There was also a tank gun version of ZiS-2 called ZiS-4. In 1941, in an attempt to improve the anti-tank performance of the T-34 tank members of the Morozov Design Bureau experimentally equipped it with the ZiS-4. Only a small number of these T-34-57 tanks were built and used as tank hunters. The idea resurfaced in 1943 after the Battle of Kursk because Germany fielded heavily armoured Tiger and Panther tanks. Only a limited number of the T-34 equipped with a slightly modified version of the ZiS-4M gun with a new breech to simplify production were produced. Although the high-velocity gun had superior armour penetration to the F-34 the small weight of its shell meant that it could not fire an adequate high-explosive round for general use. The ultimate solution for the tank was to design a new turret allowing the use of an 85 mm gun; the new model was called the T-34-85.