The development of this heavy breakthrough tank began in September 1943. It was planned to utilize certain components of the M6 tank as well as the electromechanical transmission and 105-mm T5 gun, mounted in a turret of limited traverse with 203-mm armor protection. The vehicle was intended to assault the fortifications of the German "Siegfried Line" (known as the "Westwall" to the Germans). The U.S. land forces rejected the project during the design phase. The vehicle was later modified into the T95 heavy breakthrough tank.