The Canonicus-class monitor was a class of nine monitors built for the Union Navy during the American Civil War. They saw service in the Civil War and the Spanish–American War, although two of them were never commissioned.

The Passaic-class ironclad monitors of the U.S. Navy saw service in the U.S. Civil War and the Spanish–American War. The class was an improved version of USS Monitor equipped with a 15-inch Dahlgren gun in place of one of the 11-inch guns.