On 22 April 1915, French and British troops were surprised by a yellow cloud drifting towards their lines between Steenstrate and Langemark. When the cloud reached the soldiers, they suffered violent and painful coughing fits and burning eyes. This first large-scale gas attack using deadly gas sent a wave of panic through the soldiers. On that morning of 22 April, the Germans had opened 5,730 gas cylinders filled with chlorine gas. The wind did the rest. The German troops – who protected themselves from the gas by binding damp cloths over their mouths - were able to make a four-kilometre-wide breach in the allied lines. The French general Foch moved up fresh troops equally rapidly, whereby the Germans could not advance any further.
At the beginning of the war, both German and French troops had used tear gas grenades to blind their opponents. However, this had had little effect. In 1915, the Germans switched to shells containing deadly gas. The tone was set by the attack of 22 April 1915, and both parties would use poison gas frequently in subsequent attacks.
British victims after a gas attack, 10/04/1918, Imperial War Museums, Q 11586, Thomas Keith Aitken