The Ulster Defence Regiment was a locally raised, part time and full time unit, intended to carry out security duties within Northern Ireland. Formed in 1970. Initially, seven battalions were raised, immediately making it the largest regiment in the British Army. Within two years, a further four battalions were added, taking the total to eleven.
To begin with, the Regiment consisted entirely of part-time volunteers, before a Regular Service was added in 1976. By the time the UDR became operational on 1 April 1970, it had strength of 2440. The Regular element of the Regiment eventually expanded to encompass half the total personnel. The UDR was also the first infantry regiment in the British Army to fully integrate women into its structure, when Greenfinches took over clerical and signals duties, within a short period of time Greenfinches became fully operational taking full part in Patrols and other operational duties, thus leading the way in the Army for the WRAC to follow
The Regiment was reduced to nine battalions in 1984, then to seven in 1991 through amalgamations. The Ulster Defence Regiment was presented with its Colours by Her Majesty the Queen in 1991 and on July 23, 1991 Tom King announced to the Commons that as part of the restructuring of the armed forces that plans had been agreed to merge The UDR with the Royal Irish Rangers.
On the 1 July, 1992 the merger of the Regiments was completed and the new Regiment became the Royal Irish Regiment..
The UDR is the only unit in the history of the British Army to have been on operational deployment for its entire history, from the moment it was created until it was amalgamated with the Royal Irish Rangers in 1992.