Okunoshima Poison Gas Museum

The Okunoshima Poison Gas Museum stands on Okunoshima, a small island with a 4.3-kilometer circumference in the Seto Inland Sea, administratively part of Takehara City, Hiroshima Prefecture. The museum was built by an association of poison gas victims — former factory workers and mobilized students — and donated to Takehara City; it opened in April 1988 to document a chapter of history that the Japanese military once sought to erase entirely.

In 1927, the Imperial Japanese Army selected this remote island to construct a chemical munitions plant under the direction of the Army's Institute of Science and Technology, which had initiated a secret chemical weapons development program in 1925. Production began in 1929 and continued until Japan's surrender in August 1945. Over this 16-year period, approximately 6,616 tons of toxic agents were manufactured — including mustard gas (yperite), lewisite, phosgene, hydrogen cyanide, diphenylchlorarsine, chloroacetophenone, and tear gas. Okunoshima was the Imperial Japanese Army's only poison gas manufacturing plant.

To maintain secrecy, the island and surrounding area were removed from official military maps, earning Okunoshima the moniker "the island erased from maps." In all, some 6,500 to 6,700 people worked on the island (about 3,000 to 5,000 at the peak), including conscripted workers, mobilized students and labor service corps members. Workers wore rubber suits, gas masks, gloves, and boots that were not fully airtight, leading to chronic exposure. Many suffered severe injuries to their skin, eyes, and respiratory systems, and an unknown number died from poisoning. Starting in 1931, most of the chemical agents were shipped to China for use against both military and civilian targets during the Second Sino-Japanese War.

After Japan's defeat, Allied occupation forces — from May 1946 the British Commonwealth Occupation Force, including Australian troops — conducted "Operation Lewisite" to dispose of the remaining chemical stockpiles. The island was placed strictly off-limits. In the postwar decades, Okunoshima was repurposed as a national vacation village. Feral rabbits — whose precise origin remains debated — proliferated on the island, transforming it into the popular "Rabbit Island" tourist destination.

The museum itself occupies a modest two-room building. Exhibits include equipment used in poison gas production, remnants of gas shells, gas masks, protective clothing, and documents ordering the deployment of chemical weapons in China. Photography is prohibited inside the museum. Outside, visitors can explore the remaining wartime ruins, including artillery battery positions, the former power plant, and a poison gas storage facility.