This originates from the Peninsular War when Ensign Edward Keogh of the 87th Regiment of Foot let out the cry while capturing a French Imperial Eagle at the Battle of Barrosa.

The creation followed the Options for Change proposals which recommended the amalgamation of the Royal Irish Rangers and the Ulster Defence Regiment (UDR).

This produced an overwhelmingly Ulster Protestant regiment with eleven battalions:[2] The Home Service battalions, permanently based in Northern Ireland, filled the role formerly occupied by the UDR, assisting the Royal Ulster Constabulary (with a focus on combating militant Irish republicanism), in Northern Ireland during Operation Banner.

[4] In 2000 in Sierra Leone, whilst deployed to train government troops, eleven Royal Irish soldiers and their local army liaison officer were captured by the West Side Boys insurgents.

Five hostages were later released and the remaining six were freed by the Special Air Service and The Parachute Regiment during Operation Barras: with the West Side Boys suffering severe casualties in the action.

[5] The Colonel-in-Chief, the Duke of York presented the regiment new colours to St Patrick's Church of Ireland Cathedral in Armagh on 16 June 2001: there is a plaque commemorating this event in the south aisle.

[7] The number of Home Service battalions were reduced to three by April 2003:[8] In 2005, the Provisional Irish Republican Army announced an end to its armed campaign.

The 1st battalion provided Operational Mentoring and Liaison Teams (OMLTs) to assist in training the Afghan National Army (ANA) and Afghan National Police (ANP), and the 2nd battalion were the first Territorial Army company strength grouping to provide OMLT training from NATO forces.

[18] Under the Defence in a Competitive Age programme and subsequent Future Soldier, the 1st Battalion will transfer to the 16 Air Assault Brigade.

[19] The 1st Battalion (1 R IRISH) is a Light Recce Strike Infantry unit and comes under the 16 Air Assault Brigade Combat Team.