1917 began ominously for the Allies. The February Revolution in Russia threatened the collapse of the eastern front, and the German resumption of unrestricted submarine warfare was severely degrading Allied supply lines on the western front. Initiated by General Haig, the Battle of Passchendaele had two primary objectives: to close the Ypres Salient and to lift the German blockade of the Channel by destroying their submarine bases on the Belgian coast. Preceded by two weeks of heavy bombardment, the infantry attack began on 31 July. As with the Somme, German artillery positions survived the bombardment, and inflicted heavy casualties on Allied troops moving over open terrain. Within days, heavy rainfall had transformed the battlefield into a quagmire, and the advance bogged down. Towards the end of September, improved weather allowed resumption of the offensive, and the ridge east of Ypres was taken, but at huge cost in casualties.
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