From the release:
This US anti-tank gun, classified as substitute standard under the designation 57 mm Gun M1, was based on the British 6 pounder Mk 2.
Production started early in 1942 and continued until 1945 and the M1A2 introduced the British practice of free traverse, i.e. the gun could be traversed by the crew pushing and pulling on the breech, instead of a solely geared traverse, from September 1942.
