The island's wartime history was quite different. For the 16 years it was operating, the island was kept off maps and residents told to keep its poison gas factories secret. According to this Japan Times article, the island produced 5 types of chemical gas which was mostly used in warfare in China. While working at the factory, many workers (including children) also died during manufacturing. Some argue the island might not be completely safe as there has never been any major decontamination of the whole island and there are apparently some sealed locations remaining which may have poison stored at the end of the war.