Potomac, fifth U.S. Navy ship to bear the name, was laid down at Sun Shipbuilding and Drydock Company at Chester, Pennsylvania,
on 9 June 1955 and launched on 8 October 1956, sponsored by Mrs. T. H. Robbins, Jr. She entered non-commissioned U.S. Navy service under the control of the Military Sea Transport Service (MSTS) with a primarily civilian crew on 30 January 1957.
Potomac carried fuel oil and aviation fuel to the United States armed forces overseas until 26 September 1961, when she was wracked by fire and a series of explosions while alongside the Aviation Fuels Terminal Pier at Morehead City, North Carolina. Two men were killed in the explosions, and the forward part of the ship was declared a total loss. A disastrous waterfront fire was avoided by the prompt heroic action of Potomac crew members, United States Coast Guard personnel, and U.S. Marines, who prevented the fire from igniting large fuel storage tanks adjacent to the pier.