Monitor, perhaps, or the earlier French ironclad, I think named Le Hussard or something like that?
For Monitor, it would be all iron construction, the stealth capacity of a hull that had nothing to shoot at, and a single rotating turret with very large guns that could be aimed at will, without bringing the ship to bear.
For Le Hussard (sp?) it would be the deliberate iron construction of the hull, heavily clad, that promised to trounce its wooden opposition.
Both ships operated by steam, Monitor entirely, Le Hussard with sail assist.
[later edit - looking at earlier posts the French ship I was thinking of must be the Gloire, so it looks like I've staked it all on Monitor. Not a bad thing actually, a whole nation did once.]
Jim