In late 1943, the Red Army began to push back against the Wehrmacht, and a new tank was needed for the new tactics. Rather than further modify the exist KV tanks, a new tank was drawn up from scratch. The tank was to be armed with the 85mm D5T tank gun, the same as on the T-34-85, and the turret was a very similar design, though wider in the back to accommodate a ball-mounted machine gun. The turrets and guns for the new tanks were ready in time for deployment, but the hulls were not, so the first few turrets were installed on modified KV-1S hulls, resulting in the stop-gap KV-85. The KV-85 was never supposed to exist, hence the apparent out-of-order nomenclature with the KV-85 produced as Object 239 and the IS-1 produced as Object 237. The KV-85 is also one of the rarest Soviet tanks of the War. Reportedly, one KV-85 had its turret modified to mount a 122mm D25T tank gun, as an experimental precursor to the IS-2.