USS Merrimack, variant spelling Merrimac, was a steam 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. Merrimack was the first of six screw frigates (steam frigates powered by screw propellers) begun in 1854. Like others of her class (Wabash, Roano...