All or nothing (armor)

All or nothing is a method of naval warship armor, best known for its employment on dreadnought battleships. The concept involves heavily armoring the areas most important to a ship while the rest of the ship receives no armor.^[1] The "all or nothing" concept avoided light or moderate thicknesses of armor: armor was used in the greatest practicable thickness or not at all, thereby providing "either total or negligible protection".^[2] Compared to previous armoring systems, "all or nothing" ships had thicker armor covering a smaller proportion of the hull.

The ironclad battleship HMS Inflexible launched in 1876 had featured a heavily armored central citadel, with relatively unarmored ends; however, by the era of HMS Dreadnought, battleships were armored over the length of the ship with varying zones of heavy, moderate or light armor. The U.S. Navy adopted what was formally called "all or nothing" armor in the Standard-type battleships, starting with the Nevada class laid down in 1912.^[3] The Imperial Japanese Navy soon implemented the system in its Nagato-class battleships starting in 1917, and "All or Nothing" armor was later adopted by other navies after the First World War, beginning with the Royal Navy in its Nelson class.^[4]