Hiroshima prefecture and the British Commonwealth Occupation Force: ‘Operation Lewisite’ and its legacy of seafloor relic munitions

Following Japan’s surprise attack on Pearl Harbour in 1941, the Pacific was inundated with war-related infrastructure, as well as military hardware and munitions. Consequently, tons of unexploded munition from wartime activities litter the Pacific seafloor. Additionally, after the end of the Pacific conflict in August 1945, many of the chemical and conventional weapons belonging to the Allies and the Imperial Japanese Army were dumped into the ocean. Sea dumping has left a legacy of underwater munition dumpsites off the coast of Japan and in the waters surrounding former Japanese occupied Pacific islands. The focus of this paper is on the large amounts of poisonous gas and munitions that were manufactured on Okunoshima and subsequently dumped off the coast of Japan pursuant to ‘Operation Lewisite’. It also examines Australia’s contribution to the demilitarisation of Japan within the broader context of the 1945 MacArthur-Northcott Agreement, which established the British Commonwealth Occupation Force (BCOF). Under the agreement, Australian soldiers were responsible for locating and disposing of thousands of tons of munitions and cannisters of poisonous gas hidden in a labyrinth of underground caves located in the Hiroshima prefecture, the site of the first atomic attack in history. Some eighty years later, these discarded weapons of war pose a profound threat to the marine environment and to human health. Apart from the added risk of explosion due to their age as well as an increased danger of accidental disturbance arising from increased industrial activities on the ocean floor, seafloor relic munitions are a potential source of mercury leakage within the marine environment.