T21

While not directly part of the T20 program, the T21 was devised in 1942 as a potential replacement for the M5 Light tank based on the general design of the T20. Originally, it was meant to mount the 75 mm M3, but even more powerful weapons were desired if they fit the weight limit of 20 tons. It was also to use the same suspension from the M7 medium tank. In 1943, the T21 grew to an estimated 47,000 pounds and mounted a 76 mm gun. Armor ranged from 29 mm at the front to 13 mm at the top, and it was specified to reach 35 mph. However, in 1943, the estimated weight of the tank grew to 51,000 pounds. Based on past experience of tanks growing heavier through development, Fort Knox decided the end result would just be an inadequate medium tank like what happened with the M7. In July 1943, the project was cancelled.

Honestly, I think the T21 as we have it right now is a little too powerful. In return for removing the T21’s top gun and engine (and giving it some more historical weapons and engines), I’ve buffed the tank’s turret and side armor a bit. These values are not actually known, so we can have some leeway with them. I simply took the difference between the known value of the front hull (1 1/8 inches or 29 mm) and worked some math with the values of the T20. This gave me a 54% difference between the two tanks. By applying the same metric to the other areas, I’ve quite significantly buffed the T21’s turret while slightly thinning its rear hull armor. I then converted the millimeters to inches, rounded to the nearest half-inch, and converted back to millimeters. Like the T20, the T21 is a bit “clunky” for a light tank.

Guns: 75 mm Gun M3; 75 mm Gun M3 with automatic loader; 75 mm Gun M6; 76 mm Gun M1A1

Engines: Ford GAF (500 hp); Ford GAN (525 hp)

Turrets (Turret Armor (mm)): T21 (38/25/25)

Suspensions/Alternate Hulls, Total Weight (metric tons): T21 Early (21.32); T21 Late (23.13)

Hull Armor (mm): 25/25/13

Top Speed: 56 km/h

Crew: 5 (Driver; Gunner; Loader; Commander; Radio)

Parent: M24 Chaffee
Children: TS-8/32

Sources:

Hunnicutt, R. P. Stuart. 1992.