Up until 1944, Japan had been developing its own chemical weapons programme. This arsenal was primarily produced in what would become the country’s largest facility, on the island of Ōkunoshima. Before the massive casualties inflicted on the continent, Japanese workers had been the first victims of the weapons of mass destruction they had been manufacturing. This paper seeks to provide a short overview of Japan’s chemical arsenal, taking into account the workers’ wartime conditions on the island. In the context of the rapid development of Western science at all costs, it will also highlight some of the structural deficiencies behind Japan’s military endeavours, and their immediate consequences.