Chemical warfare in the Great War

A hundred years ago, on 22 April, poison gas was first used in warfare. Though about 95% of casualties in WW1 were caused by explosives, sickness and malnutrition, there is a peculiar horror associated with the use of chemical weapons. It is also true that, apart from isolated examples, WW1 was the only instance of the systematic and widespread use of gases in war (see Box 1).

As early as 1854, the British Secretary for Science and Art, Lyon Playfair [sic], suggested bombarding the Russians in Crimea with shells filled with cacodyl cyanide, an evil-smelling substance which vapourises easily.1 Containing arsenic and cyanide, it is extremely poisonous. It was rejected by the military as being equivalent to “poisoning the wells of the enemy.” Playfair thought this argument was ridiculous since armies were quite prepared to cut people to pieces with shrapnel. He thought poison gas was a more humane way of killing the enemy.2

By 1915, both sides had already used tear gases and irritants and, despite military objections and the banning of poison gas projectiles by the 1907 Hague Convention, both would soon use lethal gases. The Convention was circumvented by releasing these gases from cylinders (Fritz Haber’s idea) when the wind was right: soon it would simply be ignored.

The first was chlorine.3 Commonly used in weak solution as a disinfectant for drinking water and swimming baths, chlorine is a pale green gas with a choking odour. It is one of the most reactive elements, which is bad news if it comes in contact with living cells. It dissolves in their moisture, releasing acid and bleach.

These substances cause irritation in the eyes, throat and bronchi. Victims experience coughing, tightness of the chest, breathlessness, bronchitis, pulmonary oedema (lungs filling with liquid) and, if in high enough concentrations, death.

The effects were terrifying and unprotected troops fled in panic. Wilfred Owen’s poem describes a soldier unable to put on his gas-mask in time during what seems to be a chlorine attack.4 An Austrian soldier describes, in his memoir, attack by British gas-bombs which left him temporarily blinded.5 Soldiers would be incapacitated and unable to fight even if not killed. Large numbers would be invalided out and suffer long-lasting ill health.

The first use of chlorine

This was planned as a trial run, using Haber’s gas cylinder method (see Box 2). The site was part of the Ypres salient and release of the gas was to be followed by an infantry attack. The local commander requested extra ammunition but this was refused since this was merely a trial. Special pioneer units, including scientists, technicians, and a meteorologist, installed the cylinders along the front line.

The Germans were ambivalent about using chlorine. Some felt it quite immoral (unlike blowing men to pieces!); it was of unknown effectiveness, particularly since the wind was changeable and might blow the gas back; and troops in the trenches were worried that Allied shells might smash the cylinders.

During many delays due to weather conditions, British and French troops found German gas cylinders and a captured officer revealed the plan: the information was never passed on to HQ. Again, the plans leaked out and were even reported in The Times. Eventually, by 11 April 1915, 5730 cylinders were installed some 8km north of Ypres. The operators were given gas masks and nearby soldiers given pads of cotton waste soaked in sodium sulfate solution to hold over their mouths and noses. The Germans waited for favourable winds. On 13 April, a German deserter, August Jaeger6, told the French and Belgians about the planned gas attack but they did not believe that the Germans would break the Hague Convention. On 15 April, a Belgian spy confirmed Jaeger’s story. No action was taken.

Finally, at 4pm on 22 April, the gas cylinders were opened, the French and Algerian front line troops were either asphyxiated or retreated in disorder,7 and the Germans found the way clear to Ypres. The gas attack had been a stunning success but the lack of troops and supplies meant that the advantage could not be pressed home. The Second Battle of Ypres, despite more gas attacks, ended some three months later in stalemate but Michael Freemantle8 speculates that the initial advantage gained could have changed the course of the war.

Gassed by John Singer Sargent (1919)
by John Singer Sargent (1919)

Everyone uses gas of many types

British commanders condemned chlorine as a cowardly weapon but immediately adopted it themselves. Their first use was in 1914 in the Battle of Loos and was a fiasco. 140 tons of gas were to be released from 5100 cylinders but a change of wind caused the clouds to be blown back to the British trenches. On top of this, the wrong keys were sent for some cylinders so they could not be opened. Retaliatory gunfire burst some of these, causing further British casualties.9

Chlorine’s effects could be quite easily mitigated by a simple wet cloth over the mouth since it is water-soluble. Urine-soaked cloths were even better since chlorine reacts with urea. Quite soon, primitive gas masks were issued and chemists responded by developing different gases.

The French chemist Victor Grignard developed phosgene, the second most used gas of the war. Also asphyxiating, but less detectable than chlorine, it had a delayed effect so that soldiers could continue to fight, rather limiting its value: only the next day would victims become unwell as their lungs stopped functioning. It was by far the most lethal gas, causing 85% of gas deaths. Gas masks were soon modified to protect against phosgene. Improved gas masks led to a race to develop other gases that could penetrate or bypass these. The most unpleasant and feared was mustard gas, introduced by the Germans in mid-1917.

Mustard causes the skin of victims to blister, while their eyes become very sore or even blind, and they vomit. It strips the lining membranes from the bronchi (tubes leading into the lungs), causing extreme pain. Fatally-wounded victims could take weeks to die.10, 11 Mustard gas was not very effective despite its horrible action: it condensed into an oily liquid and polluted the area for weeks or months, keeping out both sides.

By 1918, all sides were using all gases to support offensives, in artillery shells rather than cylinders, but gas was still only responsible for a small percentage of deaths. There were about 1.25 million casualties from gas, of which fewer than 100,000 died. Most were able to fight again after a few weeks’ recovery.

Many survivors felt that their health had been permanently damaged but a study published in the BMJ in 200712 showed they were no less healthy or long-lived than other WW1 soldiers. This “gas shock,” by analogy with “shell shock” first diagnosed in WW1, resembles the post-traumatic stress disorder described in US Vietnam veterans.

Gas was understandably more feared than its objective dangers justified; the crude gas masks also induced claustrophobia and panic. In truth, though terrifying and cruel, gas was just not very effective.

……………………………………………………………………………………………………………… Box 1

Types of poison gas used in the Great War

Tear gases (lachrymators ): these irritate the eyes, but are easily defeated by gas masks. Examples: ethyl bromoacetate and xylyl bromide.

Sneezing gases (sternutators): agents which irritate the nasal passages. These could penetrate gas masks, forcing soldiers to remove them, making them vulnerable to the choking gases fired at the same time. Example: diphenylchlorarsine.

Choking agents (asphyxiators): agents which irritate the respiratory passages, especially the lungs which fill with liquid, making it impossible to breathe. Examples: chlorine and phosgene.

Blister agents (vesicants): these cause extremely painful blistering of the skin, throat and lungs: they can cause temporary blindness and can kill. Example: mustard gas.

Blood agents: these prevent the blood carrying oxygen or stop cellular respiration. Example: hydrogen cyanide (prussic acid). While not very effective in open air, hydrogen cyanide was used in Zyklon B, the gas used by the Nazis to kill about a million people. Seventy milligrams can kill a person within two minutes.


Box 2

The tragedy of Fritz Haber

Fritz Haber, “father of industrial nitrogen fixation”, may be the most important chemist of all time. With Carl Bosch, he invented a method of making ammonia from nitrogen and hydrogen, enabling Germany to make the explosives and fertilisers essential to be able to fight on. The Haber-Bosch process to make fertilisers allowed world agricultural productivity to soar, acting as the “detonator of the population explosion,” in which the world’s population increased fourfold in 100 years. Haber received the Chemistry Nobel in 1918.

Haber was a patriot who desired his country’s victory, and his process certainly prolonged the war. But he was keen to do more and, in December 1914, he suggested releasing clouds of chlorine gas from pressurised cylinders to drift over Allied trenches. Put in charge of organising this, he recruited 500 “gas pioneers” to try various options and by 1915 the army was ready to carry out his plan.

Chlorine was known to be very unpleasant and should prevent troops from fighting; denser than air, it would blanket the ground and flow into trenches; it was cheaply available from the electrolysis of common salt; it was easily condensed to liquid; steel bottles were easily available and Haber commandeered 6000. He observed their deployment at Ypres (see above). Given the Iron Cross and the rank of captain by the Kaiser, Haber gained the dubious description of “father of chemical warfare.”

His wife Clara disagreed with his development of poison gas and committed suicide shortly after chlorine’s first use.

Keen to help his country after the war, he worked unsuccessfully on methods of extracting gold from seawater to help pay off Germany’s war debts. As director of the Kaiser Wilhelm Institute, he oversaw work on poison gases which later led to the development of Zyklon B. Initially used as a fumigant, it was only after Haber’s death that it was used to murder prisoners of the Nazis.

His patriotism counted for nothing when the Nazis came to power since he was of Jewish origin. He was forced to resign as director of the KWI and left Germany in 1933, helped by British scientists, and worked in Cambridge. Chaim Weizmann13 offered him a job in a research institute in British-administered Palestine but Haber died of heart failure on the way there in 1934. …………………………………………………………………………………………………………………………….


1 Discovered by Robert Bunsen (of Bunsen burner fame) who lost the sight of one eye when some exploded.

2 Discuss!

3 Element number 17, in Group 7 (halogens or “salt-makers”), chlorine atoms have seven electrons in their outer shell, one less than the eight needed for stability. This makes chlorine very reactive. It attacks living cells, useful against bacteria but deadly when breathed by animals. It dissolves and reacts with water, producing hydrochloric acid (probably the cause of the immediate damage) and hypochlorite ions (which cause bleaching). It can be fatal at a concentration in air of 0.1%. The 168 tons the Germans had at Ypres could have produced a lethal concentration in a cloud over 6 feet (2m) deep covering an area of 10,000 square miles. With a density two-and-a-half times that of air, it would hug the ground and flow into trenches and underground bunkers.

4 ”Gas! Gas! Quick boys! – An ecstasy of fumbling, Fitting the clumsy helmets just in time; But somebody 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.” (Dulce et decorum est).

5 “About midnight, a number of us were put out of action, some for ever. Towards morning I also began to feel pain. It increased with every quarter of an hour; and about seven o’clock my eyes were scorching as I staggered back and delivered the last despatch I was destined to carry in this war. A few hours later, my eyes were like glowing coals and all was darkness around me.” (Adolf Hitler, Mein Kampf).

6 Jaeger was exposed in 1932 by a French WW1 general and imprisoned for treason by Germany, despite pleading not guilty on ethical grounds. Held by the Nazis as a political prisoner, he was released from Dachau in 1945.

7 “A living wall of green fog, about four feet in height, moved towards the French line and spread out to a width of about 180 metres. As the wall of smoke grew higher the whole area disappeared into it. Suddenly the rifle fire from the French increased, but gradually died down… Soon we heard strange shouts coming from the green fog. The cries became weaker and more incoherent. Then masses of soldiers tumbled upon us from out of the fog and collapsed. Most weren’t wounded but they had expressions of terror on their faces. These piteous retreating men ranked with some of the best soldiers in the world; their cold-bloodedness and courage was almost legendary. Now they were staggering along like drunks.” (Eyewitness account by a British soldier in The Times)

“Stumbling and gasping in an agony of terror-stricken flight before it, scattered groups of French Algerian infantrymen with reeking, yellowed clothing and ashen purple faces, staggered across the fields, through hedges, over ditches and down the roads, regardless of everything but this unknown devil which had them by the throat. Their yellowed clothes reeked and their faces were ashen. With wild panic in their eyes they tried to escape from the murderous green mist.” (Official History of the Canadian Forces in The Great War)

8 I am indebted to Michael Freemantle whose books Gas! Gas! Quick, boys! (2012) and the more extensive The Chemists’ War: 1914-1918 (2015, Royal Society of Chemistry; ISBN 978-1-84973-989-4; £19.99) provided much information. Highly recommended!

9 You couldn’t make it up!

10 Vera Brittain, then a nurse in France, 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.” (Testament of Youth).

11 The iconic painting Gassed, by war artist John Singer Sargent, shows blinded soldiers being led to a treatment station.

12 Edgar Jones, Ian Palmer and Simon Wessely, BMJ 2007;335;1313-1315 doi:10.1136/bmj.39420.533461.25

13 Chemist Chaim Weizmann, “father of industrial fermentation” and solver of a major problem for the British, namely the shortage of acetone needed for the production of cordite. A Zionist, he later became first president of Israel.


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