With a requirement to replace the aging Curtiss C-46 Commando, the Japan Air Self-Defence Force drew up its C-X specification for an indigenous, medium-sized troop and freight transport in the early-1960s. The Nihon Aeroplane Manufacturing Company began its design in 1966 and, even before approval of the full-size mock-up, the company was contracted to build two XC-1 flying prototypes plus a static test airframe. The first of the prototypes, assembled by Kawasaki, made its maiden flight on 12 November 1970, and the flight test program of both prototypes was completed by the Japan Defense Agency in March 1973. Following construction of two pre-production aircraft, a first contract was placed for 11 production Kawasaki C-1A transports. The first production C-1A (#48-1008) flew in December 1974. By October 1981, a total of 31 C-1As had been delivered. The C-1KA, featuring a redesigned nose, upgraded avionics, first flew in 1985.
The C-1 is of conventional modern military transport design, featuring a high-wing monoplane configuration to maximize cabin volume, a fuselage with pressurized and air-conditioned flight deck and cargo hold, and a rear-loading ramp/door assembly which can be opened in flight. The landing gear is of retractable tricycle type positioned in outer blister fairings, and the aircraft's two turbofan engines are pylon-mounted beneath the wings. The C-1 is operated by a flight crew of five, and typical loads include 60 fully-equipped troops or 45 paratroops, up to 36 stretchers with attendants, and a variety of equipment or palletized cargo.
A collaborative project, the C-1 was built by Fuji (outer wings), Mitsubishi (center/aft fuselage and tail surfaces), and Nihon (control surfaces/engine pods), with Kawasaki responsible for forward fuselage, center-wing section, final assembly and testing. Although built to JASDF requirements, the C-1's maximum payload of 26,266 pounds (11,900kg) limited its value and plans for variants did not materialize.