From vague memory, the two huge issues for armor plate (especially ~150 years ago) are:
- Having the extremely heavy equipment needed to roll very thick plates. ~Nothing except warship armor was anything resembling that thick, for such equipment to even have been developed previously.
- The specialized metallurgy & treatments needed to make "hard" armor. Iron/steel plate for other purposes (boilers, etc.) was optimized for physical properties which bore very little resemblance to "resistant to penetration by high velocity cannon balls".
https://steelplates.in/how-to-manufacture-steel-plates-sheet...
From vague memory, the two huge issues for armor plate (especially ~150 years ago) are:
- Having the extremely heavy equipment needed to roll very thick plates. ~Nothing except warship armor was anything resembling that thick, for such equipment to even have been developed previously.
- The specialized metallurgy & treatments needed to make "hard" armor. Iron/steel plate for other purposes (boilers, etc.) was optimized for physical properties which bore very little resemblance to "resistant to penetration by high velocity cannon balls".