One of weapons of war the Japanese used in World War II is the use of chemical warfare. The example of the Changde chemical weapon attack had the use of chemical and biological weapons by Japan during the Battle of Changde in the Chinese Province of Hunan in April and May, 1943. In the intense fighting around Changde, Japanese forces could not push through the heavy Chinese resistance, and decided to launch poison gas artillery shells into the city, which possibly contained mustard gas or lewisite. This action was undertaken by Unit 516 of the Japanese Army during the Second Sino-Japanese War. This and other units used assorted types of chemicals in liquid or gaseous form, including mustard gas, lewisite, cyanic acid gas and phosgene in experimental and some operational uses during hostile actions against China. This was effective in spreading fear, terror and death to devastating effect against both humans and livestock.
Furthermore, the Imperial Japanese Army had tested cyanide gas on Australian and Dutch East Indies prisoners of war in 1944 in Indonesia's Kai Islands. A document found in the Australian national archives in Canberra details Japan's experiments on an Australian POW. The Japanese army's Unit 731 is widely known for experimenting on Chinese in north-eastern China with germs and chemical weapons during World War II. According to the document, a lieutenant in charge of poison gas at the No. 5 Division of the army threw bottles of cyanide gas on an Australian air force captain and a sergeant of the Dutch East Indies air force. The gas was designed for antitank warfare. The division's lieutenant colonel had ordered the lieutenant to test the effectiveness of the gas. After the POWs collapsed, Japanese military police stabbed them to death with bayonets. The lieutenant and the lieutenant colonel were sentenced to death by hanging by the military tribunal, according to the document.
The Japanese army had secretly engaged in chemical warfare -- banned under international law -- in China since shortly after the war there started in 1937. In July 1944, the General Staff Office of the Japanese army, responding to a warning from U.S. authorities for a reprisal, issued an order for banning the use of poison gas by the army. But the disclosed records show that such orders were not heeded among officers on the battle fronts facing the prospect of imminent enemy offensives.