Nicknamed Chaika (Russian: Чайка, "gull") because of its gulled upper wings,[2][3] it was operated in large numbers by the Soviet Air Force, and together with the Polikarpov I-16 monoplane, was one of the standard fighters of the Spanish Republicans during the Spanish Civil War, where it was called Chato (snub-nose).

[4] The design for the 14th fighter for the VVS, the I-14, started as an advanced (for the era) monoplane under the direction of Andrei Tupolev.

[3] Production started in 1934, initially being powered by the Shvetsov M-22, a licence-built version of the Bristol Jupiter radial engine.

[3] Production switched to the 515 kW (691 hp) Shvetsov M-25 engine (a license-built, metricified Cyclone) in late 1936.

[2] In August 1937, the Chinese Kuomintang Government signed a non-aggression pact with the USSR, and in autumn of the same year, the Soviet Union commenced to ship I-15s as a part of a programme of military aid to the Chinese Air Force (CAF) in its defensive war against Japan.

[15] In 1939 Polikarpov fighters were extensively used during the Battles of Khalkhin Gol fought around the Khalkha River in Dornod Province.

[citation needed] The I-15 was used extensively in combat by the Republicans in the Spanish Civil War and proved to be one of the best fighter biplanes of its time.

The first batch of 25 Polikarpovs arrived in Cartagena, Spain, on 28 October 1936,[6] with 15 pilots, led by future ace Pavel Rychagov.

[18] On 16 November, while dogfighting with Fiat CR.32s over Madrid, future ace Rychagov was shot down [19] and four days later the number of combat-ready Polikarpov in the central area had fallen to 15 aircraft: seven had been lost in combat, two had force-landed and one was undergoing repair.

By 1 January 1939, 197 Polikarpovs had been lost: 88 shot down by enemy aircraft and nine by anti-aircraft artillery, 27 destroyed on the ground and 67 written off in accidents.