The USS Sac City was commissioned in the Navy on 6 January 1919. At the end of January 1919, the ship sailed from Norfolk, Virginia, with a cargo destined for Montevideo, Uruguay. The ship arrived in Uruguay at the beginning of March 1919. She moved to the nearby port of Rosario, and loaded a private commercial cargo, which was taken to Gibraltar. The freighter sailed to New York City from Gibraltar in June 1919. USS Sac City was decommissioned on 17 June 1919 and sent to the U.S. Shipping Board. During her subsequent commercial service she was renamed SS Black Falcon in 1932 and SS Mary Luckenbach in 1941. While en route to Murmansk, USSR, as part of Convoy PQ-18, the ship was sunk. She was hit by an aerial torpedo dropped by a German aircraft west of North Cape, Norway, on 13 September 1