(SwStr.: t. 974; l. 205'; b. 35'; dph. 11'6"; s. 9 k.; cpl. 173; a. 2 100-pdr. Pr., 4 9" D. sb., 2 24-pdr. how., 1 heavy 12-ipdr., 112pdr.)
Iosco, a wooden, double-ended, side-wheel gunboat, was launched by Larrabee & Allen, Bath, Maine, 20 March 1863; and commissioned at the Boston Navy Yard 26 April 1864, Comdr. A. J. Drake in command.
She was at New London, Conn., 9 June when ordered to New York to complete her crew.
Iosco sailed for the Gulf of St. Lawrence 28 August to protect American fishing vessels in that vicinity. Off Nova 'Scotia and Prince Edward Island, she assisted several ships endangered by fierce storms. She towed General Burnside off a reef 15 September and aided battered Colonel Ellsworth and the English bark Empress 2 days later.
Ordered to Hampton Roads 2 October to join the 1st Division of the North Atlantic Blockading -Squadron, Iosco was stationed off Wilmington, where she captured British schooner Sybil attempting to escape to sea with 307 bales of cotton 21 November.
On Christmas Eve 1864, Iosco participated in the first amphibious attack on Fort Fisher, N.C. which protected Wilmington, one of the South's most active centers of blockade running and her last port of entry for European aid. Her guns engaged the batteries at Mound Fort and succeeded in shooting down the Confederate flag which flew above the works. During the firing a Confederate shot carried away the head of Iosco's foremast. The next day, she led nine other ships in an attack on the fortress, closing the shore as near as her draft would permit. Meanwhile her boats dragged the channel for torpedoes. Throughout the operation she protected the right flank of the Union troops ashore until they reembarked under orders from the Army commander, Major General B. F. Butler 27 December 1864.
A fortnight later Iosco was again in the thick of the fighting during the second attack on Fort Fisher. She assisted the landing of troops and covered the right flank of the Army as it fought on shore 13 January 1865. Forty-four of her own men fought beside the soldiers on the beaches while her cannon fired at the mound until the Confederates surrendered 15 January.
The remainder of Iosco's wartime service was in the North Carolina Sounds carrying out operations as Confederate resistance ceased. She sailed north 15 July and decommissioned 28 July 1865. Her engines were removed and her hull turned over to the Bureau of Construction and Repair for service as a coal hulk at the New York Navy Yard in February 1868.
Iosco (AT-29) was renamed Tatnuck (q.v.) 24 February 1919.