One of these, the, a three-masted tall ship, is kept as a commissioned ship of the US Navy (and hence is listed here), as a special commemoration for that ship alone.
One of these, the, a three-masted tall ship, is one of the Original six frigates of the United States Navy. It is the oldest naval vessel afloat, and still retains its commission (and hence is listed here), as a special commemoration for that ship alone.