To be precise, the
C.S.S. Virginia was built on the burnt-out shell of the
U.S.S. Merrimack. U.S. troops burned much of the
Gosport Navy Yard in
Norfolk,
Virginia in late April 1861 before evacuating following Virginia's
secession, but the destruction was incomplete. Almost all of the ships were destroyed (the
hull of the
Merrimack, burned to the waterline, was the only ship or ship part salvageable), but most of the armor and guns from the site itself were usable.
There was no such vessel as the C.S.S. Merrimack, and descriptions of this battle as "Monitor-Merrimack" are historically inaccurate. The ship built on the hull of the U.S.S. Merrimack was recommissioned the C.S.S. Virginia before it went out on its first foray as a Confederate warship, destroying the wooden Union vessels tooling around Hampton Roads and announcing the imminent obsolescence of wooden fleets.
Of course, historical inaccuracy didn't matter much to the Virginia Department of Transportation when Interstate 664's span from Newport News to Portsmouth, crossing waters in which the Monitor-Virginia battle occurred, was named the Monitor-Merrimack Bridge-Tunnel.