British Expeditionary Force, the home-based British army
forces that went to northern France at the start of World Wars I and II in
order to support the left wing of the French armies.
By the first decade of the 20th century, in the light of
Britain’s treaty obligations to help France defend itself against a possible
German attack, it was clear that the larger units of the British army had to be
organized and trained as units before such a war ever began, if they were to be
used quickly and effectively. The Haldane reforms provided for the organization
of the home-based forces of the regular army into an "expeditionary force”
consisting of six infantry divisions and one cavalry division.
Four of these infantry divisions and the cavalry division
went to France at the outbreak of World War I (1914), where they sustained
heavy losses. The BEF sent to France early in World War II (1939) was brought
back to England when France fell (1940), and the British effort was again
continued on other battlefields by numbered armies.