The Ordnance Board ordered four prototypes from the Rock Island Arsenal to be replacements for the M3 and M5 light tanks and these were designated the T7 Light Tank. As development progressed it was asked that a 75 mm gun be installed and this brought the vehicle up to the weight class for a medium tank.
The 57 mm gun fired a 6.25 lb shell at a muzzle velocity of 2,800'/sec.
Using the turret ring from a Canadian Ram tank, the pilot vehicle was finished in June 1942. A 75 mm M3 gun was installed eventually installed.
In February 1943, the Armored Forces didn't want both the M7 Medium and the M4 Medium so an order for 3,000 was cancelled after seven had been produced.