06/30/2009. The Japanese Naval Air Force (JNAF) awarded Kawanishi a development contract for an advanced floatplane fighter in September 1940, and design work was begun immediately on the 15-Shi fighter, or K-20 as it was designated by the company, the design team including Shizuo Kikuhara, Toshiharu Baba, Elizaburo Adachi and Hiroyuki Inoue.
The first prototype was constructed at Kawanishi's Naruo plant, and flown for the first time on May 6, 1942. The K-20 was powered by a Mitsubishi MK4D Kasei (Mars) fourteen-cylinder air-cooled radial engine, geared for contra-rotating airscrews. The complexities of the gearing necessitated by the contra-props outweighed any advantages that these airscrews offered, and the second prototype was modified to take the 1,460 hp Kasei 13 engine which was similar to the Kasei 14 but drove a single three-bladed airscrew via an extension shaft.
The second prototype was completed in October 1942, and it was found to suffer seriously from the snaking during the takeoff run that the contra-props had been intended to safeguard against. It was found to call for extreme skill in correcting for torque, especially during takeoff, and the aircraft was seriously damaged during one of its first landings when the pilot over-corrected. However, four further prototypes had been completed by the end of the year, these being joined in the test program by two more prototypes at the beginning of 1943, and the most serious shortcomings of the design were progressively eliminated, although the fighter was always to demand considerable skill in taking-off and landing.
In December 1942, the K-20 was accepted by the JNAF for production as the N1K1 Kyofu (Mighty Wind) Floatplane Fighter Model 11 at Kawanishi's Naruo and Himeji plants. Armament consisted of two 0.303 in (7.7 mm) Type 97 machineguns and two 0.787 in (20 mm)
Type 99 cannons. Production started slowly but began to gain tempo in June 1943, reaching a production peak in the following December in which month fifteen Kyofu fighters were delivered to bring deliveries to eighty-nine aircraft excluding prototypes in that year.
By that time, however, the war situation had changed, and the JNAF was no longer faced by mediocre land-based Allied fighters, and a floatplane fighter, no matter how exceptional its performance had little chance of successfully opposing the newer Allied land-based fighters.
The Kyofu was allocated to operational units, and a number were sent to the South Pacific, but their operations were somewhat restricted owing to the radically changing combat conditions. They were used in the interception role at Balikpapan in the Dutch East Indies where they proved themselves to be rugged and highly efficient aircraft.
At the beginning of 1944, production of the Kyofu was tapered off in order to enable both the Namo and Himeji plants to concentrate on a landplane derivative of the design, the NIK1-J Shiden terminating in March with the ninety-seventh machine.
During the closing stages of the war, some Kyofu floatplanes were assigned to the Ohtsu Naval Air Corps, operating from Lake Biwa on the Japanese home island of Honshu. Late production examples of the Kyofu were powered by the MK4E Kasei 15 which differed only in minor details from the Kasei 13.
The pictured aircraft is one of three N1K1's brought to the USA, presently it is on public view at the National Museum of Naval Aviation of Pensacola, Florida.