Shinyo Special Attack Base Ruins (18th Shinyo Squadron, Nominoura)

The Shinyo Special Attack Base at Nominoura on Kakeromajima Island was one of several Imperial Japanese Navy suicide motorboat installations deployed across the Nansei (Ryukyu) Islands during the final phase of World War II. The Shinyo ("Sea Quake") was a small wooden motorboat approximately 5 meters long, carrying a 250 kg bow-mounted explosive charge, designed for one-way ramming attacks against Allied vessels at speeds up to 55 km/h.

The 18th Shinyo Special Attack Squadron was formed on October 15, 1944, and its 186 members — comprising 7 officers, 50 pilots, 74 base workers, 34 maintenance crew, and 21 headquarters staff — underwent special attack training at the Kawatana torpedo school in Nagasaki Prefecture. The unit departed Sasebo on November 11, 1944, and arrived at the Nominoura inlet on Kakeromajima's north shore, facing the Oshima Strait, on November 21.

Upon arrival, the squadron immediately began construction of shore defenses. Twelve tunnel-style storage bunkers (格納壕) were excavated into the hillside along the inlet, each approximately 3 meters wide, 2.5 meters high, and 20–36 meters deep. The first 5 meters of each tunnel were reinforced with 25 cm-thick concrete. Former Oshima Middle School students were mobilized to assist in the labor-intensive construction.

The 18th Squadron was one of three Shinyo units deployed to the Amami Islands. The 40th Squadron (55 boats, 187 personnel under Captain Ando Sueki) was stationed at Setouchi on the Amami Oshima mainland from February 1945, and the 44th Squadron (55 boats) was also deployed to the archipelago. Together, these units formed a defensive screen intended to interdict any Allied approach toward mainland Japan through the Nansei Island chain.

The squadron's commander, Toshio Shimao (1917–1986) — a reserve officer commissioned ensign in May 1944 and promoted to lieutenant (junior grade) that December — had studied Oriental history at Kyushu Imperial University and would become one of Japan's most important postwar novelists. His wartime experience of waiting for death at Nominoura — the psychological torment of preparing for a one-way mission that never came — profoundly shaped his literary career. His stories "Shima no Hate" (The Farthest Edge of the Islands), "Shutsukotō-ki" and "Shuppatsu wa tsui ni otozurezu" (The Departure Never Came) draw directly from his Kakeromajima experiences, and his best-known novel "Shi no Toge" (The Sting of Death) depicts his later married life with Miho, whom he met on the island.

On August 13, 1945, two days before Japan's surrender, the 18th Squadron received sortie orders as American naval forces were reported in the vicinity. However, the enemy fleet did not appear within striking range, and the order was suspended. On August 15, the war ended. Repatriation of squadron members began on September 1, 1945.

Today the site is preserved as the Shimao Toshio Literary Monument Park (島尾敏雄文学碑公園). A 2-meter literary monument designed by sculptor Toshiaki Sakae, a Setouchi native, was unveiled on December 4, 1988, surrounded by five stone pedestals engraved with passages from Shimao's Nominoura-related works. In 2008, portions of the remains of Shimao, his wife Miho (a native of Kakeromajima), and their eldest daughter were interred on the hill behind the monument.

The storage tunnels remain accessible along the inlet trail. One bunker (the 5th Storage Building, 5 meters from the shoreline) contains a full-scale replica of a Shinyo Type 1 motorboat, restored for film productions in 1990 and 2017. The Setouchi Town Board of Education conducted systematic archaeological surveys of the six main bunker sites from fiscal years 2017–2021, with the municipality pursuing national historic site designation for the military remains on Kakeromajima.