The British Army during the First World War fought the largest and most costly war in its long history. Unlike the French and German Armies, the British Army was made up exclusively of volunteers, as opposed to conscripts, at the beginning of the conflict. Furthermore, the British Army was considerably smaller than its French and German counterparts. During the First World War, there were four distinct British armies. The first comprised approximately 247,000 soldiers of the regular army, over half of whom were posted overseas to garrison the British Empire, supported by some 210,000 reserves and a potential 60,000 additional reserves.
This component formed the backbone of the British Expeditionary Force (BEF), which was formed for service in France and became known as the Old Contemptibles. The second army was provided by the approximately 246,000-strong Territorial Force, initially allocated to home defence but used to reinforce the BEF after the regular army suffered heavy losses in the opening battles of the war. The third army was Kitchener's Army, which was composed of men who answered Lord Kitchener's call for volunteers in 1914–1915 and went into action at the Battle of the Somme in 1916. The fourth army was the reinforcement of existing formations with conscripts after the introduction of compulsory service in January 1916.
