The USS Monitor had a predecessor - Apparently.
The USS Monitor, famous for its role in the American Civil War, had a prototype predecessor built in 1862, just a few months before its famous battle with the CSS Virginia. The USS Monitor's designer, Swedish-American engineer John Ericsson, built a smaller version, the USS Monitor's "half-sister," the "Monitor's prototype" or "Monitor No. 1," but it was too slow and was not completed in time for the war.