Chemical weapons in World War I

The use of poison gas in World War I was a major military innovation. The gases ranged from disabling chemicals, such as tear gas and the severe mustard gas, to lethal agents like phosgene and chlorine. 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 4% 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. Because it was possible to develop effective countermeasures against gas attacks, it was unlike most other weapons of the period. In the later stages of the war, as the use of gas increased, its overall effectiveness diminished. This widespread use of these agents of chemical warfare, and wartime advances in the composition of high explosives, gave rise to an occasionally expressed view of World War I as "the chemists' war".

History of poison gas

1914: Tear gas

The early uses of chemicals as weapons were as a tear-inducing irritant ( lachrymatory), rather than fatal or disabling poisons. During the first World War, the French were the first to employ gas, using 26 mm grenades filled with tear gas ( ethyl bromoacetate) in August, 1914. The small quantities of tear gas delivered, roughly 19 cc per cartridge, were not even detected by the Germans. The stocks were rapidly consumed and by November a new order was placed by the French military. As bromine was scarce among the Entente allies, the active ingredient was changed to chloroacetone.

In October 1914, German troops fired fragmentation shells filled with a chemical irritant against British positions at Neuve Chapelle, though the concentration achieved was so small that it was barely noticed. None of the combatants considered the use of tear gas to be in conflict with the Hague Treaty of 1899, which prohibited the launching of projectiles containing asphyxiating or poisonous gas.

1915: Large scale use and lethal gases

Germany was the first to make large scale use of gas as a weapon when on 3 January, 1915, 18,000 artillery shells containing liquid xylyl bromide tear gas were fired on Russian positions on the Rawka River, west of Warsaw during the Battle of Bolimov. However, instead of vaporizing, the chemical froze, completely failing to have the desired effect.

The first killing agent employed by the German military was chlorine. German chemical companies BASF, Hoechst and Bayer (which formed the IG Farben conglomerate in 1925) had been producing chlorine as a by-product of their dye manufacturing. In cooperation with Fritz Haber of the Kaiser Wilhelm Institute for Chemistry in Berlin, they began developing methods of discharging chlorine gas against enemy trenches.

By 22 April, 1915, the German Army had 168 tons of chlorine deployed in 5,730 cylinders opposite Langemark-Poelkapelle, north of Ypres. At 17:00, in a slight easterly breeze, the gas was released, forming a gray-green cloud that drifted across positions held by French Colonial troops who broke ranks, abandoning their trenches and creating an 8,000 yard (4.5 km) gap in the Allied line. However, the German infantry were also wary of the gas and, lacking reinforcements, failed to exploit the break before Canadian and British reinforcements arrived. The Entente governments quickly claimed the attack was a flagrant violation of international law, but Germany argued that the Hague treaty had only banned chemical shells, rather than the use of gas projectors.

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

90 men died from gas poisoning in the trenches or before they could be got to a dressing station; of the 207 brought to the nearest dressing stations, 46 died almost immediately and 12 after long suffering.

Chlorine is a powerful irritant that can inflict damage to the eyes, nose, throat and lungs. At high concentrations and prolonged exposure it can cause death by asphyxiation.

Effectiveness and counter-measures

It quickly became evident that the men who stayed in their places suffered less than those who ran away, any movement worsened the effects of the gas, and those who stood up on the fire step suffered less—indeed they often escaped any serious effects—than those who lay down or sat at the bottom of a trench. Men who stood on the parapet suffered least, as the gas was denser near the ground. The worst sufferers were the wounded lying on the ground, or on stretchers, and the men who moved back with the cloud.

Chlorine was, however, less effective as a weapon than the Germans had hoped, particularly as soon as simple counter-measures were introduced. The gas 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 somewhat effective at reducing the effect of the gas. It was thought to be even more effective to use urine rather than water, as the ammonia would neutralize the chlorine, but it is now known that ammonia and chlorine can produce toxic fumes (NH₃ + Cl₂ —> HCl + NH₂Cl). Even if the chemistry had been correct, the amount of ammonia in human urine is extremely small. However, it was known at the time that chlorine reacted readily with urea (present in large amounts in urine) to form dichlorourea.

Chlorine required a concentration of 1,000 parts per million to be fatal, destroying tissue in the lungs, likely through the formation of hydrochloric (muriatic) acid when dissolved in the water in the lungs (2Cl₂ + 2H₂O → 4HCl + O₂). Despite its limitations, however, chlorine was an effective psychological weapon—the sight of an oncoming cloud of the gas was a continual source of dread for the infantry.

Counter-measures were quickly introduced in response to the use of chlorine gas. The Germans had issued their troops with small gauze pads filled with cotton waste, and bottles of a bicarbonate solution with which to dampen the pads. Immediately following the use of chlorine gas by the Germans, instructions were sent to British and French troops to hold wetted handkerchiefs or cloths over their mouths. Simple pad respirators similar to those issued to German troops were soon proposed by Lieut.-Colonel N.C. Ferguson, the A.D.M.S. of the 28th Division. These pads were intended to be used damp, preferably dipped into a solution of bicarbonate of soda kept in buckets for that purpose, though urine or other liquids were also used. Because such pads could not be expected to arrive at the front for several days, army divisions set about making them for themselves. The locally available muslin, flannel and gauze were used, and officers sent to Paris to buy additional quantities, and local French women were employed making up rudimentary pads with string ties. Other units used lint bandages manufactured in the convent at Poperinge. Pad respirators were sent up with rations to British troops in the line as early as the evening of April 24.

In Britain the Daily Mail newspaper encouraged women to manufacture cotton pads, and within one month a variety of pad respirators were available to British and French troops, along with motoring goggles to protect the eyes. By 6 July 1915, the entire British army was equipped with the far more effective "smoke helmet" designed by Major Cluny McPherson, Newfoundland Regiment, which was a flannel bag with a celluloid window, which entirely covered the head. The race was then on between the introduction of new and more effective poison gases and the production of effective counter-measures, which marked gas warfare until November 1918.

British gas attacks

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 (officially) said of gas:

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.

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 (140 tons arrayed in 5,100 cylinders), and the attack was dependent on a favorable 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 British Army had realized that the use of gas was needed, and mounted more gas attacks than the Germans in 1917 and 1918 due to marked increase in production of gas from the Allied nations. Germany was unable to keep up with this pace despite creating various new gases for use in battle, mostly due to very costly methods of production. Entry into the war by the United States allowed the Allies to increase mustard gas production far more than Germany. Also the prevailing wind on the Western Front was from the west, which meant the British more frequently had favorable conditions for a gas release than the Germans.

1915: More deadly gases

The deficiencies of chlorine were overcome with the introduction of phosgene, first used by France under the direction of French chemist Victor Grignard in 1915. Colorless and having an odour likened to "mouldy hay," phosgene was difficult to detect, making it a more effective weapon. Although phosgene was sometimes used on its own, it was more often used mixed with an equal volume of chlorine, the chlorine helping to spread the denser phosgene. The Allies called this combination White Star after the marking painted on shells containing the mixture.

Phosgene was a potent killing agent, deadlier than chlorine. It had a potential drawback in that some of the symptoms of exposure took 24 hours or more to manifest. This meant that the victims were initially still capable of putting up a fight; although this could also mean that apparently fit troops would be incapacitated by the effects of the gas on the following day.

In the first combined chlorine/phosgene attack by Germany, against British troops at Nieltje near Ypres, Belgium on 19 December 1915, 88 tons of the gas were released from cylinders causing 1069 casualties and 69 deaths. The British P gas helmet, issued at the time, was impregnated with phenate hexamine and partially effective against phosgene. The modified PH Gas Helmet, which was additionally impregnated with hexamethylenetetramine to improve the protection against phosgene, was issued in January 1916.

Around 36,600 tons of the gas were manufactured during the war, out of a total of 190,000 tons for all chemical weapons, making it second only to chlorine (93,800 tons) in the quantity manufactured:

• Germany 18,100 tons
• France 1,125,700 tons
• United Kingdom 1,400 tons (although they also used French stocks)
• United States 1,400 tons (although they also used French stocks)

Although it was never as notorious in public consciousness as mustard gas, it killed far more people, about 85% of the 100,000 deaths caused by chemical weapons during World War I.

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

1917: The Mustard gas

The most widely reported and, perhaps, the most 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. The Germans marked their shells yellow for mustard gas and green for chlorine and phosgene, so they called the new gas Yellow Cross. It was known to the British as HS (Hun Stuff), while the French called it Yperite (named after Ypres).

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. Once in the soil, mustard gas remained active for several days, weeks or even months, depending on the weather conditions.

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. Gas was employed primarily on the Western Front — 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 skin of victims of mustard gas blistered, their eyes became very sore and they began to vomit. Mustard gas caused internal and external bleeding and attacked the bronchial tubes, stripping off the mucous membrane. This was extremely painful and most soldiers had to be strapped to their beds. It usually took a person four or five weeks to die of mustard gas exposure.

One nurse, Vera Brittain, 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."

Near the end of the war, the United States began large scale production of an improved vesicant gas known as Lewisite, for use in an offensive planned for the spring of 1919. By the time of the armistice on November 11, a plant in Ohio was producing 10 tons per day of the substance, for a total of about 150 tons. It is uncertain what effect this new chemical would have had on the battlefield, however, as it degrades in moist conditions.

Post-war

By the end of the war, chemical weapons had lost much of their effectiveness against well trained and equipped troops. At that time, chemical weapon agents were used in one quarter of artillery shells fired but caused only 3% of casualties.

Nevertheless, in the following years, chemical weapons were used in several, mainly colonial, wars where one side had an advantage in equipment over the other. The British used adamsite against Russian revolutionary troops in 1919 and mustard against Iraqi insurgents in the 1920s; Spain used chemical weapons in Morocco against Rif tribesmen throughout the 1920s and Italy used mustard gas in Libya in 1930 and again during its invasion of Ethiopia in 1936. In 1925, a Chinese warlord, Zhang Zuolin, contracted a German company to build him a mustard gas plant in Shenyang, which was completed in 1927.

Public opinion had by then turned against the use of such weapons, which led to the Geneva Protocol, a treaty banning the use (but not the stockpiling) of lethal gas and bacteriological weapons which was signed by most First World War combatants in 1925. Most countries that signed ratified it within around five years, although a few took much longer – Brazil, Japan, Uruguay and the United States did not do so until the 1970s, and Nicaragua ratified it only in 1990.

Although all major combatants stockpiled chemical weapons during the Second World War, the only reports of its use in the conflict were the Japanese use of relatively small amounts of mustard gas and lewisite in China, and very rare occurrences in Europe (for example some sulfur mustard bombs were dropped on Warsaw on 3 September 1939, which Germany acknowledged in 1942 but indicated that it had been accidental). Mustard gas was the agent of choice, with the British stockpiling 40,719 tons, the Russians 77,400 tons, the Americans over 87,000 tons and the Germans 27,597 tons.

The mustard gas with which the British hoped to repel an invasion of the United Kingdom in 1940 was never needed, and a fear that the Allies also had nerve agents (in fact the Allies were not aware of them until the discovery of German stockpiles) prevented their deployment by Germany. Nevertheless poison gas technology played an important role in the Holocaust.

Although chemical weapons have been used in at least a dozen wars since the end of the First World War, they have never been used again in combat on such a large scale. Nevertheless, the use of mustard gas and the more deadly nerve agents by Iraq during the 8-year Iran-Iraq war killed around 20,000 Iranian troops (and injured another 80,000), around a quarter of the number of deaths caused by chemical weapons during the First World War.

Casualties

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 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.

— 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 liters) of yellow liquid from the lungs each hour for the 48 of the drowning spasms."

A common fate of those exposed to gas was blindness, chlorine gas or mustard gas being the main causes. 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. (The gasses used during that battle ( tear gas) caused temporary blindness and/or a painful stinging in the eyes. These bandages were normally water-soaked to provide a rudimentary form of pain relief to the eyes of casualties before they reached more organized medical help.)

Estimated gas casualties

Nation	Fatal	Non-fatal
Russia	56,000	419,340
Germany	9,000	200,000
France	8,000	190,000
British Empire (includes Canada)	8,109	188,706
Austria-Hungary	3,000	100,000
USA	1,462	72,807
Italy	4,627	60,000
Total	88,498	1,240,853

Mustard gas caused the most gas casualties on the Western Front, despite being produced in smaller quantities than inhalant 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 the third battle of 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 eyes, nose, armpits and groin, since it dissolved in the natural moisture of those areas. 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 (fever), and pneumonia (from blistering in the lungs).

Death by mustard gas, when it came, was dreadful. A postmortem 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 forces 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 sulfa drugs became widely available for its treatment.

One notable poison gas casualty of the Great War was Adolf Hitler, who was temporarily blinded. As a result, Hitler adamantly refused to authorise the use of poison gas on the battlefield during World War II, for fear of retaliation. However, poison gas agents such as carbon monoxide and Zyklon B were extensively used against civilians in extermination camps.

Countermeasures

None of the First World War's 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 Second 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 crystallize 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.

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 neutralize the gas — however, the chemical would wash out into the soldier's eyes whenever it rained. 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 sodium hyposulfite (commonly known as "hypo"). The British P gas helmet, partially 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 P 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.

A modified version of the P Helmet, called the PH Helmet, was issued in January 1916, and was additionally impregnated with hexamethylenetetramine to improve the protection against phosgene.

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 rubberized 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.

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 found during the war. The kilt-wearing Scottish regiments were especially vulnerable to mustard gas injuries due to their bare legs. At Nieuwpoort in Flanders some Scots battalions took to wearing women's tights beneath the kilt as a form of protection.

The Canadian soldiers are said to have found a way to minimize the effects of the mustard gas. Since the gas was sent by the wind towards them, they understood that it would minimize the exposure to the gas if the Canadians not only did not flee but ran through the gas. The French, conversely, when the gas was first used against them, fled, and therefore spent more time in the gas, suffering greater casualties.

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 (14 km) 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

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. The Germans, for example, used 5.9-inch (150 mm) artillery shells. 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 odorless 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.

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 (200 mm) 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 meters. 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

Over 16,000,000 acres (65,000 km²) of France had to be cordoned off at the end of the war because of unexploded ordnance. About 20% of the chemical shells were duds, and approximately 13 million of these munitions were left in place. This has been a serious problem in former battle areas from immediately after the end of the War until the present. Shells may be, for instance, uncovered when farmers plough their fields (termed the ' iron harvest'), and are also regularly discovered when public works or construction work is done.

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 neighboring town were evacuated, and the pile moved, using refrigerated trucks and under heavy guard, to a military camp in Suippes. 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.

Germany has to deal with unexploded ammunition and polluted lands resulting from the explosion of an ammunition train in 1919.

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
a-Chlorotoluene (Benzyl chloride)	1917	Irritant, lachrymatory	C
Bis(chloromethyl) ether (Dichloromethyl ether)	1918	Irritant, can blur vision	C
Diphenylchloroarsine (Diphenyl chlorasine)	1917	Irritant/Sternutatory	C
Ethyldichloroarsine	1918	Vesicant	C
N-Ethylcarbazole	1918	Irritant	C
Benzyl bromide	1915	Lachrymatory	C
Xylyl bromide	1914	Lachrymatory, toxic	Both
Ethyl iodoacetate	1916	Lachrymatory	A
Bromoacetone	1916	Lachrymatory, irritant	Both
Bromomethyl ethyl ketone	1916	Irritant/Skin, eyes	C
Acrolein	1916	Lachrymatory, toxic	A
Hydrocyanic acid (Prussic acid)	1916	Paralyzing	A
Hydrogen sulfide (Sulphuretted hydrogen)	1916	Irritant, toxic	A
Mustard gas (Bis(2-chloroethyl) sulfide)	1917	Vesicant (blistering agent)	Both

Effect 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 the Empire of 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. Neither Germany nor the Allied nations used any of their war gases in combat, despite maintaining large stockpiles and occasional calls for their use, possibly heeding warnings of awful retaliation.