The Polikarpov I-15 was a Sovietbiplane fighter aircraft of the 1930s. Nicknamed Chaika ("Seagull") because of its gulled upper wings, 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) in the Republican Air Force, or "Curtiss" (because its resemblance to Curtiss F9C Sparrowhawk) in the Nationalist Air Force.
The I-15 was still present on the battlefield when war broke out in Europe over Czechoslovakia in 1938. Some were present in Spain, but they saw the most action in Russia, where they were used as both an bomber interceptor and fighter. Although they preformed more adequately in taking on dive bombers.