<P> USS Merrimack, also improperly Merrimac, was a frigate, best known as the hull upon which the ironclad warship CSS Virginia was constructed during the American Civil War . The CSS Virginia then took part in the Battle of Hampton Roads (also known as "the Battle of the Monitor and the Merrimack") in the first engagement between ironclad warships . </P> <P> Merrimack was the first of six screw frigates (frigates with steam power and propeller, "screw") begun in 1854 . Like others of her class (Wabash, Roanoke, Niagara, Minnesota and Colorado), she was named after the eponymous river . In Massachusetts, the Merrimack River flows through the town of Merrimac, often considered an older spelling which has sometimes caused confusion of the name . </P> <P> Merrimack was launched by the Boston Navy Yard 15 June 1855; sponsored by Miss Mary E. Simmons; and commissioned 20 February 1856, Captain Garrett J. Pendergrast in command . She was the second ship of the Navy to be named for the Merrimack River . </P> <P> Shakedown took the new screw frigate to the Caribbean and to Western Europe . Merrimack visited Southampton, Brest, Lisbon, and Toulon before returning to Boston and decommissioning 22 April 1857 for repairs . Recommissioning 1 September 1857, Merrimack got underway from Boston Harbor 17 October as flagship for the Pacific Squadron . She rounded Cape Horn and cruised the Pacific coast of South and Central America until heading for home 14 November 1859 . Upon returning to Norfolk, she decommissioned 16 February 1860 . </P>

What metal were the monitor and merrimac made of