When M4 Sherman was standardized, the USOD started work on a successor. The Ordnance HAD Already Been working on heavily armored infantry tank design using M4 parts for the British.
The new project was started on the 25th May 1942, It Was Originally Designated M4X. Starting with the T20, the Ordnance Department developed three series of INITIALLY improved medium tank prototypes, the T20, T22, and T23. The main Difference Between the T20, T22 and T23 lay in the choice of transmission .. The T20 used to convert fluid drive torque, the T22 5-speed mechanical drive similar to the M4 drive, and the T23 used an electric drive. All Moved the transmission to the rear of the vehicle Eliminating the need for a driveshaft running the length of the vehicle. The driveshaft used in the M3 & M4 vehicles forced the turret mounted higher to Be Increasing the vehicle height.
Within each different prototype series, Variety of different suspension configurations and armament Were tried out, for example, the T20 Had An early version of the suspension HVSS later employed on the M4 Sherman, Where The torsion bar suspension T20E3 HAD.
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