Military strategists defended the use of poison gas by saying it reduced the enemy’s ability to respond and thus saved lives in offensives. Mustard gas, introduced by the Germans in 1917, blistered the skin, eyes, and lungs, and killed thousands. With the Germans taking the lead, an extensive number of projectiles filled with deadly substances polluted the trenches of World War I. Immediately after the German gas attack at Ypres, France and Britain began developing their own chemical weapons and gas masks.
The introduction of poison gas, however, would have great significance in World War I. The Second Battle of Ypres ended on May 25, with insignificant gains for the Germans. A second gas attack, against a Canadian division, on April 24, pushed the Allies further back, and by May they had retreated to the town of Ypres.
