In 1915, the British Army developed the phenate hexamine anti-gas helmet, a flannelette hood treated with chemicals to absorb chlorine, phosgene and tear gas. Colourless phosgene, the biggest chemical killer of the War, was responsible for most gas deaths. Gas, however, was responsible for less than 8% of all fatalities during the War.
The German Empire first used poison gas on the Western Front in April 1915. The initial response from the Allies was a face mask made from a cotton wool pad treated with chemicals that would stop these gases.
Gas masks were an important piece of equipment for soldiers. Gas attack booklets gave instructions for the correct way of folding and caring for a mask. The effects of gas were debilitating and potentially deadly.
The first type of gas used was xylyl bromide, an early form of tear gas. Later, chlorine gas was used which caused agonising suffocation. The nastiest and most widely-used gas was mustard gas, which killed by blistering the lungs and throat. Even masked soldiers suffered terrible blisters all over their bodies.