Poison gas

Poison gas is a chemical weapon: a toxic or irritant substance released from cylinders or fired in shells to disable enemy soldiers. By their effect these agents are divided into irritants, choking agents such as chlorine and phosgene, and blister agents such as mustard gas. The First World War saw them used on a mass scale for the first time, and the gas mask became standard equipment for the soldier at the front.

From tear gas to mustard gas

The Hague Declaration of 1899 banned projectiles whose sole object was the diffusion of asphyxiating or deleterious gases. Neither side regarded tear agents as banned. The Germans used irritant shells against the French at Neuve-Chapelle as early as October 1914, and on 31 January 1915 at Bolimów they fired some 18,000 shells filled with a tear agent at the Russians; in the frost it barely vaporised.

The chemist Fritz Haber proposed another method: release chlorine from cylinders and let the wind do the rest. On 22 April 1915 at Ypres the cloud drifted onto the French trenches and opened a gap several kilometres wide in the line. Modern historians estimate that it killed 800–1400 men. The Germans argued that the declaration banned only shells, not cylinders. Two days later chlorine fell on the Canadians at St. Julien, and in August on the defenders of Osowiec. The British replied with chlorine at Loos in September 1915, but the wind changed and gassed more than 2,000 of their own men.

Deadlier agents followed. On 19 December 1915 at Ypres the Germans for the first time on the Western Front added phosgene to chlorine; it was almost invisible and far more lethal. Gas was increasingly fired by the artillery, and the Germans marked their shells with coloured crosses. At Verdun in June 1916 more than 100,000 “Green Cross” shells, filled with diphosgene, fell on the French.

In July 1917 “Yellow Cross” appeared at Ypres: mustard gas, called yperite after the town. It blistered the skin and eyes, lingered in the ground for a long time, and its effects often showed only after many hours. On 21 March 1918, the first day of Operation Michael, it poisoned almost three thousand British soldiers in the Flesquières salient. The British did not use mustard gas of their own until late September 1918.

Masks and projectors

After the first attack soldiers covered their mouths with wet handkerchiefs, then received improvised masks and hoods treated with chemicals. Each new gas answered a new mask. “Blue Cross” got through the filter and forced men to take off their masks so that the choking gas could do its work. The British hurled whole drums of gas from Livens projectors, and at Caporetto German pioneers fired 894 projectors of the same kind. By the end of the war, according to the Canadian War Museum, chemical shells made up 35 per cent of French and German ammunition, 25 per cent of British and 20 per cent of American.

Casualties

According to the Organisation for the Prohibition of Chemical Weapons, some 124,200 tonnes of chlorine, mustard gas and other agents were released by the end of the war, and more than 90,000 soldiers died of gas. Estimates of the number gassed range from about one million to 1.3 million. The British, who kept accurate figures from 1916, recorded that 3 per cent of their gas casualties died and 70 per cent returned to duty within six weeks.

Gas seldom decided a battle, because it depended on the wind, and masks soon limited its effect. The revulsion it caused led in 1925 to the Geneva Protocol, which banned the use of chemical weapons in war.