The retreat from Empire in the post-war years brought about a reduction in the size of the Army with line infantry regiments losing their second battalions. In 1947 regiments were grouped in brigade groups and the North Irish Brigade group was created to include the Royal Inniskilling Fusiliers, Royal Ulster Rifles and Royal Irish Fusiliers.

This new system came into its own during the Korean War from 1950 to 1953. Among the early forces committed by the United Kingdom was 29 Independent Infantry Brigade which included 1st Royal Ulster Rifles. Twice during 1951 - in January at the Battle of Happy Valley and in April at the Battle of the Imjin - the Rifles suffered severe casualties which were replaced by reinforcement drafts from the North Irish Brigade. Both Inniskillings and Faughs contributed men to those drafts so that the Rifles became a representative battalion of the North Irish Brigade. (The Rifles were also influenced by their close association with the other two regiments in the Brigade to include pipers in their musical line-up: their London Irish comrades had long had pipers.)

Throughout the late 1940s and the 1950s the three regiments served in a variety of theatres such as Palestine, Malaya, Egypt, Kenya, Cyprus and Korea with much active service.

In 1968 due to further cuts to the Army the three regiments amalgamated to create a new regiment, initially of three battalions but later to reduce to two. So that neither Fusiliers nor Riflemen would be offended and so that soldiers would not be "Privates" the new Regiment would be called The Royal Irish Rangers - thus evoking the memory of another lost regiment, The Connaught Rangers.