Comparing: O-I vs. IS-3

Development of the superheavy tank was started after the Battles of Khalkhyn Gol in 1939. The vehicle was designed as a maneuverable fire unit that was unprecedented in scale—its hull alone weighted 100 tons. Only one prototype was built, without a turret and made of construction steel. Trials were discontinued due to the unreliable engine; at the end of 1944, the prototype was scrapped. The 15-cm howitzer was to be mounted on the tank after the assemble.

Mass production of the vehicle started in May 1945. On September 7,1945, IS-3 tanks took part in the Allied Victory Parade through Berlin. A total of 1170 vehicles were manufactured by the end of 1946, when production was canceled. From 1948 through the late 1950s, the tanks underwent a number of modernization refits.