The Ordnance Department had already been working on a heavily armored infantry tank design for the British, using M4 parts.

[4] After a wooden mockup produced by Fisher, Ordnance (in agreement with Armored Force Board) set out three pilot models to be built with different combinations of armament but interchangeable turrets.

[4] Starting with the T20, the Ordnance Department initially developed three series of improved medium tank prototypes, the T20, T22, and T23.

All the T20 models used the Ford GAN V8 engine with Torqmatic torque converter transmission with rear drive sprocket.

Mobility trials demonstrated this configuration to be superior to vertical volute but inferior to torsion bar suspension.

It was to have been based on the hull and turret design of the T20 but with a maximum armor thickness of 30 mm (1.2 in) it would weigh only 24 short tons (22 t) been armed with the 76 mm gun, used either a torsion bar or use the vertical volute spring suspension of the M7 Medium Tank (originally known as T7 Light Tank).

[9] The design was prepared, but the two planned pilots were built; Armored Force wanted light tanks to weigh no more than 20 short tons (18 t).

[9] With standardization of the M27 rejected, the Ordnance Department continued designing improved tanks, this time armed with 90 mm guns.

The immediate result of this line of development was the T25 series – essentially a slightly larger version of the T23 – and then the bigger, better protected T26.