FYI
Yes, poison gas was used in World War II, primarily by the Imperial Japanese Army in China against both military and civilian targets, and by Nazi Germany for the mass extermination of Jews in the Holocaust using Zyklon B and carbon monoxide in death camps, though Germany avoided large-scale battlefield use due to fear of Allied retaliation in kind. The Allies also prepared chemical weapons but largely refrained from battlefield deployment in Europe due to mutual deterrence.