Editing Western Front (World War I) (section)

=== Gas warfare ===

{{Main|Chemical weapons in World War I}}

All sides had signed the [[Hague Conventions of 1899 and 1907]], which prohibited the use of chemical weapons in warfare. In 1914, there had been small-scale attempts by both the French and Germans to use various [[tear gas]]es, which were not strictly prohibited by the early treaties but which were also ineffective.{{sfn|Richter|1994|p=7}} The first use of more lethal [[chemical weapon]]s on the Western Front was against the French near the Belgian town of [[Ypres]]. The Germans had already deployed gas against the Russians in the east at the [[Battle of Humin-Bolimów]].{{sfn|Doughty|2005|pp=148–151}}

[[File:The Second Battle of Ypres.jpg|thumb|left|An artist's rendition of Canadian troops at the [[Second Battle of Ypres]]]]
Despite the German plans to maintain the stalemate with the French and British, [[Albrecht, Duke of Württemberg]], commander of the [[4th Army (German Empire)|4th Army]] planned an offensive at Ypres, site of the First Battle of Ypres in November 1914. The [[Second Battle of Ypres]], April 1915, was intended to divert attention from offensives in the [[Eastern Front (World War I)|Eastern Front]] and disrupt Franco-British planning. After a two-day bombardment, the Germans released [[chemical weapons in World War I#1915: Large-scale use and lethal gases|a lethal cloud]] of {{convert|168|LT|t|abbr=on}} of [[chlorine]] onto the battlefield. Though primarily a powerful irritant, it can [[asphyxia]]te in high concentrations or prolonged exposure. Being heavier than air, the gas crept across [[no man's land#World War I|no man's land]] and drifted into the French trenches.{{sfn|Fuller|1992|pp=172–3}} The green-yellow cloud started killing some defenders and those in the rear fled in [[panic]], creating an undefended {{convert|6|km|mi|order=flip|adj=on}} gap in the entente line. The Germans were unprepared for the level of their success and lacked sufficient reserves to exploit the opening. Canadian troops on the right drew back their left flank and halted the German advance.{{sfn|Sheldon|2012|pp=81–95}} The gas attack was repeated two days later and caused a {{convert|5|km|mi|order=flip|abbr=on}} withdrawal of the Franco-British line but the opportunity had been lost.{{sfn|Sheldon|2012|pp=95–121}}

The success of this attack would not be repeated, as the entente countered by introducing gas masks and other [[countermeasure]]s. An example of the success of these measures came a year later, on 27 April in the [[Gas attacks at Hulluch]] {{convert|25|mi|km|order=flip|abbr=on}} to the south of Ypres, where the [[16th (Irish) Division]] withstood several German gas attacks.{{sfn|Jones|2002|pp=22–23}} The British retaliated, developing their own chlorine gas and using it at the [[Battle of Loos]] in September 1915. Fickle winds and inexperience led to more British casualties from the gas than German.{{sfn|Richter|1994|pp=69–73, 88}} French, British and German forces all escalated the use of gas attacks through the rest of the war, developing the more deadly [[phosgene]] gas in 1915, then the infamous [[mustard gas]] in 1917, which could linger for days and could kill slowly and painfully. Countermeasures also improved and the stalemate continued.{{sfn|Richter|1994|pp=182–183, 210–211}}