USS Agamenticus, a 3295-ton Monadnock class twin-turret monitor built at the Portsmouth Navy Yard, Kittery, Maine, was commissioned May 1865, just as the Civil War was ending. After brief service along the northeastern U.S. coast, she was decommissioned at Boston, Massachusetts, in September 1865. Renamed Terror in June 1869, while still laid up, she reentered commissioned service in late May 1870. The monitor operated in the western Atlantic and in the Gulf of Mexico until June 1872, when she was again laid up, this time at the Philadelphia Navy Yard, Pennsylvania. Two years later, she was broken up and her name used in building a new monitor, which was finally commissioned more than two decades later as USS Terror.