These ships are classed as destroyers, but they are much larger than any other active destroyer or cruiser. The vessels' distinctive appearance results from the design requirement for a low radar cross-section (RCS). The "Zumwalt" class has a wave-piercing tumblehome hull form whose sides slope inward above the waterline, which dramatically reduces RCS by returning much less energy than a conventional flare hull form. The appearance has been compared to that of the historic USS "Monitor" and her famous antagonist CSS "Virginia".