On 31 July 1917, British and French troops attacked German positions east and north-east of Ypres in Belgium. The assault began the Third Battle of Ypres, later widely known as Passchendaele.

British forces had occupied the Ypres Salient since the early part of the First World War. The salient projected into German-held territory and was overlooked from ridges on several sides. German artillery could observe and fire on many British positions.

Field Marshal Sir Douglas Haig planned to take the higher ground east of Ypres and break through the German defences. A further advance towards the Belgian coast might threaten ports used by German submarines.

The attack was preceded by a two-week artillery bombardment. About 3,000 guns fired millions of shells at German positions, roads and strongpoints. The bombardment damaged parts of the defensive system but did not destroy it.

It also broke up the ground. The area around Ypres was low-lying and depended on drainage channels. Shelling damaged those channels and left the fields covered with overlapping craters.

The attack began at 3.50 a.m. British and French troops advanced across a broad front in the opening action known as the Battle of Pilckem Ridge. The French made progress on the northern flank, while British units captured several objectives.

The advance did not produce the planned breakthrough. German forces remained in defended positions and counter-attacked against some of the captured ground.

Rain began during the day and continued over the following days. Water collected in shell holes and across ground where the drainage system no longer worked. Moving guns, ammunition and supplies forward became increasingly difficult.

British commanders continued the offensive through a series of battles during August, September and October. Some attacks gained ground, but German resistance and the condition of the battlefield prevented a decisive advance.

Canadian forces captured the ruins of Passchendaele village in November. By then, the Allied line had moved forward by about five miles. More than 250,000 Allied soldiers had been killed, wounded or reported missing.

The attack of 31 July began as an attempt to break through the German front and advance towards the coast. It became a campaign to take successive sections of damaged high ground east of Ypres.