Japanese fighter ki-61 trucker hat
The Ki-61 was designed by Takeo Doi and his deputy Shin Owada. It was designed in response to a tender by the Technical Branch of the Imperial Army Air Headquarters - the Koku Hombu - late in 1939, for two fighters. Each was to be built around the Daimler-Benz DB 601Aa, a derivative of which was to be manufactured as the Ha-40 by Kawasaki at its Akashi plant. The first design, known as the Kawasaki Ki-60, was for a heavily-armed specialised interceptor, which would have a high wing loading ; the second, the Ki-61 was a more lightly-loaded and armed general-purpose fighter to be used mainly in an offensive, air superiority role at low to medium altitudes. Both single-seat, single-engine fighters used the same basic construction, being of all-metal alloys with semi-monocoque fuselages and three-spar wings, with alloy-framed, fabric-covered ailerons, elevators and rudders. Priority was given to the Ki-60, which first flew in April 1941. Design of the Ki-61 did not begin until December 1940. Although the Ki-61 was broadly similar to the Ki-60, it featured several refinements using lessons learned from the disappointing flight characteristics of the earlier design.