During 1862 "St. Louis", under the command of Lieutenant L. Paulding USN, was attached to Rear Admiral Andrew Hull Foote's squadron and participated in the Battle of Lucas Bend and the capture of Fort Henry on the Tennessee River (February 6, 1862). She served as flagship for the squadron when it assisted the Union Army at the capture of Fort Donelson on the Cumberland River (February 14–16, 1862). Between April and June 1862, she operated against Fort Pillow, Tennessee.