The trench warfare of the Western Front encouraged the development of new weaponry to break the stalemate. Poison gas was one such development.
The first significant gas attack occurred at Ypres in April 1915, when the Germans released clouds of poisonous chlorine. The gas inflicted significant casualties among the British and Canadian forces at Ypres and caused widespread panic and confusion amongst the French colonial troops.
The chlorine was a strong irritant on the lungs, with prolonged exposure proving fatal. The immediate public outcry for retaliation resulted in quick adoption of defensive anti-gas measures including new companies of Royal Engineers responsible for offensive gas warfare.
Poison gas was initially released from cylinders, but this required ideal weather conditions and could be very risky.
In the first British gas attack, at Loos in September 1915, much of the gas was blown back into the faces of the British troops. From 1916, gas was employed in shells instead, which allowed attacks from a much greater range.
Gases used included chlorine, mustard gas, bromine and phosgene, and the German Army was the most prolific user of gas warfare.
Gas did not prove as decisive a weapon as was anticipated but it was effective in clearing enemy forward positions. As a result, anti-gas measures became increasingly sophisticated. Primitive cotton face pads soaked in bicarbonate of soda were issued to troops in 1915, but by 1918 filter respirators using charcoal or chemicals to neutralise the gas were common.
The physical effects of gas were agonising and it remained a pervasive psychological weapon. Although only 3 per cent of gas casualties proved immediately fatal, hundreds of thousands of ex-soldiers continued to suffer for years after the war.
This article was edited by Catriona Deery. Other IWM staff members contributed to writing an older version of this piece.