From December to March 1940, Korobkov participated in the Winter War as an adviser to the commander of the 25th Fighter Aviation Regiment and an aide to the commander of the 14th Fighter Air Army. In April, he became commander of the 12th Fighter Aviation Regiment in the Kiev Special Military District. On 7 May, he was awarded his second Order the Red Banner. During June and July, the regiment participated in the Soviet occupation of Bessarabia.