"Syren" returned to Syracuse on the morning of 19 February. On 9 March, she and sailed for Tripoli. Soon after their arrival, on 21 March 1804, she captured the armed brig "Transfer" belonging to the Pasha. Stewart took "Transfer" into US service and renamed her . She then served in the American squadron. The very next day "Syren" captured a polacca named "Madona Catapolcana" and sent her to Malta. Operations in the Mediterranean during the spring and summer of 1804 and participated in the attacks on Tripoli in August and September 1804. The ship continued to support the squadron's operation against Tripoli which forced the Pasha to accede to American demands. After a peace treaty with Tripoli was signed on 10 June 1805, the brig remained in the Mediterranean commanded by Master Commandant John Smith for almost a year helping to establish and maintain satisfactory relations with other Barbary states.