Empire of Japan (1945)
Kamikaze Aircraft – 105 Built

Throughout 1945, it was becoming clear to Japanese Army Officials that an Allied invasion of the Japanese mainland was growing ever more likely. Seeing as their navy and airforce had been mostly destroyed, they needed new weapons to fight off a probable Allied attack on Japan. Among these new weapons were Kamikaze aircraft, with many older designs having already been used in this role. However, some Kamikaze aircraft were to be specially designed for such a role, being cheap and able to be built quickly and in great numbers. One such aircraft was the Ki-115 Tsurugi (Sabre) which was built in small numbers, and never used operationally.

History

Following the extensive loss of men, materiel, and territory during the fighting in the Pacific, the Japanese Army and Navy were in a precarious situation, especially as there was a great possibility of an Allied invasion of their homeland. Unfortunately for them, the Japanese fighting forces on the ground, in the air, and on the sea were mostly mere shadows of their former selves, unable to prevent the rapid Allied advance across the Pacific. This was especially noticeable after the costly Japanese naval defeat during the Battle of Leyte Gulf in October 1944 and later Battle of Okinawa which ended in July 1945.. The desperation, or better said fanatical refusal to accept that the war was lost, led to the development and use of Kamikaze (divine wind) tactics. This name was taken from Japanese history, the term arose from the two typhoons that completely destroyed the Mongol invasion fleets.

Essentially, the Kamikaze were Japanese pilots that used their own explosive-laden aircraft as weapons, and sought to crash into important targets, such as Allied warships. This term also entered widespread use to designate all Japanese suicide craft used in this way. During the war, these tactics managed to sink over 30 Allied ships and damage many more.

The suicide attacks were mostly carried out using any existing aircraft that was operational, including older trainers and obsolete aircraft. Kamikaze are a subject with a great deal of nuance and can be difficult to understand through a conventional lens. However, supplies of these aircraft would inevitably become limited and their previous usage meant fewer would be serviceable compared to newer, more expensive models. Thus, the Japanese Army wanted a specially designed Kamikaze aircraft that could be produced in great numbers. These aircraft needed to have a simple construction and use as little of dwindling material stockpiles as possible.

On 20th January 1945, the Japanese Army contacted the Nakajima aircraft manufacturer with instructions to design and build such an aircraft. The basic requirements included a bomb load up to 800 kg (1,760 lbs). It had to be able to be powered by any available radial engine in the range of 800 hp to 1,300 hp. The maximum speed desired was 515 km/h (320 mph). Construction and design had to be as simple as possible. They also wished to speed up the whole development and production process and also to reduce the need for skilled labor. It was especially emphasized that the undercarriage had to be jettisonable, not retractable. It was not expected for the aircraft to fly back, so a retractable landing gear was not needed and this would make the production and design process somewhat quicker.

First Prototype

The job of designing this aircraft was given to Engineer Aori Kunihiro. He was supported by engineers from Ota Manufacturing and the Mitaka Research Institute. While Nakajima received the contract in January 1945, it only took two months to complete the first prototype. In March 1945, this prototype was presented to the Japanese Army and then put through a series of tests. Almost immediately, a series of faults with the design were noted. This was not surprising given that the whole design process lasted only two months. During running on the ground, the fixed and crude undercarriage was difficult to control. The pilot’s poor frontal visibility further complicated matters. This was unacceptable even for skilled pilots, while less experienced pilots would have had great difficulty in successfully operating it on the ground. The Army rejected the prototype and requested a number of modifications to be done.

Technical Specifications

The Ki-115 was designed as a low-wing mixed construction suicide attack aicraft. The front fuselage, containing the engine compartment, and the central part were built using steel panels. The engine compartment was held in place by four bolts and was specially designed to house several different potential engines. Eventually, the Japanese chose the 1,130 hp Nakijama Ha-35 14 cylinder radial piston engine. It had a fixed-pitch three blade propeller. In order to help reach its target quicker, two small auxiliary rocket engines were placed under each wing.

The wings were built using all-metal construction with stressed skin. The rear tail unit was built using wood and was covered by fabric. The cockpit was placed in the upper centre of the fuselage. It was semi-open, with a front windshield.

As requested, the Ki-115 prototype had a fixed and jettisonable undercarriage. It had a very simple design, using simple metal tubes with no shock absorbers. While two wheels were used in the front, a tailskid was used at the rear. The fixed undercarriage tested on the prototype proved to be highly ineffective. All later produced aircraft were instead equipped with a simple and easy to build shock absorber.

The armament consisted of a bomb load of up to 800 kg (1,760 lbs). This included using either a single 250 kg (550 lb), 500 kg (1.100 lb) or 800 kg (1.760) bomb. The bomb was not to be dropped on the enemy, but instead be detonated once the aircraft hit its target. Beside the bomb, no other armament was to be provided on the Ki-115.

The Fate of the Project

Once the prototype was back in Mitaka Kenkyujo (where the prototype was built), the engineers began working on improving its performance. The redesigned undercarriage, which incorporated a simple shock absorber, was completed by June 1945, by which time a series of test flights were done. By August 1945, some 104 Ki-115 aircraft were ready. Two Ki-115s were given to Hikoki K.K., where the Japanese Navy Air Force was developing its own suicide attack aircraft. By the war’s end, none of the Ki-115s built would be used in combat.

Surviving Aircraft

The Ki-115 planes were later captured by the Allies, and nearly all were scrapped. Surprisingly, two Ki-115s have survived to this day. One can be seen at the Pima Air & Space Museum. This aircraft is actually on loan from the National Air and Space Museum. The second aircraft is currently located in Japan. Not wanting to potentially damaged tis aircrafts on the side of caution no restoration attempts are planned for the near future.

The Ki-115b Proposal

In order to further improve the aircraft’s performance and reduce cost, the Ki-115b version was proposed. This included replacing the all-metal wings with ones built of wood. These new wings were larger and had to be equipped with flaps. To provide the pilot with a better view, his cockpit was moved to the front. Due to the end of the war, nothing came from this proposal.

Production and Modifications

The Ki-125 was built in small numbers only, with some 104 production planes plus the prototype. These were built by the two Nakajima production centres at Iwate (22 aircraft) and Ota (82 aircrafts). The production lasted from March to August 1945.

• Ki-115 prototype – Tested during early 1945.
• Ki-115 – In total, 104 aircraft were built, but none were used operationally.
• Ki-115b – Proposed version with larger wooden wings, none built.

Conclusion

Luckily for the Japanese pilots, the Ki-115 was never used operationally. It was a simple and crude design which was born out of desperation. If the Ki-115 was ever used in combat, it would have likely presented an easy target for enemy fighters and suffered from poor reliability due to its cheap construction.

Ki-115 Specifications
Wingspan	28 ft 2 in / 8.6 m
Length	28 ft 1 in / 8.5 m
Height	10 ft 10 in / 3.3 m
Wing Area	133.5 ft² / 12.4 m²
Engine	One 1,130 hp Nakijama Ha-35 14 cylinder radial piston engine
Empty Weight	3,616 lbs / 1,640 kg
Maximum Takeoff Weight	6,440 lbs / 2,880 kg
Maximum Speed	340 mph / 550 km/h
Cruising speed	186 mph / 300 km/h
Range	745 miles / 1,200 km
Crew	Pilot
Armament	Bomb load up to 1,760 lbs (800 kg)

Gallery

Illustrations by Ed Jackson

Credits

• Written by: Marko P.
• Edited by: Stan L. & Henry H.
• Illustrations by Ed Jackson

Sources

• R. J. Francillon (1970) Japanese aircraft of the Pacific war, Putham and Company
• D. Nešić (2007) Naoružanje Drugog Svetskog Rata Japan, Tampoprint
• D.Mondey (2006) Guide To Axis Aircraft Of World War II, Aerospace Publishing