Comparing: M6 vs. O-I

Developed from 1940 through 1942, with a total of 40 vehicles manufactured from November 1942 through February 1944. It never saw action.

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.