Why was nickel-chromium steel used for battleship armour plate?

Nickel-chromium steel was utilized for battleship armour plate primarily because it offered a superior combination of strength, toughness, and resistance to penetration compared to earlier materials.123

The development of this alloy was driven by the need to counter increasingly powerful armour-piercing shells. While early armour relied on wrought iron or compound steel-iron plates, the introduction of nickel significantly improved the resiliency of homogeneous steel plates. The subsequent addition of chromium further enhanced these properties, creating a high-strength material capable of withstanding the intense impact of naval artillery.123

Beyond its use in armaments, the alloying of nickel and chromium became a foundational development in metallurgy, as nickel toughens the steel and allows for more effective heat treatment of large sections. This evolution in steel production, supported by military demand, eventually paved the way for a wide range of modern high-strength steel applications.32