In 1956 "Fort Mandan" conducted amphibious training exercises at Vieques, Puerto Rico, and underwent overhaul at Baltimore before steaming again for the far north where she cruised in September and October. Amphibious exercises again occupied her during November 1956 and much of 1957 when she joined in "Caribex" in the Panama Canal Zone and "Narmid" 1 and 2. From September through November 1957 she was attached to MSTS for Arctic Service, successfully transporting Army men and equipment from Greenland to Newfoundland and Virginia in a winter closing-out operation.