Editing Western Front (World War I) (section)

== 1917 ==

{{Main|Hindenburg Line|Western Front tactics, 1917}}

[[File:Western Front 1917.jpg|thumb|Map of the Western Front, 1917]]
The [[Hindenburg Line]] was built between {{cvt|2|mi}} and {{cvt|30|mi}} behind the German front line.{{sfn|Marshall|1964|pp=288–289}} On 25 February the German armies west of the line began [[Operation Alberich]] a withdrawal to the line and completed the retirement on 5 April, leaving a supply desert of [[scorched earth]] to be occupied by the entente. This withdrawal negated the French strategy of attacking both flanks of the Noyon salient, as it no longer existed.{{sfn|Baldwin|1962|p=99}} The British continued offensive operations as the [[War Office]] claimed, with some justification, that this withdrawal resulted from the casualties the Germans received during the Battles of the Somme and Verdun, despite the entente suffering greater losses.{{sfn|Neiberg|2004|p=46}}

On 6 April the United States declared war on Germany. In early 1915, following the sinking of the {{RMS|Lusitania||2}}, Germany had stopped unrestricted submarine warfare in the Atlantic because of concerns of drawing the United States into the conflict. With the growing discontent of the German public due to the food shortages, the government resumed unrestricted submarine warfare in February 1917. They calculated that a successful submarine and warship siege of Britain would force that country out of the war within six months, while American forces would take a year to become a serious factor on the Western Front. The [[submarine]] and surface ships had a long period of success before Britain resorted to the convoy system, bringing a large reduction in shipping losses.{{sfn|Griffiths|1986|pp=144–145}}
[[File:Sherwood Foresters following up Germans near Brie March 1917 IWM Q 1863.jpg|thumb|British Army advancing on the Western Front (March 1917)]]

By 1917, the size of the British Army on the Western Front had grown to two-thirds of the size of the French force.{{sfn|Kennedy|1989|pp=265–266}} In April 1917 the BEF began the [[Battle of Arras (1917)|Battle of Arras]].{{sfn|Baldwin|1962|pp=99–100}} The [[Canadian Corps]] and the [[5th Infantry Division (United Kingdom)|5th Division]] of the First Army, fought the [[Battle of Vimy Ridge]], completing the capture of the ridge and the Third Army to the south achieved the deepest advance since trench warfare began. Later attacks were confronted by German reinforcements defending the area using the lessons learned on the Somme in 1916. British attacks were contained and, according to Gary Sheffield, a greater rate of daily loss was inflicted on the British than in "any other major battle".{{sfn|Sheffield|2014|loc=Chapter 7}}

During the winter of 1916–1917, German air tactics had been improved, a fighter training school was opened at [[Valenciennes]] and better aircraft with twin guns were introduced. The result was higher losses of Allied aircraft, particularly for the British, Portuguese, Belgians and Australians who were struggling with outmoded aircraft, poor training and tactics. The Allied air successes over the Somme were not repeated. During their attack at Arras, the British lost 316 [[Aircrew member|air crews]] and the Canadians lost 114 compared to 44 lost by the Germans.{{sfn|Campbell|1981|p=71}} This became known to the [[Royal Flying Corps]] as [[Bloody April]].{{sfn|Hart|2005|pp=11–13}}

=== Nivelle Offensive ===

{{Main|Battle of Arras (1917)|Nivelle Offensive|1917 French Army mutinies}}
[[File:The Battle of Arras, April-May 1917 Q6301.jpg|thumb|Ruins of [[Arras]] in April 1917]]
The same month, the French [[Commander-in-chief]], General Robert Nivelle, ordered a new offensive against the German trenches, promising that it would end the war within 48 hours. The 16 April attack, dubbed the [[Nivelle Offensive]] (also known as the [[Second Battle of the Aisne]]), would be 1.2&nbsp;million men strong, preceded by a week-long artillery bombardment and accompanied by tanks. The offensive proceeded poorly as the French troops, with the help of two [[Russian Expeditionary Force in France|Russian brigades]], had to negotiate rough, upward-sloping terrain in extremely bad weather.{{sfn|Cockfield|1999|pp=91–114}} Planning had been dislocated by the voluntary German withdrawal to the Hindenburg Line. Secrecy had been compromised and German aircraft gained air superiority, making reconnaissance difficult and in places, the creeping barrage moved too fast for the French troops.{{sfn|Uffindell|2015|p=26}} Within a week the French suffered 120,000 casualties. Despite the casualties and his promise to halt the offensive if it did not produce a breakthrough, Nivelle ordered the attack to continue into May.{{sfn|Baldwin|1962|pp=99–100}}

On 3 May the weary French 2nd Colonial Division, veterans of the Battle of Verdun, refused orders, arriving drunk and without their weapons. Lacking the means to punish an entire division, its officers did not immediately implement harsh measures against the mutineers. [[French Army Mutinies|Mutinies]] occurred in 54 French divisions<!-- yes "54 divisions" plural, not a division number --> and 20,000 men deserted. Other entente forces attacked but suffered massive casualties.{{sfn|Lyons|2000|p=243}} Appeals to patriotism and duty followed, as did mass arrests and trials. The French soldiers returned to defend their trenches but refused to participate in further offensive action.{{sfn|Marshall|1964|p=292}} On 15 May Nivelle was removed from command, replaced by Pétain who immediately stopped the offensive.{{sfn|Neiberg|2003|p=53}} The French would go on the defensive for the following months to avoid high casualties and to restore confidence in the French High Command, while the British assumed greater responsibility.{{sfn|Baldwin|1962|pp=101–102}}

===American Expeditionary Force===

On 25 June the first US troops began to arrive in France, forming the [[American Expeditionary Forces|American Expeditionary Force]]. However, the American units did not enter the trenches in [[1st Infantry Division (United States)|divisional strength]] until October. The incoming troops required training and equipment before they could join in the effort, and for several months American units were relegated to support efforts.{{sfn|Griffiths|1986|p=124}} Despite this, however, their presence provided a much-needed boost to entente morale, with the promise of further reinforcements that could tip the manpower balance towards the entente.{{sfn|Baldwin|1962|p=144}}

=== 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}}

=== Battle of Cambrai ===

{{Main|Battle of Cambrai (1917)|l1=Battle of Cambrai}}

On 20 November the British launched the first massed tank attack and the first attack using predicted artillery-fire (aiming artillery without firing the guns to obtain target data) at the [[Battle of Cambrai (1917)|Battle of Cambrai]].{{sfn|Miles|1991|pp=13–15, 32–35}} The entente attacked with 324 tanks (with one-third held in reserve) and twelve divisions, advancing behind a hurricane bombardment, against two German divisions. The machines carried [[fascine]]s on their fronts to bridge trenches and the {{convert|4|m|ft|adj=mid|order=flip|-wide}} German tank traps. Special "grapnel tanks" towed hooks to pull away the German barbed wire. The attack was a great success for the British, who penetrated further in six hours than at the Third Ypres in four months, at a cost of only 4,000 British casualties.{{sfn|Miles|1991|p=88}} The advance produced an awkward salient and a surprise German counter-offensive began on 30 November, which drove back the British in the south and failed in the north. Despite the reversal, the attack was seen as a success by the entente, proving that tanks could overcome trench defences. The Germans realised that the use of tanks by the entente posed a new threat to any defensive strategy they might mount. The battle had also seen the first mass use of German ''[[Stosstruppen]]'' on the Western front in the attack, who used infantry [[infiltration tactics]] to penetrate British defences, bypassing resistance and quickly advancing into the British rear.{{sfn|Miles|1991|pp=176–248}}