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Setonaikai NP, Hiroshima
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Look up from the rabbit paths: Okunoshima carries Japan’s tallest power-transmission tower, 226 m high. It holds cables across a 2,357 m sea crossing to the mainland.
The familiar story says 8 school rabbits were released here in 1971—but DNA studies found varied rabbit types, suggesting later introductions too. The colony’s history is more layered than one classroom release.
The army removed Okunoshima from official maps to hide its poison-gas works. Wartime secrecy reached the railway too: trains covered their sea-facing windows along the coast.
The island resort serves octopus dishes, but nearby fishing waters have a grim footnote: in April 1951, an octopus fisherman was injured by what doctors suspected was mustard gas from the seabed.
Before the secret factory, Okunoshima had 3 farming households. The national government acquired the island for military use and evicted them—an earlier erasure than the island’s disappearance from maps.
Long before the gas plant, 3 batteries with 22 guns were built here to defend Hiroshima and Kure. They never saw action in the Russo-Japanese War, and their brick remains still dot the island.
By the end of World War II, the army had made an estimated 6,500 tonnes of poison gas on Okunoshima—a staggering total produced on a small island deliberately erased from official maps.
The island’s wartime factories made more than chemical weapons: they also produced Fūgo balloon bombs, designed to carry incendiaries across the Pacific on high-altitude winds toward American cities.
Nagaura, the island’s largest poison-gas storehouse, had 6 rooms, each holding about 100 tonnes. Its original camouflage was meant to help conceal this enormous stockpile.
Roughly 50 air-raid shelters were dug across Okunoshima, and many doubled as stores for poison gas or supplies. The longest tunnels reached about 100 m; today, scattered entrances hint at what lies below.
By about 1937, the island had a 30-bed hospital with X-ray and poison-gas treatment rooms, alongside dental, eye, ear-nose-throat, medical and surgical departments—a sobering sign of factory hazards.
One wartime bunker still shows yellow and green, but the colors are embedded in the concrete rather than simply painted on. Its roughly six-tatami room once held an emergency telephone switchboard.
The ruined power station once supplied the poison-gas works; during the Korean War, U.S. forces reused it for ammunition storage. The surviving “MAG2” marking still identifies a magazine area.
On 29 July 1946, a storm drove a ship carrying toxic material for disposal aground. A leak exposed about 90 people, and 1 later died, according to an Environment Ministry report.
The Poison Gas Museum was created from the bottom up: former workers, mobilized students and other victims organized to build it, then donated it to Takehara City. It opened in April 1988.
The 1985 memorial holds the names of people who died after injuries from poison-gas production or postwar disposal. Each October, a ceremony honors them and renews a pledge not to repeat the harm.
Factory workers repaired and moved the island’s shrine when the plant opened in 1929. It hosted ceremonies and school graduations; in 1937, a monument to workers killed in gas production was raised there.
Workers’ rubber suits, masks, gloves and boots were not airtight: poison seeped through, damaging skin, eyes and throats. The museum preserves workers’ notebooks and manuals alongside equipment that could not fully protect them.
