During the Soviet–Japanese War, Dyakonov led the corps in the invasion of South Sakhalin, in which it played a key role, in cooperation with the Northern Pacific Flotilla. In difficult conditions of swampy and mountainous terrain, its units broke through Japanese fortified positions of the Koton (Kharamitog) fortified region and rapidly continued on to Shiritoru, Ochiai, and Toyohara.