Following the outbreak of the First World War, 1st Battalion Irish Guards was deployed to France almost immediately, and they remained on the Western Front for the duration of the war. During the early part of the war, the Battalion took part in the Battle of Mons and formed the Allied rearguard during the Great Retreat. The Battalion then took part in one of the bloodiest battles of 1914, the First Battle of Ypres, which began on 19 October, inflicting major casualties among the old Regular Army.