The Confederacy turned to ironclads, ships heavily armored with iron, in hopes to take away the Union's advantage at sea. So the Confederates captured a Union steamship, the Merrimack and turned it into an ironclad and renamed it the Virginia. The ironclad then sailed into Hampton Roads, Virginia, which is an important waterway guarded by Union ships. Before nightfall, the Virginia easily sank two of the Union's wooden warships, while it received minor damage. A Baltimore reporter predicted doom the next day.

The Union navy had already built its own ironclad, the Monitor, which was designed by Swedish-born engineer John Ericsson. Ericsson's ship had unusual new features like a revolving gun tower. The Monitor was called "a tin can on a shingle!" from one confederate soldier. Although the Monitor was small, it had thick planting and carried powerful guns.

When the Virginia returned to Hampton Roads later that month, the Monitors was waiting. After several hours of fighting, neither ship was seriously damaged, but the Monitor forced the Virginia to withdraw. This success saved the Union fleet and continued to blockade. The clash of the ironclads also signaled a revolution in naval warfare. The days of wooden warships powered by wind and sails were drawing to a close.