The Ki-167 was a Hiryu version specifically adapted to accommodate the so-called Sakuradan thermite bomb. The Sakuradan bomb installed in the Ki-167 was an unconventional 6,393-lb weapon, shaped somewhat like a pressure cooker with a diameter of 5 ft 3 in and the base facing forward and angled downward some 15 deg, demanded some structural modifications of the fuselage. The bomb was placed on the aircraft CG and its diameter necessitated the cutting away of some of the upper fuselage structure, the protruding portion being enclosed by a plywood fairing reminiscent of a camels hump. The rear casing of the charge was parabolic and 19.7 in thick in order to direct the blast forward.
The Sakuradan was based on a weapon developed in Germany in WWII, the plans for which were taken to Japan aboard the submarine I-30 in October 1942, and testing was conducted in the strictest secrecy at Pai-Chengzi in Manchuria. During these trials it was ascertained that the fierce flame generated by the weapon projected some 3,280 ft ahead of the point of detonation and at a distance of 985 ft from impact a medium tank could be totally destroyed. With insertion of the Sakuradan in the Hiryu, the starboard controls were deleted, the crew being reduced to pilot, engineer, navigator and radio operators, and all gun positions were faired over.
The first two Sakuradan-equipped Ki-167s were completed in February 1945, and after flight testing at Kagamigahara, these were delivered to the “special attack” unit of the 62nd Sentai at Tachiarai, to where the unit had transferred from Nishi Tsukuba. This unit also possessed several To-Go Hiryus, and the first mission with a single Sakuradan-equipped aircraft was flown from Kanoya, Kyushu, on 17 April, in concert with two To-Go Hiryus. The Ki-167 was piloted by Lt Kozaburo Kato and its target, as was that of the accompanying To-Go Hiryus, was the Allied carriers and other naval vessels off Okinawa.
The three aircraft took-off at intervals between 0715 and 0726 hours, successfully eluding interception by F6F hellcats SE of Tokunsoshima Island at about 0950 hours.
At 1010 hours, Lt Kato broke radio silence with the message: “Have found a carrier. Am attacking!” Shortly after this, Cdt Maemura, who was flying as navigator in one of the To-Go Hiryus, saw flame streaming back from the Sakuradan equipped aircraft, the nose of which suddenly pulled up sharply as it disappeared into cloud, and it was assumed that the Ki-167 was mortally hit before it could commence its attack on the target that Lt Kato had reported.
A second “special attack” unit was formed by the 62nd Sentai with two more Sakurandan equipped Ki-167s and two To-Go Hiryus, flying its first mission on 27 May from Kanoya against Allied naval forces west of Okinawa. Both Ki-167s disappeared after signalling that they were attacking targets and both To-Go Hiryus returned to base when they failed to find suitable targets. The “special attack” units of the 62nd Sentai were the only recipients of the Ki-167s, comparatively few of which were completed, at least one of these being destroyed in an accident and another as a result of sabotage. It is recorded that a unit equipped with Ki-167s under the command of Maj Isamu Katano was formed in June 1945, and was scheduled to leave Japan for an attack on Saipan on 16August, the day after official ceasefire, yet no example of the Sakuradan equipped aircraft was found by the Allies after the occupation.
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