The infantry attack began on 31 July. Constant shelling had churned the clay soil and smashed the drainage systems. The left wing of the attack achieved its objectives but the right wing failed completely. Within a few days, the heaviest rain for 30 years had turned the soil into a quagmire, producing thick mud that clogged up rifles and immobilised tanks. It eventually became so deep that men and horses drowned in it.
On 16 August the attack was resumed, to little effect. Stalemate reigned for another month until an improvement in the weather prompted another attack on 20 September. The Battle of Menin Road Bridge, along with the Battle of Polygon Wood on 26 September and the Battle of Broodseinde on 4 October, established British possession of the ridge east of Ypres.
Further attacks in October failed to make much progress. The eventual capture of what little remained of Passchendaele village by British and Canadian forces on 6 November finally gave Haig an excuse to call off the offensive and claim success.
However, Passchendaele village lay barely five miles beyond the starting point of his offensive. Having prophesied a decisive success, it had taken over three months, 325,000 Allied and 260,000 German casualties to do little more than make the bump of the Ypres salient somewhat larger. In Haig's defence, the rationale for an offensive was clear and many agreed that the Germans could afford the casualties less than the Allies, who were being reinforced by America's entry into the war. Yet Haig's decision to continue into November remains deeply controversial and the arguments, like the battle, seem destined to go on and on.
The third major battle of Ypres, also known as the Battle of Passchendaele, took place between July and November, 1917. General Sir Douglas Haig, the British Commander in Chief in France, was encouraged by the gains made at the offensive at Messines in June 1917. Haig was convinced that the German army was now close to collapse and once again made plans for a major offensive to obtain the necessary breakthrough.
The opening attack at Passchendaele was carried out by General Hubert Gough and the British Fifth Army with General Herbert Plumer and the Second Army joining in on the right and General Francois Anthoine and the French First Army on the left. After a 10 day preliminary bombardment, with 3,000 guns firing 4.25 million shells, the British offensive started at Ypres a 3.50 am on 31st July.
The German Fourth Army held off the main British advance and restricted the British to small gains on the left of the line. Allied attacks on the German front-line continued despite very heavy rain that turned the Ypres lowlands into a swamp. The situation was made worse by the fact that the British heavy bombardment had destroyed the drainage system in the area. This heavy mud created terrible problems for the infantry and the use of tanks became impossible. Eventually Sir Douglas Haig called off the attacks and did not resume the offensive until late September.
Attacks on 26th September and 4th October enabled the British forces to take possession of the ridge east of Ypres. Despite the return of heavy rain, Haig ordered further attacks towards the Passchendaele Ridge. Attacks on the 9th and 12th October were unsuccessful. As well as the heavy mud, the advancing British soldiers had to endure mustard gas attacks.
Three more attacks took place in October and on the 6th November the village of Passchendaele was finally taken by British and Canadian infantry. The offensive cost the British Expeditionary Force about 310,000 casualties. Sir Douglas Haig was severely criticised for continuing with the attacks long after the operation had lost any real strategic value.