A French armored car arrives to assist British forces near Méteren, to the south of Ypres, on April 16.
April 15 1918, Passchendaele–The German advance in Flanders had slowed as the British had been able to scrape up reinforcements from wherever they could find them. However, the slackening of the German pace was not obvious to the British commanders, who were still far too short on reserves for comfort. Furthermore, Foch seemed reluctant to commit any French troops to the battle, and they knew the Germans had enough reserves to attack again elsewhere at almost any time. The German advance south of Ypres placed the British position in the Ypres Salient in a precarious position–and in fact the Germans were planning a new attack in the north to try to cut it off. With great reluctance, Plumer ordered a withdrawal from Passchendaele Ridge–voluntarily giving up what had been won with a cost of over 250,000 casualties last fall.
On April 15, most of the British forces on Passchendaele Ridge fell back to lines much closer to Ypres, while a much smaller force manning outposts along the original front line attempted to make it seem like nothing had changed. Those men withdrew as well that night, without the Germans noticing. The British were able to substantially shorten their lines and free up divisions to reinforce other areas of the front; they were soon aided by the Belgians, who agreed to extend their line, and the French, who finally committed troops to the battle after Foch saw how desperate Plumer’s situation was. The Germans would still make some gains to the south of Ypres over the next few days but they were quickly nearing the end of their rope; on the same day the British were evacuating Passchendaele, Crown Prince Rupprecht reported that “we are all utterly exhausted and burned out….Everywhere I heard complains of the accommodation of man and horse in the totally ravaged country and the heavy losses from bombs, particularly in horses which could not be hidden from sight.”
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Sources include: Nick Lloyd, Passchendaele; Robert B. Asprey, The German High Command at War; David Stevenson, With Our Backs to the Wall.