In 1945, the IS-7 heavy tank project was developed. On its basis, promising self-propelled guns were created. In 1946, the "Object 261" project was developed, which had four variants. One of the variants involved maximizing the use of the existing chassis of the base tank. Instead of a turret, a cupola was installed, which could accommodate either a 152-mm M-31 cannon or a 203-mm howitzer. The possibility of using an electromechanical transmission was also considered. At the end of 1947, the command issued new requirements for the SAU, and the project was not further developed.