Second Battle of Ypres begins - Apr 22, 1915 - HISTORY.com

On this day in 1915, German forces shock Allied soldiers along the Western Front by firing more than 150 tons of lethal chlorine gas against two French colonial divisions at Ypres in Belgium.

Toxic smoke had 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, however, the Germans began to actively develop chemical weapons. In October 1914, small tear-gas canisters were placed 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. Now referred to 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 no-man’s land and down into their trenches. The Germans targeted four miles of the front with the wind-blown poison gas, decimating two divisions of French and Algerian colonial troops. The Germans, perhaps as shocked as the Allies by the devastating effects of the poison gas, failed to take full advantage, and the Allies managed to hold most of their positions.

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. The Second Battle of Ypres ended on May 25, with insignificant gains for the Germans. The introduction of poison gas, however, would have great significance in World War I.

Immediately after the German gas attack at Ypres, the French and British began developing their own chemical weapons and gas masks. With the Germans taking the lead, an extensive number of projectiles filled with deadly substances polluted the trenches during the next several years of war. Mustard gas, introduced by the Germans in 1917, blistered the skin, eyes and lungs, and killed thousands. Military strategists defended the use of poison gas by saying it reduced the enemy’s ability to respond and thus saved lives in offensives. In reality, defenses against poison gas usually kept pace with offensive developments, and both sides employed sophisticated gas masks and protective clothing that eventually negated the strategic importance of chemical weapons.

The United States, which entered World War I in 1917, also developed and used chemical weapons. Future President Harry S. Truman was the captain of a U.S. field artillery unit that fired poison gas against the Germans in 1918. In all, more than 100,000 tons of chemical weapons agents were used in World War I, some 500,000 troops were injured from their use and almost 30,000 died, including 2,000 Americans.