Ontario served with a merchant complement until she decommissioned on 7 April 1913 to undergo conversion to a repair ship. After conversion, she recommissioned 23 December 1914 as USS Prometheus (Repair Ship No. 2). After a cruise to Alaskan waters in 1915, she was assigned to duty with the Atlantic Fleet, 16 May 1916 operating out of Norfolk, Virginia and bound for Bermuda, remaining there until 29 January 1918. While at Bermuda she was ordered to join the Naval forces at Brest, France to provide repair services, and she did a commendable job until she sailed on 16 January 1919 for New York. Upon arrival at New York she was assigned to Battleship Force 1 for duty in conjunction with the upkeep of vessels engaged in overseas transportation of troops. She was classified as AR-3 on 17 July 1