Showing a cloud of unidentified (poisonous?) gas produced by mobile cylinders during World War I. The Hague Declaration of 1899 and the Hague Convention of 1907 forbade the use of "poison or poisoned weapons" in warfare, yet more than 124,000 tons of gas were produced by the end of World War I. The first large-scale use of gas as a weapon was on the Western Front was on April 22, 1915, by the Germans at Ypres, against Canadian and French colonial troops. Chemical weapons were primarily used to demoralize, injure, and kill entrenched defenders, against whom the indiscriminate and generally slow-moving or static nature of gas clouds would be most effective. Official figures declare about 1,176,500 non-fatal casualties and 85,000 fatalities directly caused by chemical warfare agents during the course of the war.
