The Chieftain's Hatch of world of tanks: Testing T29, T30

T29 and its variants has been a subject on the forum recently, (And other websites), and I may have had something to do with that. Since it is a topic of conversation, however, a quick look at what happened to them. Sadly, nothing dramatic. Long and boring wall of text follows!

Toward the latter part of World War II, it became apparent that armored vehicles of greater fire power were required for attacks on fortified positions and on heavily armored and armed enemy combat vehicles. Consequently, in 1944 the development of a heavy tank was authorized, to weigh approximately 60 tons. The armor basis was to approach nine inches at the front and to be the maximum possible under the weight limitations. Power was to be supplied from a 750-horsepower Code G engine driving through a cross-drive transmission, then under development incorporating new transmission and steering principles. Two turrets were to be developed for this basic chassis. One to incorporate a 105 mm gun and the other to incorporate a 155 mm gun with suitable rammer for the separate loading ammunition. The designations Heavy Tank T29 and Heavy Tank T30 were assigned to the 105 mm and 155 mm versions respectively. Later authorization was granted to construct two pilot models of Heavy Tank T34 to be identical with the T30 except that the 120 mm gun was to be used as basic armament.

The significant portion of the test was on the CD 850-1 Cross-Drive Transmission

"This unit combines the functions of transmission, steering unit, ands vehicle braking. As a transmission, it incorporates two hydraulically selected mechanical gear ranges driving through a single phase hydraulic torque converter of conventional design. Actually, a portion of the engine power is transmitted through a mechanical patch by-passing the torque converter. This mechanical power, in addition to the hydraulic power, is applied equally to both output shafts except that in steering, all of the mechanical power is applied to one side to provide the speed difference between tracks. This steering is accomplished through a hydraulically actuated controlled differential. Vehicle braking is accomplished by built-in disk brakes actuated mechanically with a foot pedal in the driver’s compartment. Steering and shifting are accomplished by a manual dual-control unit installed in the driver’s compartment and controlled mechanically to the transmission.

A later model of this transmission, designated CD 850-2, incorporated a polyphase type torque converter in place of the single phase unit in the earlier model. This type of torque converter achieves higher operating efficiencies at high speeds by operating as a fluid coupling after the point of 1:1 torque multiplication is reached."

tank and expect an improvement:

"One of the most important [reasons for the disparity] being the greater torque and horsepower of the GAC engine at engine speeds up to approximately 2200 rμn as compared with the AV 1790-3 engine. The GAC torque curve peaks at approximately 1800 rpm whereas the AV 1790-3 torque curve reaches a maximum at approximately 2200 rpm. Since the torque of the AV 1790-3 is greater than that of the GAC above 2200 rpm the AV 1790-3 develops greater horsepower at maximum speed. It is noteworthy that the engine speeds obtained during the performance tests were, for the most part~ near or below 2200 rpm. The engine speeds attained in wide open throttle operation are controlled by the load imposed on the engine through the transmission. Inasmuch as the CD 850-1 transmission incorporates a torque converter, the design of which must be matched closely with the performance of the engine used with it, it is apparent that the low maximum engine speeds attained under full load and power are a result of incorrect matching of the converter with the engine. This is probably true to a large extent with both the GAC engine (T29 vehicle) and the AV 1790-3 engine (T30 vehicle) although the vehicle characteristics obtained with the GAC engine are superior"

While the vehicles were undergoing testing, the Army also used them for other purposes which may have required the use of a large vehicle, such as this 80-ton flatcar. The last line of the caption amuses me, for some reason.

It’s on occasions like this which some of the lesser-thought-of features come to the fore. The vehicle test report points out that “it was discovered that some of the external accessories, headlight brackets in particular, interfered with the efficient blocking of the vehicle on the railway car. This indicates that in the early design stages, thought should be given to the placement of accessories relative to possible blocking  methods which will be used on the vehicle.

Eventually, of course, the vehicles were scattered to the winds, but there is a nice collection of T29, T29E3, T34 and T30 now side-by-side in Fort Benning.