M6a1 m6a1 was an American heavy tank used in ww2 the M6A1 is surprisingly mobile, and it is a definite asset in battle. The M6A1 has an impressive armament consisting of the 76mm M7 cannon, the 37mm M3 cannon, and three . 50 caliber M2HB machine guns. The two cannons are both in the turret, with the 76mm on the centerline and the 37mm offset to the left.