Passchendaele (Third Battle of Ypres): 1917 Allied offensive on the Western Front

The war year 1917 was marked by the collapse of the Russian Empire. After Romania had been largely occupied by the Central Powers at the end of 1916/beginning of 1917, calm had already essentially returned to the Eastern Front. The signs of disintegration in the Russian army were already obvious in the spring of 1917. The German Western Front had been significantly shortened by a retreat (Unternehmen Alberich) to the Siegfried position in March 1917 in order to save forces, which put the Western Allies under pressure.

The Allies launched several major offensives on the Western Front, which did not bring about any significant changes. The reasons for this were poor planning, underestimation of German fighting strength, poorly planned use of new weapons such as tanks and guns, and ultimately the exhaustion of materiel. In April, the British attempted a breakthrough in the Artois (Battle of Arras, 9 April to 16 May) and the French a week later on the Aisne and in the Champagne (16 April to the end of May). In this they used more troops and guns than at the Battle of Verdun. The result, however, was heavy losses, especially on the French side. Mutinies occurred, to which the French military leadership initially responded with draconian punishments (hundreds of death sentences). The French commander-in-chief on the Western Front and eponym of the offensive, General Robert Nivelle, had to vacate his post, which he had only taken over in December 1916, in May 1917. His successor, General PhilippePétain, confined himself largely to the defensive for the rest of 1917, bringing the mutinies under control by providing better rations and rest periods to spare the troops. A gradual improvement in morale occurred.

Germany declared unrestricted submarine warfare on February 1, 1917, putting pressure on the British Navy and merchant fleet. However, this also had the effect that the USA entered the war against Germany (on 6 April 1917), which the German army leadership greatly underestimated. However, greater effects of this entry into the war did not become apparent until the year of the war, 1918, where they were ultimately decisive in Germany's defeat. The USA, despite its official neutrality, was rather inclined towards the positions of the Entente; at that time many expected an entry into the war (sooner or later) in their favour. The U.S. president from 1913 to 1921 was the Democrat Woodrow Wilson. He had been re-elected in the November 1916 presidential election and had led his country into war after the increased submarine incidents and the Zimmermann Dispatch.

The British commander-in-chief Sir Douglas Haig planned an operation in the Flanders area as early as 1916. These plans were postponed because of the Battle of the Somme (1 July to 18 November 1916). With the Battle of Fromelles, only a diversionary attack for the Battle of the Somme in Flanders took place in July 1916. A Franco-British double offensive at Arras and on the Aisne was initially scheduled for the spring of 1917, but failed to achieve the desired success. Haig subsequently turned his attention back to Flanders - partly because the bulk of the French army was incapable of coordinated operations due to severe mutinies over a period of months. His long-cherished intention was to break through to the Belgian coast and capture the German submarine bases at Ostend and Zeebrugge, thus eliminating the danger posed by the German U-boats. It was also intended to shorten the front line and enable German troops to be encircled.

Haig believed, as he had with the Somme offensive, that the German army was on the verge of collapse. Prime Minister David Lloyd George was very critical of the offensive, but gave his blessing to the plans.

In order to guarantee a success of the main offensive, the German positions of the Wytschaete arc on the ridge of the Wijtschate and Mesen (Wytschaete and Messines) had to be captured first, otherwise no attack on the submarine bases was possible.