Purchased by the Union Navy in 1861 for $52,500 (equivalent to $1,800,000 in 2023), she was converted to a warship and saw action during the Battle of Port Royal on November 7.

On February 25, 1862, en route to join the Mortar Flotilla, she was wrecked on the Currituck Banks in a storm and was burned to prevent capture.

[1] Power came from the set of two screw propellers,[3] which were driven by two condensing engines measuring 26 in (66 centimetres) by 32 in (81 cm).

[13] Seven years later, the vessel towed the schooner Spring Hill (later known as United States) to Nantasket Roads in preparation for Isaac Israel Hayes's Arctic expedition.

[14] In 1860, the Wilmington Daily Herald described her as "as sound now as when first built" and compared her favorably to the similar, but wooden, vessel Enoch Train.

[17] After being outfitted in Boston, R. B. Forbes left on August 25 under the command of Acting Master William G. Gregory for the Washington Navy Yard, where she spent most of September.

[2] R. B. Forbes was first assigned to service in the Chesapeake Bay area, but then was ordered to join the South Atlantic Blockading Squadron.

[1] During the way, she was caught in a storm on February 25, off of Nags Head, North Carolina, and driven onto the Currituck Banks.