On the 7th of April 1941 the Russian army set out its revised requirements for the KV-3 and the requirements for two new Heavy Break through tanks, the KV-4 (super Heavy) & KV-5.
The Russian KV-5 Heavy Tank was too use the same ZIS-6 107mm main gun as the KV-3 and KV-4, but was more heacily armoured with frontal armour of 170mm thick, side armour 150mm and 170mm on the turret. The vehicle was to also be powered by a single 1200hp engine.
Development cracked on during June 1941 and was almost complete in August 1941, but changes had to be made to the hull design as a 1200hp engine was not available, so two parallel-mounted conventional V-2 engines would have had to be installed instead.
The Kirov Plant had started to manufacturer components, however with The Siege of Leningrad, all of the plants resources were thrown in to meet the increased demand for KV-1 tank production and the project ceased with no prototypes built.