1915-1918
On April 22, 1915, near the town of Ypres, Belgium, the modern era of chemical warfare began when the German military opened about 6,000 cylinders of liquid chlorine along a four-mile front against French and French-Algerian soldiers. This initial attack of 168 metric tons of toxic gas killed approximately 5,000 Allied soldiers with 10,000 wounded. The attack was so effective that after months of stalemate trench warfare a four-mile-wide hole was opened in the Allied line in just 36 hours. So surprised were the Germans by the overwhelming effectiveness of this new weapon they were unable to fully exploit the massive opportunity chemical weapons had created. The German high command had initiated this treaty-breaking chemical warfare, and eventually the Allies would respond in kind. According to some estimates, by the end of the war one-third of all artillery munitions contained gas.
Although incredibly effective in the early stages of use, chemical weapon defenses, mainly in the form of continually improved gas masks, advanced rapidly throughout the war. Thus, by the end of the conflict, as the use of chemical weapons increased, the number of casualties attributed to these weapons declined. By the time the armistice was declared on November 11, 1918, an estimated 124,000 metric tons of 21 different chemicals were used by both sides, delivered mainly via 66 million artillery shells. As much as one million casualties had been caused by these weapons with approximately 90,000 fatalities and many more blinded and disfigured. Of the American Expeditionary Force’s (AEF) 272,000 casualties, approximately 26.8 percent were caused by chemical weapons. However, only 2 percent of these casualties were fatal. During the interwar period, the low fatality rate of the AEF would be a prime argument for the continued use of chemical weapons in warfare.