The Sherman lineage can be traced directly to the T5 medium tank. The T5 and the later M2 and M2A1 tanks influenced the design and mechanical layout of the M3 medium, which became known as the Lee/Grant. Entering production in early 1941 the M3 featured a sponson-mounted 75mm (M2) in the hull and a 37mm weapon in a traversable turret. It was clear the M3 represented an interim solution to the need for a tank that could take on quality opposition on equal terms. Development work continued on a tank capable of carrying a 75mm weapon in a fully traversable turret. In May 1941 a wooden mock up was approved and by September 1941 the first pilot model, designated the T6, was delivered to the Aberdeen Proving Ground. The T6 was approved for production in October 1941 as the M4 Medium Tank. The first examples featured a fully cast “turtle-back” hull and carried the 75mm (M2 L/31) cannon in a round, cast, turret. With production targets set as high as 2000 vehicles per month a simpler to produce, welded, hull was introduced for manufacturers who did not have the facilities to produce large castings. The welded hull was standardized in October 1941 as the M4 Medium, with the cast hull variant designated the M4A1.

The M4 and M4A1 used the tried and tested solution of adopting an aircraft engine to power the tank and the Continental radial was fitted. However, with the massive demands of aircraft production it soon became clear that the supply of such engines would soon fall short of that which was needed to keep up with Sherman production. A number of alternative power pack solutions were explored and adopted and this led to various new designations of Sherman.

The M4A2 adopted two GMC 6-71 diesel engines. The M4A3, standardised in January 1942 adopted the new Ford GAA V8 tank engine.The M4A3 is arguably the single most important version of the Sherman and was the model standardised for US army service after the war. The M4A4 utilised the Chrysler “multibank” engine,