In 1922 the Irish Free State seceded from the United Kingdom and most of the Irish regiments were disbanded. The survivors were originally only to be The Royal Inniskilling Fusiliers and the Royal Irish Rifles, (renamed The Royal Ulster Rifles), each with two battalions. The Inniskillings offered up their Second Battalion to save The Royal Irish Fusiliers.
This left the Faughs and Inniskillings as single-battalion regiments. They were linked from 1924 with a common depot at St Lucia Barracks, Omagh, becoming a two-battalion regiments again in 1937. In that year also The London Irish Rifles became a Territorial Army Battalion of The Royal Ulster Rifles.
In the inter-war years the three regiments served in many parts of the world and soldiers saw active service in Iraq, India and Palestine.