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MXY7 Ohka

Country Japan Manufacturer Yokosuka Naval Air Technical Arsenal Primary Role Other Maiden Flight 23 October 1944

Contributor: C. Peter Chen

ww2dbaseIn 1943, Japanese Navy 405th Squadron transport pilot Ensign Mitsuo Ohta submitted a rudimentary design that detailed a purpose-built suicide aircraft. Ohta's design was ignored until spring of 1944 when it was picked up by Professor Taichiro Ogawa of the Aeronautical Research Institute of the University of Tokyo, who refined Ohta's design. The Japanese Navy did not pay official attention to it until Jun 1944 when Japan was defeated in the Mariana Islands. The idea that originated by Ohta was given to the Naval Air Technical Arsenal at Yokosuka, and the new research project which officially began on 16 Aug 1944 under codename Project Marudai under Commander Masao Yamana. The aircraft was given the nickname of Ohka, "Cherry Blossom". The original plan was to use KR-10 liquid-fuel rocket engines which were being built in Nagasaki based on German Walther rocket engine plans, but ultimately the engineers changed to using solid rocket boosters due to cost and complexity concerns. The first unpowered prototypes and K-1 training versions were completed in early Sep 1944; later in the same month, the testing of rocket engines began in parallel. On 23 Oct 1944, the first unmanned flight took place over Sagami Bay southwest of Tokyo; 8 days later, the first manned flight using a K-1 training aircraft was conducted. The first successful test of a rocket-powered Ohka Type 11 took place on 19 Nov 1944, which led to the formal authorization of production under the designation MXY7. While each of the prototypes had three fuselage-mounted rocket boosters and two wing-mounted rocket boosters, the production version was to only have the three fuselage-mounted rocket boosters.

ww2dbaseIn Sep 1944, the Japanese Navy 721st Squadron "Divine Thunder Unit" (Jinrai Butai) was formed under Captain Motoharu Okamura based at Konoike airfield, Ibaraki, Japan to begin training of already-experienced pilots for flights of the aircraft that were soon to be known as MXY7 Ohka rocket-assisted glide bombs. The 722nd Squadron "Torpedo" (Tatsumaki) was planned to be formed, but personnel reserved for this squadron ultimately became replacements for the 721st Squadron. The first 50 Ohka Type 11 aircraft were delivered to carrier Shinano in Nov 1944, but they were lost when Shinano was torpedoed and sunk in transit on 28 Nov. This and other general shipping delays caused by the American blockade caused operations of this new weapon to be held up until 21 Mar 1945; on this date, the 321st Squadron's first combat sortie from Kanoya airfield at Kyushu, Japan resulted in failure, with most aircraft of the attack force (18 G4M2 bombers of 711th Squadron under Lieutenant Commander Goro Nonaka carrying 16 Ohka aircraft, and 30 escorting A6M5 fighters) shot down before reaching the target American fleet. Japanese naval leadership decided that future Ohka missions were to be dispatched in much smaller groups to avoid detection.

ww2dbaseEarlier in the same month, on 8 Mar, US intelligence first detected the new Ohka aircraft at Konoike airfield and gave the name "Viper" for the new discovery. On 1 Apr 1945, an Ohka mission was launched off Okinawa, Japan and damaged USS West Virginia; on the same day, a cache of 15 Ohka aircraft was captured by the United States Marines on Okinawa, who nicknamed them baka, Japanese for "fool", as the discovery was made on April Fool's Day.

ww2dbaseOn 12 Apr, a combat sortie saw destroyer USS Mannert L. Abele being struck by an Ohka aircraft shortly after the same ship was struck by a special attack fighter off Okinawa, Japan; as the destroyer broke in half and sank, she became the first ship to be sunk by an Ohka attack. Two days later, 7 G4M bombers approached American ships off Okinawa, but all were shot down before they were able to launch their Ohka payloads. On 16 Apr, an Ohka attack off Okinawa by six G4M bombers resulted in failure. On 28 Apr, four G4M bombers attacked yet again using the Ohka weapon but without success. On 4 May and 11 May, another two attacks damaged a minesweeper and a destroyer. The final Ohka attack took place on 22 Jun, with all six Ohka aircraft missing their targets. Americans on the receiving end of the attacks reported that, as the Ohka aircraft entered their final approaches, ie. with the rocket boosters engaged, they were nearly unstoppable due to the fast speed.

ww2dbaseIn early 1945, Model 21 variant design was being developed, with smaller warhead (only 600 kilograms, half the size of that mounted on Model 11 production variant aircraft) and shorter wingspan so that these new Ohka aircraft could be mounted under the smaller and faster P1Y1 Ginga bombers; Model 21 efforts were canceled before any prototypes were created. Another variant design, Model 22, was developed starting in 15 Feb 1945 with the Hitachi Tsu-11 jet engine being the intended source of propulsion. The first drop test of Ohka Model 22 was conducted on 26 Jun 1945 in failure, with the aircraft exploding in an in-flight accident. On 12 Aug, another flight test was scheduled, but was canceled in-flight due to an immature ignition of the jet engine. Only a few Model 22 aircraft were built before the war ended. Finally, the Ohka Model 33 (with Ne-20 turbojet engine) and Model 43 (capable of independent flight) variant designs were also being developed. Model 33 efforts were canceled before completion, while Model 43 completed on 26 Apr 1945. The construction of the launch base for Model 43 aircraft began in Jul 1945 on the Miura Peninsula south of Tokyo and a wooden prototype was tested there in Aug 1945 shortly before the war ended.

ww2dbaseUltimately, Model 11, the original production variant, was the only variant design that saw combat. 755 Ohka Model 11 aircraft (155 at Yokosuka and 600 at Kasumigaura), 45 K-1 training aircraft, and about 40 to 50 prototypes of various variant designs were built.

ww2dbaseSource:

Steven Zaloga, Kamikaze: Japanese Special Attack Weapons 1944-45

Last Major Revision: Sep 2011

MXY7 Ohka Timeline

SPECIFICATIONS

Model 11



Machinery Three Type 4 Mark 1 Model 20 rocket motors Solid propellant, 587 pound-force each Armament 1x1,200kg ammonal warhead Crew 1 Span 5.12 m Length 6.06 m Height 1.16 m Wing Area 6.00 m² Weight, Empty 440 kg Weight, Loaded 2,140 kg Speed, Maximum 1,040 km/h Speed, Cruising 804 km/h Range, Maximum 36 km

Photographs

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