Over half of all the Airacobras produced went to the Soviet Union, and they were the most numerous of the foreign fighters in the Soviet air force inventory. A total of 4924 P-39s were delivered to the Soviet Union between December 1941 and February 1945, of which 4758 actually reached their destinations.
Soviet pilots had first seen the Airacobra in Great Britain, when a group of pilots was sent to No. 601 Squadron at RAF Duxford for training. The British had found the Airacobra unsuitable for their own use and were more than happy to turn over their Airacobras to the Soviets, and some 212 of the 675 Airacobra Is ordered by the RAF were diverted to the USSR. The Airacobras first entered service with the Soviet Air Force in May of 1942.
It is in Soviet service that the Airacobra was used to its best effect. Soviet Air Force military doctrine was that its primary mission was to support the ground operations of the Soviet Army, and the P-39 was a natural for this role since it had an excellent low altitude performance and was heavily armed. Contrary to many published reports, the Soviet Airacobra was not primarily used as a ground-attack aircraft and tank buster, although it is certainly true that it often strafed targets of opportunity. It was actually primarily used as a low-altitude escort fighter for ground attack aircraft such as the Il-2 and later the Il-10.
The Airacobra was quite popular with its Russian pilots, who appreciated its heavy armament, its excellent low-altitude performance, and its ability to absorb an incredible amount of battle damage. When operating at low altitudes, the Airacobra was often able to hold its own against top-of-the-line German fighters. Some Soviet pilots felt that the P-39 outclassed even the Messerschmitt Bf 109 and Focke Wulf FW 190 at altitudes below 10,000 feet. Some of the users of the type were Guard (ie. elite) Fighter Regiments 16 GIAP, 19 GIAP, 21 GIAP, 72 GIAP, 100 GIAP, 213 GIAP (previously 508 IAP) and Fighter Regiments 196 IAP, 255 IAP, 508 IAP (later 213 GIAP).
Several Soviet Airacobra aces are known. Lieutenant Colonel of the Guards Alexander I. Pokryshin, a Soviet ace with 59 kills to his credit, scored 48 of these in a P-39. He was awarded the Distinguished Flying Cross by President Roosevelt. There are eight other P-39 pilots with at least 20 kills. Among top Airacobra aces were Grigorii A Rechkalov (44 kills) , Nikolai D Gulayev (36 kills), Ivan I Babak, Aleksandr F Klubov, Andrei I Trud, and the brothers Boris B Glinka and Dmitrii B Glinka
The Soviets preferred the 20-mm Hispano cannon of the P-400 over the 37mm of other Airacobra variants because of its greater reliability. In addition, the trajectory of the shells from the 20-mm cannon more closely matched that of the 0.50-inch guns, making for a greater concentration of fire. In the P-39Q, the Soviets usually removed the underwing guns or had them removed at the factory, preferring a better performance over the enhanced firepower.
The Airacobra remained in Soviet service well after the war was over. When the original US-built armament became unserviceable, it was replaced by the Soviet 20-mm B-20 cannon and the 12.7mm Berezin UBS machine guns. How long the Soviets operated their P-39s after the war was over is not known. However, it does appear that some P-39s ended up with the air force of North Korea. They saw some combat with the North Korean Air Force during the early months of the Korean War in the summer of 1950.