21 March, 1804 The Secretary of the Navy ordered Lt. Cassin, supervisor of the Washington Navy Yard, to prepare her for sea.[49] President Jefferson reinforced Preble's squadron in April and ordered four frigates to sail as soon as possible. President, Congress, Constellation and Essex were placed under the direction of Commodore Samuel Barron.[48] Congress was captained by John Rodgers and two months were spent preparing the squadron for the voyage. She sailed from Alexandria, Virginia on 28 May, 1804.[50] She arrived at Hampton Roads on 8 May.[51] They departed in late June[52] and arrived at Gibraltar on 12 August. Congress and Essex were immediately sent to patrol off the coast of Tangier and when they returned to Gibraltar two weeks later, Congress continued on to Tripoli.[53][54]
Congress, accompanied by Constellation, assumed blockade duties of Tripoli and captured one xebec before sailing for Malta on 25 October for repairs.[54] On 6 November Rodgers assumed command of Constitution and in his place, Stephen Decatur assumed command of Congress.[55] The next recorded activity of Congress is in early July 1805 when she was sent in company with Vixen to blockade Tunisia. They were joined on the 23rd by additional U.S. Navy vessels.[56][Note 2] In early September, Congress carried the Tunisian ambassador back to Washington DC.[57][58] Afterward, placed in ordinary at the Washington Navy Yard, she served as a classroom for midshipmen training through 1807.[59]