<P> Under the terms of the Entente Cordiale, the British Army's role in a European war was to embark soldiers of the British Expeditionary Force, which consisted of six infantry divisions and five cavalry brigades that were arranged into I Corps and II Corps . In October 1914, 7th Division arrived in France, forming the basis of III Corps and the cavalry had grown to form the Cavalry Corps of three divisions . By December 1914, the BEF had expanded to such an extent that the First Army and the Second Army were formed . </P> <P> By the end of 1914, after the battles of Mons, Le Cateau, the Aisne and Ypres, the old regular British Army had suffered massive casualties and lost most of its fighting strength but had managed to help stop the German advance . </P> <P> The force was commanded by Field Marshal Sir John French until December 1915, when he was replaced by General Sir Douglas Haig . The BEF's Chief of Staff on mobilisation was General Archibald Murray . He was replaced in January 1915 by General William Robertson . Lieutenant - General Launcelot Kiggell then served as Chief of Staff from December 1915 to January 1917 when he was succeeded by Lieutenant - General Herbert Lawrence . The two initial Army Corps were commanded by Douglas Haig (I Corps) and Horace Smith - Dorrien (II Corps). </P> <P> As the Regular Army's strength declined, the numbers were made up, first by the Territorial Force, then by volunteers from Field Marshal Kitchener's New Army . By the end of August 1914, he had raised six new divisions and by March 1915, the number of divisions had increased to 29 . The Territorial Force was also expanded, raising second and third line battalions and forming eight new divisions, which supplemented its peacetime strength of 14 divisions . The Third Army was formed in July 1915 and with the influx of troops from Kitchener's volunteers and further reorganisation, the Fourth Army and the Reserve Army, became the Fifth Army in 1916 . </P>

Who commanded the british expeditionary force in world war one