It was ordered to be developed by the Ordnance Committee in April 1942. It was only to be temporary until a more powerful design could be developed.
Originally designed for US and British service but none saw service with US forces. Production for Britain was initiated on October 18, 1942.
Placed on an M3 half-track. The gun was mounted in the center of the vehicle behind the front bulkhead. A gunner's seat pivoted independently of the main gun.
M1 gun could penetrate 55 mm armor at 1,000 yards. Muzzle velocity of 2,800 ft/sec. Gun was positioned between the 2 windshields and placed in a quick release traveling lock.