Chemical weapons

chemical weapons
A Western Front soldier and his dog, both wearing gas masks

The stalemate on the Western Front prompted the most intensive use of chemical weapons in human history. Despite an 1899 treaty that banned the use of poisonous gas as a military weapon, all major combatants used them at one point or another. They were used most extensively during 1915 and 1916.

Early usage

The first deployments of poison gas were with irritants like tear gas, which was intended to inconvenience and temporarily disable the enemy rather than cause death.

The French used tear gas in grenades in the opening months of the war and the Germans reciprocated soon after. These early attempts used small amounts of gas which either froze or were quickly dispersed by the weather. As a consequence, they had little military impact.

In January 1915, the Germans employed chemical warfare on a larger scale by launching a barrage of tear gas shells against Russian soldiers. This heavier, more sustained deployment had greater impact.

Chlorine gas

Around this time, German scientists were also busy refining and producing chlorine, a gas designed to kill rather than injure or hinder.

A by-product of clothing manufacture, chlorine gas was released upwind of enemy positions. It drifted at ground level, appearing as a pale green cloud. This was followed soon after by a noxious smell reminiscent of swimming pools and bleach.

The initial deployment of chlorine against French, British and Canadian troops was both devastating and caused considerable panic in Allied ranks. Once inhaled, chlorine gas infiltrated and corroded the lungs, causing painful suffocation and excruciating death.

The Allies respond

It did not take long for them to develop strategies and counter-measures to deal with chlorine attacks. Gas masks containing chemically-impregnated cotton filters were effective at protecting soldiers from chlorine gas. Even holding a rag soaked with water or urine over one’s mouth and nose offered some protection.

Incensed by Germany’s use of poison gas, the Allies began expanding their own stocks. British chemists were quick to develop and manufacture their own weaponised form of chlorine gas.

The first Allied chlorine gas attack at the Battle of Loos (September 1915) was disastrous. An unexpected wind change blew the gas away from the German trenches; some of it reached the British line and killed soldiers there.


In the same year, French military chemists began to utilise an even more potent substance called phosgene. Unlike chlorine, phosgene was invisible and had only a faint smell of mouldy hay. This made its presence more difficult to detect.

Like chlorine gas, phosgene also caused lung damage and suffocation. Its effects were not always immediate, however. A soldier could ingest it but suffer no ill effects for several hours.

The Germans launched phosgene against British positions shortly before Christmas 1915, disabling more than 1,000 men. Phosgene would be responsible for more than 80,000 deaths, or over three-quarters of the gas fatalities in World War I.

Mustard gas

chemical weapons
A British soldier affected by mustard gas burns

The most notorious chemical weapon of the war was mustard gas, a severe irritant that caused chemical burns on the skin, the eyes and in the airways.

Though not as deadly as chlorine or phosgene, mustard gas was more effective as an anti-personnel weapon.

Gas masks could be used to negate the effects of phosgene or chlorine – but mustard gas caused injury wherever there was exposed skin. It also settled on the ground as an oily liquid and could remain active and dangerous for days, even weeks depending on the weather.

An instrument of terror

The pain of mustard gas was intense and its psychological impacts profound. Those exposed to it developed large painful yellow blisters. Men with severe doses died agonising deaths as their lungs burned and blistered inside them. Many mustard gas victims were blinded, some permanently, while some endured respiratory problems for the rest of their lives.

It is not surprising that gas attacks were the trench soldier’s worst fear, as recounted in this Wilfred Owen poem:

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.


chemical weapons
A poster warning soldiers of Lewisite gas, which purportedly smelled “like geraniums”

Germany was the most active exponent of chemical warfare during 1915. By 1917, this situation had reversed, with the Allies producing several thousand tons of poison gas.

Scientists in the United States invented a new compound called Lewisite. It had similar effects to mustard gas but was able to penetrate protective clothing and was allegedly more deadly.

More than 20,000 tons of Lewisite were produced, tested and stockpiled, though the end of the war came before it could be deployed on the battlefield.

Public reaction

The horrors of gas warfare caused public indignation, both during and after World War I.

In 1925, a Geneva convention was signed outlawing the use of chemical weapons. Adolf Hitler, who had himself been a victim of mustard gas in 1918, indignantly refused to deploy poison gas during World War II.

Nevertheless, the major powers retained stockpiles of these weapons – and indeed still do.

“The use of chemicals left an abhorrent image of helpless soldiers in makeshift gas masks, struggling for breath, or ranks of soldiers blinded by mustard agent attacks. In reality though, chemical weapons caused relatively few deaths and injuries compared to conventional weapons. When the war was over, chemical weapons had caused less than 4 per cent of all casualties… One could ask why they have gained such a fulsome reputation when their use did not fundamentally affect the course of World War I, or arguably of any war since then.”
Eric Croddy, writer

chemical weapons

1. Despite an 1899 treaty banning their use, both sides entered the war with stockpiles of chemical weapons.

2. Chemical weapons began with the deployment of tear gas grenades in 1914, followed by chlorine gas in 1915.

3. Germany was the most prolific manufacturer and user of gas, though the Allies reciprocated and soon caught up.

4. Deadly gases like phosgene and chlorine were used but mustard gas was the most common chemical weapon.

5. The effects of chemical weapons caused outrage, particularly after the conclusion of the war, which led to international treaties banning their use in wartime.

Title: “Chemical weapons”
Authors: Jennifer Llewellyn, Steve Thompson
Publisher: Alpha History
Date published: September 2, 2017
Date accessed: September 27, 2023
Copyright: The content on this page may not be republished without our express permission. For more information on usage, please refer to our Terms of Use.