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The KV-85 is the heavily modified sixth variant of the KV-1 heavy tank family. It was a stopgap design comprised of a modified KV-1S hull connected to an IS-85 (IS-1) turret and mounted with an 85 mm D-5T tank gun. By the middle of the Second World War, all existing KV-1 variants were considered obsolete. Its firepower was less effective than it had been in the early war. To fight the increasingly strong German tanks, the Soviet Union required a new heavy tank with enhanced firepower. By 1943, there were 21 heavy tank designs, but they were all cancelled due to assessments of weak firepower and poor mobility, which cost the Red Army dearly. The final KV-1 variant, the KV-1S, exacerbated things by being a substantially inferior tank that attempted to balance two opposed attributes: armour and speed. Kotin divided his TsKB-2 department in two in order to speed up the development of heavy tanks. The first team chose to upgrade the KV-1S variant, while the second began work on the IS-85 (later renamed IS-1), a considerably better balance of speed and armour. The original KV-85 design was substantially different from the one that was ultimately adopted. It was a slightly modified KV-1S with a forcibly mounted 85 mm D-5T tank gun in a KV-1S cast turret. There appears to have been only one prototype, which was found unsatisfactory. This is probably owing to the shortage of turret space. Fortunately, the IS-85 turret was available at this point, but not the IS hull. Due to severe technical delays in IS-85 manufacturing as well as urgent needs for more heavy tanks with heavier weaponry, a new tank was created by modifying an existing KV-1S chassis and putting an IS-85 turret on top. The KV-85 was accepted for service by the State Defense Committee on August 8th, immediately after trials, resulting in 148 KV-85s being constructed as a stopgap from September to December at Chelyabinsk. The fifth crew member (the radio operator) was no longer required due to increased demand for larger ammunition racks (70 rounds) and the size of the gun breech.
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