A naval battle between two ironclad ships during the American Civil War would herald the change in ship technology leading to the use of metal over wood in shipbuilding. Wood was used in shipbuilding for centuries. Ships built for combat would often have thickened wooden hulls to reduce the impact of cannons and musket fire. The downside of building huge warships was sometimes they would be too heavy. They might be well armed and deliver heavy blows but smaller more maneuverable warships would be able to move around her easily and perhaps just outside their cannon limits. 

By the 19th century, the idea of using metal armor of some kind on ships was being considered. With cannon technology able to deliver massive blows, wood was no longer practical in battle. If you were up against a ship armed with those cannons, you probably would think twice about taking them on knowing they could sink you with just a few cannon shots and possibly out of distance of your own guns. The heavy weight of the metal made it impractical for sail powered vessels but the development of steam technology changed that. The French were the first to use ironclad ships during the Crimean War (1854-1855). Their armored ships withstood significant damage but their floating batteries defeated Russian coastal fortifications. The French would follow later with the first oceangoing ironclad frigate Gloire in 1859. The British would build the  HMS Warrior.

At the start of the American Civil War, the Union Navy was not that much interested in ironclad ships. Once they learned the Confederate Navy was converting a ship to an ironclad (the Virginia), they realized the necessity of having one of their own. The feared the Confederate ship would cause damage not only to Union ships and coastal cities and riverfronts. Congress approved funding of armored ships and the rush was on to build the USS Monitor. Construction was begun on 25 October 1861 and launched on 30 January 1862. The Virginia had sunk two Union frigates (Cumberland and Congress) and on 8 March 1862 forced the steam frigate Minnesota aground near Hampton Roads, Virginia before the Monitor arrived that night.

On 9 March 1862, the USS Monitor and CSS Virginia engaged in battle. The four hour battle that ensued saw neither ship destroy or seriously damage the other despite close range heavy cannon fire. However while it was a draw, the Monitor succeeded in defending the Minnesota and other Union ships threatened by Virginia. Thus the Union was able to hold on to Hampton Roads leaving the Confederacy with Norfolk and several rivers. Also as a result of the battle, the North would build more ironclads improving on the design in the process. The Confederacy would start construction on Virginia II.

Two months later the Confederacy was forced to scuttle the Virginia when Union forces attacked James Peninsula forcing a retreat. The Monitor was sunk in a storm off Cape Hatteras, North Carolina on 31 December 1862 with a loss of 16 seaman and four officers. The wreck was not located until 27 August 1973 but not confirmed until 1974 when clear photos taken proved it was the Monitor. When the U.S. Navy formally abandoning its claim on the wreck in the 1950’s, it was open to anyone. Since it was located in North Carolina territorial limits, the wreck and a specific radius around it was declared a marine sanctuary on 30 January 1975 and a National Historic Landmark in 1986.

Sources:

History.com
Monitor National Marine Sanctuary
USS Monitor Center
Wikipedia