What ship fought against the Monitor at the Battle of Hampton Roads—was it the Merrimac, Merrimack, or Virginia? And why is there so much confusion over the name of this ship? Even the people who built and served on the Confederate ironclad (the Virginia, at that point) seem to have gotten it wrong from time to time. It all goes back to the complicated circumstances (and spelling challenges) of the Civil War era.
The original U.S.S. Merrimack, named after a river in New Hampshire and Massachusetts, was launched in 1798 and lost at sea off the coast of Cape Cod soon after. The second U.S.S. Merrimack, also named for the river, was launched in 1855. Apparently a couple of the line drawings used in her construction spelled the ship's name as "Merrimac" (which is the name of a town in Massachusetts). Even Catesby Jones, who captained the Virginia in her battle against the U.S.S. Monitor, wrote letters home regarding his service on the former Merrimac. However, her official Navy name was Merrimack.
It was this ship that was scuttled by the Union at the outbreak of the Civil War, then raised and rebuilt as an ironclad by the Confederacy. As a Southern ironclad, she carried a new name—the C.S.S. Virginia. A number of U.S. Navy officers who had sailed with the Merrimack before the start of the war were from the South, and when they went home to fight for the Confederacy they carried their memories of the Merrimack with them. Those Confederate sailors had trouble calling her by her new name. The Union soldiers never bothered—to them she was their Merrimack through and through.
To further confuse the issue, an additional U.S.S. Merrimack was launched in 1941, and two U.S.S. Merrimacs served the U.S. Navy in the late 1800s. The final touch—the reason history books teach schoolchildren about the Monitor and the Merrimack—is that the Union won the war, and thus also the battle of the names.