Battle of Hampton Roads, aka the Battle of the Monitor and Merrimack

Naval history was made on March 8, 1862, when the first Confederate ironclad steamed down the Elizabeth River into Hampton Roads to attack the woodensided U.S. blockading fleet anchored there. Built on the hull of the U.S.S. Merrimac (which had been scuttled and burned when the Federals abandoned the Gosport Navy Yard in April, 1861), the new warship had been christened C.S.S. Virginia, but in common usage retained its original name. After ramming and sinking the twenty-four-gun woodenhulled steam-sailing sloop Cumberland, the Merrimac headed for the fifty-gun frigate Congress. An awestruck Union officer watched the one-sided fight as the Merrimac fired "shot and shell into her with terrific effect, while the shot from the Congress glanced from her iron-plated sloping sides, without doing any apparent injury."

http://www.civilwarhome.com/ironclad.htm