High Quality Content by WIKIPEDIA articles! The Polikarpov I-15 (Russian: И-15) was a Soviet biplane fighter aircraft of the 1930s. Nicknamed Chaika (Russian: И-15 Чайка, "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.