The M3 turret had three pistol ports and shortened recoil mechanism. It was also equipped waith a 37mm M6 gun, which was adequate early in the war, but by 1942, the German counterparts far surpassed the range of the M3. The narrow width of the M3 could not accommodate a larger gun. The M3A1 was fitted with a Westinghouse gyrostabilizer, a turret basket and an oil gear hydrolic traverse mechanism, but lacked a turret cupola. The earlier version of the M3A1, the Stuart III, was powered by Continental W-970-9A-7 cylinder radial gas 250 hp engine but by mid 1941, the Stuart IVs came off the production lines with Guiberson T-1020 air cooled radial diesel engine.