On April 22, 1915, German forces shocked Allied soldiers along the western front by firing more than 150 tons of lethal chlorine gas against two French colonial divisions at Ypres, Belgium. This was the first major gas attack by the Germans, and it devastated the Allied line.
Toxic smoke has been used occasionally in warfare since ancient times, and in 1912 the French used small amounts of tear gas in police operations. At the outbreak of World War I, the Germans began actively to develop chemical weapons. In October 1914, the Germans placed some small tear-gas canisters in shells that were fired at Neuve Chapelle, France, but Allied troops were not exposed. In January 1915, the Germans fired shells loaded with xylyl bromide, a more lethal gas, at Russian troops at Bolimov on the eastern front. Because of the wintry cold, most of the gas froze, but the Russians nonetheless reported more than 1,000 killed as a result of the new weapon.
On April 22, 1915, the Germans launched their first and only offensive of the year. Known as the Second Battle of Ypres, the offensive began with the usual artillery bombardment of the enemy’s line. When the shelling died down, the Allied defenders waited for the first wave of German attack troops but instead were thrown into panic when chlorine gas wafted across noman’s land and down into their trenches. The Germans targeted four miles of the front with the wind-blown poison gas and decimated two divisions of French and Algerian colonial troops. The Allied line was breached, but the Germans, perhaps as shocked as the Allies by the devastating effects of the poison gas, failed to take full advantage, and the Allies held most of their positions.