WW1 was the first armed conflict in history in which man used poisonous chemicals to defeat the enemy as both sides used them in an attempt to overcome the stalemate of trench warfare. The German Army was the first army to employ a chemical as a weapon; it was in the Second Battle of Ypern, on April 22, 1915, in Belgium, that a German, special, chemical warfare unit, called “disinfection unit”, released more than 150 tons of chlorine gas from thousands of gas cylinders through a system of metal pipes or tubes. To release this lethal gas, they had to wait until the wind was favorable to the Germans. Creeping along the artillery-shell-torn ground, the gas blew like a thick, white cloud towards where the enemy troops were. It is estimated that more than 5,500 colonial Moroccan and Algerian soldiers of the French Army got killed and wounded in this first gas attack on the Western Front.
In September and December, 1915, both the British and the French armies would use chlorine and phosgene gas against enemy troops at Loos and Ypres, respectively, using the same method the Germans had used a few month earlier. By 1917, the Imperial German Army had developed the mustard gas, a lethal gas that burned the skin and mucus membrane of the respiratory tract and lungs; but this time, the Germans used a different and safer methods to deliver it on the enemy. Contained in special artillery shells, the mustard gas was shot by the German howitzers, landing on both the Franch and British troops. Thus, the Allied armies learned from the Germans and would also employ both phosgene and mustard gas delivered in artillery shells until the end of this armed struggle. By the end of World War I, approximately 400,000 German and Allied soldiers had been killed with gas.