All or nothing (armor)

All or nothing is a method of armoring battleships, which involves heavily armoring the areas most important to a ship while the rest of the ship receives significantly less armor. 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". 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. "All or nothing" armor was later adopted by other navies after the First World War, beginning with the Royal Navy in its Nelson class.

Traditionally, a warship's armor system was designed both separate from, and after, the design layout. The design and location of various component subsystems (propulsion, steering, fuel storage & management, communications, range-finding, etc.) were laid out and designed in a manner that presented the most efficient and economical utilization of the hull’s displacement. Then armorers would attempt to design the application of barriers and deflectors which would protect vital areas of the hull, the superstructure, and its interior compartments from enemy shellfire, underwater mines, and torpedo attacks. There would also be attention paid to the limiting of sympathetic damage to hull compartments and spaces, caused as a consequence of primary damage to those hull compartments that directly received shellfire or underwater explosions.

The result of this approach was that armorers were "decorating" a warship’s hull, interior compartments, and spaces with armor, not according to any overall scheme or protective design. Taken collectively, the total weight of armor yielded by this absence of an overall plan for protection was in total, far greater than a realistic hull displacement could float. Consequently, naval architects of the hull and its propulsion system would demand a reduction in the weight of armor applied until the hull displacement and the deadweight of the hull returned the ship's hull form to the range, speed, and stability of the original design performance as specified.

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