The Australian infantry wears small box respirators to ward off the harmful effects of poison gas.

Courtesy Australian War Memorial 1915: Poison gas is used for the first time on the Western Front at the Second Battle of Ypres.

Although the attack opened up an 8,000-yard gap in the Allied line, as French and Algerian troops broke and ran, the Germans failed to exploit the success because their own infantry balked at attacking in an area that had just been gassed.

The Germans weren't the first to use debilitating gas as a weapon during World War I: The French launched tear-gas attacks against German positions in the first month of fighting. But chlorine gas represented an escalation in chemical warfare, still very new at the time. Unlike tear gas, chlorine gas could kill.

Fortunately for its intended victims, a chlorine-gas attack resulted in a green cloud and a strong odor that was easily detected. Countermeasures were also easy and effective. Placing a wet cloth over the mouth and nose was one method used at the Second Battle of Ypres, and, while primitive, generally diluted the worst effects of the gas.

Although the Allies, especially the British, protested against this new type of warfare (and used it in anti-German propaganda) they embraced it and refined it themselves as the war dragged on. The French produced phosgene, a deadlier gas than chlorine and, being colorless, one that was harder to detect.

The most effective chemical agent of World War I, mustard gas, was introduced by the Germans in 1917. It was not designed to kill (although a high enough dose often resulted in a lingering, agonizing death) but to incapacitate. Exposure resulted in blistering skin, difficulty in breathing, vomiting and blindness.

Despite the terrible effects suffered by gassing victims, gas itself was not particularly effective as a tactical weapon, mainly because it was hard to direct and subject to the vagaries of the wind. Wind shifts often resulted in gas being blown back on the attacker. Countermeasures were also improving; both sides produced reliable gas masks that essentially eliminated the danger.

But the idea of being gassed was terrifying, so it did have value as a psychological weapon.

Perhaps the most famous victim of gassing was a German corporal named Adolf Hitler, who was temporarily blinded during a British gas attack in 1918.

(Source: World War I.com, Spartacus)

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