Comparing: IS vs. IS-6 vs. IS-4

The IS-1 (IS-85) heavy tank was a thorough modernization of the KV-1. The tank featured the 85-mm D-5T gun. The IS-1 entered mass production in October 1943, but work was discontinued at the beginning of 1944, as the IS-2 (IS-122) tank entered mass production in December 1943. A total of 107 vehicles were manufactured.

Plans for this vehicle were drawn up in the construction bureau of the Chelyabinsk Kirov plant from December 1943 to the summer of 1944. Further development and the construction of the first prototype took place at the Uralmash plant. However, the vehicle had no advantages over the other heavy tank designs under consideration, and its armor was seen as inferior to the IS-4 (Object 701), so the IS-6 was not selected for production.

The project was developed by the Design Bureau of the Chelyabinsk Kirov Plant starting in December 1943. In April 1944 two prototypes of the Object 701 were built. After prototype trials, the design was improved. In late 1944 and early 1945 two more prototypes underwent trials. The Object 701 No. 5 was recommended for adoption into service. However, production was called off in favor of the IS-3 just entering mass-production. After IS-3 production was suspended in 1946, production of the IS-4 began, continuing until 1949. A total of 25 IS-4M tanks were built in 1951. Later all previously produced tanks were modernized to the level of the IS-4M. According to different sources, between 235 and 258 vehicles were built in total; they were stationed in the Far East.