A not-so-special attacker

The Japanese Kamikaze attacks that began on U.S. fleets in October 1944 were very successful and offered the Japanese military at least some hope of a weapon that could offset the vast American qualitative and quantitative superiority at sea. But to be successful, the Kamikazes — officially known as the Special Attack Force — had to attack in overwhelming numbers, and the Japanese were running short of aircraft, even the obsolete ones used for many Kamikaze attacks.

In January 1945, the Japanese aircraft company Nakajima was ordered by the Imperial Japanese Army to produce a very simple, easy to fly aircraft for the sole purpose of a one-way suicide attack. The aircraft was to carry a 1,760-pound bomb in a recessed mount under the fuselage — of course, with no release mechanism. It had to be easy to manufacture by semi-skilled labor — often students working part time shifts at factories — and easy to fly, since it was to be flown on one-way missions by pilots with very little training.

No specific engine was chosen because the aircraft was to have a universal engine mount that could use any of a variety of surplus engines.

The result was the Nakajima Ki-115 “Tsurugi” — Sabre, though the Japanese Navy called their version “Toka,” Wisteria Blossom. It was a small — 28 feet long with a 28 foot wing span — low wing monoplane with an easy to manufacture circular fuselage of steel covered with steel skin panels, a tin engine cowling, and aluminum stressed skin wings. The tail surfaces and ailerons were fabric-covered.
It had very primitive flight instruments and welded steel-tube main landing gear that did not retract but dropped off after takeoff, since the Ki-115 was never intended to land.

The first prototype was ready in March 1945, but problems arose even before the first flight. The simple landing gear did not have shock absorbers, and taxi tests showed it was virtually impossible to handle on the ground, so shock absorbers had to be added.

Adding to the taxing problem was the fact that the pilot sat in an open cockpit to the rear of the fuselage, just above the wing trailing edge, and had terrible forward visibility.

In flight, the Ki-115 showed appalling maneuverability, and there was a real question whether even a skilled pilot had enough control of the aircraft to be to guide it into a ship. There were several crashes in the test program and as the tests progressed, it was clear the Ki-115 would require many changes. It was not until June 1945 that it was considered ready for production, with new landing gear and auxiliary flaps on the wing trailing edges. Additionally, the production versions had provision for a solid fuel rocket under each wing to accelerate the Ki-115 to more than 320 knots in its terminal dive.

The Japanese had plans to construct some 8,000 Ki-115s a month in simple production facilities workshops across Japan. However, the heavy B-29 bombing disrupted these plans, and only 104 production aircraft had been built — all by Nakajima — by the time the war ended, and none of these were used operationally.
Only one Ki-115 survives, taken from Japan by U.S. Navy intelligence and shipped back to the U.S. aboard one of the three aircraft carriers that returned Japanese aircraft to the U.S. for evaluation. It was given to the National Air and Space Museum in 1949 and is currently being prepared for a long-term loan to the Pima Air and Space Museum at Tucson, Ariz., where it will be conserved in a partially reassembled state.

(For questions or comments, contact Dr. Michel at marshall.michel@spangdahlem.af.mil.)