The Military History of Okunoshima
Okunoshima, once a small fishing and farming community, was transformed by the country’s military during the first half of the twentieth century. The island held strategic importance during a time of escalating regional conflicts that have left a lasting impact on its landscape and history.
Strategic coastal defense
Military installations were first built on the island in 1902 against the backdrop of growing tensions between Japan and Russia over rival territorial ambitions in East Asia. In anticipation of open conflict, the government constructed three artillery batteries on Okunoshima as part of a coastal defense network for the Seto Inland Sea. These installations were meant to prevent enemy vessels from threatening military ports in Hiroshima and Kure. The attacks never materialized as the Russian Baltic Fleet was defeated at Tsushima Strait, ending the Russo-Japanese War (1904–1905). The batteries were dismantled in 1924.
Chemical weapons facility
Between 1929 and 1944, the Imperial Japanese Army (IJA) used the island to covertly manufacture chemical weapons, which were used in the Second Sino-Japanese War (1937–1945). The few residents of Okunoshima were ordered to leave, and the island was erased from official maps. By the war’s end, the IJA had manufactured an estimated 6,500 tons of poison gas on Okunoshima.
U.S. requisition
After Japan’s surrender in World War II, Allied forces took over Okunoshima, disposing of the chemical stockpiles by burning, burying, and sinking them at sea. From 1951 to 1956, Okunoshima was repurposed as an ammunition depot by American forces. Shells and bombs were stored on the island for use in the Korean War (1950–1953).
