First World War poison gas treatment. Soldier being cleaned in a poison gas decontamination room in France during the First World War (1914-1918). The medical staff are wearing protective clothing and masks to prevent being contaminated. The First World War saw the first large-scale use of chemical weapons, with a chlorine gas attack by German forces on French positions at the Second Battle of Ypres on 22 April 1915. Around 85,000 soldiers died due to the use of chemical weapons over the remaining years of the war. This is the American Evacuation Hospital Number 2, at Baccarat, France. The US entered the war on 6 April 1917, playing a crucial role in helping Britain and France to defeat Germany and its allies. Photographed on 8 June 1918.