Editing Chemical weapons in World War I (section)

==Use of poison gas==
{{Further|Technology during World War I}}

===1914: Tear gas===
The most frequently used chemicals during World War I were [[Tear gas|tear-inducing irritants]] rather than fatal or disabling poison. During [[World War I]], the [[French Army in World War I|French Army]] was the first to employ tear gas, using 26&nbsp;mm [[grenade]]s filled with [[ethyl bromoacetate]] in August 1914. The small quantities of gas delivered, roughly {{Cvt|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 [[Triple Entente|Entente]] allies, the active ingredient was changed to [[chloroacetone]].<ref>{{Cite book
 | first=Ludwig Fritz | last=Haber | year=1986
 | title=The Poisonous Cloud: Chemical Warfare in the First World War
 | publisher=Oxford University press
 | isbn=0-19-858142-4 }}</ref>

In October 1914, German troops fired [[fragmentation (weaponry)|fragmentation]] [[shell (projectile)|shell]]s filled with a chemical irritant against British positions at [[Battle of Neuve Chapelle|Neuve Chapelle]]; the concentration achieved was so small that it too was barely noticed.<ref name="heller84">{{Cite journal
 | last=Heller | first=Charles E
 | date=September 1984
 | url=http://purl.access.gpo.gov/GPO/LPS58603
 | title=Chemical Warfare in World War I: The American Experience, 1917–1918
 | journal=Leaveanworth Papers
 | issue = 10
 | publisher=US Army Command and General Staff College
 }}</ref>
None of the combatants considered the use of tear gas to be in conflict with the Hague Treaty of 1899, which specifically prohibited the launching of projectiles containing [[asphyxia]]ting or poisonous gas.<ref>{{Cite book
 | first=L. B. | last=Taylor |author2=Taylor, C. L.
 | year=1992 | title=Chemical and Biological Warfare
 | edition=Revised | publisher=Franklin Watts
 | isbn=0-531-13029-0 }}</ref>

===1915: Large-scale use and lethal gases===
[[File:Russian Red Cross nurses tending gassed Russians brought in direct from trenches on stretchers 1915.jpg|thumb|alt=People laid out on stretchers|Russian Red Cross nurses tend to gassed Russians brought from the front lines, 1915]]

The first instance of large-scale use of gas as a weapon was on 31 January 1915, when Germany fired 18,000 [[artillery]] shells containing liquid [[xylyl bromide]] tear gas on [[Imperial Russian Army|Russian positions]] on the [[Rawka River]], west of [[Warsaw]] during the [[Battle of Bolimov]]. Instead of vaporizing, the chemical froze and failed to have the desired effect.<ref name="heller84" />

The first killing agent was [[chlorine]], used by the German Army.<ref>{{cite journal|last1=Van der Kloot |first1=W. |s2cid=145243958 |title=April 1915: Five Future Nobel Prize-winners inaugurate weapons of mass destruction and the academic-industrial-military complex |journal=[[Notes and Records]] |date=2004 |volume=58 |issue=2 |pages=149–260 |doi=10.1098/rsnr.2004.0053 }}</ref> 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 [[asphyxia]]tion.<ref>{{Cite book
 |author1=Romano, James A. |author2=Lukey, Brian J. |author3=Salem, Harry | title=Chemical warfare agents: chemistry, pharmacology, toxicology, and therapeutics | edition=2nd | page=5
 | publisher=CRC Press | year=2007 | isbn=978-1-4200-4661-8 }}</ref> German chemical companies [[BASF]], [[Hoechst AG|Hoechst]] and [[Bayer]] (which formed the [[IG Farben]] conglomerate in 1925) had been making chlorine as a by-product of their dye manufacturing.<ref>{{Cite web
 |author1=Legg, J. |author2=Parker, G. | year=2002
 | url=http://www.greatwar.co.uk/westfront/ypsalient/secondypres/prelude/gasdev.htm
 | title=The Germans develop a new weapon: the gas cloud
 | publisher=The Great War | access-date=6 August 2007 }}</ref> In cooperation with [[Fritz Haber]] of the [[Kaiser Wilhelm Institute]] for Chemistry in [[Berlin]], they began developing methods of discharging chlorine gas against enemy [[trench]]es.<ref name="Haber">{{cite web|title=Fritz Haber|url=https://www.sciencehistory.org/historical-profile/fritz-haber|website=Science History Institute|access-date=20 March 2018|date=June 2016}}</ref><ref>{{Cite book | first=Werner | last=Abelshauser | year=2003 | title=German Industry and Global Enterprise, BASF: The History of a Company | publisher=Cambridge University Press | isbn=0-521-82726-4 | url=https://archive.org/details/germanindustrygl00wern }}</ref>

It may appear from a ''feldpost'' letter of Major Karl von Zingler that the first chlorine gas attack by German forces took place before 2 January 1915: "In other war theatres 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&nbsp;...".<ref>{{Cite journal | last=Aksulu | first=N. Melek | title=Die Feldpostbriefe Karl v. Zinglers aus dem Ersten Weltkrieg | journal=Nobilitas, Zeitschrift für deutsche Adelsforschung | date=May 2006 | volume=IX | issue=41 | page=57 | url=http://perweb.firat.edu.tr/personel/yayinlar/fua_241/241_26862.pdf | access-date=28 December 2008 | quote=Rousselare 2 Januar 15&nbsp;... Auf anderen Kriegsschauplätzen ist es ja auch nicht besser und die Wirkung von unserem Chlor soll ja sehr gut sein. Es sollen 140 englische Offiziere erledigt worden sein. Es ist doch eine furchtbare Waffe&nbsp;... | url-status=dead | archive-url=https://web.archive.org/web/20090305060856/http://perweb.firat.edu.tr/personel/yayinlar/fua_241/241_26862.pdf | archive-date=5 March 2009 }}</ref>  This letter must be discounted as evidence for early German use of chlorine, however, because the date "2 January 1915" may have been hastily scribbled instead of the intended "2 January 1916," the sort of common typographical error that is often made at the beginning of a new year. The deaths of so many English officers from gas at this time would certainly have been met with outrage, but a recent, extensive study of British reactions to chemical warfare says nothing of this supposed attack.<ref>{{Cite book
 | first=Marion | last=Girard | year=2008
 | title=A Strange and Formidable Weapon: British Responses to World War I Poison Gas
 | publisher=University of Nebraska Press
 | isbn=978-0-8032-2223-6 }}</ref> Perhaps this letter was referring to the chlorine-phosgene attack on British troops at [[Wieltje]] near Ypres, on 19 December 1915 (see below).

By 22 April 1915, the [[German Army in World War I|German Army]] had 167 [[ton]]s of chlorine deployed in 5,730 cylinders from [[Langemark-Poelkapelle]], north of [[Ypres]]. At 17:30, in a slight easterly breeze, the liquid chlorine was siphoned from the tanks, producing gas which formed a grey-green cloud that drifted across positions held by troops of the [[45th Infantry Division (France)]], specifically the 1st [[Tirailleurs]] and the 2nd [[Zouaves]] from Algeria.<ref>General R. Huré, ''L'Armee d'Afrique 1830–1962'', Charles-Lavauzelle, 1972, p. 283.</ref> Faced with an unfamiliar threat these troops broke ranks, abandoning their trenches and creating an {{convert|8,000|yd|km|adj=on}} gap in the Allied line. The German infantry were also wary of the gas and, lacking reinforcements, failed to exploit the break before the [[1st Canadian Division]] and assorted French troops reformed the line in scattered, hastily prepared positions {{convert|1000|–|3000|yd|m}} apart.<ref name="heller84" /> The Entente governments 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.<ref>{{Cite book | first=Jonathan B. | last=Tucker | year=2006 | title=War of Nerves: Chemical Warfare from World War I to Al-Queda | publisher=Pantheon Books | isbn=0-375-42229-3 | url=https://archive.org/details/warofnerveschemi00tuck }}</ref>

In what became the [[Second Battle of Ypres]], the Germans used gas on three more occasions; on 24 April against the 1st Canadian Division,<ref>{{Cite web
 | author=Staff
 | date=29 July 2004
 | url=http://www.vac-acc.gc.ca/remembers/sub.cfm?source=history/firstwar/canada/Canada4
 | title=On the Western Front: Ypres 1915
 | publisher=Veteran Affairs Canada
 | access-date=8 April 2008
 | archive-url=https://web.archive.org/web/20081206024237/http://www.vac-acc.gc.ca/remembers/sub.cfm?source=history%2Ffirstwar%2Fcanada%2FCanada4
 | archive-date=6 December 2008
 | url-status=dead
 }}</ref> on 2 May near Mouse Trap Farm and on 5 May against the British at [[Battle of Hill 60 (Western Front)|Hill 60]].<ref>{{Cite book
 | first=Victor | last=Lefebure |author2=Wilson, Henry
 | title=The Riddle of the Rhine: Chemical Strategy in Peace and War
 | year=2004 | publisher=Kessinger Publishing | isbn=1-4179-3546-4 }}</ref> 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."<ref>Edmonds and Wynne (1927): p. 289.</ref>

On 6 August, German troops under Field Marshal [[Paul von Hindenburg]] used chlorine gas against Russian troops defending [[Osowiec Fortress]]. Surviving defenders drove back the attack and retained the fortress. The event would later be called the [[Attack of the Dead Men]].

Germany used chemical weapons on the [[Eastern Front (World War I)|Eastern Front]] in an attack at [[Rawka (river)]], west of Warsaw. The [[Imperial Russian Army|Russian Army]] took 9,000 casualties, with more than 1,000 fatalities. In response, the artillery branch of the Russian Army organised a commission to study the delivery of poison gas in shells.<ref name="sic15">{{Cite journal |last=Kojevnikov |first=A. |date=June 2002 | title=The Great War, the Russian Civil War, and the Invention of Big Science |journal=Science in Context |volume=15 |issue=2 |pages=239–275 | url=https://www.history.ubc.ca/documents/BigScience2002.pdf |pmid=12467271 |doi=10.1017/S0269889702000443 |s2cid=23740816 |access-date=11 October 2009 |archive-url=https://web.archive.org/web/20120613102624/https://www.history.ubc.ca/documents/BigScience2002.pdf |archive-date=13 June 2012 |url-status=dead}}</ref>

====Effectiveness and countermeasures====
[[File:Nach Gasangriff 1917.jpg|thumb|British emplacement after German gas attack (probably phosgene)]]

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.<ref>Edmonds and Wynne (1927): pp.&nbsp;177–178.</ref> Chlorine was less effective as a weapon than the Germans had hoped, particularly as soon as simple countermeasures 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 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 with [[urea]] (present in urine) to form dichloro urea.<ref>For example, see: {{Cite journal
 | last=Chattaway | first=Frederick Daniel
 | date=22 December 1908
 | title=The Action of Chlorine upon Urea Whereby a Dichloro Urea is Produced
 | journal=Proceedings of the Royal Society of London
 | volume=81
 | issue=549 | pages=381–388 |  doi=10.1098/rspa.1908.0094
| jstor=93011| bibcode=1908RSPSA..81..381C| doi-access=free}}</ref>

Chlorine required a concentration of 1,000 parts per million to be fatal, destroying [[Biological tissue|tissue]] in the lungs, likely through the formation of [[hypochlorous acid#Formation, stability and reactions|hypochlorous and hydrochloric acids]] when dissolved in the water in the lungs.<ref>{{Cite web
 | last=O'Leary | first=Donal | year=2000
 | url=http://www.ucc.ie/academic/chem/dolchem/html/elem/elem017.html
 | title=Chlorine | publisher=University College Cork
 | access-date=2 August 2007 }}</ref> Despite its limitations, chlorine was an effective psychological weapon—the sight of an oncoming cloud of the gas was a continual source of dread for the infantry.<ref>{{Cite journal|author1=Jones, E. |author2=Everitt, B. |author3=Ironside, S. |author4=Palmer, I. |author5=Wessely, S. | title=Psychological effects of chemical weapons: a follow-up study of First World War veterans
 | journal=Psychological Medicine | volume=38 | issue=10
 | pages=1419–1426 | pmid=18237455| year=2008| doi=10.1017/S003329170800278X|s2cid=2448895 }}</ref>

[[File:A sentry watching for any sign of gas attacks. He is squatting beside a notice which reads, 'gas gong'. The gong appears to be a large metal drum, like an oil drum. The drumstick is hanging from a (4687961895).jpg|thumb|right|A sentry stands watch next to a "gas gong".]]

Countermeasures 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 [[Sodium bicarbonate|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 wet handkerchiefs or cloths over their mouths. Simple pad respirators similar to those issued to German troops were soon proposed by Lieutenant-Colonel N. C. Ferguson, the Assistant Director Medical Services of the [[28th Division (United Kingdom)|28th Division]]. These pads were intended to be used damp, preferably dipped into a solution of bicarbonate kept in buckets for that purpose; 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. Locally available muslin, flannel and gauze were used, officers were sent to [[Paris]] to buy more 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.<ref name="ew217" />

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. The ''Mail''{{'}}s design was useless when dry and caused suffocation when wet—the respirator was responsible for the deaths of scores of men.{{Citation needed|date=September 2021}} By 6 July 1915, the entire British army was equipped with the more effective "[[Hypo helmet|smoke helmet]]" designed by Major [[Cluny Macpherson (physician)|Cluny MacPherson]], [[Royal Newfoundland Regiment|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 countermeasures, which marked gas warfare until the armistice in November 1918.<ref name="ew217">Edmonds and Wynne (1927): p. 217.</ref>

====British gas attacks====
The British expressed outrage at Germany's use of poison gas at Ypres and responded by developing their own gas warfare capability. The commander of [[II Corps (United Kingdom)|II Corps]], [[Sir Charles Fergusson, 7th Baronet|Lieutenant General Sir Charles Ferguson]], said of gas:

{{Blockquote |It is a cowardly form of warfare which does not commend itself to me or other English soldiers&nbsp;... 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.<ref>{{Cite book
 | author=Cook, Tim
 | year=1999
 | title=No Place to Run: The Canadian Corps and Gas Warfare in the First World War
 | publisher=UBC Press
 | page=37 | isbn=0-7748-0740-7}}</ref>}}

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 favourable wind. 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.<ref name="heller84" /> This was compounded when the gas could not be released from all the British canisters because the wrong turning keys were sent with them. Subsequent retaliatory German shelling hit some of those unused full cylinders, releasing gas among the British troops.<ref>{{Cite journal | publisher = First World War | journal =  Weaponry | url = http://www.firstworldwar.com/weaponry/gas.htm | title = Gas }}</ref> Exacerbating the situation were the primitive flannel gas masks distributed to the British. The masks got hot, and the small eye-pieces misted over, reducing visibility. Some of the troops lifted the masks to get fresh air, causing them to be gassed.<ref>{{cite book
 | first=Philip | last=Warner | year=2000
 | title=The Battle of Loos | page=37
 | series=Wordsworth Military Library
 | publisher=Wordsworth Editions | isbn=1-84022-229-8
 | url=https://books.google.com/books?id=OClz6xxwgCUC&pg=PA37 }}</ref>

<gallery widths="200px" heights="135px">
File:British infantry advancing at Loos 25 September 1915.jpg|British infantry advancing through gas at [[Battle of Loos|Loos]], 25 September 1915
File:World War I, British soccer team with gas masks, 1916.jpg|Football team of British soldiers with gas masks, Western front, 1916
File:Englische Gasbomben.jpg|A British gas bomb from 1915
</gallery>

===1915: More deadly gases===
[[File:American Red Cross and Medical Research Committee, "An Atlas of Gas Poisoning" plate I (square).jpg|thumb|Microscopic section of human lung from phosgene shell poisoning from ''An Atlas of Gas Poisoning'', 1918]]

The deficiencies of chlorine were overcome with the introduction of [[phosgene]], which was prepared by a group of French chemists led by [[Victor Grignard]] and first used by France in 1915.<ref>{{Cite book
 | first=Mary Jo | last=Nye | year=1999 | page=193
 | title=Before big science: the pursuit of modern chemistry and physics, 1800–1940 | publisher=Harvard University Press
 | isbn=0-674-06382-1 }}</ref> Colourless and having an odour likened to "mouldy hay," phosgene was difficult to detect, making it a more effective weapon. Phosgene was sometimes used on its own, but was more often used mixed with an equal volume of chlorine, with the chlorine helping to spread the denser phosgene.<ref name="cbwinfo">{{Cite web | author=Staff | year=2004 | url=http://cbwinfo.com/Chemical/Pulmonary/CG.shtml | title=Choking Agent: CG | publisher=CBWInfo | access-date=30 July 2007 | url-status=dead | archive-url=https://web.archive.org/web/20070814054640/http://cbwinfo.com/Chemical/Pulmonary/CG.shtml | archive-date=14 August 2007 }}</ref> The Allies called this combination ''White Star'' after the marking painted on shells containing the mixture.<ref>{{Cite book
 | author=Kiester, Edwin | title=An Incomplete History of World War I
 | page=74 | volume=1 | publisher=Murdoch Books | year=2007
 | isbn=978-1-74045-970-9 |display-authors=etal}}</ref> German phosgene came in the form of diphosgene, codenamed ''Grün Kreuz'' (Green cross). This was less effective than its allied counterpart, being less toxic and slower to evaporate, but was easier to handle in shell manufacture early in the war.{{sfn|Haber|2002|pp=86-87}}

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; this could also mean that apparently fit troops would be incapacitated by the effects of the gas on the following day.<ref>{{Cite web | author=Staff | date=22 February 2006 | url=http://www.bt.cdc.gov/agent/phosgene/basics/facts.asp | title=Facts About Phosgene | publisher=CDC | access-date=23 May 2008 | url-status=dead | archive-url=https://web.archive.org/web/20030417022453/http://www.bt.cdc.gov/agent/phosgene/basics/facts.asp | archive-date=17 April 2003 }}</ref>

In the first combined chlorine–phosgene attack by Germany, against British troops at [[Wieltje]] near Ypres, Belgium on 19 December 1915, 88 tons of the gas were released from cylinders causing 1069 casualties and 69 deaths.<ref name="cbwinfo" /> The British P gas helmet, issued at the time, was impregnated with [[sodium phenolate]] and partially effective against phosgene. The modified [[PH helmet|PH Gas Helmet]], which was impregnated with phenate hexamine and [[hexamethylene tetramine]] (urotropine) to improve the protection against phosgene, was issued in January 1916.<ref name="cbwinfo" /><ref>{{Cite book
 | first=Ludwig Fritz | last=Haber | year=1986
 | title=The poisonous cloud: chemical warfare in the First World War | page=70 | publisher=Oxford University Press
 | isbn=0-19-858142-4 }}</ref><ref>{{Cite book
 | first=Pradyot | last=Patnaik | year=2007
 | title=A comprehensive guide to the hazardous properties of chemical substances | page=85 | edition=3rd
 | publisher=Wiley-Interscience | isbn=978-0-471-71458-3 }}</ref>

Around 36,600 tons of phosgene were manufactured during the war, out of a total of 190,000 tons for all [[chemical weapon]]s, making it second only to chlorine (93,800 tons) in the quantity manufactured:<ref>{{cite web|url=http://www.mitretek.org/mission/envene/chemical/history/ww1.html |title=A Short History of Chemical Warfare During World War I |access-date=18 September 2013 |archive-url=https://web.archive.org/web/19991023051711/http://www.mitretek.org/mission/envene/chemical/history/ww1.html |archive-date=23 October 1999 }}</ref>

* Germany 18,100 tons
* France 15,700 tons
* United Kingdom 1,400 tons (also used French stocks)
* United States 1,400 tons (also used French stocks)

===1916: Austrian use===
[[File:WWI - Monte San Michele - 29th June 1916 Italian casualties after a gas attack.jpg|thumb|right|Italian dead after the Austrian gas attack on Monte San Michele]]

On 29 June 1916, the [[Austro-Hungarian Army]] attacked the [[Royal Italian Army]]'s [[Brigade "Ferrara"]] on [[Monte San Michele]] with a mix of  [[phosgene]] and [[chlorine]] gas.<ref>Rauchensteiner, Manfried, ''The First World War and the End of the Habsburg Monarchy, 1914–1918'' (Vienna, Austria: Böhlau Verlag, 2014), [https://books.google.com/books?id=ZEpLBAAAQBAJ&pg=PA543 pp. 543–544.]</ref> Thousands of Italian soldiers died in this first chemical weapons attack on the [[Italian Front (World War I)|Italian Front]].

===1917: Mustard gas===
[[File:American Red Cross and Medical Research Committee, "An Atlas of Gas Poisoning" plate X (square).jpg|thumb|Microscopic section of human lung from mustard gas poisoning from ''An Atlas of Gas Poisoning'', 1918]]

The most widely reported chemical agent of the First World War was [[mustard gas]]. Despite the name it is not a gas but a volatile oily liquid, and is [[Dispersion (chemistry)|dispersed]] as a fine mist of liquid droplets.<ref name="acs">{{Cite journal |last=Tinnesand |first=Michael |date=April 2005 |title=Mustard Gas |url=https://www.acs.org/content/dam/acsorg/education/resources/highschool/chemmatters/gc-mustard-gas-personal-safety-and-natl-security.pdf |journal=ChemMatters |via=American Chemical Society}}</ref> It was introduced as a [[vesicant]] by Germany on July 12, 1917, weeks prior to the [[Third Battle of Ypres]].<ref name="heller84" /><ref>{{Cite book |last1=Fries |first1=Amos A. (Amos Alfred) |url=http://archive.org/details/chemicwar00frierich |title=Chemical Warfare |last2=West |first2=Clarence J. (Clarence Jay) |date=1921 |publisher=New York [etc.] McGraw-Hill Book Company, inc. |others=University of California Libraries |pages=176}}</ref> The Germans marked their shells yellow for mustard gas and green for chlorine and phosgene; hence they called the new gas ''Yellow Cross''. It was known to the British as ''HS'' (''Hun Stuff''), and the French called it ''Yperite'' (named after [[Ypres]]).<ref>{{Cite book
 | first=Steven L.
 | last=Hoenig
 | year=2002
 | title=Handbook of Chemical Warfare and Terrorism
 | publisher=Greenwood Press
 | location=Westport, Connecticut
 | isbn=0-313-32407-7
 | url=https://archive.org/details/handbookofchemic0000hoen
 }}</ref>

[[File:mustard gas burns.jpg|thumb|left|A Canadian soldier with mustard gas burns, 1917/1918]]

Mustard gas is not an effective killing agent (though in high enough doses it is fatal) but can be used to harass and disable the enemy and pollute the battlefield. Delivered in artillery shells, mustard gas was heavier than air, and it settled to the ground as an oily liquid. Once in the soil, mustard gas remained active for several days, weeks, or even months, depending on the weather conditions.<ref>{{Cite web
 |author=Staff
 |date=22 February 2006
 |url=http://www.bt.cdc.gov/agent/sulfurmustard/basics/facts.asp
 |title=Facts About Sulfur Mustard
 |publisher=Centers for Disease Control and Prevention
 |access-date=10 August 2006
 |url-status=dead
 |archive-url=https://web.archive.org/web/20060809143200/http://www.bt.cdc.gov/agent/sulfurmustard/basics/facts.asp
 |archive-date=9 August 2006
}}</ref>

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. Fatally injured victims sometimes took four or five weeks to die of mustard gas exposure.<ref>{{Cite book
 |author1=Sidell, F. R. |author2=Urbanetti, J. S. |author3=Smith, W. J. |author4=Hurst, C. G. |editor1=Sidell, F. R. |editor2=Takafuji, E. T. |editor3=Franz, D. R. | year=1997 | chapter=Chapter 7. Vesicants
 | title=Medical Aspects of Chemical and Biological Warfare
 | publisher=Office of The Surgeon General, Department of the Army, United States of America
 | chapter-url=http://www.globalsecurity.org/wmd/library/report/1997/cwbw/
 | access-date=8 August 2007 |isbn=99973-209-1-3|oclc=489185423|lccn=97022242}}</ref>

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."<ref>{{Cite book
 | last=Brittain | first=Vera
 | title=Testament of Youth: An Autobiographical Study of the Years 1900–1925
 | year=1933 | publisher=The Macmillan Company
 | location=New York
 | isbn=0-14-012251-6 }}</ref>

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 (military)|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.<ref>{{Cite web |date=2018-03-21 |title=German Spring Offensives 1918 |url=http://www.eastsussexww1.org.uk/index.php? |access-date=2023-02-28 |website=WW1 East Sussex |language=en-US}}</ref>

Gas never reproduced the dramatic success of 22 April 1915; 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 warfare|trench system]] was ideal for achieving an effective concentration. Germany also used gas against Russia on the [[Eastern Front (World War I)|Eastern Front]], where the lack of effective countermeasures resulted in deaths of over 56,000 Russians,<ref name="duffy2000">{{Cite web
 | first=Michael | last=Duffy | date=22 August 2009
 | title=Weapons of War – Poison Gas
 | work=firstworldwar.com
 | url=http://www.firstworldwar.com/weaponry/gas.htm
 | access-date=25 October 2009 }}</ref> while Britain experimented with gas in [[Palestine (region)|Palestine]] during the [[Second Battle of Gaza]].<ref>{{Cite book
 |author1=Dolev, Eran |author2=Lillywhite, Louis | title=Allenby's military medicine: life and death in World War I Palestine | publisher=I. B. Tauris | year=2007
 | pages=37–38 | isbn=978-1-84511-290-5 }}</ref> Russia began manufacturing chlorine gas in 1916, with phosgene being produced later in the year. Most of the manufactured gas was never used.<ref name="sic15" />

[[File:Surrounded by invisible death (2866724033).jpg|thumb|Australian gunners of the 55th Siege Battery working during a gas attack, 1917]]

The British Army first used mustard gas in November 1917 at [[Cambrai]], after their armies had captured a stockpile of German mustard gas shells. It took the British more than a year to develop their own mustard gas weapon, with production of the chemicals centred on [[Avonmouth Docks]].<ref>{{cite book |editor-last=Large |editor-first=David |title=The Port of Bristol, 1848–1884}}</ref><ref>{{cite web|url=http://www.bristolpast.co.uk/#/avonmouth/4546933962|title=Photographic Archive of Avonmouth Bristol BS11|publisher=BristolPast.co.uk|access-date=12 May 2014}}</ref> (The only option available to the British was the Despretz–Niemann–Guthrie process.) This was used first in September 1918 during the breaking of the [[Hindenburg Line]] with the [[Hundred Days' Offensive]].

The Allies mounted more gas attacks than the Germans in 1917 and 1918 because of a 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 as a result of 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.<ref>{{Cite book
 | last=Crowell | first=Benedict
 |author2=Wilson, Robert Forrest | year=1921
 | title=The Armies of Industry: Our Nation's Manufacture of Munitions for a World in Arms, 1917–1918
 | publisher=Yale University Press | pages=491, 500
 | volume=5 | url=https://books.google.com/books?id=xgFNAAAAMAAJ | access-date=8 December 2008
 | isbn=1-60105-114-X }}</ref><ref name="Gross">{{cite journal |last1=Gross |first1=Daniel A. |title=Chemical Warfare: From the European Battlefield to the American Laboratory |journal=Distillations |date=Spring 2015 |volume=1 |issue=1 |pages=16–23 |url=https://www.sciencehistory.org/distillations/magazine/chemical-warfare-from-the-european-battlefield-to-the-american-laboratory |access-date=20 March 2018}}</ref> Also the prevailing [[wind]] on the [[Western Front (World War I)|Western Front]] was blowing from west to east,<ref>{{Cite book
 | author=Lockwood, John C. |editor1=Hewitt, C. N. |editor2=Jackson, A. V. | year=2003 | chapter=Chapter 3. The Earth's Climates
 | title=Handbook of Atmospheric Science: Principles and Applications
 | publisher=Blackwell Publishing
 | pages=72–74 | isbn=0-632-05286-4 }}</ref> which meant the Allies more frequently had favourable conditions for a gas release than did the Germans.

When the United States entered the war, it was already mobilizing resources from academic, industry and military sectors for research and development into poison gas. A Subcommittee on Noxious Gases was created by the National Research Committee, a major research centre was established at [[Camp American University]], and the 1st Gas Regiment was recruited.<ref name="Gross" /> The 1st Gas Regiment eventually served in France, where it used phosgene gas in several attacks.<ref name="Addison">{{cite book |last1=Addison |first1=James Thayer |title=The Story of the First Gas Regiment |date=1919 |publisher=Houghton Mifflin Company |location=Boston and New York |url=https://archive.org/details/storyoffirstgasr01addi |pages=[https://archive.org/details/storyoffirstgasr01addi/page/50 50], 146, 158, 168|access-date=14 April 2017}}</ref><ref name="Gross" /> The Artillery used mustard gas with significant effect during the [[Meuse-Argonne Offensive]] on at least three occasions.<ref>''Annual Report of the Secretary of War, 1919'', pp. 4386–4387</ref> The United States began large-scale production of an improved vesicant gas known as [[Lewisite]], for use in an offensive planned for early 1919. By the time of the [[First Armistice at Compiègne|armistice on 11 November]], a plant near [[Willoughby, 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, as it degrades in moist conditions.<ref>{{cite book
|title=Handbook of Chemical and Biological Warfare Agents, Second Edition
|author=D. Hank Ellison
|date=2007
|page=456
|publisher=[[CRC Press]]
|isbn=978-0-8493-1434-6}}</ref><ref>{{cite book
|last=Hershberg
|first=James G.
|title=James B. Conant: Harvard to Hiroshima and the Making of the Nuclear Age
|year=1993 |publisher=Stanford University Press
|location=Stanford, CA
|isbn=0-8047-2619-1
|page=47}}</ref>