Outnumbered and exhausted, the British Expeditionary Force, under the command of General Sir John French, raced north from the mobile fighting of the first two months of the war to join two divisions of reinforcements recently landed in Belgium. They advanced east from St Omer, met and halted the German army at the Passchendaele Ridge to the east of the Belgian town of Ypres. Both sides dug in for trench warfare. The town of Ypres was rapidly demolished by artillery and air attack.
The Germans called the battle "The Massacre of the Innocents" (German "Kindermord"). Many of the German units conisted of enthusiastic students. Their offensive had been stopped by a British force, which although outnumbered was highly professional having learned many lessons from the Boer War. The BEF was supported for the first time by battalions from the Army of India and the British Territorials without whose support the Germans would surely have broken through. With tenacity and some good luck the ragged British line held on. The BEF was effectively destroyed at First Ypres but bought the British valuable time to reinforce the lines.
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The Second Battle of Ypres was the first time Germany used chemical weapons on a large scale on the Western Front in World War I and the first time a colonial force (Canadians) forced back a major European power (Germans) on European soil, which occurred in the battle of St. Juliaan-Kitcheners' Wood.
At Second Ypres, the smallest tactical unit in the infantry was a company; by 1917 it would be the section.
A Third Battle of Ypres, more commonly known as Passchendaele was fought in the autumn of 1917.