Hirao Kaiten Base Remains

The Hirao Kaiten Base (平生回天基地) was established on March 1, 1945, on the Atata Peninsula (阿多田半島) of Hirao Town, Yamaguchi Prefecture, adjacent to the Navy Submarine School Yanai Branch that had been completed in 1942. Officially designated the Hirao Assault Unit (平生突撃隊) under the Second Special Attack Squadron of the Kure Naval District, it was the third of four kaiten training bases in the Inland Sea area, after Ozushima (September 1944) and Hikari, and alongside Oga in Oita Prefecture.

The kaiten (回天, literally "turn the tide of heaven") was a human-guided torpedo — a modified Type 93 torpedo fitted with a cockpit, periscope, and a 1.55-ton explosive warhead. Measuring approximately 15 meters in length and 1 meter in diameter, it could travel at 30 knots. At the Hirao base, young enlisted men around 18 years old and officers in their twenties underwent intensive training, making round trips around Hirao Bay and practicing attacks on moving vessels using periscope navigation.

The base conducted two operational sorties. On July 18, 1945, submarine I-58 departed carrying six kaiten manned by Hirao-trained pilots as part of the Tamon Unit (多聞隊). Five of the six pilots were killed in action on the supply routes between Okinawa and the American bases in the western Pacific. A second sortie by the Shinshu Unit (神州隊) departed on August 16, 1945 — one day after the Emperor's surrender broadcast — but returned without engaging. In total, nine men from the Hirao base lost their lives: five in combat operations and four during training accidents or by suicide after the war's end.

Today, the base area on the Atata Peninsula is largely overgrown and inaccessible, though remnants of horizontal tunnel structures remain visible from the peninsula's tip. A memorial monument honoring the nine fallen kaiten pilots was first erected in July 1959. In November 2004, the monument was relocated and restored, and the Atata Exchange Hall (阿多田交流館) was opened adjacent to the memorial grounds. The exchange hall houses approximately 400 artifacts including photographs, documents, personal belongings, and calligraphy of the young kaiten pilots, as well as a full-scale kaiten replica originally built for the 2006 film 'Deguchi no nai Umi' (Sea Without Exit). The Hirao Town History and Folklore Museum separately preserves and displays an actual fuselage section of a Type 2 kaiten.

The Hirao Kaiten Base is significant as one of the four known kaiten training bases and illustrates the desperate final measures of the Imperial Japanese Navy in the closing months of the Pacific War. While the Ozushima base is better known and better preserved, Hirao's memorial facilities ensure that the sacrifices made at this lesser-known base are not forgotten.