The M4 Sherman, officially Medium Tank, M4, was the most widely used medium tank by the United States and Western Allies in WW2. The M4 Sherman proved to be reliable, relatively cheap to produce, and available in great numbers. Thousands were distributed through the Lend-Lease program to the British Commonwealth and the Soviet Union. The tank was named by the British for the American Civil War General William Tecumseh Sherman.
The M4 Sherman evolved from the M3 Medium Tank, which had its main armament in a side sponson mount. The M4 retained much of the previous mechanical design, but housed the main 75mm gun in a fully traversing turret. One feature, a one-axis gyrostabilizer, was not precise enough to allow firing when moving but did help keep the reticle on target, so that when the tank did stop to fire, the gun would be aimed in roughly the right direction. The designers stressed mechanical reliability, ease of production and maintenance, durability, standardization of parts and ammunition in a limited number of variants, and moderate size and weight. These factors, combined with Sherman’s then-superior armour and armament, outclassed German light and medium tanks fielded in 1939 to 42. The M4 went on to be produced in large numbers. It spearheaded many offensives by the Western Allies after 1942.
When the M4 tank (Sherman I by the British naming system) went into combat in North Africa with the British Army at El Alamein in late 1942, it increased the advantage of Allied armour over Axis armour and was superior to the lighter German and Italian tank designs. For this reason, the US Army believed that the M4 would be adequate to win the war, and no pressure was exerted for further tank development. Logistical and transport restrictions, such as limitations imposed by roads, ports, and bridges, also complicated the introduction of a more capable but heavier tank. Tank destroyer battalions using vehicles built on the M4 hull and chassis, but with open-topped turrets and more potent high-velocity guns, also entered widespread use in the Allied armies. Even by 1944, most M4 Shermans kept their dual purpose 75mm gun. By 1944, the M4 was inferior in firepower and armour to increasing numbers of German heavy tanks, but was able to fight on with numerical superiority and mutual support from growing numbers of fighter-bombers and artillery pieces. Some Shermans were produced with a more capable gun, the 76mm gun M1, or refitted with an Ordnance QF17-pounder by the British (the Sherman Firefly).
The original Sherman design included both cast and welded upper hulls. In the rush to increase production, it was noted that cast hulls could be manufactured cheaper and faster than welded hulls, with “a large saving on welding rod and labour.” However, in October 1942, it was concluded that while conversion to all cast hulls might be advantageous, it was not feasible under the current industrial conditions. In that same month, the Ordnance Department in conjunction with the Chrysler Corporation, began design work on a cast front end that offered a partial solution to the higher cost of the all welded upper hull, since the front is where a good deal of the welding man-hours was spent. Also, the front casting was a fraction of the size of a complete cast hull, so could be produced by smaller capacity foundries, the M4 Composite (or Sherman I Hybrid in British terms) was created.