Australian infantry with gas masks. Ypres, 1917.
WWI was the first global conflict that initiated the first widespread use of chemical weapons- about 3000 chemicals were investigated for military use and 50 toxic agents were deployed on the battlefields across Europe, killing about 90,000 to 100,000 people and leaving 1.3 people injured.
Source: Chemical & Engineering News
Unit 731- The Forgotten Asian Auschwitz
The Japanese invasion of China during the Second Sino-Japanese war has left a strong legacy of hate and disgust among many Chinese today. Much of the atrocities committed by the Japanese are now known to most historians. By far, the most despicable and forgotten act against humanity committed by the Imperial Japanese government was its covert biochemical weapons program. Euphemistically labelled as the "Epidemic Prevention and Water Purification Department" of the Imperial Japanese Army, the Japanese conducted a wide range of cruel and inhumane experiments on prisoners who were often innocent.