Bermagui was laid down by the Ailsa Shipbuilding Company, Troon, Scotland in 1912 for the Illawarra & South Coast Steam Navigation Company. In December 1939, the ship was requesitioned by the RAN as an auxiliary, and was commissioned on 11 December. She was fitted with one 12-pounder 12cwt QF gun, one .303 inch Vickers machine gun, and four Type D depth charges. During the war, Bermagui was attached to the naval base HMAS Maitland in Newcastle, New South Wales and served as an auxiliary minesweeper, boom defence vessel, and minefield tender.