[1] Having entered the military in October 1929, he was based in Gomel until being transferred to the 83rd Training Squadron in Smolensk, which soon became a flight school.

There he studied with future twice Hero of the Soviet Union Stepan Suprun before graduating in July 1931; he became a member of the communist party in 1930.

When he returned from Mongolia, he spoke with Mikhail Kaganovich, Nikolai Polikarpov, Alexander Yakovlev, and Stalin about the design of Soviet fighters.

[5] Less than a year after returning from Mongolia, Denisov began his role in the Winter War as the commander of the 7th Air Army,[6] which managed to break through the Mannerheim Line.

Many of his colleagues from Spain, Khalkhin Gol and Finland, including Pavel Rychagov, Yakov Smushkevich, and Ivan Proskurov, were arrested on fabricated charges of treason shortly before the German invasion;[8] Denisov survived the purges.

In February 1943 he was made commander of the 283rd Fighter Aviation Division, which took part in the battles for Kursk, Chernigov, Pripiyat, and Gomel before he was removed from the post in December due to failure to maintain discipline among his unit.