USS Monarch was a side paddle wheel ram in the United States Army. Monarch was built as a towboat at Fulton, Ohio, in 1853. She was converted to a ram in 1862 for service in the Ellet Ram Fleet under Lt. Col. Charles Ellet, Jr. operating on the Mississippi River in the American Civil War in conjunction with the Western Flotilla.
Monarch was purchased at Pittsburgh in April 1862 and commissioned there, Capt. R. W. Sanford in command.
After fitting out at New Albany, Monarch began active duty with the Ram Fleet. Steaming downriver in May, she scouted Fort Pillow in June and joined USS Benton, USS Louisville, USS Carondelet, USS St. Louis, USS Cairo and her sister ship, USS Queen of the West, in the Battle of Memphis 6 June. Engaging the Confederate River Defense Fleet, the rams destroyed seven of the southern ships, wiping out the Defense Fleet as an effective naval force. Monarch rammed CSS Colonel Lovell and General Beauregard. The Union forces took Memphis 6 June, clearing the upper Mississippi of southern forts and naval craft. On 26 June, Monarch and Lancaster pursued General Earl Van Dorn down the Mississippi and up the Yazoo River, the Confederates burning the ship below Yazoo City to prevent her capture.