USS Sebago was a large (832 long tons (845 t)) steamer with very powerful guns and four howitzers, purchased by the Union Navy during the beginning of the American Civil War.

With her large crew of 156 sailors, she served the Union Navy during the blockade of ports and waterways of the Confederate States of America as a gunboat.

Sebago — a double-ended, sidewheel gunboat built by the Portsmouth Navy Yard, Kittery, Maine — was launched on 30 November 1861; and commissioned on 26 March 1862, Lieutenant Edmund W. Henry in command.

Then, on 30 June, after General Robert E. Lee had defeated McClellan in the Seven Days campaign and had driven the Army of the Potomac from the York to the James River, Sebago steamed downstream, rounded Old Point Comfort, and ascended the James escorting Army transports.

After peace returned, Sebago sailed north and was decommissioned at the New York Navy Yard on 29 July 1865.