First Major Poison Gas Attack — Second Battle of Ypres

Germany released approximately 168 tonnes of chlorine gas from 5,730 cylinders along a four-mile front near Langemarck in Belgium, the first large-scale use of chemical weapons in war. The greenish-yellow cloud drifted toward French and Algerian troops who, with no protective equipment, fled in panic, creating a gap four miles wide in the Allied line. Canadian troops held the breach until reserves arrived. The attack violated the Hague Conventions and shocked world opinion.