Ōkunoshima island

The island played a key role during World War II as a poison gas factory for much of the chemical warfare that was carried out in China.

The island was chosen for its isolation, conducive to security, and because it was far enough from Tokyo and other areas in case of disaster. Under the jurisdiction of the Japanese military, the local fish preservation processor was converted into a toxic gas reactor. Residents and potential employees were not told what the plant was manufacturing and everything was kept secret; working conditions were harsh and many suffered from toxic-exposure related illnesses.