Yokosuka MXY7 Ohka

MXY-7 Ohka
Ohka Model 11 replica at the Yasukuni Shrine Yūshūkan war museum.
Role	Kamikaze aircraft
National origin	Japan
Manufacturer	Yokosuka Naval Air Technical Arsenal
First flight	October 1944 (unpowered), November 1944 (powered).
Introduction	1945
Retired	1945
Primary user	Imperial Japanese Navy Air Service
Produced	1944–1945
Number built	852

The Yokosuka MXY-7 Ohka (櫻花; Shinjitai: 桜花; "cherry blossom"; Hebon-shiki transcription Ōka) was a purpose-built, rocket powered human-guided anti-shipping kamikaze attack plane^[1] employed by Japan towards the end of World War II. United States sailors gave the aircraft the nickname Baka^[2] (Japanese for "fool" or "idiot").^[3]

Design and development

The MXY-7 Navy Suicide Attacker Ohka was a manned flying bomb that was usually carried underneath a Mitsubishi G4M2e "Betty" Model 24J bomber to within range of its target; on release, the pilot would first glide towards the target and when close enough he would fire the Ohka's three solid-fuel rockets, one at a time or in unison,^[4] and fly the missile towards the ship that he intended to destroy.

The design was conceived by Ensign Mitsuo Ohta of the 405th Kokutai,^[5] aided by students of the Aeronautical Research Institute at the University of Tokyo. Ohta submitted his plans to the Yokosuka research facility. The Imperial Japanese Navy decided the idea had merit and Yokosuka engineers of the Yokosuka Naval Air Technical Arsenal (Dai-Ichi Kaigun Koku Gijitsusho, or in short Kugisho^[6]) created formal blueprints for what was to be the MXY7. The only variant which saw service was the Model 11, and it was powered by three Type 4 Mark 1 Model 20 rockets. 155 Ohka Model 11s were built at Yokosuka, and another 600 were built at the Kasumigaura Naval Air Arsenal.^[4]

The final approach was almost unstoppable because the aircraft gained high speed (403 miles per hour (649 km/h) in level flight and 576 miles per hour (927 km/h) or even 650 miles per hour (1,050 km/h) 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 was actually used in this way. It appears that the operational record of Ohkas includes three ships sunk or damaged beyond repair and three other ships with significant damage. Seven US ships were damaged or sunk by Ohkas throughout the war. The USS Mannert L. Abele was the first Allied ship to be sunk by Ohka aircraft, near Okinawa on 12 April 1945.^[7][8]

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 Kamakura, and the Yasukuni Shrine in Tokyo.

Disarming the bomb

Thermojet powered Model 22, note the jet intake

The only operational Ohka was the Model 11. Essentially a 1,200 kg (2,646 lb) 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 37 km (20 nmi; 23 mi) of the target, making them very vulnerable to defending fighters. There was one experimental variant of the Model 11, the Model 21, which had thin steel wings manufactured by Nakajima. It had the engine of the Model 11 and the airframe of the Model 22.^[9]

The Ohka K-1 was a unpowered trainer version with water ballast instead of warhead and engines, to provide pilots with handling experience. 45 were built by Dai-Ichi Kaigun Koku Gijitsusho.^[10]

The Model 22 was designed to overcome the short standoff distance problem by using a Campini-type thermojet engine, the Tsu-11. 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 600 kg (1,320 lb) warhead. None appear to have been used operationally, and only three of the experimental Tsu-11s engines are known to have been produced.

The Model 33 was a larger version of the Model 22 powered by an Ishikawajima Ne-20 turbojet with a 800 kg (1,760 lb) warhead. The mothership was to be the Nakajima G8N Renzan. Model 33 was cancelled due to the likelihood that the Renzan would not be available.^[11]

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.^[9] 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.^[12]

Finally, the Model 53 would also use the Ne-20 turbojet, but was to be towed like a glider and released near its target.^[9]

Operational history

The Yokosuka MXY7 Ohka was used mostly against American ships invading Okinawa, and if launched from its mothership, could be extremely effective due to to its high speed in the dive.^[13] In the first two attempts to ship the Ohkas to Leyte Gulf through aircraft carriers, the carriers Shinano and Unryu were sunk by the US submarines USS Archer-Fish and USS Redfish, in which in both cases the explosions of their Ohkas contributed to their sinkings, preventing their presence at the Battle of Leyte Gulf.

On 21 March 1945, 16 Ohka-carrying "Betty" bombers were to be escorted by 55 Zeros to attack Task Group 58.1 (Hornet, Bennington, Wasp, and Belleau Wood). Another two "Bettys" were to escort and provide navigation and observation. Due to technical problems, 25 Zeros had to turn back or could not take off. The Ohka attack force was intercepted by 16 US Navy Grumman F6F Hellcat fighters and the Ohkas were immediately jettisoned by the "Bettys," some 113 km (70 mi) from the target. None of the "Bettys" returned, no ships were attacked and 16 of the Jinrai Butai were killed, with only 15 damaged Zeros making it back to their base.

Attacks intensified in April 1945. On 1 April 1945, six "Bettys" attacked the U.S. Fleet off Okinawa. At least one made a successful attack, with its Ohka thought to hit one of the 406 mm (16 in) turrets on the battleship West Virginia, causing moderate damage. Postwar analysis indicated that no hits were recorded and that a near-miss took place. ^[14] The transports Alpine, Achernar, and Tyrrell were also hit by kamikaze aircraft, but it is unclear whether any of these were Ohkas from the other "Bettys". None of the "Bettys" returned.

The American military quickly realized the danger and concentrated on extending their "defensive rings" outward to intercept the "Betty"/Ohka combination aircraft before the suicide mission could be launched. ^[14]On 12 April 1945, nine "Bettys" attacked the U.S. Fleet off Okinawa. The destroyer Mannert L. Abele was hit, broke in two, and sank, witnessed by LSMR-189 CO James M. Stewart. Jeffers destroyed an Ohka with AA fire 45 m (50 yd) from the ship, but the resulting explosion was still powerful enough to cause extensive damage, forcing Jeffers to withdraw. The destroyer Stanly was attacked by two Ohkas. One struck just above the waterline just behind the ship's bow, with the charge punching completely through the other side of the hull before splashing into the sea and detonating like a depth charge, causing little damage to the ship, and the other Ohka narrowly missed (likely due to the pilot being killed by anti-aircraft fire) and crashed into the sea, knocking off the Stanly's ensign in the process. One Betty returned. On 14 April 1945, seven "Bettys" attacked the U.S. Fleet off Okinawa. None returned. None of the Ohkas appeared to have been launched. Two days later, six "Bettys" attacked the U.S. Fleet off Okinawa. Two returned, but no Ohkas hit their targets. Later, on 28 April 1945, four "Bettys" attacked the U.S. Fleet off Okinawa at night. One returned. No hits were recorded.^[14]

May 1945 saw another series of attacks. On 4 May 1945, seven "Bettys" attacked the U.S. Fleet off Okinawa. One Ohka hit the bridge of a minesweeper, Shea, causing extensive damage and casualties. Gayety was also damaged by a near-miss by an Ohka. One "Betty" returned. On 11 May 1945, four "Bettys" attacked the U.S. Fleet off Okinawa. The destroyer Hugh W. Hadley was hit and suffered extensive damage and flooding. The vessel was judged beyond repair. On 25 May 1945, 11 "Bettys" attacked the US Fleet off Okinawa. Bad weather forced most of the aircraft to turn back, and none of the others scored hits.

On 22 June 1945, six "Bettys" attacked the U.S. Fleet off Okinawa. Two returned, but no hits were scored. Postwar analysis concluded that the Ohka's impact was negligible with no US Navy capital ships actually hit during their attacks due to an extremely effective set of defensive tactics that were employed. ^[14]

Variants

Model 43 K-1 Kai rocket assist trainers, note the landing skid

Operational variants

• Kugisho/Yokosuka MXY-7 "Ohka" Model 11 Rocket Suicide Attacker. 755 built.

Non-operational variants

• Kugisho/Yokosuka "Ohka" Model 21 Rocket Suicide Attacker. Steel wings; one built.
• Kugisho/Yokosuka "Ohka" Model 22 Motorjet Suicide Attacker. 50 built.
• Kugisho/Yokosuka "Ohka" Model 33 Turbojet Suicide Attacker. Renzan drop launch.
• Kugisho/Yokosuka "Ohka" Model 43A Ko Turbojet Suicide Attacker. Submarine launched.
• Kugisho/Yokosuka "Ohka" Model 43B Otsu Turbojet Suicide Attacker. Cave launched.
• Kugisho/Yokosuka "Ohka" Model 53 Turbojet Suicide Attacker. Towed launch.

Trainer variants

• Kugisho/Yokosuka "Ohka" K-1 Suicide Attack Trainer
• Kugisho/Yokosuka "Ohka" Model 43 K-1 Kai Suicide Attack Trainer

Surviving examples

K1 Ohka Trainer, National Museum of the US Air Force

Thermojet powered, Model 22 Ohka. National Air and Space Museum

The rear of Ohka, Royal Air Force Museum Cosford

Some 852 were built, mostly Model 11. Surviving Ohkas include:

• Model 11: Royal Air Force Museum, Cosford. Ohka is Number I-13 captured 1 April 1945 at Yontan, Okinawa.
• Model 11: Fleet Air Arm Museum, Yeovilton.
• Model 11: Museum of Science and Industry in Manchester, Manchester.
• Model 11: Defence Explosives Ordinance School, Kent.
• Model 11: Indian Air Museum, New Delhi.
• Model 11: Iruma Air Force Base, Iruma, Saitama.
• Model 11: Marine Corps Air-Ground Museum, Quantico, Virginia.
• Model 11: Yanks Air Museum Chino, California. Ohka Number I-10.
• Model 11: Planes of Fame Museum, Chino, California. Ohka Number I-18 captured at Yontan.
• Model 22: Smithsonian National Air and Space Museum, Washington, D.C. (restored 1993).
• K-1 (rebuilt to represent a Model 11, but retaining the landing skid): National Museum of the United States Air Force, Dayton, Ohio.
• K-1: U.S. Navy Museum, Washington, D.C. Exhibit Photo.
• Model 43 K-1 Kai: Smithsonian National Air and Space Museum, Washington, DC.

Specifications (Model 11)

Data from Japanese AIrcraft of the Pacific War^[15]

General characteristics

• Crew: One
• Length: 6.06 m (19 ft 11 in)
• Wingspan: 5.12 m (16 ft 9½ in)
• Height: 1.16 m (3 ft 9⅓ in)
• Wing area: 6 m² (64.583 ft²)
• Empty weight: 440 kg (970 lb)
• Loaded weight: 2,140 kg (4,718 lb)
• Powerplant: 3 × Type 4 Mark 1 Model 20 rocket motors Solid propellant, 2.60 kN (587 lbf) each

Performance

• Maximum speed: 804 km/h in dive (576 mph in dive)
• Range: 36 km (23 mi)
• Wing loading: 356.7 kg/m² (73.1 lb/ft²)
• Thrust/weight: 0.38
• Dive speed (3× Rocket motors Full-Boost): 1,040 km/h (650 mph)

Armament

• 1,200 kg (2,646 lb) Ammonal warhead

See also

• Japanese Special Attack Units
• Secret and special weapons in Showa Japan
• Flying bomb
• Fritz X
• The Cockpit, an anthology of short films containing one about an Ohka pilot, reflecting Japanese sentiments of them

Aircraft of comparable role, configuration and era

• Fieseler Fi 103 (V-1 flying bomb)
• Messerschmitt Me 328
  

Related lists

• List of military aircraft of Japan
  

References

Notes

1. ^ "Ohka" aerospaceweb.org. Retrieved: 16 October 2010.
2. ^ Francillon 1971, p. 118.
3. ^ Stafford, 2000, p. Index.
4. ^ ^{a b} Francillon 1979, p. 477.
5. ^ Francillon 1979, p. 476.
6. ^ Mikesh and Abe 1990, p. 262.
7. ^ Francillon 1971, p. 117.
8. ^ Francillon 1979, p. 478.
9. ^ ^{a b c} Francillon 1979, p. 481.
10. ^ Francillon 1979, pp. 478, 482.
11. ^ Francillon 1979, pp. 441, 479.
12. ^ Francillon 1979, p. 482.
13. ^ Mayo, Wayland. "Japanese Suicide Weapons: The Kugisho MXY7-K1 Ohka." b-29s-over-korea.com. Retrieved: 1 August 2011.
14. ^ ^{a b c d} Kightly, James. "Yokosuka Ohka Kamikaze Pilot." Aeroplane, Volume 39, No. 7, Issue no. 459, July 2011, pp. 30–31.
15. ^ Francillon 1979, pp. 481–482.

Bibliography

• Francillon, Ph.D., René J. Japanese Aircraft of the Pacific War. London: Putnam & Company Ltd., 1970 (2nd edition 1979). ISBN 0-37-030251-6.
• Francillon, Ph.D., René J. "Mitsubishi G4M "Betty" and Ohka Bomb" Aircraft in Profile, Vol. 9. Windsor, Berkshire, UK: Profile Publications Ltd., 1971. ISBN 0-85383-018-5.
• Maloney, Edward T. and the Aeronautical Staff of Aero Publishers, Inc. Kamikaze (Aero Series 7). Fallbrook, California: Aero Publishers, Inc., 1966.
• Mikesh, Robert C. and Shorzoe Abe. Japanese Aircraft, 1910-1941. London: Putnam Aeronautical Books, 1990. ISBN 0-85177-840-2.
• Sheftall, M.G. Blossoms in the Wind: Human Legacies of the Kamikaze. New York: New American Library, 2005. ISBN 0-45121-487-0.
• Stafford, Edward P. Little Ship, Big War: The Saga of DE343. Annapolis, Maryland: Naval Institute Press, 2000. ISBN 1-55750-890-9.

External links

• "Baka... Flying Warhead", C.I.C. (Combat Information Center), U.S. Office of the Chief of Naval Operations, June 1945.
• Morinoske: Pilot testimonials
• Thunder Gods 1989 book about Ohka squadron
• The Cherry Blossom Squadrons 1973 book about Ohka squadron
• USS LSM(R)-193
• Popular Science,August 1945, Japanese Gamble On Human Bombs
• The History of Kamikaze Ohka 桜花 (Japanese)