The first day of the Battle of the Somme had been an unmitigated disaster, but for the rest of the battle the Germans suffered more than the British. Although the British army was in a vulnerable state, there was also promise for the following year. The British army had steadily improved its tactical ability and introduced the new weapons - tanks, light machine guns and mortars.
1917 started well as the Germans withdrew about 20 miles over a 65-mile stretch of the front between Arras and Soissons. Unfortunately, the Germans had withdrawn to a heavily fortified position - the Hindenburg Line.
The battles around Arras in April and May 1917 (the first, second and third Battles of the Scarpe, the Battle for Vimy Ridge, and the first and second Battles of Bullecourt) were fought in order to support the French offensive at the Aisne River further south. The battles were generally successful in reaching their immediate and small-scale objectives, although Bullecourt was a costly failure.
The ports of Bruges, Ostend and Zeebrugge (used by German U-boats to attack Britain's trade and food supplies) relied on the railway junction at Roulers, five miles beyond the northern end of the German held Messines-Wytschaete-Passchendaele ridge. If Roulers could be captured, German U-boats would be unable to attack.
The third Battle of Ypres began in June 1917. Capture of the Messines-Wytschaete section of the ridge was a success, but the weather broke and the battlefield became a quagmire of mud. In better weather during September the British pulled themselves onto the drier Passchendaele ridge around the Gheluvelt plateau. However, due to very heavy rain, the field was a quagmire again by November. On 6 November 1917 Passchendaele village was captured, and the offensive came to a halt - stuck, literally, in the mud.