Fedyuninsky served as the commander of the 24th Motorized Regiment in the Battle of Khalkhin Gol, where he won the Hero of the Soviet Union for his valour.

In the Bain-Tsagan battle, Fedyuninsky's regiment, accompanied by tanks, broke through to the rear of the Japanese troops, causing great damage to the enemy.

Having disrupted logistic communications, which led the Japanese to a quick retreat from the bridgehead, they had captured near Mount Bain Tsagan on the western bank of the Khalkhin Gol River.

Fedyuninsky's regiment captured a lot of equipment and heavy artillery, which was left over by Japanese troops, after they were forced to clear the bridgehead.

Following the start of Operation Barbarossa in 1941, Fedyuninsky was the commander of the 15th Rifle Corps, stationed in the regions of Brest and Kovel in the Byelorussian Soviet Socialist Republic.

The corps, which consisted of three divisions, with the beginning of the war, unlike many other formations, successfully fought defensive battles and inflicted several tangible counterattacks on the advancing German troops.

The headquarters of the Supreme Command assigned Fedyuninsky the personal responsibility for breaking the blockade of Leningrad on the right wing of the Volkhov Front.

At the end of the Tallinn offensive, his unit took part in battles with Army Group North locked in the Courland Pocket and in the East Prussian Operation.

He is an honorary citizen of the cities of: Volkhov, Kingisepp, Tallinn, Bryansk, Karachev, Gomel, Choibalsan (Mongolia), Flomberha (Poland).