The M5A1's design was standardized in September 1942. By July 1944 is was classified as Substitute Standard.
All welded. Had improved turret with more room and radio bulge in rear, with the antenna above the bulge. There was a plate in the bulge that allowed the 37 mm gun to be removed for maintenance. Another periscope in turret for viewing rear better. The commander had a direction finder fastened to the turret roof to indicate the straight ahead position. There was also a spotlight provided.
The antiaircraft gun mounting was moved to the right side of the turret. The commander could traverse the turret and fire the antiaircraft gun at the same time.
Larger escape hatches and positive water sealing door latches installed. An additional escape hatch in the floor of the hull is installed. Pistol ports are supplied with locks.
The M5A1 had the Combination Gun Mount, M44, installed in the turret. This had a direct 3-power telescope.
The 37 mm gun fired a 1.9 lb shell at a muzzle velocity of 2,600'/sec.