Kawasaki Ki-100
The Kawasaki Ki-100 was a Japanese Army fighter created in early 1945 by fitting a Mitsubishi radial engine to Ki-61 airframes left engineless by their unreliable liquid-cooled engines. Intended as a stopgap, it proved manoeuvrable, rugged and reliable, and Allied pilots found it a formidable opponent in the war's final months. Only one survives, on display at the RAF Museum London.
Why It Mattered
The Ki-100 was not planned as a new fighter at all. It was a rescue job, created in the last months of the war when a proven airframe lost its engine supply and production lines stood full of aircraft that could not fly. The result, in the RAF Museum's judgment, was one of the finest Japanese fighters of the Second World War. It arrived too late to change anything, entering service only in 1945, months before the surrender. But for the Japanese Army pilots who flew it in the war's final months, it was a machine that Allied airmen found genuinely formidable.
Design Notes
The Ki-100's parent was the Ki-61 Hien, one of the Imperial Japanese Army's main fighters, whose liquid-cooled engine proved troublesome in service. Engineless Ki-61 airframes accumulated in storage awaiting engines, and Kawasaki modified three of them to accept a Mitsubishi radial engine instead. The radial chosen was Mitsubishi's 14-cylinder Ha-112-II, which matched the power of the inline engine it replaced with much greater reliability. The rebuilt aircraft went to units as the Ki-100-1a, while newly built aircraft, designated Ki-100-1b, were given bubble canopies. Armament was two 20 mm cannon mounted in the cowling and two 12.7 mm machine guns in the wings. Pilots valued the type's combination of manoeuvrability, ruggedness and reliability.
Operational History
The first prototype made its maiden flight on 1 February 1945. Flight testing moved quickly, and 272 of the stored Ki-61 airframes were rebuilt to Ki-100-1a standard between February and June 1945. They were pressed into service as Army Type 5 fighters, and a further 118 new Ki-100-1b airframes were manufactured before the Japanese surrender. The type made its combat debut on the night of 9 March 1945, in the defence of the home islands. The conversion had been created to give the Army a fighter able to meet high-altitude American bomber raids, and Ki-100 units were used against the bombers and their escorts. Japanese pilots claimed successes in these actions, but the claims and counter-claims remain contentious. Published production totals also disagree: an American postwar survey counted 378 aircraft, while a later standard reference gives 396.
Afterlife
Only one Ki-100 survives anywhere in the world. It is a Ki-100-1b completed in the last week of June 1945. Captured by Allied forces at Tan Son Nhut airbase in Saigon in August 1945, it eventually came into the hands of the RAF Museum. The museum catalogues the aircraft as object 85/A/68, and it is on display at the RAF Museum London, in Hangar 5.