Poison gas was used extensively during the First World War. Although chemical weapons accounted for fewer than three percent of all casualties, ghostly images of soldiers in gas masks symbolized the grotesque industrialization of modern warfare. The French and Germans were the first to use gas on a large scale as of 1915, but the British quickly followed. Chemical warfare was largely ineffectual, and the public outcry in all the combatant countries led to its prohibition in the interwar years. This image shows four German soldiers wearing gas masks while manning an anti-aircraft gun.