By 1944, it was becoming clear to the military leaders of Japan that the war was lost, unless there was a miracle. So, they decided to create a miracle–or, more accurately, to re-create one. In the 13th century, Mongol invasions of Japan were thwarted when a fierce typhoon struck and destroyed the Mongol fleet. In late 1944, the Japanese military turned to suicide air attacks to help beat back the US forces that were approaching Japan. The result was the Kamikaze (“Divine Wind”) forces. And the pinnacle of the Kamikaze forces was the MXY-7 “Ohka” piloted bomb, the only plane in the world that was deliberately designed to kill its pilot.
The Ohka piloted bomb, on display at the Smithsonian Udvar-Hazy Center
The Samurai spirit that was inculcated into the Japanese military emphasized that death in battle in the service of the Emperor was the highest honor. As a result, suicide attacks were common on the Pacific battlefields. On land, waves of Japanese troops would make “banzai charges”, only to be mowed down by US machine guns. The first air suicide attack happened on the very first day of the war, at Pearl Harbor, when Lt Fusata Iita’s Zero fighter was hit in the fuel tank. Unable to return to his carrier, Iita intentionally crash-dived his Zero into the American hangar at Kaneohe Field.
By 1944, however, Japan’s naval and air forces had been largely destroyed, making large-scale conventional attacks on US fleets impossible. In response, Japanese officers asked air crews in the Philippines to volunteer to intentionally crash-dive their planes into the American carriers. The “special attacks” began in October 1944 during the battle for Leyte Gulf. Forty American ships were hit by Kamikazes, sinking 5 and heavily damaging 23. By 1945, Kamikaze attacks were being made by Japanese squadrons all over the Pacific. (The Americans had all sorts of stories about how the Kamikaze pilots had been chained inside their airplanes, or how they had been taught how to take off but not how to land–the reality was that all of the Kamikaze pilots were regular pilots who volunteered for “special attacks”.)
The idea for a purpose-built suicide plane came from Ensign Mitsuo Ohta, a transport pilot, who submitted rough plans for a rocket-engine piloted bomb with a 2,000-pound warhead. The Japanese Navy tested ten different models, all of which were unsuitable, before settling on a feasible design. The Navy Technical Arsenal (Kushigo) drew up blueprints for the craft and began production by the end of February 1945. Called the MXY-7 Model 11 “Ohka” (“Cherry Blossom”), it was 20 feet long with a wingspan of almost 17 feet, and carried a 1200 kg (2646 lb) warhead in the nose section. It was powered by three solid-fuel rocket engines, which drove it at a top speed of 500 mph in level flight, or almost 650 mph in a dive. Basic flight controls allowed the pilot to steer the craft, and a crude metal gunsight at the front of the cockpit allowed him to aim at a ship. About 750 Model 11 Ohkas were built. The Ohka pilots were named the “Thunder Gods”. The Americans took to calling it the “Baka” bomb–the Japanese word for “idiot”.
The Ohka’s rocket engines only burned for a little over one minute, giving it a range of less than 25 miles. In combat, the Ohka had to be carried close to the US fleet by a “mother ship”, the twin-engine “Betty” bomber, then released to fly to its target. This turned out to be the Ohka’s most crippling defect. The Betty bomber itself was very vulnerable to American fighters, and most Ohkas were shot down along with their mother ship before they could even be released. Sometimes the threatened Betty crews would release the Ohka too soon, and the suicide pilot would crash uselessly into the sea short of his target.
The most heavy use of the Ohka came during the Okinawa campaign in April 1945. The Japanese launched almost 1500 Kamikaze planes against the US/British fleet at Okinawa, and sank or heavily damaged about 30 ships. Ohka piloted bombs struck the US destroyers Abele, Stanly, Hadley, Jeffers, and Gayety, and the minesweeper Shea. The Abele was sunk, and the Hadleydamaged beyond repair.
To correct the problem of limited range, engineers at Kushigo developed a more powerful set of engines. Instead of using solid rocket motors, the new Model 22 Ohka would use an Ishikawajima Tsu-11 “thermojet” engine, in which a four-cylinder conventional piston engine was used to drive a compressor, and the compressed air, along with injected fuel, was driven into the combustion chamber and ignited. Distinctive air intakes were added to the rear sides of the Model 22 Okha. The new engine gave the Model 22 a much greater range, but because the engine itself was bigger, it reduced the size of the warhead that the Ohka could carry, from 1200 kg to just 600 kg (1320 lb). The new Ohkas could be carried aloft by twin-engine “Frances” bombers, or launched from ramps in concealed caves. The Japanese planned to produce hundreds of the Model 22 Ohkas and deploy them at the coasts to attack the US invasion fleet, but the war ended before production could begin. Only 3 functional Tsu-11 thermojet engines and 50 Model 22 airframes were completed before Japan surrendered.
Another version, the Model 33, was planned to use the same Nakajima Ne-20 turbojet engine as the Kikka jet fighter (see my diary on the Kikka here: https://lflank.wordpress.com/2014/09/16/kikka-japans-ww2-jet-fighter/), but this engine never went into production and no Model 33’s were ever built.
One of the surviving Model 22 Ohkas, along with its Tsu-11 jet engine, are on display at the Smithsonian’s Udvar-Hazy Center in Washington DC.