The Yokosuka MXY-7 is a purpose-built, rocket-powered human-guided kamikaze attack aircraft"Ohka" aerospaceweb.org Retrieved: 16 October 2010 that was produced by the Yokosuka Naval Air Technical Arsenal and deployed by Japan toward the end of World War II. Allied personnel commonly referred to the aircraft as "Baka Bombs" (baka being a Japanese pejorative term meaning "fool" or "idiot").Lardas 2022, p. 12.
The Ohka was conceived during 1943 by Ensign Mitsuo Ohta and, following design assistance from the Aeronautical Research Institute of the University of Tokyo, received formal approval to proceed from the Imperial Japanese Navy on 16 August 1944. Development was carried out in secret, partially to not impact the Japanese public's perception of the conflict. Effectively a flying bomb, the Ohka was intentionally designed to be as cheap as possible to construct, typically featuring plywood wings and an aluminium fuselage while only being furnished with rudimentary cockpit instrumentation. While initially planned to be produced entirely in-house by the military, the high rate of production desired by military planners eventually necessitated the production of the wings and tail units to be subcontracted out to private firms, such as the Nippon Aircraft Company. The Navy ordered full-rate production to proceed ahead of powered flights being performed in November 1944.
The principal variant, and the only one to see combat, was the Model 11; it was armed with a warhead and was powered by three Type 4 Model 1 Mark 20 solid-fuel rocket motors. Starting on 21 March 1945, the Ohka flew combat missions against Allied ships in the Pacific Ocean theater. Although extremely fast, the Ohka had a very short range of , thus it had to be carried into action as a parasite aircraft by a much larger bomber that frequently proved to be vulnerable to carrier-borne fighters. The Ohka participated in the Battle of Okinawa of 1945, during which it succeeded in sinking or damaging several escort vessels and transport ships, although it was never attributed as having heavily damaged any capital ships. The Japanese developed several versions of the Ohka, including the K-1 unpowered trainer aircraft and the turbojet-powered Model 22. While efforts were made to overcome the aircraft's shortcomings, particularly its short range, the Surrender of Japan came before any of the improved combat models saw deployment.
Design and development Background
The MXY-7 Navy Suicide Attacker Ohka was a manned flying bomb that was conceived by Ensign Mitsuo Ohta of the 405th Kōkūtai, who had witnessed the multiple air attacks by the Allies and observed that the defensive efforts of the Imperial Japanese Navy had been decreasing in effectiveness, thus resolving to design an expendable kamikaze aircraft purpose-built for suicide attacks upon enemy warships. While Ohta had started work on the design in 1943, the authorities would not take an interest until the following year. Ohta obtained design assistance from several figures at the Aeronautical Research Institute at the University of Tokyo, which included the construction of a scale model and wind tunnel tests. This involvement of civilian engineers by Ohta ahead of approaching his superiors was likely a violation of protocol, but this infraction was seemingly overlooked.Grunden 2005, p. 150.
Having integrating the data from the university's research, on 5 August 1944, Ohta submitted his proposal at the First Navy Aeronautical Technology Arsenal. Eleven days later, the Japanese Naval General Staff ordered engineers at the Navy Aeronautical Research Department at Yokosuka to commence formal development of the concept. From this point, development of the Ohka was carried out in secret, headed by Lieutenant Commander Yamana Masao while Major Miki Tadanao served as chief designer.Grunden 2005, pp. 152, 234. Part of the reason for such secrecy was to avoid the spreading of awareness at Japan's military circumstances to be developing such an aircraft. This desire led to the early dismissal of interest in the subcontracting of production work to the private sector; instead, production was initially exclusively confined to military facilities.Grunden 2005, pp. 150-151. The navy designation Marudai was assigned to the project, which was partially based on the first ideograph in Ohta's name. It took less than one month to produce the first prototype, as well as ten production-standard aircraft by the end of September 1944, which were referred to as the Yokosuka MXY-7 Model 11.
Both due to the single-use nature of the aircraft, and the resource shortages present across Japan's wider economy towards the end of the conflict, there was considerable pressure to design the Ohka to be as affordable as possible. It was decided that the Model 11 would primarily composed of aluminium and plywood, materials that were both readily available and could be readily used by unskilled labourers. While the fuselage was composed of aluminium, both the wing and tail assemblies were made of plywood; the cockpit was enclosed by a plexiglass canopy, and only rudimentary instrumentation was provided (a speedometer, altimeter, and attitude indicator).Grunden 2005, p. 151.
In October 1944, glide testing started at Sagami Bay, just south of Tokyo; powered trials commenced one month later. Irrespective of the results of these trials, the Navy had already ordered full-rate production to proceed. While officials had sought 150 aircraft to be produced by the end of November, the Naval Aeronautical Technology Institute proved to be incapable of production at such a rate. Accordingly, in spite of the strong sentiment that the Ohka's production should solely remain a military matter, the Navy was compelled to subcontract work to private firms, such as the Nippon Aircraft Company, to produce wings and tail sections for the aircraft.
Production models The only operational variant of the Ohka was the Model 11. It was essentially a bomb with wooden wings, powered by three Type 4 Model 1 Mark 20 solid-fuel rocket motors, the Model 11 achieved great speed, but with limited range. This was problematic, as it required the slow, heavily laden mother aircraft to approach within of the target, making it vulnerable to defending fighters. 155 Ohka Model 11s were produced at Yokosuka, and another 600 aircraft were built at the Kasumigaura Naval Air Arsenal. There was a single experimental variant of the Model 11, referred to as the Model 21, which had thin steel wings manufactured by Nakajima, which also combined the engine of the Model 11 and the airframe of the Model 22.
Operationally, the Ohka was usually carried underneath a Mitsubishi G4M2e Model 24J "Betty" bomber to within range of its target.Lardas 2022, pp. 10-11.Grunden 2005, pp. 151-152. On release, the pilot would first glide towards the target and when close enough he would fire the Ohkas three Type 4 Model 1 Mark 20 solid-fuel rocket motors, one at a time or in unison, and fly the missile towards the ship that he intended to destroy. The final approach was difficult for a defender to stop because the aircraft gained high speed ( in level flight and or even in a dive. Later versions were designed to be launched from coastal air bases and caves, and even from submarines equipped with aircraft catapults, although none were actually used in this way. The was the first Allied ship to be sunk by Ohka aircraft, near Okinawa, on 12 April 1945. Over the course of the conflict, Ohkas sank or damaged beyond repair three ships and significantly damaged three more ships, with a total of seven U.S. ships damaged or sunk by Ohkas.
The Ohka pilots, members of the Jinrai Butai (Thunder Gods Corps), are honored in Japan at Ohka Park in Kashima City, the Ohka Monument in Kanoya City, the Kamakura Ohka Monument at Kenchō-ji Zen temple in Kamakura, Kanagawa, and the Yasukuni Shrine in Tokyo.
The Ohka K-1 was an unpowered trainer version with water ballast in place of a warhead and engines, that was used to provide pilots with handling experience. Unlike the combat aircraft, it was furnished with flaps and a landing skid. The water ballast would be dumped prior to landing. The K-1 remained a challenging aircraft to fly, possessing a relatively high landing speed of . 45 K-1s were produced by Dai-Ichi Kaigun Koku Gijitsusho.
The Model 22 was designed to overcome the short standoff distance problem by using a Campini-type motorjet engine, the Ishikawajima Tsu-11, giving a level speed of only at but extending the range to . This engine was successfully tested, and 50 Model 22 Ohkas were built at Yokosuka to accept this engine. The Model 22 was to be launched by the more agile Yokosuka P1Y3 Ginga "Frances" bomber, necessitating a shorter wing span and much smaller warhead. The first flight of a Model 22 Ohka took place in June 1945; none appear to have been used operationally, and only approximately 20 of the experimental Tsu-11 engines are known to have been produced.Grunden 2005, pp. 152-153.
The Model 33 was a larger version of the Model 22 powered by an Ishikawajima Ne-20 turbojet with an warhead. The launch aircraft was to be the Nakajima G8N Renzan, but the Model 33 was cancelled due to the likelihood that the Renzan would not be available.Grunden 2005, p. 153.
Other unbuilt planned variants were the Model 43A with folding wings, to be launched from submarines, and the Model 43B, a catapult/rocket-assisted version, also with folding wings so that it could be hidden in caves. A trainer version was also under development for this version, the two-seat Model 43 K-1 Kai Wakazakura (Young Cherry), fitted with a single rocket motor. In place of the warhead, a second seat was installed for the student pilot. Two of this version were built. Finally, the Model 53 would also use the Ne-20 turbojet, but was to be towed like a glider and released near its target.
Operational history On 21 March 1945, the first operational use of the Ohka took place, involving a total of 18 G4M motherships; this attack was unsuccessful due to fighter interception, resulting in the loss of all G4Ms along with 26 of the 30 escort fighters.Grunden 2005, p. 152. It was used mostly against U.S. ships invading Okinawa, and if launched from its mothership, could be effective because of its high speed in the dive.Mayo, Wayland. "Japanese Suicide Weapons: The Kugisho MXY7-K1 Ohka" b-29s-over-korea.com Retrieved: 1 August 2011 In the first two attempts to transport the Ohkas to Leyte Gulf using aircraft carriers, the carriers and were sunk by the U.S. submarines and .
Attacks intensified during April 1945. On 1 April 1945, six G4Ms attacked the U.S. fleet off Okinawa. At least one aircraft made a successful attack; its Ohka was thought to have hit one of the 406 mm (16 in) turrets on the battleship , causing moderate to extensive damage. However, postwar analysis indicated that no hits were recorded and that there had been a near miss. The transports , , and were also hit by kamikaze aircraft, but it is unclear whether any of these were Ohkas from the other G4Ms. None of the G4Ms returned.