According to historians Yoshiaki Yoshimi and Seiya Matsuno , the chemical weapons were authorized by specific orders given by Emperor Hirohito himself , transmitted by the chief of staff of the army . For example , the Emperor authorized the use of toxic gas on 375 separate occasions during the Battle of Wuhan from August to October 1938 . They were also profusely used during the invasion of Changde . Those orders were transmitted either by prince Kotohito Kan ' in or general Hajime Sugiyama . The Imperial Japanese Army had used mustard gas and the US-developed ( CWS-1918 ) blister agent lewisite against Chinese troops and guerrillas . Experiments involving chemical weapons were conducted on live prisoners ( Unit 731 and Unit 516 )
Unit 731
Unit 731
Chemical warfare