The USS Monitor was an ironclad warship used by the Union Navy during the US Civil War. It was a radical design that sat low on the waterline to present a very small target, and had a revolving turret rather than a broadside battery. The turret traversed with steam power, being about to make a full rotation in just under 23 seconds. During the Battle of Hampton Roads the turret was fitted with a pair of 11-inch guns.
It was rushed to take part in the second day of the Battle of Hampton Roads to oppose the Confederate ironclad that the CSA called the CCS Virginia that had been wrecking havoc on wooden Union ships. The USS Monitor engaged the Confederate ironclad for hours in the first ever battle of ironclad ships. In the end neither ship gained a decisive advantage before withdrawing.
The USS Monitor continued to help the union blockade Norfolk until the Confederacy was forced to scuttle its own ironclad as Union land forces closed off Norfolk and the river beyond it. The USS Monitor then sailed to support the Union army in the Battle Of Drewry’s Bluff. After that it moved to participate in the Union blockade of North Carolina, but floundered during a storm and sank.
Wikipedia, used generously as reference.