Later , plague was used during the Second Sino-Japanese War as a bacteriological weapon by the Imperial Japanese Army . These weapons were provided by Shirō Ishii 's units and used in experiments on humans before being used on the field . For example , in 1940 , the Imperial Japanese Army Air Service bombed Ningbo with fleas carrying the bubonic plague . During the Khabarovsk War Crime Trials , the accused , such as Major General Kiyashi Kawashima , testified that , in 1941 , 40 members of Unit 731 air-dropped plague-contaminated fleas on Changde . These operations caused epidemic plague outbreaks
Unit 731
Unit 731
Bubonic plague