The British and Americans worked together on this design to produce a tank that would be used by both countries. The head of the Ordnance Department went to Britain in September 1941 to discuss designing a better armed and armored vehicle than the Churchill.
In December 1941 studies were conducted to put a 6 pdr or a 75 mm gun in a vehicle that would share many of the parts of a M4 Medium. Features of the M6 Heavy were also included.
The British ordered 8,500 in March 1942, but the pilot model took until 1944 to be completed. By that time the Churchill was a successful infantry support tank and the project was dropped.