5th (County Londonderry) Battalion, Ulster Defence Regiment (5 UDR) was formed in 1970 as part of the 7 original battalions specified in the The Ulster Defence Regiment Act 1969, which received Royal Assent on 18 December 1969 and was brought into force on 1 January 1970. It was, along with the rest of the regiment, amalgamated with the Royal Irish Rangers in 1992 to form the Royal Irish Regiment.