Completed in August 1862 for civilian trade on the Wabash River, she was instead purchased by the Union Navy for military service in October.

Commissioned in December, she cleared naval mines on the Yazoo River later that month before participating in the operations against Confederate-held Fort Hindman in January 1863.

[1] Some of these civilian ships were converted into tinclad warships, a process that involved building a wooden casemate and then at least partially covering it with thin metal armor for protection, reinforcing certain internal structures, removing the existing pilothouse and installing a new armored one, adding cannons as armament, and generally removing the texas.

[3] Romeo had been completed in August 1862 at Brownsville, Pennsylvania, for John I. Rhoades, who was also the owner of a vessel that became USS Juliet.

On December 21, she left Helena, and then moved up the Yazoo River along with other vessels in support of a Union Army attempt to capture Confederate-held Vicksburg, Mississippi.

[6] It then spent through January 3, 1863, operating on the Yazoo and its tributaries, patrolling the area and skirmishing with Confederate land forces.

[4] On December 29, 1862, Romeo joined the tinclad USS Marmora in moving up the Old River to shell Confederate positions near Vicksburg.

[9] On January 10, army forces assaulted the fort, while some of the Union vessels provided supporting fire; the Confederates surrendered the next day.

[13] On April 18, Acting Volunteer Lieutenant John V. Johnston was transferred to Romeo to take command of the vessel.

[14] In late April, Romeo was part of a feint designed to draw Confederate attention from the primary Union movement further downstream at Grand Gulf, Mississippi.

Through the rest of the Vicksburg campaign, Romeo provided naval support, engaging Confederate troops at river landings to help cut off the city.

[16] June 6 saw the appearance of Romeo and the tinclad USS Petrel play a role in causing Confederate forces to abandon a planned assault on Young's Point.

[20] Late on July 2, Confederate forces in the Donaldsonville, Louisiana, area deployed an artillery battery to ambush Union shipping.

[23] An inspection on September 24 revealed that Romeo needed repairs to her machinery and capstan, and that water was accumulating in her hold.

After the Meridian campaign drew Confederate troops away from the Yazoo City area, the Union forces occupied the place on February 9.

[4] On May 24, Confederate artillery opened fire on the tinclad USS Curlew from the banks of the Mississippi River in Arkansas.

[33] The artillery left when the timberclad USS Tyler approached the area, and Curlew moved upriver to join Romeo.

Two vessels from the Mississippi Marine Brigade escorted the transport downriver, while Romeo returned to Columbia for repairs.

[35] Later that month, a patrol from Romeo captured a Confederate officer who had been on the staff of John S. Marmaduke,[36] although he later escaped from another vessel by jumping overboard.

[40] Two crewmen from Romeo were captured in March 1865; Acting Rear Admiral Samuel Phillips Lee attributed the loss to a lack of carefulness on the part of Baldwin.

[3] She was laid up in ordinary, and Acting Volunteer Lieutenant Joseph G. Megler was assigned to take charge of her while she awaited sale.