The appearance of the German Panther tank in the summer of 1943 convinced the Red Army to make a serious upgrade of its tank forces for the first time since 1941. Soviet tanks needed bigger and more powerful guns to take on the growing numbers of Panthers and the few Tigers.
A stopgap upgrade to the KV series was the short-lived KV-85 or Objekt 239. This was a KV-1S with a new susspension and a new turret designed for the IS-85 or IS-1, mounting the same 85 mm D-5T gun as the SU-85 and early versions of the T-34/85; demand for the gun slowed production of the KV-85 tremendously and only 148 were built before the KV design was replaced. The KV-85 was produced in the fall and winter of 1943-44; they were sent to the front from September 1943 and production of the KV-85 was stopped by the spring of 1944 once the IS-2 entered full scale production.
With his off-road speed of 13 km/h, the KV-85 have the same speed then the KV-1, but the armor rises to 75mm front armor. The gun is the same as the T34/85. But the combination between the slower KV-1 structure and the faster T34/85, make the KV-85 a slower but heavier tank then the T34/85. Its hard for the enemy to penetrate the armor with tanks like the Pzkpfw III. But when the enemy will use heavier tanks like the almighty Tiger tank, soon it will be know that this design needs another update wich lead to the IS tanks.