Krupp armour was a type of steel armour used in the construction of capital ships starting shortly before the end of the 19th century. It was developed by Germany's Krupp Arms Works in 1893 and quickly replaced Harvey armour as the primary method of protecting naval ships.
The initial manufacturing of Krupp armour was very similar to Harveyized armour; however, while the Harvey process generally used nickel-steel, the Krupp process added as much as 1% chromium to the alloy in order to gain additional hardness. Also, while Harveyized armour was carburized by heating the steel and physically placing charcoal on its surface for long durations (often several weeks), Krupp armour took this basic idea a large step forward. Instead of attempting to inefficiently introduce carbon at the surface from coals, Krupp armour achieved greater depth of carbon cementation by applying carbon-bearing gases to the heated steel. Once the carburization process was complete, the metal was then transformed into face hardened steel by rapidly heating the cemented face, allowing the high heat to penetrate thirty to forty percent of the steel's depth, then quickly quenching first the superheated then both sides of the steel with powerful jets of either water or oil.
Krupp armour was swiftly adopted by the world's major navies; ballistic tests showed that 10.2 inches (25.9 cm) of Krupp armour offered the same protection as 12 inches (30.4 cm) of Harvey armour. By the early 20th century it was in turn rendered obsolete by the development of Krupp cemented armour.
- Brown, David K. (2003). Warrior to Dreadnought, warship development 1860-1905. Caxton Publishing Group. ISBN 1-84067-529-2.
- Gene Slover's US Navy Pages - Naval Ordnance and Gunnery
- Article on armour plates in 1911 edition of Encyclopædia Britannica