In 1944, the American army adopted the 120 mm M1 AA gun. The gun had excellent characteristics, including high penetration. It is not surprising that the Bureau of Ordnance started development of a tank gun on its basis in January of 194. The gun was indexed T53. In May of 1945, the Bureau recommended to install two of these guns in T30 tanks, putting a start to the T34.
In late 1946, the AMX company proposed a self propelled gun design on the AMX M4 chassis. The vehicle was lengthened to 9 road wheels per side. Its mass would be 58.5 tons, and it would be equipped with a 120 mm gun and a MAC Mle. 1931 machinegun. Even though this design was not produced, further development of this project resulted in the Foch SPG armed with that same gun. This project was the first where French engineers used a 120 mm tank gun, the French version of the T53. The French mostly borrowed the ballistics of the gun, radically changing both the barrel and other components.
AMX started working on an M4 tank with an altered front and a lightened turret in spring of 1950. During planning, variants ranging from 50.5 to 70 tons were explored. Such a vehicle was rejected, but a new proposal was made in September of 1950. The only unchanged part was the turret, in which the engineers wanted to put a 120 mm gun.
It is noticeable from the first sketches that this gun differed from the SPG version. Unlike the SPG's composite barrel, the tank gun had a monobloc barrel, same as the T53. Although, it was not introduced immediately, and early plans still had a composite barrel. The new turret was going to be installed on the stock AMX M4 hull, but it was discovered that the lighter turret would fit more comfortably on a larger turret platform.