Забайкальский фронт
From 1937 Kovalyov was the commander of Kiev Military District, then from 1938, he was the commander of Belarussian Military District. He was the commander of the Belarusian Front during the Soviet invasion of Poland in September 1939. Kovalyov was also the commander of the 15th Army (Soviet Union) and led the Soviets to victory. As well as leading during the Winter War (1939–1940). He was the commander of Kharkov Military District, then Inspector of Infantry for the Red Army Commander of the Transbaikal Front during 1941.