Use of poison gas in World War I

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A poison gas attack in .
A poison gas attack in World War I.

The use of poison gas was a major military innovation of the First World War. The gases used ranged from tear gas to disabling chemicals such as mustard gas and killing agents like phosgene. This chemical warfare was a major component of the first global war and first total war of the 20th century. The killing capacity of gas was limited — only 3% of combat deaths were due to gas — however, the proportion of non-fatal casualties was high and gas remained one of the soldiers' greatest fears. Unlike most other weapons of the period, it was possible to develop effective countermeasures to gas. Hence in the later stages of the war as the use of gas increased, in many cases its effectiveness was diminished.



The early uses of chemicals as weapons were as a tear inducing irritant (lachrymatory), rather than fatal or disabling poisons. Although many believe that gases were first used in World War I, there are accounts that sulfur gas was used in the 5th century B.C. by the Spartans. During World War I, the French were the first to employ gas, using grenades filled with tear gas (xylyl bromide) in August 1914. Germany retaliated in kind in October 1914, firing shrapnel shells filled with a chemical irritant against French positions at Neuve Chapelle though the concentration achieved was so small it was barely noticed.

Germany was the first to make large scale use of gas as a weapon. On 31 January, 1915, 18,000 artillery shells containing liquid xylyl bromide tear gas (known as T-Stoff) were fired on Russian positions on the Rawka River, west of Warsaw during the Battle of Bolimov. Instead of vaporizing, the chemical froze, completely failing to have an impact.

Chlorine became the first killing agent to be employed. German chemical conglomerate IG Farben had been producing chlorine as a by-product of their dye manufacturing. In cooperation with Fritz Haber of the Kaiser Wilhelm Institute in Berlin, they began developing methods of discharging chlorine gas against enemy trenches. By 22 April 1915, the German Army had 160 tons of chlorine deployed in 5,730 cylinders opposite Langemarck, north of Ypres. At 17:00, in a slight easterly breeze, the gas was released, forming a grey-green cloud that drifted across positions held by French Colonial troops who broke, abandoning their trenches and creating an 8,000 yard (7 km) gap in the Allied line. However, the German infantry were also wary of the gas and failed to exploit the break before Canadian and British reinforcements arrived.

In what became the Second Battle of Ypres, the Germans used gas on three more occasions; on 24 April against the Canadian 1st Division, on 2 May near Mouse Trap Farm and on 5 May against the British at Hill 60. At this stage, defences against gas were non-existent; the British Official History stated that at Hill 60:

"90 men died from gas poisoning in the trenches; of the 207 brought to the nearest dressing stations, 46 died almost immediately and 12 after long suffering."

Chlorine was inefficient as a weapon. It produced a visible greenish cloud and strong odour, making it easy to detect. It was water-soluble so the simple expedient of covering the mouth and nose with a damp cloth was effective at reducing the impact of the gas. Chlorine required a concentration of 1,000 parts per million in order to be fatal, destroying tissue in the lungs. Despite its limitations, chlorine was an effective terror weapon, and the sight of an oncoming cloud of the gas was a continual source of dread for the infantry.

The British expressed outrage at Germany's use of poison gas at Ypres but responded by developing their own gas warfare capability. The commander of British II Corps, Lt.Gen. Ferguson said of gas:

Missing image
British infantry advancing through gas at Loos, 25 September, 1915.
"It is a cowardly form of warfare which does not commend itself to me or other English soldiers. We cannot win this war unless we kill or incapacitate more of our enemies than they do of us, and if this can only be done by our copying the enemy in his choice of weapons, we must not refuse to do so."

In the end, the British Army embraced gas with enthusiasm and mounted more gas attacks than any other combatant. This was due partly to the fact that the British spent most of the latter years of the war on the offensive. Also the prevailing wind on the Western Front was from the west which meant the British more frequently had favourable conditions for a gas release than the Germans. The first use of gas by the British was at the Battle of Loos, 25 September, 1915 but the attempt was a disaster. Chlorine, codenamed Red Star, was the agent to be used (150 tons arrayed in 5,500 cylinders), and the attack was dependent on a favourable wind. However, on this occasion the wind proved fickle, and the gas either lingered in no man's land or, in places, blew back on the British trenches.

The deficiencies of chlorine were overcome with the introduction of phosgene, first used by Germany in December 1915. Phosgene was a potent killing agent, deadlier than chlorine and difficult to detect, being colourless and having an odour likened to "mouldy hay". Phosgene's disadvantage was that it was light-weight and readily dissipated, so it was initially mixed with the heavier chlorine. The other drawback was that the symptoms of exposure took 24 hours or more to manifest, meaning that the victims were initially still capable of putting up a fight.

Estimated production of gases (by type)
Nation Production (metric tons)
Irritant Lachrymatory Vesicant Total
Austria-Hungary 5,080 255 5,335
Britain 23,870 1,010 520 25,400
France 34,540 810 2,040 37,390
Germany 55,880 3,050 10,160 69,090
Italy 4,070 205 4,275
Russia 3,550 155 3,705
USA 5,590 5 175 5,770
Total 132,580 5,490 12,895 150,965

The most famous and effective gas of the First World War was mustard gas, a vesicant, which was introduced by Germany in July 1917 prior to the Third Battle of Ypres. Known to the British as HS (or Hun Stuff), mustard gas was not intended as a killing agent (though in high enough doses it was fatal) but instead was used to harass and disable the enemy and pollute the battlefield. Delivered in artillery shells, mustard gas was heavier than air, settled to the ground as an oily sherry-looking liquid and evaporated slowly without sunlight.

The polluting nature of mustard gas meant that it was not always suitable for supporting an attack as the assaulting infantry would be exposed to the gas when they advanced. When Germany launched Operation Michael on 21 March, 1918, they saturated the Flesquières salient with mustard gas instead of attacking it directly, believing that the harassing effect of the gas, coupled with threats to the salient's flanks, would make the British position untenable.

Gas never reproduced the dramatic success of 22 April, 1915; however, it became a standard weapon which, combined with conventional artillery, was used to support most attacks in the later stages of the war. The Western Front was the main theatre in which gas was employed — the static, confined trench system was ideal for achieving an effective concentration — however, Germany made use of gas against Russia on the Eastern Front, where the lack of effective countermeasures would result in deaths of thousands of Russian infantry, while Britain experimented with gas in Palestine during the Second Battle of Gaza.

The universal horror with which gas was viewed led to the Geneva Protocol, a post-war treaty banning on the use of lethal gas which was signed in 1925 (though not ratified by some countries until many decades later). No subsequent war has made such large-scale use of poison gas as the First World War, though poison gas technology played an important role in the Holocaust and has been widely used as a method of execution.

Gas casualties

Missing image

The contribution of gas weapons to the total casualty figures was relatively minor. British figures, which were accurately maintained from 1916, recorded that only 3% of gas casualties were fatal, 2% were permanently invalid and 70% were fit for duty again within six weeks. All gas casualties were mentally scarred by exposure, and gas remained one of the great fears of the front-line soldier.

"It was remarked as a joke that if someone yelled 'Gas', everyone in France would put on a mask. ... Gas shock was as frequent as shell shock." (H. Allen, Towards the Flame, 1934)
Gas! Gas! Quick, boys! An ecstasy of fumbling,
Fitting the clumsy helmets just in time,
But someone still was yelling out and stumbling
And floundering 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.
(Wilfred Owen, "Dulce Et Decorum Est", 1917)

Death by gas was particularly horrific. According to Denis Winter (Death's Men, 1978), a fatal dose of phosgene eventually led to "shallow breathing and retching, pulse up to 120, an ashen face and the discharge of four pints (2 litres) of yellow liquid from the lungs each hour for the 48 of the drowning spasm."

A common fate of those exposed to gas was blindness, tear gas or mustard gas being the main causes. It became a frequent spectacle to see lines of blinded soldiers, hand on the shoulder of the man in front, being guided by a sighted man to a dressing station. One of the most famous First World War paintings, Gassed by John Singer Sargent, captures such a scene of mustard gas casualties which he witnessed at a dressing station at Le Bac-du-Sud near Arras in July 1918.

Nation Gas Casualties (estimated)
Fatal Non-fatal
Russia 50,000 400,000
Germany 10,000 190,000
France 8,000 182,000
Britain 8,000 181,000
Austria-Hungary 3,000 97,000
USA 1,500 71,500
Italy 4,500 55,000
Total 85,000 1,176,500

Mustard gas caused the most gas casualties on the Western Front, despite being produced in smaller quantities than irritant gases such as chlorine and phosgene. The proportion of mustard gas fatalities to total casualties was low; only 2% of mustard gas casualties died and many of these succumbed to secondary infections rather than the gas itself. Once it was introduced at Ypres, mustard gas produced 90% of all British gas casualties and 14% of battle casualties of any type.

Mustard gas was a source of extreme dread. In The Anatomy of Courage (1945), Lord Moran, who had been a medical officer during the war, wrote: "After July 1917 gas partly usurped the role of high explosive in bringing to head a natural unfitness for war. The gassed men were an expression of trench fatigue, a menace when the manhood of the nation had been picked over."

Mustard gas did not need to be inhaled to be effective — any contact with skin was sufficient. Exposure to 0.1 ppm was enough to cause massive blisters. Higher concentrations could burn flesh to the bone. It was particularly effective against the soft skin of the face and genitals. Typical exposure would result in swelling of the conjunctiva and eyelids, forcing them closed and rendering the victim temporarily blind. Where it contacted the skin, moist red patches would immediately appear which after 24 hours would have formed into blisters. Other symptoms included severe headache, elevated pulse and temperature, and pneumonia.

Death by mustard gas, when it came, was dreadful. A post-mortem account from the British official medical history records one of the first British casualties:

Case four. Aged 39 years. Gassed 29 July 1917. Admitted to casualty clearing station the same day. Died about ten days later. Brownish pigmentation present over large surfaces of the body. A white ring of skin where the wrist watch was. Marked superficial burning of the face and scrotum. The larynx much congested. The whole of the trachea was covered by a yellow membrane. The bronchi contained abundant gas. The lungs fairly voluminous. The right lung showing extensive collapse at the base. Liver congested and fatty. Stomach showed numerous submucous haemorrhages. The brain substance was unduly wet and very congested.

A British nurse treating mustard gas cases recorded:

"They cannot be bandaged or touched. We cover them with a tent of propped-up sheets. Gas burns must be agonizing because usually the other cases do not complain even with the worst wounds but gas cases are invariably beyond endurance and they cannot help crying out."
British gas casualties on the Western Front
Date Agent Casualties (official)
Fatal Non-fatal
April – May 1915 Chlorine 350 7,000
May 1915 – June 1916 Lachrymants 0 0
December 1915 – August 1916 Chlorine 1,013 4,207
July 1916 – July 1917 Various 532 8,806
July 1917 – November 1918 Mustard gas 4,086 160,526
April 1915 – November 1918 Total 5,981 180,539

Many of those who survived a gas attack were scarred for life. Respiratory disease and failing eye sight were common post-war afflictions. Of the Canadians who, without any effective protection, had withstood the first chlorine attacks during 2nd Ypres, 60% of the casualties had to be repatriated and half of these were still unfit by the end of the war, over three years later.

In reading the statistics of the time, one should bear the longer term in mind. Many of those who were fairly soon recorded as fit for service were left with scar tissue in their lungs. This tissue was susceptible to tuberculosis attack. It was from this that many of the 1918 casualties died, around the time of the Second World War, shortly before the sulfa drugs became widely available for its treatment.


Missing image
German infantry wearing improvised gas masks, 1915.

None of the First World War combatants were prepared for the introduction of poison gas as a weapon. Once gas had appeared, development of gas protection began and the process continued for much of the war producing a series of increasingly effective gas masks.

Even at 2nd Ypres Germany, still unsure of the weapon's effectiveness, only issued breathing masks to the engineers handling the gas. At Ypres a Canadian medical officer, who was also a chemist, quickly identified the gas as chlorine and recommended that the troops urinate on a cloth and hold it over their mouth and nose, the theory being the uric acid would crystallise the chlorine. The first official equipment issued was similarly crude; a pad of material, usually impregnated with a chemical, tied over the lower face. To protect the eyes from tear gas, soldiers were issued with gas goggles.

Missing image
British Vickers machine gun crew wearing PH gas helmets with exhaust tubes.

The next advance was the introduction of the gas helmet — basically a bag placed over the head. The fabric of the bag was impregnated with a chemical to neutralise the gas — whenever it rained, the chemical would wash out into the soldier's eyes. Eye-pieces, which were prone to fog up, were initially made from talc. When going into combat, gas helmets were typically worn rolled up on top of the head, to be pulled down and secured about the neck when the gas alarm was given. The first British version was the Hypo helmet, the fabric of which was soaked in calcium hypochlorite. The British PH gas helmet, effective against phosgene and with which all infantry were equipped with at Loos, was impregnated with phenate hexamine. A mouthpiece was added through which the wearer would breathe out to prevent carbon dioxide build-up. The adjutant of the 1/23rd Battalion, The London Regiment, recalled his experience of the PH helmet at Loos:

"The goggles rapidly dimmed over, and the air came through in such suffocatingly small quantities as to demand a continuous exercise of will-power on the part of the wearers."
Missing image
Australian infantry wearing Small Box Respirators, Ypres, September 1917.

Self-contained box respirators represented the culmination of gas mask development during the First World War. Box respirators used a two-piece design; a mouthpiece connected via a hose to a box filter. The box filter contained granules of chemicals that neutralised the gas, delivering clean air to the wearer. Separating the filter from the mask enabled a bulky but efficient filter to be supplied. Nevertheless, the first version, known as the Large Box Respirator (LBR) or "Harrison's Tower", was deemed too bulky — the "box" canister needed to be carried on the back. The LBR had no mask, just a mouthpiece and nose clip; separate gas goggles had to be worn. It continued to be issued to the artillery gun crews but the infantry were supplied with the "Small Box Respirator" (SBR).

The Small Box Respirator featured a single-piece, close-fitting rubberised mask with eye-pieces. The box filter was compact and could be worn around the neck. The SBR could be readily upgraded as more effective filter technology was developed. The British-designed SBR was also adopted for use by the American Expeditionary Force. The SBR was the prized possession of the ordinary infantryman; when the British were forced to retreat during the German Spring Offensive of 1918, it was found that while some troops had discarded their rifles, hardly any had left behind their respirators.

Missing image
German soldier and horses wearing gas masks.

It was not only humans that needed protection from gas; horses and mules, which were the main means of transport, were also vulnerable to gas and needed to be provided with protection. As animals were never used near the front-line, protection from gas only became necessary when the practice of firing gas shells into rear areas was adopted.

For mustard gas, which did not need to be inhaled in order to inflict casualties, no effective countermeasure was ever found. The kilt-wearing Highland regiments of Scotland were especially vulnerable to mustard gas injuries due to their bare legs. At Nieuport some Scots battalions took to wearing women's tights beneath the kilt as a form of protection.

Missing image
Gas alert by Arthur Streeton, 1918.

Gas alert procedure became a routine for the front-line soldier. To warn of a gas attack, a bell would be rung, often made from a spent artillery shell. At the noisy batteries of the siege guns, a compressed air strombus horn was used, which could be heard nine miles away. Notices would be posted on all approaches to an affected area, warning people to take precautions.

Other British attempts at countermeasures were not so effective. An early plan was to use 100,000 fans to disperse the gas. Burning coal or carborundum dust was tried. A proposal was made to equip front-line sentries with diving helmets, air being pumped to them through a 100 ft (30 m) hose.

However, the effectiveness of all countermeasures is apparent. In 1915, when poison gas was relatively new, less than 3% of British gas casualties died. In 1916, the proportion of fatalities jumped to 17%. By 1918, the figure was back below 3%, though the total number of British gas casualties was now nine times the 1915 levels.

Delivery systems

Missing image
A British cylinder release at Montauban on the Somme, June 1916 — part of the preparation for the Battle of the Somme.

The first system employed for the mass delivery of gas involved releasing the gas from cylinders in a favourable wind such that it was carried over the enemy's trenches. The main advantage of this method was that it was relatively simple and, in suitable atmospheric conditions, produced a concentrated cloud capable of overwhelming the gas mask defences. The disadvantages of cylinder releases were numerous. First and foremost, delivery was at the mercy of the wind. If the wind was fickle, as was the case at Loos, the gas could backfire, causing friendly casualties. Gas clouds gave plenty of warning, allowing the enemy time to protect themselves, though many soldiers found the sight of a creeping gas cloud unnerving. Also gas clouds had limited penetration, only capable of affecting the front-line trenches before dissipating.

Finally, the cylinders had to be emplaced at the very front of the trench system so that the gas was released directly over no man's land. This meant that the cylinders had to be manhandled through communication trenches, often clogged and sodden, and stored at the front where there was always the risk that cylinders would be prematurely breached during a bombardment. A leaking cylinder could issue a telltale wisp of gas that, if spotted, would be sure to attract shellfire.

A British chlorine cylinder, known as an "oojah", weighed 190 lb (86 kg), of which only 60 lb (27 kg) was chlorine gas, and required two men to carry. Phosgene gas was introduced later in a cylinder, known as a "mouse", that only weighed 50 lb (23 kg).

Delivering gas via artillery shell overcame many of the risks of dealing with gas in cylinders. Gas shells were independent of the wind and increased the effective range of gas, making anywhere within reach of the guns vulnerable. Gas shells could be delivered without warning, especially the clear, nearly odourless phosgene — there are numerous accounts of gas shells, landing with a "plop" rather than exploding, being initially dismissed as dud HE or shrapnel shells, giving the gas time to work before the soldiers were alerted and took precautions.

Missing image
Loading a battery of Livens gas projectors.

The main flaw associated with delivering gas via artillery was the difficulty of achieving a killing concentration. Each shell had a small gas payload and an area would have to be subjected to a saturation bombardment to produce a cloud to match cylinder delivery. Mustard gas, however, did not need to form a concentrated cloud and hence artillery was the ideal vehicle for delivery of this battlefield pollutant.

The solution to achieving a lethal concentration without releasing from cylinders was the "gas projector", essentially a large-bore mortar that fired the entire cylinder as a missile. The British Livens projector (invented by Captain W.H. Livens in 1917) was a simple device; an 8-inch diameter tube sunk into the ground at an angle, a propellant was ignited by an electrical signal, firing the cylinder containing 30 or 40 lb (14 or 18 kg) of gas up to 1,900 metres. By arranging a battery of these projectors and firing them simultaneously, a dense concentration of gas could be achieved. The Livens was first used at Arras on 4 April, 1917. On 31 March, 1918 the British conducted their largest ever "gas shoot", firing 3,728 cylinders at Lens.

Unexploded weapons

Unexploded WWI ammunition, including chemical ammunition, was a major problem in former battle areas after the end of the War, and has ever since been present. Shells may be, for instance, uncovered when farmers plough their fields; more importantly, shells are regularly discovered when public works or construction work is done. While classical shells pose a risk of explosion, their disposal is relatively easy. It is not the case with chemical shells.

An additional difficulty is the current stringency of environmental legislation. In the past, a common method of getting rid of unexploded chemical ammunition was to detonate or dump it at sea; this is nowadays prohibited in most countries.

The problems are especially acute in some Northern regions of France. The French government no longer disposes of chemical weapons at sea. For this reason, piles of untreated chemical weapons accumulated. In 2001, it became evident that the pile stored at a depot in Vimy was unsafe; the inhabitants of the neighbouring town were evacuated, and the pile moved, using refrigerated trucks and under heavy guard, to a military camp in Suippes. [1] ( [2] ( The French government announced the construction of an automated plant for the dismantling of chemical munitions inherited from previous wars; this factory, codenamed SECOIA, is to be operational in 2007.[3] ( The capacity of the plant is meant to be 25 tons per year (extensible to 80 tons at the beginning), for a lifetime of 30 years.[4] (

In Belgium, a similar plant was planned in 1993 and brought in service in 1999, two years late, indicating the difficulties in disposal of such wastes. Germany, too, has to deal with unexploded ammunition and polluted lands resulting from the explosion of an ammunition train in 1919.[5] (

Gases used

A=Allies, C=Central Powers
Name First use Type Used by
Chlorine 1915 Irritant/Lung Both
Phosgene 1915 Irritant/Skin and mucous membranes, corrosive, toxic Both
Chloromethyl chloroformate 1915 Irritant/Eyes, skin, lungs Both
Trichloromethyl chloroformate 1916 Severe irritant, causes burns Both
Chloropicrin 1916 Irritant, lachrymatory, toxic Both
Stannic chloride 1916 Severe irritant, causes burns A
Chlorobenzene (Phenyl chloride) 1917 Irritant, lachrymatory C
Bis(chloromethyl) ether (Dichloromethyl ether) 1918 Irritant, can blur vision C
Diphenylchloroarsine (Diphenyl chlorasine) 1917 Irritant/Sternutatory C
Ethyldichlorarsine 1918 Vesicant C
N-ethylcarbazol 1918 Irritant C
Benzyl bromide 1915 Lachrymatory C
Xylyl bromide 1915 Lachrymatory, toxic C
Methyl chlorosulfonate 1915 C
Ethyl iodoacetate 1916 Lachrymatory A
Bromoacetone 1916 Lachrymatory, irritant Both
Methyl-ethyl ketone 1916 Irritant/Skin, eyes C
Acrolein 1916 Lachrymatory, toxic A
Hydrocyanic acid (Prussic acid) 1916 Paralysing A
Hydrogen sulfide (Sulphuretted hydrogen) 1916 Irritant, toxic A
Mustard gas 1917 Vesicant Both

Impact on World War II

In the Geneva Gas Protocol of the Third Geneva Convention, signed in 1925, the signatory nations agreed not to use poison gas in the future, stating "the use in war of asphyxiating, poisonous or other gases, and of all analogous liquids, materials or devices, has been justly condemned by the general opinion of the civilised world."

Nevertheless, precautions were taken in World War II. In both Axis and Allied nations, children in school were taught to wear gas masks in case of gas attack. Italy did use poison gas against Ethiopia in 1935 and 1936, and Japan used gas against China in 1941. Germany developed the poison gases tabun, sarin, and soman during the war, and, infamously, used Zyklon-B in Nazi extermination camps. Germany did not use any of these gases in combat, possibly heeding Allied warnings of awful retaliation.


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