Answer:
At the outbreak of World War I, the British Expeditionary Force, initially made up of only four infantry divisions, later increased to seven infantry divisions and three cavalry divisions, was transferred to Belgium under General Sir John French. He participated in the first Battle of Mons, where he suffered heavy losses, and later helped to block the German advance in the First Battle of the Marne.
However, the term "British Expeditionary Force" refers only to the British forces present in France prior to the first Battle of Ypres, on November 22, 1914. At the end of the battle, the British forces reorganized and the BEF left to exist officially. when his men were divided between the two new British armies that had just been formed.