On April 22, 1915, a sickly green cloud drifted toward Allied trenches — the first large-scale poison gas attack in history, and it nearly broke the entire Western Front.
On April 22, 1915, German forces opened valves on 5,730 cylinders of chlorine gas along a 4-mile front near Ypres, Belgium. The greenish-yellow cloud drifted into Allied trenches at dusk, choking soldiers who had no protection against the new weapon. Within minutes, French and Algerian troops were fleeing in panic, tearing a 4-mile gap in Allied lines.
German commanders had a near-miraculous opportunity: a gaping hole in the Allied front with virtually no defenders. But they hesitated. Their own troops were reluctant to advance into the gas cloud, and commanders had not expected success so quickly. By the time they moved, Canadian and British forces had plugged the gap.
Canadian soldiers, caught in the gas attack, improvised survival measures on the spot — urinating on handkerchiefs or rags and holding them over their mouths. The ammonia helped neutralize the chlorine. Their stubborn defense of the flanks helped prevent a complete Allied collapse and became one of Canada's defining moments of the war.
The city of Ypres sat in a 'salient' — a bulge in the front line surrounded on three sides by German forces. Nicknamed 'Wipers' by British troops, it had no real strategic value by 1915, but Allied commanders refused to give it up for its symbolic importance. Holding it cost hundreds of thousands of lives over three years.
The introduction of chemical warfare at Ypres transformed the war. Both sides rapidly developed new agents — phosgene (more lethal than chlorine), then mustard gas, which burned skin and blinded soldiers. The gas mask became standard equipment. By the war's end, 1.3 million soldiers had been gassed on all fronts, with over 90,000 killed.
The battle ended in stalemate after five weeks of fighting and roughly 105,000 total casualties. The front lines barely moved. Ypres remained in Allied hands — a hollow victory whose cost would be repeated twice more in subsequent battles at the same location.