She was fitted out as a ram at Pittsburgh and headed down the Ohio River 29 April to join a fleet of rams which Ellet was organizing to counter the Confederate River Defense Fleet. This group of southern rams had been fitted out in the lower Mississippi and threatened to emulate the dreaded southern ironclad ram "Virginia" in routing wooden hulled Union ships. On 10 May the Confederate flotilla made a spirited attack on Union gunboats and mortar schooners at Plum Point Bend, Tennessee, sinking and forcing the "Mound City" aground. A fortnight later all but one of the rams had joined the Union flotilla above Fort Pillow ready for action. As the ram fleet and Western Flotilla prepared to attack, General Halleck's capture of Corinth, Mississippi, on 30 May cut the railway lines which supported the Confederate positions at Forts Pillow and Randolph, forcing the South to abandon these river strongholds.