A day after CSS Virginia devastated the Union's wooden fleet, the Union's own ironclad USS Monitor arrived and the two armored ships pounded each other for hours with cannon fire that mostly bounced off their iron plating. The inconclusive duel nonetheless signaled a revolution in naval warfare, rendering wooden warships obsolete overnight and triggering an international arms race in ironclad design.
The day before, the Confederate ironclad CSS Virginia, rebuilt from the scuttled hull of the USS Merrimack, had sailed into Hampton Roads and slaughtered the Union's wooden blockading fleet, sinking the USS Cumberland and burning the USS Congress while cannonballs simply bounced off her sloped iron armor. Union sailors watched in horror as their finest wooden warships proved utterly helpless.
Overnight, the Union's own experimental ironclad, USS Monitor, arrived at Hampton Roads after a harrowing journey down the coast that nearly sank her. On the morning of March 9, 1862, she interposed herself between Virginia and the grounded Union frigate Minnesota, and the two strange, low-slung armored vessels began a close-range duel that lasted roughly four hours.
Neither ship could seriously damage the other; shells that would have obliterated wooden hulls simply dented iron plate. The battle ended in a tactical draw, with both ships withdrawing, but naval architects worldwide understood immediately that wooden warships were finished. Within years, every major navy on earth was racing to build ironclads of its own.