The T-34 medium tank was the mainstay of Soviet mechanized forces in World War II, produced in huge numbers.

The T-43 was generally similar to the T-34, but had a new armour layout and turret design, a space-efficient torsion bar suspension instead of the T-34's Christie type, and a new five-speed gearbox.

Testing at Kubinka showed that the heavier T-43 couldn't match the T-34's mobility, while its armour was still not heavy enough to stop the German 88mm gun.

After the Battle of Kursk, Soviet planners realized that the T-34's biggest drawback was the ineffectiveness of its 76.2mm gun against the frontal armour of the new German Tiger and Panther tanks.

The decision to improve on an existing design rather than commit to a major retooling of the factories was characteristic of Soviet philosophy which held enormous production level as paramount.