USS Agamenticus was laid down sometime in 1862 by the Portsmouth (N.H.) Navy Yard; and launched on 19 March 1863. Prior to her commissioning, the ship received an additional deck amidships, extending between the two turrets and over the machinery spaces. This "hurricane deck," added during 1864, provided better ship control and navigational facilities which wartime experience had shown was needed by monitor-type ships. Agamenticus was commissioned on 5 May at Portsmouth, Lt. Comdr. C. H. Cushman in command.
Agamenticus operated off the northeast coast of the United States from Maine to Massachusetts until she was decommissioned at the Boston Navy Yard on 30 September 1865, and remained laid-up at Boston for nearly five years. Renamed Terror on 15 June 1869, the monitor joined the North Atlantic Fleet on 27 May 1870. She primarily operated between Key West, Fla., and Havana, Cuba, over the next two years. During this time, the monitor and other units of the North Atlantic Squadron stood ready to protect American interests during unrest in Cuba and the West Indies. Early in 1870, the monitor steamed north to join a small, ad hoc squadron being formed under the aging Admiral David Farragut to take part in funeral services for George Peabody who had died in London. The remains of the well-known merchant and philanthropist were being returned to the United States by HMS Monarch escorted by United States corvette Plymouth. The American warships met the British turreted battleship off the New England coast late in January and escorted her into the harbor at Portland, Maine. The American ships then proceeded to Boston. Superintending the funeral service was Admiral Farragut's final official duty.
Terror remained with the North Atlantic Fleet until relieved on station at Key West by the single-turreted monitor Saugus on 17 May 1872. Terror, towed by the tug Powhatan, headed north for Philadelphia where she was placed out of commission and laid up on 10 June 1872. The ship then remained in ordinary at League Island into 1874.
During this time, from 1872 to 1874, her deterioration progressively worsened, with dry rot eating away her timbers. She was broken up in 1874 to be nominally rebuilt at Philadelphia by William Cramp and Sons.
Part of the text is incorporated from the United States Navy's Dictionary of American Naval Fighting Ships, a work in the public domain.