Poison gas, first used by the Germans in 1915. Primarily used against entrenched defenders. Most devastating chemical weapon was mustard gas, introduced by the Germans in 1917, it which was a type of chemical burn. Delivered by artillery shells. The gas caused chemical burns and blisters both inside and outside of the body. It could cause external and internal bleeding. Death could be extremely painful and slow. Gas masks were an effective protection against poison gas, so its effectiveness diminished. One British nurse, Vera Brittain, wrote: "I wish those people who talk about going on with this war whatever it costs could see the soldiers suffering from mustard gas poisoning. Great mustard-coloured blisters, blind eyes, all sticky and stuck together, always fighting for breath, with voices a mere whisper, saying that their throats are closing and they know they will choke." (Duffy).
The British soldier-poet Wilfred Owen wrote about experiencing a gas attack in the trenches in 1917.
Gas! GAS! Quick, boys! — An ecstasy of fumbling, Fitting the clumsy helmets just in time; But someone still was yelling out and stumbling, And flound'ring like a man in fire or lime... Dim, through the misty panes and thick green light, As under a green sea, I saw him drowning. In all my dreams, before my helpless sight, He plunges at me, guttering, choking, drowning. (Owen)