[1] The biggest differences from its direct ancestor, the IS-3, were a longer hull, seven pairs of road wheels instead of six, a larger turret mounting a new gun with fume extractor, an improved diesel engine, and increased armour.

The IS-3 was plagued with construction and mechanical problems, and the IS-4 was too heavy to cross bridges in Europe and relegated to the Russian Far East region as result.

[2] Kotin personally led a design team to work on project Object 730 to meet the GBTU (Main Armored Vehicle Directorate) requirements for a new heavy tank: it had slightly to be better than the IS-2 and weight no more than 50 metric tons.

[6] While the T-10 had thicker armor than the T-54, it suffered from a low rate of fire of three rounds per minute due the use of separate loading ammunition, limited gun depression (a common feature of Soviet tanks), a limit of 30 rounds of ammunition for the main gun, lack of internal space for the crew, and lack of cross-country mobility.

[7] The mobile nature of armoured warfare in World War II had demonstrated the drawbacks of the slow heavy tanks.

In the final push towards Berlin, mechanized divisions had become widely split up as heavy tanks lagged behind the more mobile T-34s.

[8] Antitank guided missiles (ATGMs) started to be deployed widely during this period, and would become an effective replacement for the heavy tanks' long-range firepower.

Eventually, lighter and more modern reactive or composite armour was used to give the MBTs a further edge in protection without slowing them down.