Among the most notorious weapons of WWI was chemical warfare, employed for the first time against Canadian troops during the Second Battle of Ypres on 22 April 1915. This marked the first time chlorine gas was used on the battlefield. Provisions of the 1899 Hague Convention disallowed the usage of shells solely to disseminate toxic gases, and so chemical agents were instead mixed with high explosives. Although the German army is often credited with being the first to use chemical warfare, it was in fact first used by the French, when in August 1914 they fired tear-gas grenades against the Germans.

Despite the agonizing effects of exposure to poison gas, its victims composed only a small percentage of the war’s total casualty figures; by the war’s end, 90,000 had died and 1.2 million were injured.