The Third Battle of Ypres (Passchendaele)
Since October 1914, when Germany had established naval bases on the Belgian coast, at Ostend and Zeebrugge, British strategists had advocated a military offensive in Flanders to nullify this threat to British maritime communications. By the summer of 1917 the strategic situation dictated an attack from the Ypres salient to capture those ports. Germany’s unrestricted submarine offensive from February 1917 (see Map 29) obliged the army to do something before the war was lost at sea. The French army’s temporary incapacity following the May 1917 mutinies meant that the British army also had to do something to take pressure off its ally. Freed from his obligation to conform to French strategy, Haig would be able to mount an independent British offensive for the first time.