The Monitor is most famous for the Battle of Hampton Roads, where she met the CSS Virginia (also known by its original name, the Merrimack). When Virginia seceded from the Union, the ships in the navy yard in Norfolk were scuttled to keep them from being seized by the Confederacy. Though the Merrimack was burned to the waterline, it was salvageable and the Confederates converted it into the iron-clad Virginia. When the North caught wind of this, the Monitor was hastily commissioned. Designed by John Ericsson, the bulk of the Monitor sat below the waterline to shield it from enemy fire. One of Ericsson's innovations was to have a fully armored gun turret atop the ship that could fire in every direction.
The Monitor and the Virginia met on March 9, 1862, during the Battle of Hampton Roads. The Confederates were attempting to destroy the Union blockade of Norfolk and Richmond. The previous day, the Virginia had inflicted serious damage on the Union navy, but when the Monitor arrived, she was able to hold the Virginia off and defend the Union ship Minnesota, which had run aground during the previous day's conflict. Though neither the Monitor nor the Virginia suffered serious damage, by the end of the second day's fighting, the Confederates decided to withdraw to Norfolk for repairs. The Virginia was scuttled just two months later when the Confederates abandoned Norfolk.
The Monitor didn't fare much better--on December 31, 1862, she ran into bad weather off Cape Hatteras, North Carolina, and sank. The wreck was discovered in 1973 and is now the centerpiece of the Monitor National Marine Sanctuary.
You can read more about efforts to preserve the decaying ship at http://www.marinersmuseum.org/uss-monitor-center/uss-monitor-center.
Though the Brooklyn Navy Yard is now closed (and its famed Admiral's Row on the verge of destruction), you can go down to Battery Park, where a handsome statue stands to John Ericsson. In his hand, he clutches a model of the Monitor.
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