat as far to right as possible and retain or increase, if possible, the present fore and aft adjustment. (4) Relocate supporting brace which runs across floor and up side wall to provide more left shoulder room for driver and to permitlower- ing of seat. (5) Move oil line guard to the right. (6) Shorten steering levers and move forward 4". (7) Move clutch pedal 3" to the left. c. Turret seats. (1) Provide turret seats with vertical adjustment in three 1" increments from 29" to 31" from the centerline of the periscope window. (2) Consideration should be given to possible removal of turret floor to gain more leg room. III. VISION DEVICES a. Driver's Vision (1) Provide three wide field vision units mounted in the hatch, as shown in Figure 4® b. Gunner's periscopic sight, and vision unit. (1) Replace present long periscope with standard periscopic sights, and arrange mounting to accommodate alternatively M4, T8 or MIO sights. 3 (2) Redesign turret roof to carry armor back from periscope level or even crowned up, as shown in Figure 5, to permit use of standard periscope and to gain head room. (3) Provide vision unit in left side armor of turret, see Figure 5. c0 Commander's Vision (1) Modify commander's vision to provide for mounting of periscopic binoculars in a rotor of increased size together with one vision unit in armor on the right side of the turret, see Figure 6. ^2) Provide also for mounting of wide field periscope in place of periscopic binoculars0 IV. HATCHWAYS a. Driver's hatch (1) Redesign driver's hatch in accordance with suggestion in Figure 4. This will permit passage through it as well as improved vision. (2) Eliminate present hatch raising mechanism and provide spring loaded hinges on new hatch with positive-acting catch to hold it in open position. bo Turret hatches Provide improved gaskets around hatches to reduce leakage of rain into turret. c. Escape hatch (1) Limit stowage over escape hatch to light-weight items which are easily removed for rapid access to hatch. (2) If turret floor is removed, consideration should be given to relocation of escape hatch to permit use of the valuable space over present hatch for stowage of important items. V. GUN CONTROLS a. Remove excessive play from turret traverse mechanism. b. Provide larger elevating hand wheel. c. Provide more substantial firing mechanism. 4 VI. MISCELLANEOUS a. Provide effective sealing around gun mount and other openings to minimize entry of liquid CWA. b. Mounting of shell casing collecting bag. (1) Relocate fastening pins on inside of recoil guard to eliminate needless interference. (2) Provide ear tabs on bag to insure easier attachment and better fit. c. Move turret light 6 inches to right. d. Make possible checking of recoil oil without removing Cal. 30 e. Make storage battery more accessible, if possible. f. Provide means for holding water drain valves in open position. g. Arrange final drive oil drain for easier accessibility. h. Relocate First Aid Kit to permit access to 37 mm ammunition box to right of driver. io Relocate headlights and guards as far forward as possible. j. Redesign or relocate turret ammunition stowage so that ammunition can be removed when gun is fully elevated. k. Install dust guards over tracks. (Note: Comments and recommendations by Colonel Wo H. Nutter, G.S.C., Chief of Staff, Armored Center are as follows: 1. This headquarters does not consider that any further modifica- tions of the Light Tank T9E1 are warranted. Inasmuch as the entire production of Light Tanks, T9E1 has been completed, any modifications of this tank would have to be in the nature of a field modification. Those modifications which were considered absolutely essential from the standpoint of mechanical re- liability and fightability have already been incorporated in production. With our limited facilities for field and depot modification, it is considered un- wise at this time to over-burden them with a great many modifications on a tank whose mechanical life has been set at twenty-five hours. 2. It is the opinion of this headquarters that the recommendations of the Medical Research Laboratory should be considered in the future design of the airborne tank and should not be incorporated as further modifications on existing models T9 El.. 5 APPROVED WILLARD MACHLE Colonel, Medical Corps Commanding 2 Inclso #1 - Appendix #2 - Figs. 1 to 6 inclusive 6 APPENDIX Io GENERAL The discussion that follows and the conclusions and recommendations presented above are based upon the following assumption as to the special purposes and limitations of the tank under review: a0 The vehicle is intended primarily for transport by air and must, therefore, be kept within a certain maximum weight. It is recognized that this limits the freedom of design from many points of view. bo The tank is intended for use in engagements of short duration but probably of high intensity. Physiological considerations which are of par- ticular concern for prolonged operation should not, therefore, receive primary consideration. On the other hand, the probable use of the vehicle requires that the crew shall be able to function with dispatch and minimum interference when engaged. It is this criterion which has dictated many of the changes proposed in this report rather than question of crew comfort or overall fatigue, or maintenance of efficiency over a long period.c • The internal dimensions of this tank are so restricting that all necessary crew functions are carried out only with difficulty and in pract- ically every case movements must be made in an awkward and unnatural manner. The space restrictions particularly handicap men of average size and larger but even small men cannot act with the freedom required for efficient per- formance of their functions. In view of the assumed use of the vehicle in short, sharp engagements where maximum efficiency is required, it is clear that the present restrictions in space seriously limit the probable useful- ness of the vehicle. A study of the space requirements indicate that the following basic changes must be made in order to accommodate the entire range of armored per- sonnel and provide enough room for effective operation: (1) move turret forward, (2) redesign turret basket framework and enlarge or remove floor, (3) redesign driver*s hatch and alter contours of armor over driver, (4) install adjustable seats, (5) relocate certain items of stowage, (.6) relocate gun controls. These changes of the required magnitude to accommodate all personnel will increase the weight of the vehicle beyond the acceptable limit. On the 1 other hand, the number of changes and the magnitude of each change will be greatly reduced if tank crews are chosen from something less than the entire range of sizes of personnel Further discussion is therefore based upon the evaluation of-vehicle in relation to men of limited size. It is recognized that this is a radical departure from common practice but the exigencies of situation appear to warrant it. For detailed reasons which will emerge later, the following limitations in crew size are recommended: (a) Maximum sitting height (.erect, no helmet) 36" Per cent population 36% (b) Maximum shoulder width (nude) 17o5" Per cent population 35% (c) Maximum standing height 69" Per cent population 36% (d) Maximum 165 lbs.* These proposed limitations reduce to about 1/3 the number of men from which crews for the T9 tank may be choseno Iio IMPROVEMENTS IN CREW POSITIONS A. DRIVER'S COMPARTMENT 1. Sitting Height: The distance from the present fixed seat to the roof is 35" and the seat to periscope distance is 28$", see Figure 1. Re- ference to Figure 2 shows that no individual among available personnel can use the periscope without considerable slump and only 10% can sit erect, without helmet. With helmet, no one is accommodated in the erect position. To meet the height requirements of a major fraction of personnel, it would be nec- essary to increase the seat to roof distance some 3", which would undoubtedly increase the weight of the vehicle excessively and would restrict gun depression As a minimum improvement, the seat should be lowered 1J". This will not allow erect sitting for all of the 36% smallest recommended for selection but would be an acceptable compromise. 2. Seat location, in relation to controls, etc.: The following points are presented for consideration with little discussion since they are reasonably self-evident. * Of importance primarily from standpoint of air transporto Included here only as a suggested limitation for consideration, if necessary. 2 a. Steering levers should be shortened and moved forward 4" for better use by the men of limited stature to be selected for this tanko bo The seat should be moved to the right as far as possible to provide more natural access to clutch and accelerator and to reduce in- terference of the shoulder and left arm with the vertical brace on the side wallo If possible, this brace should be moved forward or back to eliminate this interference.- \ The clutch pedal should be moved to the left about 3". c0 The seat back is poorly located and difficult to operate as designed. It should be incorporated into the seat structure itself, making use of a telescopic mounting for easy removal. d. Further improvement in the driver's position will result from the following: relocate hydraulic fluid can (on side wall) so that it does not interfere with driver's knees; move oil line guard further to the right; relocate first aid kit to permit direct access to 37 nim ammunition stowage rack to right of driver. B. TURRET 1. Shoulder Width: The distance between the side wall of the turret and the 37 mm gun at the shoulder line of the commander and gunner is 18". Referring to Figure 3, it will be seen that this corresponds to the shoulder measurement of the 50 percentile man without clothes. A com- bat jacket increases shoulder width about 3/4" and heavy winter clothing even more. A value of 17°5" may be selected as a maximum unde width which would allow clearance, with some crowding, for the clothed man0 According to Figure 3 this maximum shoulder width includes approximately 35% of personnel. 2. Seat adjustment: A fixed seat is not acceptable to the gunner or commander since both must be able to adjust their eyes to the periscope for maximum effective use of the sight or vision device. An adjustable seat is required but the adjustment may be simple, perhaps in the form of a sliding plate. Holding to the same limitations in seat to eye height as proposed above for the use of the periscopes, the gunner's and commander's seats should be mounted with three (3) adjustment in 1" increments from 29" (for shortest man) to 31" from the center line of the periscope window. 3o Turret basket: The excessive taper of the basket confines the average man too much so that his feet and legs must be drawn back in an awkward, cramped position with no opportunity for relief. Limiting the standing height of crew members to 69" will improve this situation. 4. Turret lig^t: Move light fixture approximately 6" to the right to provide unrestricted illumination. 3 5. Radio: As mounted, the radio projects beyond the back of the turret hatches and is an annoyance to the commander and an unnecessary hazard. It should be set back 1^" and the brace holder relocated to remove the hazard. 6. Gun controls: The elevating wheel is too small for convenient use and the traverse wheel interferes with the gunner's lego An excessive play was noted in the gun controls and the mechanism work unevenly. The firing mechanism is not substantial. In view of the assumed requirement for efficient use of this vehicle in short, sharp engagement, careful study and improvement of controls from the standpoint of design, operation and location is recommended. 7o Bag for shell casings: The cal0 30 machine gun must be removed in order to check the recoil oil. The 37 mm ''brass" bag does not fit the recoil guard and the snap pins for securing the bag dig into the legs when the turret crew members are riding standing up in the open turret. The pins should be placed on the inside of the guard and ear tabs attached to the bag for easy fastening. 8. Consideration may properly be given to the elimination of the turret floor in any redesign of the vehicle. This would improve utilization of the limited space within the vehicle from several points of view. III. HATCHWAYS A. BOW HATCH It is understood that in the present tank, the bow opening was not designed for use as an entrance hatch. Very little experience shows, however, that getting in and out of the driver's compartment through the turret is awkward and extremely difficult. In view of the special use of the vehicle, it may be proper to review this limitation and, redesign the bow opening so that it will serve as a practical entrance port. In connection with this, attention is directed to Section IV on Vision in which certain improvements in driver vision are recommended. In a new design of the opening, the following objectionable features of the present design should be corrected: 1. Replace present adjusting mechanism with spring-loaded hinges. 2. Move headlight and guard downward on front so that it will not interfere with use of hatch and also to eliminate the necessity of looking directly through the light beam when driving at night in dust or fog. B. TURRET HATCHES No specific comment is made with respect to the size or mounting of the turret hatches. Excessive leakage of rain around the doors was noted and suitable gaskets are recommended to minimize the needless annoyance. 4 C. ESCAPE HATCH The necessity to maintain ready access to the escape hatch results in the loss of considerable space for stowage within the vehicle. This space can be used only for the stowage of light, easily moved items and does not properly include water cans and the like for which stowage provisions must be made elsewhere. If the turret floor were to be removed, the escape hatch might be located in another position and this valuable space employed for other purposes. It has the distinct advantage of being most accessible to the commander when the gun is forward. IV. VISION DEVICES A. GENERAL VISION The importance of gaining all-around vision at least through the combined efforts of all the crew has been particularly evident from recent operational reports. This is especially true of a vehicle the primary function of which is to operate in propinquity to enemy infantry and as a highly mobile, quick hitting weapon. This makes it essential that all vision devices be readily accessible and that a wide field of view be provided. This require- ment has not been met with the present equipment. On the contrary there has been a reduction in field of view as compared with that available in the M4 . tanks. The effort in this study has been to provide such combined all-around vision with a minimum sacrifice of silhouette and weight. B. DRIVER'S VISION One good feature may be noted in the driver's vision, namely, that the opening of the hatch gives him command of the forward semi-circle of horizontal vision without changing his seat position and with a minimum of effort. The attempt here is to retain this feature and at the same time give him adequate vision with the hatch closed. The additional requirement of an adequate escape hatch inevitably leads to a solution in which three vision devices are located in a broad hatch. The accompanying drawing illustrates the disposition of three standard vision blocks by which he gains horizontal view from well over to the right to well back of the left flank with complete overlap. The vertical range is as great as the contours of the tank permit. The ballistic value of the surrounding hatch is not diminished in comparison with the general armored protection provided. See Figure 4 for details. Co COMMANDER'S VISION Most important element in the commander's vision is the rotatable periscope which can be employed in any required direction. This unit may be either a periscopic binocular or a wide field periscope depending upon the type of employment contemplated, or they may be interchangeable if necessary,. In addition to this, a special wide field periscope is located to the right of the commander providing downward vision to 45° and upward vision entirely adequate for all purposes. The standard periscope behind the commander in the hatch is retained for more effective backward vision. Downward vision to the left is manifestly impossible for the commander, hence the burden for 5 this task is placed upon the gunner0 Despite the present tendency toward a vision cupola, such a device is not recommended for this vehicle as it would prohibitively increase both weight and silhouette. Suitable crowning behind the vision units would take care of his head room reguirements within the general limits as to the size of personnel discussed in other portions of this report. See Figure 5 for details0 D. GUNNER'S VISION In addition to the gunner's task of fire control, he is provided with forward vision through the periscopic sight unit and lateral vision especially downward to supplement the blind spot of the commander,, A wide field periscope disposed in the side of the tank identical to that provided for the commander on the right is provided for the gunner on the left. See Figure 6. E. FIRE CONTROL The increased length of the present periscope and greater power of the telescope have greatly reduced the field of view in this periscope as compared with the periscope employed in the ML tanko In the telescope the field is reduced from 12° to about 6° and the loss in field is not offset by the increased power from 1O4L to about 1„9. The unit power field likewise has been decreased because of the greater length of the case and greater space occupied by the telescope0 The monocular lateral field is about 24° and for a single eye placement the vertical field has been reduced from 6 to degreeso The introduction of this new and inferior periscope appears to have been occasioned by the crowning down of the armor behind the periscopeo In view of the already restricted sitting height (See Section II B) it seems especially desirable that the armor be carried back from the periscope level, if not crowned up slightly. This leads to raising the hatch or shaping the forward portion of the hatch to meet the crowned-up armor. The former in- creases the weight slightly; the latter somewhat reduces the simplicity of the manufacturero In any case the present limitation on the fighting efficiency of the vehicle is too severe to offset the cost necessary for proper arrangement. With these small changes it would be possible to use a standard M4 periscope and ultimately substitute the T-8, see Figure 6. With the use of the shorter periscopes, it will be necessary to provide adjustment of seat level for men of different heights as indicated in Section II Bo V. ventilation Ventilation is provided as a by-product of engine ventilation and suffers from the limitations of this method of ventilation which have been noted previously with respect to the M4 vehicle. Owing to the relatively greater area of openings in the hull and turret, however, there is better distribution of air flow through the vehicle than in the larger tank. 6 Certain variations in ventilation rate and distribution are possible. The overall rate of air flow through the crew compartment can be altered by opening or closing shutters on the bulkhead. Local pattern of flow in the upper part of the turret can be changed to a certain degree by operation of a small disc-type fan mounted in the turret roof ventilator. The capacity of this fan is low and its effect is negligible. A. CONTROL OF GUN FUMES Standard gun fume tests* were conducted to determine the carbon monoxide exposure from the 37 mm and cal. 30 machine guns. In all of these tests the bulkhead shutters were closed and the tank engine operated at an idling speed of 800-900 RPM. The tank was buttoned up. Tests were conducted with turret ventilator fan off and operating on intake and exhaust. Results of the tests are summarized in Table 1. In no case was the CO concentration high enough to cause any concern. Ammonia or other irritating fumes were not present in sufficient concentration to cause trouble. It may be concluded from these tests that, from standpoint of control of gun fumes, present ventilation is adequate, even under minimum conditions, as long as the main engine is running. No effective control is provided for operation with engine dead. TABLE 1 CARBON MONOXIDE CONCENTRATIONS FROM WEAPONS IN T9 TANK Weapon Ventilation No. Bursts or Belts Average CO Cone., Per Cent Gunner Commander Driver 37 mm Fan Off 5 0.016 0o015 to 0.039 0o006 37 mm Fan on Intake 1 - 0.013 - 37 mm Fan on Exhaust 1 - 0.015 Cale 30 MG Fan Off 5 0 o 029 0.029 0o020 Calo 30 MG Fan on Exhaust 1 - 0.016 - * Methods of conducting gun fume tests, sampling and analysis as described in previous gun fume reports (.See Report on Control of Gun Fumes in M4 Series Medium Tanks, Project,Nos. 3-1, 3-5, dated 15 February 1943)• 7 B. GAS PROTECTION No quantitative tests were conducted with respect to vulnerability of the tank to attack by CW agentso The use of negative-pressure ventilation, however, makes this tank as vulnerable to attack by gases and vapors as other tanks similarly ventilated. It may be pointed out, further, that because of the relatively open spaces around the main gun mount, there will be easy penetration of liquid splash. Owing to the limited space and weight of this tank there is no possibility of changing the crew-compartment ventilation system to the positive-pressure type. It must be accepted, therefore, that other means of protection against chemical warfare attack will be provided. 8 FIG. I EXISTING DRIVER COMPARTMENT DIMENSIONS FIG. I FIG. 2 SEAT-EYE HEIGHT-INCHES EYE HEAD HEIGHT PERCENTILE SITTING AND EYE-SEAT HEIGHT DISTRIBUTIONS CURVES FIG. 2 FIG. 3 INCHES PERCENTILE BI-DELTOID DISTRIBUTION CURVE FIG. 3 7-9 Mtf-XW - A^^ese Maw* ^rAA.-^ um/UT ^ar K3.sv^trr SCA^' ^ALF ^Zf r/G 3 v T/ee_c&- ~N- y &/m/E£' /\ut/ T-A/e&ZMe TANK AC^'^CP Affcp/CAc ^3£AC^ lAffOATATO^K AfAjoe ats ffCA^srr J, /^AC^ Ac. /V -!^ TS A,C.- Ck£ TAN< •<■ "etr. E,fS^ ^3S& ?S SECT/CM A-A