Gas was employed massively as a weapon during WWI, and its use was so atrocious that it was prohibited right after the war. Gas didn’t cause many deaths, but it caused terrible, sometimes permanent health problems, and above all, its psychological effect on the troops was devastating. 

Trenches never sat very far from one another: a few yards, a mile at most. Therefore, armies capitalised on the Industrial Revolution to produce weapons that could kill at close range, such as grenade, machine guns or shell artillery – but this didn’t prove effective once the opposing armies barricade each in their trench. 

A German chemist, Fritz Haber, thought then that chemical weapons could end the impasse. German soldiers under his direction released chlorine gas from storage cylinders and let the wind transport that gas to the opposing trench. 
Haber chose chlorine because it was a byproduct of the German dye industry and therefore easily available without diverting resources from conventional weapons production. It was also heavier than air and could then sink into the trenches rather than drift toward the sky. A powerful irritant to the eyes, noses, lungs and throats, at high concentration, it could cause death by asphyxiation. 
The attack on 22 April 1915 near Ypres was probably one of the most successful. Never expecting such an attack, many soldiers were gravely wounded by the gas, for which they had no protection. Not a small number of them died. 

But afterwards, the use of gas as a weapon was controversial since it presented many difficulties:

1. They were only effective in high concentration, and it was not easy to maintain that in the open.
2. It was easy enough to protect themselves against it with masks.
3. It was nearly impossible to control because it depended on winds and drafts and on the general weather situation. 

Even so, gas continued to be employ because, despite all its shortcomings, it had a huge psychological effect on the troops: it terrorised them. 

Gas could cause terrible suffering, and even if it didn’t kill, it could damage a person’s life forever. Masks could easily divert it, but masks were so uncomfortable that soldiers could only wear them for short, usually no longer than half an hour. But gas could invade the tranches at any time, both during rests and during battles. Some gases were invisible and didn’t smell, so sometimes soldiers breathed them before they knew what was happening. Some gases floated on the ground and drifted towards the trenches like a ghost. And in the case of mustard gas, it could linger undetected in the environment for weeks. 
The call, ‘gas!’ was one of the most dreaded in the trenches. 

The use of chemical warfare with gas was so inhuman that the Geneva Protocol of 1925 prohibited any use of it, even during conflicts. 
Though gas was occasionally used afterwards, it was never in the great amount used during WWI.

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Gas masks

A variety of gas masks were devised and divvied out among the troops, and in a matter of months after the first attack, they became quite sophisticated. The most common were hoods, often made from canvas or rubber, with plastic viewing windows and tubing connected to a canister containing a filter that purified the incoming air. 

Masks were quite effective in neutralising gas attacks, but they had their limits. They were extremely uncomfortable because they made breathing difficult and muffled both hearing and sight, making communication a challenge. Therefore, it was impossible to use them all the time and neutralise gas attacks altogether. Masks were mandatory for humans and animals in no man’s land. Every soldier carried one – and dreaded the moment when the call was out that gas was on the ground. Then soldiers hasten to put their mask on, hoping it functioned and was equipped with the right filters for that day’s gas. 

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RESOURCES

Mario Isnenghi  and Giorgio Rochat, La Grande Guerra, 1914-1918, Il Mulino, Bologna, 2014
Chemical Warfare in World War I: The American Experience 1917-1918 by Charles E. Heller (pdf)

The Atlantic – How the Great War Shaped the World
Canedian War Museum – Poison Gas
International Encyclopedia of the First Warls War – Gas Warfare
IWM – How Gas Became a Terror Weapon in the First World War
BBC News – How deadly was the poison gas of WWI?
University of Kansas Medical Center – Gas in the Great War

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