The side wheel gunboat Mount Vernon, built at Philadelphia, Pennsylvania, 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 the subsequent Battle of Suffolk at the Norfleet House Battery, Mount Washington exchanged artillery fire with the Confederates at Hampton Roads, 14 April, meeting sharp musketry.

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.