The British variant of the M3 medium tank, called the General Grant I in Britain, was manufactured by Baldwin, Pressed Steel Car Company, and Pullman Standard Car Company. Besides the different turret, there were other small differences such as a periscope for the driver. Improvements were gradually made to the Grant during production, including the addition of full sand-skirts over the suspension and the new WE-210 rubber-block track. Production of the custom-built Grant I tank could not meet the British need for tanks caused by high casualty rates in the desert campaign, so Britain also acquired the American version of the M3 medium tank, which was known locally as the General Lee I.
The British Grant turret was fitted to most hull types, including the M3, M3A2, M3A3, and M3A5. It does not appear to have been fitted to either the M3A1 or M3A4 hulls, even though the British allotted designations to such variants. In total, about 1,660 tanks were completed with the Grant turret, or a bit more than a quarter of the total production.
During the course of production, a variety of incremental improvements were undertaken across the entire M3 family. British reports indicated that the side doors were susceptible to spall damage, so an escape hatch was added to the belly and the hull doors welded shut. In the final production runs, the hull doors were completely absent.