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Defoliation bacilli bombs, made between 1932 and 1933 were used by the Imperial Japanese Army to spread bubonic plague across China. The deployment of these lethal munitions provided the Japanese with the ability to launch devastating biological attacks, infecting agriculture, reservoirs, wells and populated areas with anthrax, plague-infected fleas, typhoid, dysentery and cholera. The alumni of Unit 731, the unit that prepared these weapons, became top bioweapons researchers and were not prosecuted as war criminals. According to Richard Drayton, a Cambridge University history lecturer, researcher Shirō Ishii later moved to Maryland, where he conducted research into bioweapons. However, according to Ishii's daughter Harumi, he stayed in Japan, where he died of throat cancer at the age of 67.