This took place on 1938 during the Sino-Japanese war in which WW2 (officially in history) hasn't begun yet so the moderators can move this post if it doesn't belong here. According to the book Tower of Skulls: A History of the Asia-Pacific War by Richard B. Frank, the Japanese used poison gas at the Battle of Wuhan. A quote from the book ; "Next at Madang, the Japanese eschewed a frontal attack on major Chinese fortifications in favor of encirclement by 24 June. They doused the Chinese with poison gas and Madang fell on 29 June". The book mentioned poison gas a few times but wasn't specific with how the poison gas was "doused". How was the poison gas used? By spraying it from aircraft?