At the outbreak of war, a number of units from both Irish Cavalry and Infantry Regiments formed part of the British Expeditionary Force that was immediately sent to France. Other Regular Irish battalions were based in the Middle East and India but would soon return to Europe.
During August 1914, Unionist leaders, such as Sir Edward Carson, and also the Irish Parliamentary Party leader, John Redmond, encouraged members of the Ulster Volunteer Force (UVF) and the Irish National Volunteers (INV) to join the fight against Germany and three Infantry Divisions were created to accept volunteers from all parts of Ireland.
It has been estimated that around 24,000 from both the UVF and INV joined the British Army in 1914 - with thousands more Irish Reservists answering the recruitment call - and the 50,000 volunteers would form the nucleus of the 10th (Irish), 16th (Irish) and 36th (Ulster) Divisions.
In 1915, army recruitment in Ireland continued at the previous year's levels before reducing markedly to below 20,000 during the last three years of the war.