Their concept for the new ship centred on housing the guns in a citadel. This was an armoured box made of four and a half inch thick wrought iron plates bolted to 18 inches of teak, then mounted on the hull's one inch thick plating.

Behind this went the frames and timbers making a barrier three feet thick. It was impenetrable to contemporary guns, even at point-blank range.

The bow and stern were constructed with one inch thick wrought iron plates. Special compartments limited the spread of water.

This was the first time this technique had been used but it soon became standard world-wide.

The vessel was christened Warrior, a name inherited from a distinguished third rater recently broken up. She and her sister ship The Black Prince were to become the most feared ships afloat.