In 1940 the Navy instructed Kawanishi Aircraft, who had prior experience in the development of superb floatplanes, to produce an aircraft to be known as the 15-shi floatplane fighter, Kawanishi designed and produced a large, single-seat midwing, floatplane of all metal construction. It had a large centerline float, and a small strut mounted outrigger float near each wing tip. It was powered by an excellent Mitsubishi Kasei radial engine and first flew in December 1943. It was designated the N1K1 Type 11 "Kyofu" and code named "Rex" by the allied forces during the war.