The Royal Navy had not been keen to sacrifice its advantage in steam ships of the line, but was determined that the first British ironclad would outmatch the French ships in every respect, particularly speed. A fast ship would have the advantage of being able to choose a range of engagement which could make her invulnerable to enemy fire. The British specification was more a large, powerful frigate than a ship-of-the-line. The requirement for speed meant a very long vessel, which had to be built from iron. The result was the construction of two s; and . The ships had a successful design, though there were necessarily compromises between 'sea-keeping', strategic range and armor protection; their weapons were more effective than those of "Gloire", and with the largest set of steam engines yet fitted to a ship they could steam at 14.3 knots (26.5 km/h). Yet the "Gloire" and her sisters had full iron-armor protection along the waterline and the battery itself. "Warrior" and "Black Prince" (but also the smaller "Defence" and "Resistance") were obliged to concentrate their armor in a central "citadel" or "armoured box", leaving many main deck guns and the fore and aft sections of the vessel unprotected. The use of iron in the construction of "Warrior "also came with some drawbacks; iron hulls required more regular and intensive repairs than wooden hulls, and iron was more susceptible to fouling by marine life.