American Civil War: USS Monitor and CSS Virginia (rebuilt from the engines and lower hull of the USS Merrimack) fight to a draw in the Battle of Hampton Roads, the first battle between two ironclad warships.

The American Civil War was a civil war in the United States between the Union and the Confederacy, which was formed in 1861 by states that had seceded from the Union. The central conflict leading to war was a dispute over whether slavery should be permitted to expand into the western territories, leading to more slave states, or be prohibited from doing so, which many believed would place slavery on a course of ultimate extinction.

USS Monitor was an ironclad warship built for the United States Navy during the American Civil War and completed in early 1862, the first such ship commissioned by the Navy. Monitor played a central role in the Battle of Hampton Roads on 9 March under the command of Lieutenant John L. Worden, where she fought the casemate ironclad CSS Virginia to a stalemate. The design of the ship was distinguished by its revolving turret, which was designed by American inventor Theodore Timby; it was quickly duplicated and established the monitor class and type of armored warship built for the American Navy over the next several decades.

CSS Virginia was the first steam-powered ironclad warship built by the Confederate States Navy during the first year of the American Civil War; she was constructed as a casemate ironclad using the razéed original lower hull and engines of the scuttled steam frigate USS Merrimack. Virginia was one of the participants in the Battle of Hampton Roads, opposing the Union's USS Monitor in March 1862. The battle is chiefly significant in naval history as the first battle between ironclads.

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 in the first engagement between ironclad warships.