How did iron and steel armour improve the protection of warships?

The transition from wooden hulls to iron and steel armour was a critical evolution in naval warfare, driven by the need to counter increasingly powerful rifled guns and explosive shells.12

Early protection relied on wrought iron plates backed by thick wood, which provided essential resistance for early ironclads. To improve upon this, engineers developed compound armour—steel backed by iron—to leverage the surface hardness of steel alongside the resiliency of iron.31

Technological advancements further refined these defenses:
* Homogeneous Steel: An oil-tempering process created steel plates with superior resiliency, which were later enhanced by the addition of nickel.3
* Face-Hardening: The Harvey process applied carbon to the face of steel plates at high temperatures, significantly increasing hardness.3
* Advanced Alloys: The Krupp firm later introduced hot-gas tempering, and the subsequent addition of chromium to nickel steel became a standard for world navies, providing robust protection against armour-piercing projectiles.34

These innovations allowed warships to survive the escalating destructive power of naval artillery, ultimately shaping the design of the modern battleship.31