With the appearance of new German Tiger heavy tanks on the Russian front, Soviet engineers developed a new generation of armoured vehicles, based on the T-100 prototype. The torsion bar suspension was mounted higher in the hull, lowering the tanks height from the ground and allowing the installation of a larger turret able to hold a 100 mm cannon, in the JS-1 or a 122mm cannon in the JS-2. These went into service at the end of 1943.