 In their specific outer appearances, i.e.being essentially floating gun batteries encased in armored citadels, albeit powered, the low-freeboard Union and Confederate casemate ironclads were almost uniquely North American.However, the concept of a fixed armored citadel mounted on a warship housing the main armament itself, was further explored by European navies in the last trimester of the 19th century, by the French and British navies in particular, in no small part due to the inspiration gained from the Battle of Hampton Roads.