British combat reports on the M3 towards the end of 1941 criticised the lack of a turret basket and the resulting difficulties experienced by the gunner and commander »walking round« with the turret being traversed.
A new turret design was initiated to incorporate a turret basket together with other new design improvements.
To facilitate escape from the vehicle, separate hatches for gunner and loader were incorporated, and the cupola was removed and replaced by a rotating periscope for the loader who now with the best all round vision doubled up as commander.
Entering production in May 1942, the tank with the new turret »D58133« became known as the »M3A1«,

340 of which were sent to the Soviet Union in 1942.

The first production series, shown here, kept the riveted hull of the M3 that, in its later production stage, already had the sponson machine guns removed and the apertures plated over.
The main armament changed from the M5 gun to the slightly longer M6 L/56 gun which improved range and armour penetration capabilities.
The addition of two 25gal. external fuel drums had become common practice as well, thus doubling the range of the Light Tank M3A1.

Special Thanks to Mr. Claude Gillono, France, for providing precious information.