M5 Gun Motor Carriage. By 1941 the US realized the need for a self-propelled anti-tank gun larger than the 37mm. This interesting design mounted the 3-inch M1917 gun on a Cletrac M2 fast tractor, a vehicle used by the USAAF to move aircraft. There was no platform for the crew, who dismounted to fire the gun. The M5 was never produced, as the M3 half-track was considered to be a better carriage for the gun.