"Dumbarton Castle" commissioned at Rosyth on 26 March 1982, and was assigned the pennant number P265. In April 1982, the Falklands War began when Argentine forces invaded the Falkland Islands on 2 April. "Dumbarton Castle" sailed from her base at Rosyth on 26 April for HMNB Portsmouth to be fitted with additional communications equipment and a desalination plant to better suit her to support the British task force sailing to retake the Falklands. "Dumbarton Castle" left Portsmouth on 1 May, arriving at Ascension Island on 11 May, where she was employed as a despatch vessel, ferrying stores between Ascension and the Task Force, and between warships of the task force. She returned to Rosyth in August 1982. "Dumbarton Castle" was awarded the battle honour "Falkland Islands 1982" for her service in the war.