World War 2 In Review

File:Ohka carried under the belly of a Betty of 721st Naval Air Group.jpg

Mitsubishi G4M2E Model 24 Tei bomber from Kokutai 721 carrying an Ohka.

The Yokosuka MXY-7 Ohka (Ōka, "cherry blossom") is a purpose-built, rocket-powered human-guided kamikaze attack-aircraft deployed by Japan against Allied ships in the Pacific Ocean theater toward the end of World War II. Although extremely fast, the Ohka had a very short range, so it had to be carried into action as a parasite aircraft by a much larger bomber that was vulnerable to carrier-borne fighters. In action during the Battle of Okinawa in 1945, Ohkas succeeded in sinking or damaging some escort-vessels and transport ships, but never sank any major warships. The Japanese developed improved versions in an attempt to overcome the aircraft's shortcomings, but they came too late for deployment.

Allied personnel referred to the aircraft as "Baka Bombs" (baka being a Japanese pejorative term meaning "fool" or "idiot").

Design and Development

The MXY-7 Navy Suicide Attacker Ohka was a manned flying bomb that was usually carried underneath a Mitsubishi G4M2e Model 24J "Betty" 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, and fly the missile towards the ship that he intended to destroy.

The design was conceived by Ensign Mitsuo Ohta of the 405th Kōkūtai, aided by students of the Aeronautical Research Institute at the University of Tokyo. Ohta submitted his plans to the Yokosuka research facility. While Ohta had started work on the design in 1943 the authorities would not take an interest until the following year. 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) created formal blueprints for what was to be the MXY-7. 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.

The final approach was difficult for a defender to stop because the aircraft gained high speed (650 km/h (400 mph) in level flight and 930 km/h (580 mph) or even 1,000 km/h (620 mph) 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 Allen M. Sumner-class destroyer USS Mannert L. Abele was the first Allied ship to be sunk by Ohka aircraft, near Okinawa on 12 April 1945. Over the course of the war, 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 only operational Ohka was the Model 11. Essentially a 1,200-kilogram (2,600 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 it 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.

The Ohka K-1 was an unpowered trainer version with water ballast instead of warhead and engines, that was used to provide pilots with handling experience. Unlike the combat aircraft, it was also fitted with flaps and a landing skid. The water ballast was dumped before landing but it remained a challenging aircraft to fly, with a landing speed of 130 mph (210 km/h). Forty-five were built 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 276 mph at 13,125 feet but extending the range to 81 miles. 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-kilogram (1,300 lb) 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.

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

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

The Yokosuka MXY-7 Ohka 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. In the first two attempts to transport the Ohkas to Leyte Gulf using aircraft carriers, the carriers Shinano and Unryu were sunk by the U.S. submarines Archerfish and Redfish.

Attacks intensified in April 1945. On 1 April 1945 six G4Ms attacked the U.S. fleet off Okinawa. At least one made a successful attack; its Ohka was thought to have 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. 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 G4Ms. None of the G4Ms returned.

The U.S. military quickly realized the danger and concentrated on extending their "defensive rings" outward to intercept the G4M/Ohka combination aircraft before the suicide mission could be launched. On 12 April 1945 nine G4Ms attacked the U.S. fleet off Okinawa. The destroyer Mannert L. Abele was hit, broke in two, and sank. 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 above the waterline just behind the ship's bow, its charge passing completely through the hull and splashing into the sea, where it detonated underwater, causing little damage to the ship. The other Ohka narrowly missed (its pilot probably 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 G4Ms attacked the U.S. fleet off Okinawa. None returned. None of the Ohkas appeared to have been launched. Two days later, six G4Ms attacked the U.S. fleet off Okinawa. Two returned, but no Ohkas had hit their targets. Later, on 28 April 1945, four G4Ms attacked the U.S. fleet off Okinawa at night. One returned. No hits were recorded.

May 1945 saw another series of attacks. On 4 May 1945 seven G4Ms attacked the U.S. fleet off Okinawa. One Ohka hit the bridge of a destroyer, Shea, causing extensive damage and casualties. Gayety was also damaged by an Ohka's near miss. One G4M returned. On 11 May 1945 four G4Ms 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 G4Ms attacked the fleet off Okinawa. Bad weather forced most of the aircraft to turn back, and none of the others hit targets.

On 22 June 1945 six G4Ms attacked the fleet. Two returned, but no hits were recorded. Postwar analysis concluded that the Ohka's impact was negligible, since no U.S. Navy capital ships had been hit during the attacks because of the effective defensive tactics that were employed. In total, of the 300 Ohka available for the Okinawa campaign, 74 actually undertook operations, of which 56 were either destroyed with their parent aircraft or in making attacks. The Allied nickname for the aircraft was "Baka", a Japanese word meaning "foolish" or "idiotic".

Type: Kamikaze (piloted suicide) anti-ship aircraft / missile

National origin: Japan

Manufacturer: Yokosuka Naval Air Technical Arsenal

Status: Retired

Primary user: Imperial Japanese Navy Air Service

Number built: 852

Manufactured: 1944–1945

Introduction date: 1945

First flight: 21 March 1944 (unpowered), November 1944 (powered).

Retired: 1945

Variants

MXY-7: Rocket powered suicide attacker, unpowered glider prototypes; ten built

Navy Suicide Attacker Ohka Model 11: Long designation of the operational attacker

Ohka Model 11: Suicide attacker powered by 3 × 2.616 kN (588 lbf) Navy Type 4 Mark 1 Model 20 solid-fueled rocket motors, firing for 8–10 seconds; 755 built

Crew: 1

Length: 6.066 m (19 ft 11 in)

Wingspan: 5.12 m (16 ft 10 in)

Height: 1.16 m (3 ft 10 in)

Wing area: 6 m2 (65 sq ft)

Empty weight: 440 kg (970 lb)

Gross weight: 2,140 kg (4,718 lb)

Powerplant: 3 × Type 4 Mark 1 Model 20 solid-propellant rocket motors, 2.62 kN (588 lbf) thrust each

Maximum speed: 648 km/h (403 mph, 350 kn) at 3,500 m (11,500 ft)

Never exceed speed: 926 km/h (575 mph, 500 kn) terminal dive velocity

Range: 37 km (23 mi, 20 nmi)

Wing loading: 356.7 kg/m2 (73.1 lb/sq ft)

Thrust/weight: 0.38

Armament: 1,200 kg (2,600 lb) Ammonal warhead

Ohka Model 21: Suicide attacker, fitted with steel-built wings built by Nakajima; one built

Ohka Model 22: Suicide attacker, powered by an Ishikawajima Tsu-11 thermo-jet engine with reduced span wings and 600 kg (1,300 lb) warhead, to be carried by Yokosuka P1Y1 Ginga bombers. 50 built by the First Naval Air Technical Arsenal (Dai-Ichi Kaigun Koku Gijitsusho)

Ohka Model 33: Suicide attacker, powered by an Ishikawajima Ne-20 turbojet engine, with an 800 kg (1,800 lb) warhead, to be carried by the Nakajima G8N1 Renzan bomber

Ohka Model 43A Ko: Suicide attacker, powered by a Ne-20 turbojet engine, with folding wings, to be catapult launched from submarines

Ohka Model 43B Otsu: Suicide attacker similar to the Model 43A for catapult launching from caves

Ohka Model 53: Suicide attacker for aerotow launch, powered by a Ne-20 turbojet engine

Ohka K-1: Suicide attack training glider

Ohka Model 43 K-1 Kai Wakazakura ("Young Cherry"): Two-seat suicide attack glider trainer with flaps and retractable skid undercarriage, fitted with a single Type 4 Mark 1 Model 20 rocket motor, for limited powered flight

"Suzuka-24" (Japanese designation unknown): Alleged interceptor version with warhead replaced by a fuel tank for a Ne-20 jet engine and two 20 mm autocannon (Unknown Ho-5 or Type 99 with 60 / 150 rounds per gun) mounted on top. Supposedly employed at least twice against B-29 formations in April 1945

Surviving Aircraft

India

On display

Model 11 on static display at the Indian Air Force Museum in Palam, New Delhi.

Japan

On display

Model 11 on static display at Iruma Air Force Base in Iruma, Saitama.

On static display at the Kawaguchiko Motor Museum in Narusawa, Yamanashi.

United Kingdom

On display

Model 11 on static display at the Fleet Air Arm Museum in Yeovilton, Somerset.

Model 11 on static display at the Imperial War Museum in London.

Model 11 on static display at the Royal Air Force Museum Cosford in Cosford, Shropshire.

Model 11 on static display at the Science and Industry Museum in Manchester.

United States

On display

Model 11 on static display at the National Museum of the Marine Corps in Triangle, Virginia.

Model 11 on static display at the Planes of Fame Air Museum in Chino, California.

Model 11 on static display at the Yanks Air Museum in Chino, California.

Model 22 on static display at the Steven F. Udvar-Hazy Center of the National Air and Space Museum in Chantilly, Virginia, the only surviving Model 22.

Model 43B K-1 Kai Wakazakura on static display at the Pima Air & Space Museum in Tucson, Arizona. It is on loan from the National Air and Space Museum.

K-1 on static display at the National Museum of the United States Air Force in Dayton, Ohio.

K-1 on static display at the National Museum of the U.S. Navy in Washington, D.C.

Replicas on Display

Japan

Model 11 on static display at the Yūshūkan of the Yasukuni Shrine in Tokyo.

Model 11 on static display at Usashi Heiwa Museum in Usa, Oita.

United States

Model 11 on static display at the National Warplane Museum in Geneseo, New York.

Bibliography

Aeronautical Staff of Aero Publishers in cooperation with Edward T Maloney (1966). Kamikaze. Fallbrook, California, USA: Aero Publishers.

Ellis, Ken. Wreck & Relics, 23rd Edition Manchester: Crecy Publishing Ltd, 2012.

Francillon, René J. (1979). Japanese Aircraft of the Pacific War (2nd ed.). London: Putnam & Company.

Francillon, René J. (1971). Mitsubishi G4M "Betty" and Ohka Bomb. Aircraft in Profile, Vol. 9. Windsor, Berkshire, UK: Profile Publications Ltd.

Maloney, Edward T. and the Aeronautical Staff of Aero Publishers, Inc. Kamikaze (Aero Series 7). Fallbrook, California: Aero Publishers, Inc., 1966.

Mikesh, Robert C.; Abe, Shorzoe (1990). Japanese Aircraft, 1910–1941. London: Putnam Aeronautical Books.

O'Neill, Richard (2001). Suicide Squads: The Men and Machines of World War II Special Operations. Washington DC: The Lyons Press.

Sheftall, M.G. Blossoms in the Wind: Human Legacies of the Kamikaze. New York: New American Library, 2005.

Stafford, Edward P. Little Ship, Big War: The Saga of DE343. Annapolis, Maryland: Naval Institute Press, 2000.

Zaloga, Steven J. (2011). Kamikaze: Japanese Special Attack Weapons 1944–45. New Vanguard #180. Botley, Oxfordshire: Osprey Publishing.

Yokosuka MXY-7 Ohka flying bomb Japanese Navy Air Force. Wartime illustration.

Ohka Model 11 replica at the Yasukuni Shrine Yūshūkan war museum.

An Ohka Model 11 being disarmed. Possibly the I-13 captured April 1, 1945 at Yontan airfield.

An Ohka Model 11 discovered April 1945 at Yontan airfield, Okinawa. This is the MXY7 Model 11 Number I-13 captured April 1, 1945 at Yontan airfield and now on display at Aerospace Museum, Cosford.

Thermojet powered Model 22; note the jet intake on the side just forward of the tail. This is an experimental Model 22 which never went into production. From the background hangers, this appears to be taken at Yokosuka Naval base where all model 22's were built. It is unlikely the Model 22 could have been anywhere else since testing of the integration of troublesome Tsu-11 jet engine occurred here. Unlike the Alameda example now in the NASM, this unit has intact ducts and appears from the exhaust tube to have one of the 3 TSU-11 hybrid Jet engines known to have been produced.

1945: A MXY-7 Ohka Model 22 at Yokosuka minus its wings. Note the air intakes indicating jet, not rocket power.

MXY7 K-1 Kai Two-seat trainer powered by a single Type 4 Mk I Model 20 rocket motor and fitted with flaps and landing skis; 2 built at Yokosuka. These are the two being inspected by Navy personnel.

Near the end of World War II, Vice Admiral Onishi Takijino recommended that the Japanese navy form special groups of men and aircraft to attack American warships in the Philippines. The Japanese used the word Tokko (Special Attack) to describe these units, known to the Allies as the kamikaze. Some 5,000 pilots died making Tokko attacks. The Ohka (Cherry Blossom) Model 22 was designed to allow a pilot with minimal training to drop from a Japanese navy bomber at high altitude and guide his aircraft with its warhead at high speed into an Allied warship. Plans were afoot in 1944 to adapt a Yokosuka Pl Y Ginga to carry the Model 22. While several rocket-powered Ohka 11s still exist, this Ohka 22 is the only surviving version powered by a motor-jet, a reciprocating engine that pressurized a combustion chamber into which fuel was injected and ignited. Unlike the Ohka 11, the Ohka 22 never became operational. Picture taken at the National Air and Space Museum's Steven F. Udvar-Hazy Center in Chantilly, Virginia.

Yokosuka MXY7 Ohka Model 11, on display at Indian Air Force Museum, Palam, New Delhi, India.

K-1 Ohka Trainer, National Museum of the U.S. Air Force.

Yokosuka MXY 7 Ohka flying bomb, picture taken at Steven F. Udvar-Hazy Center. The NASM Ohka is a rare Model 22, powered by an early type of jet engine, which unlike the rocket engine of the Model 11, gave it much greater range- an important feature since Model 11's needed to be launched within 20 miles of target by slow moving mother ships which were easy prey for fighters. According to the Smithsonian this Ohka was taken from Japan to Alameda, Ca in late 1945, with the first photo taken in December 1945. Then to the Smithsonian in 1948, where it was on display at Smithsonian Arts and Industries Building until it was moved in the early 1970s for storage at Paul E. Garber Facility in Suitland, Maryland facility. It was restored there in 1993. It is unlikely this was captured anywhere else besides the Yokosuka research hangers, since Aichi was unable to perform any assembly on Model 22s, Yokosuka built all Model 22s, and all the research for the troublesome Tsu-11 engine integration were conducted at Yokosuka.

The rear of Ohka, Royal Air Force Museum Cosford.

Yokosuka Ohka Model 22.

April 20, 1945: Yokosuka MXY-7 Ohka ("Baka" bomb) control panel.

1944: Mitsubishi G4M2E Model 24 Tei bomber just released MXY7 Ohka. Wind tunnel model experiment.

1945: Imperial Japanese Navy Stand-by aircrews relax in front of a Mitsubishi G4M2e Model 24 Tei ("Betty") bomber carrying a Kugisho/Yokosuka MXY-7 Ohka ("Baka") Model 11 manned rocket-propelled suicide plane.

1945: Stills from gun camera footage of an attack on an Imperial Japanese Navy Mitsubishi G4M2e Model 24 Tei ("Betty") bomber carrying a Kugisho/Yokosuka MXY-7 Ohka ("Baka") Model 11 manned rocket-propelled suicide plane.

Ohka rocket bomb motor nozzle.

Ohka Type 11 with "Betty" mothership.

Tsu-11 rocket motor.

1945: Cutaway illustration of "Baka Rocket Propelled Piloted Aircraft Bomb" (Yokosuka MXY-7 Ohka) from the Technical Air Intelligence Center (TAIC), Naval Air Station, Anacostia, D.C.

August 1945: Popular Science.

Yokosuka MXY7 Ohka Model 11. Guarded by an MP at Yonatan Airfield, Okinawa, circa April-May 1945.

Yokosuka MXY7 Ohka which had been captured on Okinawa. Photographed 26 June 1945, while under study by experts at N.A.M. Unit. Photo by 4th Naval District.

Rear view of Japanese Baka Bomber, showing rocket tubes, at Okinawa. September 1945.

Front view of Japanese Baka Bomber, showing rocket tubes, at Okinawa. September 1945.

U.S. Marines examine a “Baka Bomber”, Japanese suicide rocket bomb on Okinawa’s Yontan airfield, where several of the craft were abandoned by the enemy when U.S. Tenth Army forces captured the enemy airbase. The rocket-propelled bomb is steered by a lone pilot who is carried to his death.

Known as “Little Joe,” this radio-controlled power bomb was shipboard launched. The bomb was also known with the designation KAN. It carried 100 lb and was a general purpose bomb straight up to 10,000 feet at 400 mph to intercept and destroy Baka Bombers. It was powered by jet assisted take off and rockets, a short range surface to air missile.

Yokosuka Ohka Model 22.

Yokosuka MXY-7 Ohka.

Yokosuka MXY-7 Ohka (Cherry Blossom) Model 11, codenamed Baka purpose-built, rocket powered human-guided anti-shipping kamikaze attack plane. This one was on Okinawa being examined by American servicemen in 1945.

I-18 was captured by US forces at Yontan Airfield on Okinawa on 1 April 1945 and was subsequently transported to the United States for public display during War Bond drives. It it is currently owned by the Planes of Fame Air Museum and on public display at the Museum's site in Chino, California.