This was a Japanese unrealised plan to use transport aircraft to land a number of kamikaze teams of Giretsu Kuteitai airborne special forces unit on the Mariana islands group for attacks on the bases used by the USAAF’s Boeing B-29 Superfortress heavy bombers for raids on targets in the Japanese home islands (July/August 1945).
This was the second such attack planned on bases in the Mariana islands group with the specific intent of destroying B-29 bombers, and it was planned that 60 transports would deliver 900 commandos on the nights of 19 to 23 August 1945, but on 15 August Japan surrendered and the operation was cancelled.
The seed for 'Ken' was sown by a similar undertaking planned but not implemented by the Imperial Japanese army late in 1944. On 24 November of that year, a formation of B-29 bombers made the first US air raid on Tokyo from the Mariana islands group, and the 1st Raiding Brigade was ordered to establish a special unit for a commando mission. The Japanese knew that any bombing of the airfields of the Mariana islands group that they might be able to make would be wholly insufficient to delay the construction of the bases the American were building for the USAAF’s strategic bomber force, and the Imperial General Headquarters therefore planned to despatch an airborne commando raid in which a special assault force would crash-land on the airfields on Saipan island and destroy the B-29 bombers located there.
Captain Michiro Okuyama was selected to lead the special unit: as the commander of the 1st Raiding Regiment's Engineer Company, he was trained in sabotage and demolition techniques. Others of the regiment’s men who had missed earlier operations were also eager for action. Okuyama had been the first member of the original Japanese army parachute training unit, and was entrusted by brigade headquarters with choosing the 126 men for what he knew was a suicide mission. Okuyama chose most of the men from his own company, and this special team was later designated as the 'Giretsu' Kuteitai (respect for faith airborne unit). This was organised as Okuyama’s command section and five platoons each commanded by a lieutenant.
On 5 December the unit moved to the Japanese army air force’s air academy at Saitama, where 10 intelligence officers, experts in sabotage, joined it from the Nakano intelligence school. Two of the intelligence officers were assigned to each platoon, bringing the unit’s strength to 136 men. The unit was placed under the direct command of Lieutenant General Michio Sugawara’s 6th Air Army. At Saitama a mock-up of a B-29 was prepared. As the standard Type 99 magnetic charge could not be attached to the B-29’s aluminium skin, two types of special weapons were developed. One had a 4.4-lb (2-kg) explosive charge, fitted with a suction cap on its top, at the end of a pole: gripping the pole, the raider pushed it up under the B-29’s wing, and pulled a cord to ignite the delay fuse. The other weapon was the chain charge, a rope some 13 to 16 ft (4 to 4.9 m) long, with explosive charges attached along its length, and a small sandbag weight was attached to one end to facilitate throwing it over the target aeroplane’s fuselage or wing.
The army commandos began a programme of intense training, and in this Okuyama stressed that each man must destroy at least two or three aircraft, even if he was mortally wounded in the process.
On 22 December the 'Giretsu' Kuteitai undertook a demonstration for senior staff officers. The commandos ran swiftly through the darkness as though it were daylight, and skilfully attached their explosives to aircraft.
But while the men were ready, the preparation of the associated air transport had been delayed. Captain Suwabe’s 3rd Independent Flying Unit had been allocated the task of delivering the 'Giretsu' Kuteitai after converting from scout aircraft to the Mitsubishi Ki-21 'Sally' twin-engined medium bomber. The pilots lacked adequate experience in their new aircraft, however, as as yet were unable to make long over-water flights. Even so, the attack was scheduled for 17 January 1945, and the commandos moved to Hamamatsu air base on the island of Honshu. US air raids then damaged the airfields on Iwo Jima island which had been scheduled for refuelling, and the operation was cancelled. The disappointed 'Giretsu' Kuteitai commandos returned to Nyutabaru and the 1st Raiding Brigade.
After the raid on the bases in the Mariana islands group had been terminated, plans were made for attacks on airfields on Iwo Jima captured by the US Marines during March in 'Iceberg', but these too were cancelled when the defence of Iwo Jima failed.
At this stage the Imperial Japanese navy started to plan its 'Ken' attack similar to that of the 'Giretsu KuteitaiUnit’s aborted raid on the Mariana islands group. Some 300 men of Lieutenant Commander Daiji Yamaoka’s 1st Kure Special Naval Landing Force began preparations at the end of June. The unit had been formed for submarine-delivered raids on US-held islands, but was now to be carried in 30 Mitsubishi G4M 'Betty' twin-engined bombers as these had the range to allow an unrefuelled one-way mission to the Mariana islands group.
The raid was initially planned for execution on 24 July, but on 14 July US carrierborne warplanes raided Misawa naval air base on Honshu island, and the operation’s bombers were destroyed or damaged. The raid was then postponed to 19 August.
Although the plan had been conceived by the Imperial Japanese navy, at the end of July the Imperial General Headquarters ordered that 300 paratroopers of the army’s 1st Raiding Regiment, under the command of Captain Sunao Sonoda, be included and that the associated force of 60 bombers readied.
Japan’s surrender of 15 August put an end to the operation.