The Heavy Tank T1E1 was an American prototype that served as the basis for the M6 tank. By 1943, US armored forces had shifted their doctrine towards producing large numbers of medium tanks, such as the M4 Sherman. Consequently, development of the M6 heavy tank was virtually halted. Nevertheless, testing of several prototypes continued at the Aberdeen Proving Ground. As part of these tests, the 76 mm gun on the T1E1 prototype was replaced with a 90 mm T7 gun. The results showed that the M6 tank chassis with an electromechanical transmission was a satisfactory platform for mounting a more powerful gun. However, there were some shortcomings. For example, the turret was inconveniently located, and the space behind the armor was limited. Furthermore, the platform itself was considered outdated, which is why the modification never went into mass production.

The T1E1 (90) was introduced in Update 2.39 "Dance of Dragons". Unlike the earlier T1E1, this vehicle is equipped with a new 90mm T7 gun instead of the old 76mm M7 gun. The new gun has excellent penetration and a variety of ammunition, including a powerful APCBC shell. This makes it particularly effective against well-protected targets at long ranges. Its firepower is sufficient to counter even the most formidable opponents, such as German Tigers and Panthers, or Soviet IS tanks. Otherwise, the vehicle remains unchanged, retaining its good protection and mobility. However, due to its high silhouette, it is difficult to find cover on some maps.