Even in 1933, Polikarpov, simultaneously with I-16, developed a new fighter - biplane I-15. Under the scheme, and design it was a continuation of a failed I-5, but with improved aerodynamics and a more powerful engine air-cooled M-25. A characteristic feature of the aircraft was the original form of the upper wing on a "seagull", help to reduce air resistance and better visibility from the cab. Flight tests of the I-15 took place in December 1933 Fighter reached a maximum speed of 370 km / h and climbed 9000 meters. The following year, it began mass production. Later, a modification of the I-15bis, which was found to direct the upper wing, reinforced center-mounted design and bomb racks.