Mitsubishi assigned the task of designing the new fighter to a team led by Jiro Horikoshi (original creator of the similar but unsuccessful Mitsubishi 1MF10, and later responsible for the famous A6M Zero). The resulting design, designated Ka-14 by Mitsubishi, was an all-metal low-wing fighter, with a thin elliptical inverted gull wing and a fixed undercarriage, which was chosen as the increase in performance (estimated as 10% in drag, but only a mere 3% increase in maximum speed) arising from use of a retractable undercarriage was not felt to justify the extra weight. The first prototype, powered by a 447 kW (600 hp) Nakajima Kotobuki 5 radial engine, flew on 4 February 1935. The aircraft far exceeded the requirements of the specification, with a maximum speed of being reached. The second prototype was fitted with a revised, ungulled wing, and after various changes to maximize maneuverability and reduce drag, was ordered into production as the A5M.