America’s War-Winning Tank

The United States had few modern tanks when war broke out in Europe on September 1, 1939. News from the front lines revealed that the Germans fielded a medium tank with a 75mm cannon. Despite the limited information at hand, the army decided that its newest tank, the Medium Tank M2, was no match for the new German tank. Since it was only a matter of time before the US was pulled into the war, a new American tank had to be developed that could defeat it. The work put into the Medium Tank M2 served as a foundation for a new medium tank that could be competitive in the current war.

The United States already had a candidate for the gun. The T6 was a promising AA gun developed from the 75mm M1897 field gun and had the semiautomatic breech that a tank gun required. It was developed into the T7 tank gun. Since no turret large enough to accommodate such a gun was available, the 75mm gun was installed in a sponson mount. This concept was previously tested in the Medium Tank T5E2, an earlier experimental tank. Due to the rush, the new medium tank was accepted into service as the Medium Tank M3 on July 11, 1940, before the first example had even been presented. The army was not thrilled about the vehicle’s unconventional layout, but it was regarded as sufficient for a temporary solution.1

Characteristics of a tank that would have its main gun in a turret were drawn up on August 31, 1940. Engineers began working on this new tank on February 1, 1941, as soon as the design of the Medium Tank M3 was finished. This design was approved on April 18, 1941. For the sake of expediency, the lower hull, engine, drivetrain and suspension would be taken from the M3. As many components as possible were reused to speed up the design and development process. The 69in turret ring specified gave the tank a number of options for armament: the same 75mm M2 gun used in the Medium Tank M3, a 105mm howitzer, two 37mm M6 guns, a British 57mm 6-pounder, or three .50 calibre machine guns. All options but the last included a .30 calibre coaxial machine gun. The first option was selected as this gun had already proven itself in the Medium Tank M3.

Some historians interpret the consideration of a British gun as evidence that the Canadian Ram tank, also based on the M3 chassis, influenced the design of the new American tank. This is unlikely: the Ram tank arrived at the Aberdeen Proving Grounds in July, by which time the choice of armament was already made. Additionally, the Canadian tank that arrived at Aberdeen

ABOVE: A complete GM 6046 engine at the Musée des Blindés in Saumur, France. Each half has its own set of accessories, including two air filters. Issues with the filters were common in early M4A2 tanks.

ABOVE: A cutaway tank showing the layout of the GM 6046 engine and its accessories in an M4A2(76)W HVSS tank. Canadian War Museum, Ottawa, Canada. The engine fitted perfectly into the existing compartment without any need to enlarge the tank’s hull.