In early 1943, Russian troops managed to capture a German Tiger tank, the most powerful tank in the world at that time, and were aware of the differences with their own heavy tanks. Then, they started a program to create a tank that would be able to deal with guarantees to these machines. The project accelerated even more after the Battle of Kursk, because Germans suffered a severe punishment, but the limitations of the Russian tanks in the face-to-face encounters were clear. Then, it was decided to couple the 85mm D5-T tank gun to a new turret built for the new “Izdeliye 237” tank, and then, to mount this turret on the KV-1S heavy tank chassis. This design was known as “Objekt 239” and a prototype was presented in August 1943 before Stalin, who ordered its construction immediately. The new tank was designated as KV-85, and was a fearsome adversary on the battlefield. Unfortunately, it had the misfortune that only 148 units were built between September and December 1943, because it was developed as an interim model until the arrival of the excellent IS heavy tank family.
KV-85 gallery and more info