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. 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 to 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
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. 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.

1914: tear gas
Germany was the first to make large scale use of gas as a weapon. On 3 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. However, instead of vaporizing, the chemical froze, completely failing to have the desired effect.

1915: large scale use and lethal gases
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."

British gas attacks
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 odor 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.
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.

Germany 18,100 tons
France 15,700 tons
United Kingdom 1,400 tons (although they also used French stocks)
United States 1,400 tons (although they also used French stocks) 1915: more deadly gases
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.

Post-war
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. It is a frequent misconception that lines of blinded soldiers, hand on the shoulder of the man in front, being guided by a sighted man to a dressing station were a frequent spectacle. 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. However, 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.
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." However, poison gas agents such as carbon monoxide and Zyklon B were extensively used against civilians in extermination camps.

Casualties
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 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."
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 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.





Countermeasures
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 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 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.

Delivery systems
Unexploded WWI ammunition, including chemical ammunition, 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, and are also regularly discovered when public works or construction work is done. While classical shells pose a risk of explosion, their disposal is relatively easy.

Unexploded weapons

Effect on World War II