Comparing: O-I vs. O-Ni vs. O-Ho

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.

A further development of the O-I with improved anti-tank guns. The military command's plan was to improve the earlier models and achieve a higher level of armor protection on the vehicle. Existed only in blueprints. No finished prototypes were built and the vehicle never saw action.

The O-Ho was a further development of the idea of a superheavy tank with improved armor protection. The vehicle had a good set of guns that allowed for all-angle fire. The project was discontinued due to the war ending. No finished prototypes were built and the vehicle never saw action.