M4 Sherman - U.S. Design Prototype

U.S. Design Prototype

The U.S. Army Ordnance Department designed the Medium Tank M4 as a replacement for the M3 Lee and Grant Medium Tanks. The M3 was an up-gunned development of the M2 Medium Tank of 1939, itself derived from the M2 Light Tank of 1935. The M3 was developed as a stopgap measure until a new turret mounting a 75 mm gun could be devised. While it was a big improvement when tried by the British in Africa against early German panzers, the placement of a 37 mm gun turret on top gave it a very high profile, and the unusual inflexible side-sponson mounted main gun could not be aimed across the other side of the tank.

Detailed design characteristics for the M4 were submitted by the Ordnance Department on 31 August 1940, but development of a prototype had to be delayed while the final production designs of the M3 were finished and the M3 entered full-scale production. On 18 April 1941, the U.S. Armored Force Board chose the simplest of five designs. Known as the T6, the design was a modified M3 hull and chassis, carrying a newly designed turret mounting the Lee's main gun. This became the Sherman.

The Sherman's reliability benefited from many features first developed in U.S. light tanks during the 1930s, including vertical volute spring suspension, rubber-bushed tracks, and rear-mounted radial engine with drive sprockets in front. The designated goals were to produce a fast, dependable medium tank able to support infantry, provide breakthrough striking capacity, and defeat any tank then in use by the Axis nations, though it would later fall short against the much heavier tanks deployed by Germany.

The T6 prototype was completed 2 September 1941. Unlike later M4s, the hull was cast and had a side hatch, which was eliminated from production models. The T6 was standardized as the M4 and production began in October.