Phosgene was then only frequently used by the Imperial Japanese Army against the Chinese during the Second Sino-Japanese War . Gas weapons , such as phosgene , were produced by Unit 731 and authorized by specific orders given by Hirohito ( Emperor Showa ) 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
Unit 731
Unit 731
Phosgene