In December 1942, after being awarded an officer rank, he became a commissar, and a year later he was assigned to the 181st Special Reconnaissance Detachment of the Northern Fleet.

[2] In October 1944, during the Petsamo-Kirkenes Offensive, the naval scouts under the command of Leonov landed on the shore occupied by the Wehrmacht, and for two days made their way to the designated point in the harsh off-road conditions, unable to make fire in order to warm up and prepare food.

Thus, Leonov's detachment, by its actions, created favorable conditions for the landing of Soviet troops in the ice-free port of Liinakhamari and the subsequent capture of Petsamo and Kirkenes.

As a front-line intelligence officer attached to the 140th Separate Reconnaissance Detachment of the Soviet Pacific Fleet headquarters, the unit under his command took part in the amphibious landing of the Soviet troops into Japanese-occupied Korea, where they landed at the port cities of Seishin, Genzan and Rajin-guyok, in the northeastern portion of the peninsula.

[4][5][2] After the war, Leonov continued his military service in the Northern Fleet and in the Central Office of the Soviet Navy.

In 1950 he graduated from the Caspian Higher Naval Red Banner School named after Sergei Kirov in Baku, Azerbaijan SSR, and in 1952, he was promoted to Captain 2nd Rank.