Armored 
Medical Research Laboratory 
Fort Knox, Kentucky 
Second Partial Report 
On 
PRcRECi NO, 45 - Operational and Physiological Characteristics 
of the Tank T26E3 
SUBJECT: THE PHYSIOLOGICAL WORK RATES OF THE DRIVER AND LOADER 
IN THE TANK T26E3 IN RELATION TO FATIGUE AND EFFICIENCY 
OF PERFORMANCE, 
Project No. 4-5 
19 June 194-5 ARMORED MEDICAL RESEARCH LABORATORY 
Fort Knox, Kentucky 
Project No. 45 
SPMEA 724-41 
19 June 191*5 
lo PROJECT: No, 45 - Operational and Physiological Characteristics of the 
Tank T26E3, Second Partial Report, Subject; The Physiological Work Rates of 
the Driver and Loader in the Tank T26E3 in Relation to Fatigue and Efficiency of 
Performance, 
a. Authority: Letter AGF File 470,8, dated 17 July 1944, GNRQT-6/91272, 
b. Purpose: (l) To determine the physiological work rate of the driver 
in the Tank T26E3; (2) To determine the physiological work rate of the loader in 
the Tank T26E3; (3) To evaluate these work rates in relation to fatigue, efficiency 
of operation, and tolerance to severe humidity and heat. 
2. DISCUSSION: 
a, The physiological work rate, determined by oxygen consumption, is one 
measure of the muscular effort required to perform a task0 If tasks within tanks 
can be accomplished at low work rates, the sparing of muscular effort will diminish 
crew fatigue and improve performance, particularly when the general conditions of 
work are poor. That changes in tank design can lower work rates without impair- 
ment of mechanical operation has been demonstrated in a previous report \1/ in which 
the rates for specific duties were compared in tanks M4A3, M5, M24 and T23o Lower • 
work rates were observed to result from improvement in driving controls, in am- 
munition stowage, and in the riding qualities of a tank. 
b. In addition to fatigue reduction, low work rates allow men to work 
effectively in more severe conditions of heat and humidity0 
c. Details of tests and results are given in the Appendix,, 
3o CONCLUSIONS: 
a, The work rate of driving the tank T26E3 is moderate. 
b. The work rate of loading in the tank T26E3 is high. Impaired 
loader performance will result from excessive fatigue and reduced tolerance to 
severe humidity and heat. 
c. The efficiency of loading, measured by loading speed, is poor in 
comparison to previously studied tanks„ 
d. Higher work rates and reduced loading speeds result from increased 
size and weight of rounds, and are modified by the stowage of rounds„ Uo RECOMMENDATIONS: 
a* That measures be instituted in the T26E3, by restowage of rounds and/or 
by mechanical aids, to reduce loading work rates and to promote loading speed0 
bo That the effect of stowage of rounds on the work rate, and the marked 
rise in work rate resulting ffom increased size and weight of rounds be carefully 
considered in future tank development* 
NOTE: 
Comments by Headquarters Armored Center with reference to this project are 
contained in the following indorsement: 
Pl5 (2£ May 1*5) GNREG 
HQ ARMD CENTER, Ft Knox, Kyc 
3d Ind* 
13 June 191*5 
TO: Dir, AMRL, Ft Knox, Ky0 
lo This headquarters concurs in conclusions and recommendations of the above 
report* 
2o All evidence points to the great importance of keeping the weight of tank 
ammunition within the capabilities of the average man for effective handling and for 
the maintenance of a rate of fire* It is largely for this reason, too, that this 
office insists on the development of a high velocity gun with a minimum caliber and 
maximum armor penetrationc The present trend towards a larger caliber is, in my 
opinion, definitely beyond the capabilities of the average man for handling the 
ammunition and the proposal for two piece ammunition for separate loading overlooks 
entirely the necessity for maintaining a high rate of fire in a tank* 
/s/ Co L, Scott 
C. Lo SCOTT 
Major General, U0 S0 Army 
Commanding 
1 Incl: 
n/c 
Submitted by: 
Charles R, Park, 1st Lt, MC 
APPROVED 
WILLARD MAChLE 
Colonel, Medical Corps 
Commanding 
2 Incls. 
#1 - Appendix 
#2 - References APPENDIX 
lo Selection of Tests: 
a. The duties of individual crew members are similar in the tanks M4A3, 
M24, T23 and T26E3. The‘work rates for each duty have been found to vary con- 
siderably, however, from one tank to the next, and these variations have been 
attributed to the differences in structural design and operational characteristics 
of the tanks.(l) 
b. Observation of the duties of the assistant driver, gunner, and tank 
commander within the tank T26E3, and observation of the structural and operational 
characteristics of the tank itself in respect to these crew positions indicated 
close similarity to the tank M24. The work rates of these crew members in the 
tank T26E3 were assumed therefore to be close to these previously reported for 
the tank and less than the rates for either the driver or loader*,, Direct 
determinations were not made. Structural and operational characteristics of the 
T26E3 should effect considerably the work rates of the driver and loader in com- 
parison to other tanks and these duties were therefore selected for study. 
c. It should be noted that the work of the driver is often for long 
periods of time, whereas the work of the loader is characteristically in short 
bursts of activity. 
2. Procedure 
a0 Three subjects were used for these tests (see Table l)c Each subject 
breathed through a plastic valve attached to a light helmet and expired air was 
collected in 200 L. Douglas bags. Duplicate analyses for O2 and CO2 were performed 
on each collection. 
b0 Results have been recorded in Cals/hr., Cals/kg/hr., 
and Cals above restingo 
Table 1 
PHYSICAL CHARACTERISTICS OF SUBJECTS 
Subject 
Age 
Ht. (ins.) 
Wt, (kg.) 
S.Ao (m^) 
Bro 
22 
67 
69 
lo81 
Bar 
22 
69 
69 
lo85 
Rid 
23 
69 
71 
lo86 
* Increase in work rates in the tank T26E3 for the gunner and tank commander over 
those found in the tank M24 will occur whenever these men assist in moving 90 ram 
rounds within the tank. Work rates for stowage of rounds in the tank T26E3 will 
probably be high (40C-450 Cals/hr) and of long duration. 
Inclo #1 
1 3o Description of Teats and Results: 
a. Driving: Each subject drove a buttoned tank T26E3 over rolling, 
cross country terrainQ The ground was dry, hard, and moderately rough,, Numerous 
slopes of 5-10° were traversed,. The equivalent of 1„3 right angle turns was 
made in each minute. The results are given in Table 20 
Table 2 - WORK RATES OF DRIVING 
Subject 
Cals/hr 
Cals/m^/hr 
Cals/kg/hr 
Cals Above Resting 
Bro 
207 
114 
3o0 
117 
Bak 
194 
105 
104 
Rid 
191 
103 
20? 
101 
AVERAGE 
197 
107 
208 
107 
Collection period: 6-9 minutes„ 
b0 Loading: The following aspects of the loader's task were selected 
for study: (l) Loading 5 rounds at maximum speed from the ready rack; (2) Load- 
ing 10 rounds at maximum speed from the ready rack; (3) Moving 10 rounds from the 
floor racks* to the ready rack; (4) Throwing 10 empty shell cases from the floor 
through the turret hatche Each test was performed by 2 or 3 men0 The results are 
listed in Table 3 below with the time required for each operation shown in the 
right hand column0 
Table 3 - WORK RATES OF LOADING 
Task Performed 
Subject 
Cals/hr 
Cals/m^/hr 
Cals/kg/hr 
Cals Above 
Resting 
Tiiae 
Seconds 
Load 5 rounds from 
Bro 
904 
499 
13 »1 
814 
63 
ready rack 
Rid 
959 
516 
13*5 _ 
869 
50 . 
AVERAGE 
. 932 
508 
13=3 . 
842 
57 
Load 10 rounds from 
Bak 
1055 
570 
15o3 
965 
35 
ready rack 
Bro 
985 
544 
14o3 
895 
91 
AVERAGE 
1020 
. 557 .. 
14o8 
930 
88 
Throw 10 empties from 
Bro 
1255 
693 
18.2 
1165 
25 
turret floor out thru 
hatch 
Bak 
704 
380 
10c 2 
614 
25 
AVERAGE 
980 
537 
14o2 
890 
... 25 
Move 10 rounds from 
Bak 
640 
346 
9o3 
550 
135 
left floor racks to 
Bro 
576 
318 
804 
486 
172 
ready rack 
Rid 
624 
341 
8o9 
5.44 
129 
AVERAGE 
617 
335 
8o9 
527 
145 
Recovery periods: 5-6 minutes. 
* Four rounds were taken from the bottom of the left floor rack next to the gun and 
6 rounds from the top of the floor rack next to the ready rack,, All rounds were 
properly securedo 
Incl. #1 
2 4o Discussion: 
a. Driving: In a previous study,1(1) the work rate of the driver was 
found to be moderately high in the tanks MAA3 and M5, considerably reduced in 
tank M24, and markedly, reduced in the tank T23. The reductions were attributed 
to the elimination of the effort of gear shifting, improvement in the positioning 
and functioning of the steering levers, and improvement in the riding qualities 
of the tank. Estimates from previous studies are combined with present tests in 
Chart No0 1 to show the relative position of the tank T26E3» 
COMPARATIVE WORK RATES OF DRIVING * 
CHART-1 
M4A3 AVERAGE SPEED 10 M.P.H. 
M 5 AVERAGE SPEED 15 M.P.H. 
M24 AVERAGE SPEED 15 M.RH. 
T23 AVERAGE SPEED 12 M.PH. 
T26E3 AVERAGE SPEED 8 M.PH. 
It is seen that the T26E3 compares well with previous tanks. It should 
be noted that if work per distance covered is considered in place 'of work rate, the 
work in the T26E3 is relatively greater because of the tank's slower driving speedo 
Operation of the steering levers has been stated to require up to 100 
lbs. of force.(2) This presumably accounts for the greatest part of the driver's 
work rate. The riding qualities of the tank in the driver's position were good and 
little effort was dissipated to maintain equilibriumc Comment was made that the 
levers were too far forward when driving buttoned downQ 
b. Loading: Studies of loading in the tanks M4A3, U2A, T23, and T26E3 
were made with two particular observations in mind; (l) the overall work rate; 
and (2) the efficiency of the operation as measured by loading speeds. The dif- 
ferences in work rates and efficiency appear to depend in turn on two factors: 
(l) The size and weight of the rounds, and (2) the stowage of the rounds and 
position of the loader relative to the breecho Chart No. 2 illustrates the com- 
parative work rates and relative speeds of loading in A tanks„ 
* Values reduced for "average man" of 150 lbs. weight and 558" heighto 
** This figure gives rate of task per se0 Add 90 Cals/hr for total work rate in 
Cals/hro 
Inclo #1 
3 CHART-2 
COMPARATIVE WORK RATES OF LOADING 
M 24 LOADING SPEED MOST RAPID 
M4A3 LOADING SPEED RAPID 
T 23 LOADING SPEED SLOWER 
T26E3 LOADING SPEED SLOWEST 
The difference in work rate between the tank M4A3 and tank M24 was 
attributed to better ammunition stowage in the latter allowing more efficient 
operation® The high work rate with a slower loading speed in the tank T23 was 
attributed chiefly to larger, heavier 76 mm rounds. In the tank T26E3 a very 
marked rise in work rate and further reduction in loading speed is seen. These 
effects are chiefly the result of the size and weight of the 90 mm rounds, but 
in addition, rounds are not readily accessible except in the case of the ready 
rack and top layer of the floor racks to the left of the breech® 
The work rate of loading in the T26E3 arises from several separate 
operations® The first is the loading of rounds into the breech from the ready 
rack. This may be accomplished rapidly but demands a very high work rate. The 
second is moving rounds from less accessible racks to the ready rack in prepara- 
tion for further firing. This is an operation perfomed at a lower work rate but 
for a longer period of time. The third is disposal of empty brass which is 
quickly accomplished but still entails a high work rate (see Table No, 3). Chart 
No. 2 is based on loading 10 rounds, disposing of empty brass, and replacing in 
the ready rack 10 rounds from the most accessible racks in each tank studied. The 
rates are higher than would be the case were the subjects more experienced and 
unencumbered by the respiratory apparatus, but probably not higher Lhan in combat 
where nervous tension will appreciably raise the work rate. 
Hie work rate in the T26 computed for loading, throwing out brass, 
and replacing 10 rounds averages ?85 cals/hr for a period of 4 minutes, 18 seconds. 
To indicate the significance of this in more familiar terms, the work rate is the 
same as that determined for an athlete running one half mile in the same period 
of time. Considerable muscular fatigue would be inevitable unless the subject 
were exceptionally physically fit® 
Should the loader be called on to load 20 to 30 rounds in rapid suc- 
cession, it seems highly probable that the physical effort would be exhausting or 
* Values reduced for "average man" of 150 lbs. weight and 5*6" height 
Incl. / I 
4 that a necessary work rate reduction would be foade by slowing the loading speedo 
Work rates of this magnitude will impair the ability of the loader to operate in 
severe conditions of humidity and heato Physical fatigue with resultant impaired 
performance may be anticipated should the loader be required to load the entire 
stowage of the tank one or more times during the course of a day's operationso 
Such a task involves lifting and moving 2940* lbs aider mechanically disadvantageous 
conditions. 
A recent report of recommendations relative to present and future 
development of armored equipment sets 5 Cals/kg/hr as the top acceptable limit 
for work rates up to 1 hour's duration within armored This limit 
will be frequently exceeded by the loader in the tank T26E3. 
The loading speeds as measured in these tests (Table 3) are consider 
ably below possible loading speeds obtained by more experienced subjects and by 
men unencumbered by respiratory apparatus0 The trend toward lower speeds with 
larger rounds is, however, valid. It seems likely that loading from the ready 
rack can be accomplished sufficiently rapidly, but that loading from other racks 
may at times be too slow0 
* Each round weighs approximately 42 lbs0; 70 rounds are stowed0 
Inclo #1 
5 REFERENCES 
(l) Armored Medical Research Laboratory, Sub-Project No0 5-13, dated 
24 March 1945° Appraisal of Kind and Degree of Physical Effort 
Required of Tank Crews in Relation to Fatigue0 
(2) Office of the Chief of Ordnance, Detroit, dated 22 March 1945«. 
Subject: Minutes.of Meeting on Deficiences on Heavy Tank, T26 Serieso 
(3) Report of the Armored Equipment Board, Headquarters Armored Center, 
Fort Knox, Ky0, dated 1? November 1944c (SECRET) 
Incle #2