 The M3 Gun Motor Carriage ( GMC ) was a United States Army tank destroyer equipped with one 75 mm gun and was produced by Autocar . After the fall of France , the U.S. Army decided to make a self @-@ propelled artillery piece from the M1897A4 gun on the M3 chassis , which was designated the T12 . After some improvement , the M3 GMC was accepted in 1941 and produced until 1943 .
The M3 GMC was a fully enclosed vehicle with a 600 hp engine , which provided a maximum speed of 40 mph (6.5 km/h) .