In 1940, the U.S. Army recognized the need to replace the M2. The new tank was developed, with thicker armor lengthened hull, and a trailing idler wheel to act as another road wheel to decrease ground pressure and improve weight distribution. The M3 turret basket and an Oil Gear hydraulic traverse mechanism, but lacked a turret cupola. The 4,410 units powered by Continental W-970-9A 7-cylinder radial gas 250 hp engine was referred to as Stuart III by the British and the 211 M3A1s equipped with Guilberson T-1020-4 air-cooled radial diesel engine were called Stuart IV. In both cases, the 15-ton tank with a crew of 4 moved fast in the field. The only drawback was the inferior 37mm gun. By 1942, it was not sufficient in the field.
