Most known as Stuart III, this variant had a new turret with turret basket and no cupola. The turret rotated using a power traverse as opposed to the manually rotated M3. Its faster rotation speed required changes in its construction, in particular a basket fitted with seats for the crew members. 

The M23 mantlet was fitted with a 37 mm M6 cannon featuring a gyro stabilizer that significantly boosted accuracy while on the move. That did, however, require more training for gunners, a difficult assignment under battlefield conditions. 

The sponson-mounted immobile M1919A4 machine guns were replaced with additional ammunition storage, pushing the tank's capacity to 116 shells and 6,400 bullets.

Two triangular hatches on its roof served as exits for the crew. The gunner and reloader had periscopes. M3A1s with Guiberson diesel were called "Stuart IV" by British. They were produced 4,621 from May 1942 to February 1943.

This is a detail walkaround video of a Restored M3A1 Stuart light tank. Video was filmed at the 2016 Red Ball military Vehicle show Gilbert PA.