Editing Western Front (World War I) (section)

=== Flanders offensive ===

{{Main|Battle of Messines (1917)|Third Battle of Ypres}}

[[File:At close grips2.jpg|thumb|Two United States soldiers run toward a bunker past the bodies of two German soldiers.]]
In June, the British launched an offensive in Flanders, in part to take the pressure off the French armies on the Aisne, after the French part of the Nivelle Offensive failed to achieve the strategic victory that had been planned and French troops [[1917 French Army mutinies|began to mutiny]].{{sfn|Baldwin|1962|pp=101–102}} The offensive began on 7 June, with a British attack on [[Battle of Messines (1917)|Messines Ridge]], south of Ypres, to retake the ground lost in the First and Second battles in 1914. Since 1915 specialist [[Royal Engineer tunnelling companies]] had been digging tunnels under the ridge, and about {{convert|500|t|LT|abbr=on}} of explosives had been planted in 21 mines under the German defences.{{sfn|Bostyn|2002|p=227}} Following several weeks of bombardment, the explosives in 19 of these mines were detonated, killing up to 7,000 German troops. The infantry advance that followed relied on three creeping barrages which the British infantry followed to capture the plateau and the east side of the ridge in one day. German counter-attacks were defeated and the southern flank of the Gheluvelt plateau was protected from German observation.{{sfn|Edmonds|1991|p=87}}

On 11 July 1917, during [[Operation Hush|''Unternehmen Strandfest'']] (Operation Beachparty) at Nieuport on the coast, the Germans introduced a new weapon into the war when they fired a powerful blistering agent [[Sulfur mustard]] (Yellow Cross) gas. The artillery deployment allowed heavy concentrations of the gas to be used on selected targets. Mustard gas was persistent and could contaminate an area for days, denying it to the British, an additional demoralising factor. The entente powers increased production of [[Chemical weapons in World War I|gas for chemical warfare]] but took until late 1918 to copy the Germans and begin using mustard gas.{{sfn|Sheldon|2007|pp=35–36, 39}}

From 31 July to 10 November the [[Third Battle of Ypres]] included the [[First Battle of Passchendaele]] and culminated in the [[Second Battle of Passchendaele]].{{sfn|Liddle|2013|p=112}} The battle had the original aim of capturing the ridges east of Ypres then advancing to Roulers and Thourout to close the main rail line supplying the German garrisons on the Western front north of Ypres. If successful the northern armies were then to capture the German submarine bases on the Belgian coast. It was later restricted to advancing the British Army onto the ridges around Ypres, as the unusually wet weather slowed British progress. The Canadian Corps relieved the [[II ANZAC Corps]] and took the village of Passchendaele on 6 November,{{sfn|Baldwin|1962|p=103}} despite rain, mud and many casualties. The offensive was costly in manpower for both sides for relatively little gain of ground against determined German resistance but the ground captured was of great tactical importance. In the drier periods, the British advance was inexorable and during the unusually wet August and in the Autumn rains that began in early October, the Germans achieved only costly defensive successes, which led the German commanders in early October to begin preparations for a general retreat. Both sides lost a combined total of over a half million men during this offensive.{{sfn|Sheffield|2002|p=216}} The battle has become a byword among some British revisionist historians for bloody and futile slaughter, whilst the Germans called Passchendaele "the greatest martyrdom of the war."{{sfn|Sheldon|2007|pp=vi, 316}}