The side‑wheel gunboat Mount Vernon, built at Philadephia in 1846, was seized by order of the War Department 21 April 1861 and transferred to the Navy on that date for active duty with the Potomac Flotilla, Lt. J. Glendy Sprosteon in command.
After fitting out at the Washington Navy Yard (striking the wharf in the process), Mount Vernon was ready for duty. In May she reconnoitered the Potomac and up the Rappahannock River 16 May to Urbana, meeting no southern forces. She chased a steamer 16 May and noted, the 18th, that people on shore were most mistrustful. During the summer, she served as a utility boat. Dispatched 26 June to seize a small sloop convoying armed men from the Maryland to Virginia shores, she departed the Washington Navy Yard 28 June for Fortress Monroe. On 5 July, she towed Teaser, the sloop captured by Pocahontas, from Namjemoy Beach to Washington. Part of the James River Squadron later in July, she was in Aquia Creek in August, where Yankee dispatched her for Freehora. She carried troops to Aiken's Landing 17 August.
In this area for the remainder of 1861, Mount Vernon changed her name to Mount Washington 4November 1861 to prevent confusion. She carried provisions for the squadron in 1862, arriving Norfolk from Washington 12 July with ordnance stores. She towed Passaic to Hampton Roads 24 December 1862.
Mount Washington saw heaviest action in 1863 in the Suffolk Campaign. She towed Ossipee to Washington 8 January, joining the campaign in April. She found Cohasset aground at the mouth of the Nampony 13 April and learned that the Confederates planned to cross the river to attack the Union's rear forces at Suffolk and to silence the gunboats for this purpose. Mount Washington exchanged artillery fire with the Confederates at Hampton Roads, 14 April, meeting sharp musketry. Later in April, she and Stepping Stones were fired on at Norfleet's Point. Towing West End downriver, Mount Washington ran aground but moved off with the next high tide. Four Negroes boarded her a few days later, reporting no sign of Confederates; nevertheless, Mount Washington was fired on moments later, and a severe engagement ensued.
After this venture, Mount Washington moved to the mouth of the Western Branch, 6 May, where she was completely riddled and disabled. Participating in the naval action against the batteries at Hatt's Point 12 May nearly destroyed her. She towed Sangandon off Jamestown Island 4 June. She joined the North Atlantic Blockading Squadron at Norfolk 25 February 1865. In April, she served as supply ship downriver until decommissioning. She was sold at public auction at Baltimore 21 June 1865. Redocumented 18 October 1865, she continued to serve American commerce until 1880.
