Built in 1862 at Monongahela, Pennsylvania, as a civilian vessel, she was purchased for military service on September 17 and converted into a tinclad warship.

From February to April, Marmora participated in the Yazoo Pass expedition, and in June burned and destroyed the settlements of Eunice and Gaines Landing, Arkansas, after Union vessels were fired on by Confederate troops.

Continuing to serve on the Mississippi River, Marmora was declared surplus in May 1865 and was put in reserve status at Mound City, Illinois, the next month.

[13] Marmora left Carondelet for Cairo, Illinois, on October 22, 1862, under the command of Acting Volunteer Lieutenant Robert Getty.

[15] On November 21, Captain Henry A. Walke received orders to move with a naval force from Helena, Arkansas, to the mouth of the Yazoo.

[3] On November 28, Walke's flotilla reached Milliken's Bend, Louisiana, where he sent part of the crew of Marmora on a tugboat,[18] USS Laurel,[20] on a scouting mission.

[23] Several Union Navy naval rams arrived at the mouth of the Yazoo in early December 1862, including USS Queen of the West.

One of the men aboard Marmora shot one with a musket,[25] resulting in an explosion that shook the entire ship, despite her being at least 50 feet (15 m) from the mine.

[29] Those on Cairo heard men from Marmora shooting at objects in the river and continued ahead thinking the tinclad was under assault.

[30] Both Cairo and Marmora put small boats into the water to investigate the mines, which were found to be connected to the shore by wires.

[31] Cairo and Marmora began to maneuver after launching the boats, and the Confederate batteries on Drumgould's Bluff fired on the vessels at long range.

The naval vessels were to cover Sherman's left flank and draw Confederate attention away from the main Union assault.

Forest Rose ran aground, but Marmora freed her, and the two vessels returned to the rest of the Union fleet in the early afternoon.

[38] On December 29, Porter's gunboats provided supporting fire,[3] but Sherman's men were repulsed in the Battle of Chickasaw Bayou.

[1] On January 4, Porter reorganized his force, and Marmora was assigned to a division led by Lieutenant Commander Watson Smith.

Marmora was to advance upriver with several other ships,[44] but she instead found herself spending the day towing Carondelet, which was low on coal, up to Helena.

[49] In early 1863, Grant and Porter made a plan that has become known as the Yazoo Pass expedition to bypass the Confederate stronghold of Vicksburg by moving through nearby waterways.

Marmora, with seven other warships and three coal barges, entered Moon Lake on February 20[50] or 21,[51] where they waited for a number of transports carrying Union Army troops.

[54] On March 8, Marmora, a towboat, and a transport containing the 29th Iowa Infantry Regiment were left behind at a point on the Tallahatchie River to guard two coal barges.

[59] Marmora arrived at Helena on March 27, slowed by boiler problems,[60] before leaving to return to the Yazoo Pass expedition the same day,[3] along with a coal barge.

The next day, the steamer Nebraska, a transport with the United States Quartermaster Department, was fired on in the same area, prompting retribution from Marmora.

[3][68] Bache's ships met Brigadier General John W. Davidson's division of cavalry on August 9, at Clarendon, Arkansas; this movement occurred around the time of the beginning of the Little Rock campaign.

The next day, both vessels returned to Clarendon: Linden escorted transports carrying Union Army soldiers commanded by Major General Frederick Steele, while Marmora towed barges.

[70] Bache took Marmora, the gunboat USS Cricket, and Lexington, accompanied by part of the 32nd Iowa Infantry Regiment, on an expedition beginning on August 12, to locate Confederate cavalry believed to be in the area.

Lexington and Marmora continued on the White River, while Cricket moved up the Little Red, where she captured two Confederate gunboats, Tom Sugg and Kaskaskia.

[73] On September 19, Acting Master Elias Rees, who was commanding the tinclad, reported that the ship was in a state of disrepair, with the boilers and machinery in poor condition and several small leaks in the hull.

[84] Three seamen from Marmora's howitzer crew received the Medal of Honor for their actions at Yazoo City: William J. Franks, Bartlett Laffey, and James Stoddard;[83][84] All three men's Medal of Honor citations noted that they had been "bravely standing by his gun despite enemy rifle fire which cut the gun carriage and rammer".

[91] In February 1865, Marmora accepted the surrender of seven Confederate soldiers,[1] and that same month escorted the ironclad USS Cincinnati to New Orleans, Louisiana.

[96] The war was winding down in April and May with a Confederate defeat,[97] and on May 29, Marmora was one of a number of vessels reported as surplus by the Mississippi Squadron.

[1] Extracts from her ship's log were later published more times in the Official Records of the Union and Confederate Navies than those of any other tinclad; naval historian Myron J. Smith suggests that this may indicate that Marmora was a favorite vessel of the compilers.