In response to a 1939 Imperial Japanese Army Air Service tender, Kawasaki developed two fighters around the Daimler-Benz DB 601Aa engine: the Ki-60 (interceptor) and the Ki-61 (general-purpose fighter).
Designers
Takeo Doi and Shin Owada led the Ki-61 project, refining lessons from the underperforming Ki-60.
Engine
Powered by the Kawasaki Ha-40, a licensed version of the DB 601Aa, the Ki-61 was the only Japanese WWII fighter to use a liquid-cooled, inverted V-12 engine.
Airframe and Features
Construction
All-metal, semi-monocoque fuselage with three-spar wings.
The engine bearers were integrated into the forward fuselage, with fixed side panels.
Protection
Included self-sealing fuel tanks and pilot armor—features uncommon in Japanese fighters at the time, reflecting European combat lessons.
Radiator
A prominent ventral radiator bath beneath the wing leading edge distinguished its silhouette.
Operational History
First Flight
December 1941
Combat Debut
Participated in the defense during the Doolittle Raid over Yokohama on 18 April 1942.
Service
Used extensively throughout the Pacific War in air superiority, bomber interception, and escort roles.
Misidentification
Its European-style design led Allied forces to initially mistake it for a Messerschmitt Bf 109 or Macchi C.202, earning it the Allied reporting name Tony.
Production and Legacy
Units Built
Approximately 3,078 aircraft.
Variants
Included the Ki-61-I (Ko, Otsu, Hei, Tei subtypes) and the Ki-61-II, which faced engine reliability issues.
Evolution
When Ha-40 production ceased, airframes were retrofitted with radial engines, resulting in the Kawasaki Ki-100.
