Ironclad

[CivilWarTalk]

ironclad

A warship with a wooden hull sheathed in iron for protection against gunfire.

 

[Mark F. Jenkins]

Not to be confused with an iron-hulled ship, which might be an ironclad or might not. The sidewheel gunboat USS Michigan on the Great Lakes was iron-hulled, but not an ironclad... an analogous difference would be an automobile and a tank. Both of steel, but the steel in the tank is specifically designed and intended as protection, where it's merely structural in the automobile.