Rappahannock rivers and Chesapeake Bay protecting water approaches to Washington, D.C. against possible Confederate naval attack. She seized steamer James Guy off Machodoc Creek, Virginia on 21 May and fired on and damaged Confederate sidewheel steamer, in Aquia Creek, Va. on 7 July. Assigned to the newly established South Atlantic Blockading Squadron, Pocahontas departed Washington on 15 October for Newport News, Virginia and sortied from Hampton Roads on the 29th with Flag Officer Samuel F. Du Pont's fleet. Bombardment of Port Royal Under the command of Percival Drayton, Pocahontas arrived at Port Royal, South Carolina, either after its defensive forts had been destroyed by other Union vessels or near the end of the battle; Drayton's brother Thomas was commanding Confederate troops on shore in a literal instance of the "brother against brother" phrase used to describe the American Civil War. At the battle, Pocahontas was apparently piloted into the anchored by its executive officer, a man who would later achieve international fame as a renowned naval theorist: Lt. Alfred Thayer Mahan. The joint Army-Navy task force captured Port Royal Sound on 7 November, winning for the Union what Du Pont called "the most important point to strike, and the most desirable to have first and to hold...." Port Royal, he continued, "alone admits the large ships – and gives us a naval position on the sea coast as our Army is holding across the Potomac." Subsequent Union naval operations along the Confederate coast fully substantiated Du Pont's appraisal of Port Royal's strategic value. Blockade duty During the following months, Pocahontas operated along the coasts of South Carolina, Georgia, and Florida, performing blockade duty, reconnoitering rivers and inlets, and supporting amphibious operations. She helped to capture Tybee Island, Georgia on 24 November and assisted in towing ships of the "Stone Fleet" to Maffitt's channel and sank them from 20–26 January 1862 to block the approaches to Charleston from the sea. From 28 February-15 March, she participated in an expedition which captured St. Simons Island and Brunswick, Georgia, and Fernandia, Florida. She then continued blockade duty through the spring and early summer. On 14 August, Pocahontas and tug Treaty fought Confederate troops ashore along some of the Black River while trying to capture steamer Nina. Later that month she was ordered north for repairs and arrived Philadelphia Navy Yard on the 31st. Assigned to the West Gulf Blockading Squadron, Pocahontas departed Philadelphia,