Potomac, sixth U.S. Navy ship to bear the name, was laid down as SS Shenandoah at Sun Shipbuilding and Drydock Company at Chester, Pennsylvania, on 1 March 1964 and launched on 10 October 1964.

The U.S. Navy acquired Shenandoah on 10 October 1964, and delivered her to Keystone Shipping Company on 11 December 1965.

During this time she participated in sorties, exercises, and training activities, assisted in a humanitarian food relief effort for Rwanda, assisted forces in Bosnia and Herzegovina, and earned the U.S. Navy's "E" for excellence ship award during convoy exercises in the Indian Ocean.

SS Potomac left Diego Garcia and the MPF in 2000 and was transferred back to the RRF.

She was transferred to the Maritime Administration for lay up in the National Defense Reserve Fleet at Beaumont, Texas.