In June 1942, the Soviet Main Directorate of Armoured Forces (GABTU) issued a requirement to two tank-design bureaus to compete in designing a "universal tank", which would combine the heavy armour of heavy tanks with the mobility of the T-34 medium tank. The SKB-2 heavy tank design bureau in Chelyabinsk started the KV-13 program, which two years later resulted in a line of successful Iosif Stalin heavy tanks. The Uralvagonzavod complex in Nizhny Tagil developed the T-43 medium tank. Uralvagonzavod included the Morozov Design Bureau, the designers of T-34, who were able to draw on its previous work on the advanced T-34M project. T-34M had been cancelled in 1941, when Germany invaded the USSR. The T-43 project received low priority, as the primary focus was on increasing production of the T-34.