French Zouave infantry killed by gas, Second Battle of Ypres, Belgium, 22 April 1915, (1929).

French Zouave infantry killed by gas, Second Battle of Ypres, Belgium, 22 April 1915. On 22 April 1915 the Germans released 168 tons of chlorine gas over a four mile front, in the first gas attack of the war. Initially French and Algerian troops (Zouaves) of the 45th and 78th Divisions were attacked with the gas, inflicting heavy casualties and causing widespread panic, with the survivors abandoning their positions. Although the Allies initially condemned the attack as barbaric, by the end of the war both sides had made extensive use of poison gas. (Photo by The Print Collector/Print Collector/Getty Images)