The battle of Armentières was part of the Race to the Sea, the series of battles that decided the line of the Western Front as trench warfare took over in the autumn of 1914. Officially the battle took place between the river Douve and a line between Estaires and Foumers and was fought by III corps. To the south it merged into the battle of La Bassée, to the north into the battle of Messines.
On 12 October III corps was ordered to advance to the river Lys from St. Omer, where it had arrived on 10 October. The battle is taken to begin on 13 October, when III corps found the Germans defending the line of a small stream, the Meterenbecque, from a strong position on a ridge behind the line. A request for help from the cavalry corps was refused as they were also engaged in battle, and so III corps was forced to launch a frontal assault on the German lines. After a day long battle, which cost III corps 708 casualties, the Germans pulled back.
On the same day news reached the British that the Germans had occupied Lille, a serious blow to the overall British strategy, which was for an advance to the north east of Lille. Sir John French remained convinced that the Germans were only present in small numbers in front of the British, and would remain convinced of this until the German attacks began at Ypres.
III corps continued to advance over the next six days. It was facing units of the German Sixth Army, who on 14 October were ordered to stand on the defensive while the Fourth Army attacked from Menin to the coast (this attack would develop into the battle of the Yser and dominate the first battle of Ypres.
On 15 October III corps was ordered to capture Armentières, repair the bridges over the Lys and prepare for the advance towards Lille. The town was captured on 17 October, and the advance continued until 19 October.
The remainder of the battle saw the British on the defensive, facing a series of repeated but unsuccessful German attacks. Armentières remained in British hands throughout the fighting, although the front line was pushed back slightly. The biggest attack came on 29 October, the opening day of the battle of Gheluvelt, the most successful German attack at Ypres. The battle officially ends on 2 November, when the danger posed by the retreat of the Cavalry Corps after the fighting at Gheluvelt had passed, although fighting continued on the Armentières front throughout November.