(SwGbt: t. 832, 1. 228'2", b. 33'10", dph. 11'3", dr.9'3"; cpl. 156; a. 1 100-pdr. P.r., 1 9" D. sb., 4 24-pdr. how.)
The first Sebago-a double-ended sidewheel gunboat built by the Portsmouth (N.H.) Navy Yard-was launched on 30 November 1861; and commissioned on 26 March 1862, Lt. Edmund W. Henry in command.
Sebago departed Portsmouth on 6 April 1862 and headed for Hampton Roads to join the North Atlantic Blockading Squadron and reached Newport News on the 11th. She was ordered to the York River to support General McClellan's push up the peninsula toward Richmond and operated in that river and its tributaries supporting Union Army operations. Then, on 30 June, after General Lee had defeated McClellan in the Seven Days Campaign and had driven the Army of the Potomac from the York to the James, Sebago steamed downstream, rounded Old Point Comfort, and ascended the James escorting Army transports.
Transferred to the South Atlantic Blockading Squadron later that month, Sebago departed Hampton Roads on 25 July and arrived off Charleston on the 29th to begin a year of blockade duty off the approaches to that important and historic Southern port. On 18 June 1863, the double ender ran aground in Wassaw Sound and suffered some damage. As she was due for an overhaul, she sailed north on 29 July and was decommissioned at the New York Navy Yard on 9 July.
Repairs and overhaul completed, Sebago was recommissioned on 2 December 1863 and sailed for the Gulf of Mexico for duty in the West Gulf Blockading Squadron in which she served through the end of the Civil War. The highlight of her operations in the gulf came on 5 August 1864 when she participated in the Battle of Mobile Bay.
After peace returned, Sebago sailed north and was decommissioned at the New York Navy Yard on 29 July 1865. She was sold at New York City on 19 January 1867.