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, however, was limited – only four percent of combat deaths were due to gas. Because it was possible to develop effective countermeasures against attacks, gas 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".
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 cm³ 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 until they could not defend themselves. 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.
Germany was the first to make large-scale use of gas as a weapon when on 31 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 and failed 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.
According to the fieldpost letter of Major Karl von Zingler, the first chlorine gas attack of German military should have been before 2 January 1915: "In other war theaters it does not go better and it has been said that our Chlorine is very effective. 140 English officers have been killed. This is a horrible weapon...".
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 from Martinique who broke ranks, 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, lacking reinforcements, failed to exploit the break before the First Canadian Division and assorted French troops reformed the line in scattered, hastily prepared positions 1,000 to 3,000 yards apart. 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.
Germany used chemical weapons on the eastern front in an attack at Rawka, south of Warsaw. The Russian army took 9,000 casualties, with more than 1,000 fatalities. In response, the artillery branch of the Russian army organized a commission to study the delivery of poison gas in shells.
It quickly became evident that the men who stayed in their places suffered less than those who ran away, as any movement worsened the effects of the gas, and that 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 it was known at the time that chlorine reacted readily with urea (present 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 acid when dissolved in the water in the lungs (2Cl 2 + 2H 2 O → 4HCl + O 2 ). 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. The Germans 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, picurs were sent to British and French troops to hold wet 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 kept in buckets for that purpose, though 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 24 April.
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. The response was enormous and a million gas masks were produced in a day. Unfortunately, the Mail' s design was useless when dry and caused suffocation when wet—the respirator was responsible for the deaths of scores of men. By 6 July 1915, the entire British army was equipped with the far more effective "smoke helmet" designed by Major Cluny MacPherson, 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 the armistice in November 1918.
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 , w