British Army During World War I

The British Army during World War I fought the largest and most costly war in its long history. Unlike the French and German Armies, its units were 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 war, there were three distinct British Armies. The "first" army was the small volunteer force of 400,000 soldiers, over half of which were posted overseas to garrison the British Empire. This total included the Regular Army and reservists in the Territorial Force. Together, they formed the British Expeditionary Force (BEF), which was formed for service in France and became known as the Old Contemptibles. The 'second' army was Kitchener's Army, formed from the volunteers in 1914–1915 destined to go into action at the Battle of the Somme. The 'third' was formed after the introduction of conscription in January 1916, and by the end of 1918, the army had reached its maximum strength of 4,000,000 men and could field over 70 divisions. The vast majority of the army fought in the main theatre of war on the Western Front in France and Belgium against the German Empire. Some units were engaged in Italy and Salonika against Austria-Hungary and the Bulgarian Army, while other units fought in the Middle East, Africa and Mesopotamia—mainly against the Ottoman Empire—and one battalion fought alongside the Japanese Army in China during the Siege of Tsingtao.

The war also posed problems for the army commanders, given that prior to 1914, the largest formation any serving General in the BEF had commanded on operations was a division. The expansion of the army saw some officers promoted from brigade to corps commander in less than a year. Army commanders also had to cope with the new tactics and weapons that were developed. With the move from manoeuvre to trench warfare, both the infantry and the artillery had to learn how to work together. During an offensive, and when in defence, they learned how to combine forces to defend the front line. Later in the war, when the Machine Gun Corps and the Tank Corps were added to the order of battle, they were also included in the new tactical doctrine.

The men at the front had to struggle with supply problems; the shortage of food and disease was rife in the damp, rat-infested conditions. Along with enemy action, many troops had to contend with new diseases: trench foot, trench fever and trench nephritis. When the war ended in 1918, British Army casualties, as the result of enemy action and disease, were recorded as 673,375 dead and missing, with another 1,643,469 wounded. The rush to demobilise at the end of the war substantially decreased the strength of the army, from its peak of 4,000,000 men in 1918 to 370,000 men by 1920.