New German armoured vehicles that arrived at the front lines in 1943, particularly the Ferdinand, caused serious changes in prospective Soviet heavy tank designs. In November of 1943, GABTU created tactical-technical requirements for a 55 ton heavy tank. Soviet designers did not simply increase the thickness of armour like their foreign colleagues. Work started on determining the optimal angles for the the turret and hull that would allow a drastic increase in protection with a minimal increase in thickness.
Work on this new tank coincided with the beginning of direct competition between the SKB-2 design bureau headed by N.L. Dukhov and experimental factory #100 headed by J.Ya. Kotin. This competition was similar to what happened in Leningrad in 1938-40 between the Kirov factory and factory #185.
Now the fierce competitors were not only in the same city, but in the same organization. Factory #100 was defined within ChKZ in March of 1942 and began working on experimental development, inheriting the 200 index for its creations from the Kirov factory (Objects 233, 237, etc). ChKZ's SKB-2 began using 700 indices. Its first tank was the Object 701, a proposed replacement for the IS-2 (Object 240).
Meanwhile, instead of working on a modernization for the IS-2, factory #100 began working on its own prospective tank, later indexed IS-6. This tank was developed in close cooperation with NII-48, which promoted the use of sloped armour. In order to keep information about the IS-6 from surfacing too soon, work was performed in strictest secrecy. A special room was allotted where only certain designers were allowed to enter (Shashmurin, Neidman, Turchaninov, Mitskevich, etc), as well as Kotin himself. Military representative at factory #100 Vovk was not allowed into the room, and he raised a ruckus on this subject in April of 1944.