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 (1876) launched in 1876 had featured a heavily armored central citadel, with relatively unarmored ends; however, by the era of HMS Dreadnought (1906), 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 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.

Rationale
The logic of the design was simple. If the ship was hit in vital areas (the ammunition and propellant magazines; the propulsion plant; the fire-control and command sections), her survival was in jeopardy. On the other hand, if the ship were hit in non-vital areas (non-explosive stores, crew berthing and rest areas, offices and administrative areas), it would most likely not result in the ship's destruction.

The "all-or-nothing" philosophy of armor design required the rethinking of the ship’s design, her armor system and the integration of the ship’s design architecture with the armor protection system. With this rethinking of design, naval architects had to examine every system and function of a warship, and determine which functions and systems were critical (and in what priority) to the survival and mission accomplishment of the warship. This analysis led to designs in which all vital systems and functions were located in a single area within the hull of the vessel, the armored citadel; within and beneath which the propulsion plant, communications systems, weapons, ammunition stores, and command & control of the ship resided. Everything else resided outside of this armored citadel. When battle stations were called, the whole crew retreated into this area behind armored bulkheads and armored watertight doors, which were sealed so that each compartment within, and the armored citadel as a whole, were virtually immune to enemy action by any but concentrated and direct attack.



The all or nothing system was intended to ensure that battleships could survive against the heaviest armor-piercing shells currently in use, while at the same time being able to carry a powerful armament and retain a useful speed and endurance. This was made possible by dispensing with the large areas of relatively light armor which had been used in previous battleship designs; the weight saved was used to strengthen the armor protecting the "vitals" of the ship. In effect, the scheme accepted vulnerability to medium-caliber and high-explosive shells striking the unarmored sections of the hull, in order to improve resistance against large-caliber armor-piercing shells without increasing the overall weight of armor. The unarmored parts of the ship would not offer enough resistance to armor-piercing shells to trigger their firing mechanisms (designed to explode after penetrating armor) so the shells would pass through without exploding, while the vital parts could have armor thick enough to resist the heaviest shells.

In the ideal form of the system, all of a battleship's armor would be concentrated to form an armored "citadel" around the ship's magazine spaces: an armored box of uniform thickness designed to defend against the largest enemy guns. Save for the turrets, the ammunition hoists, conning tower and part of its steering gear, nothing in the way of armor protected the remainder of the ship. By stripping away the armor from all other parts of the ship the armor of the citadel could be made thicker.

The armored citadel can be visualized as an open-bottomed rectangular armored raft with sloped sides sitting within the hull of the ship. From this box, shafts known as barbettes would lead upwards to the ship's main gun turrets and conning tower. Through compartmentalization and the redundancy of key systems, any damage done to the ship outside of this armored box would be survivable, and as long as those systems within the box remain intact, the ship could continue to fight.

To maximize the thickness of armor available for a given weight it was desirable that the citadel be as small as possible. This was achieved by concentrating the ship's main battery in three turrets of triple or even two turrets of quadruple (quad) gun mountings, as opposed to World War I battleships which typically had four twin turrets for their large caliber guns (with HMS Agincourt having seven twin turrets). In some cases the turrets had an all-forward layout, such as the Royal Navy's and the French navy's.

Evolution
The majority of the battleships up through World War I vintage had armor disposed in belts of varying thickness around the hull, concentrating the main thickness at the point where the majority of the enemy shells would impact. The result of long years of experience, these bands of armor were effective protection when ships fought at close range. As the caliber of guns grew and fire-control systems improved, engagement ranges increased, so that a greater number of hits would result from plunging fire against the ship's thin deck armor rather than its well protected sides.



Although the U.S. Navy had begun work on the first all or nothing ship in 1911, with the USS Nevada (BB-36), the Royal Navy did not believe that long range gunnery would be important nor of the vulnerability of the ship's magazine spaces. However, experiences in the First World War, particularly the Battle of Jutland, showed that a ship could survive extensive damage as long as this was outside their magazine spaces, but any shell that breached the defenses of these spaces had catastrophic effects. The logical conclusion was that there was no point in having armor which could not stop a shell penetrating into the magazine spaces, and that any armor that did not contribute to this goal was wasted armor. The most important finding of the gunner trials on SMS Baden was that the 7 in thick medium armor was completely useless against large-caliber shells. As a result, the British navy adopted in the the "all or nothing" armor pioneered by the United States Navy.

The end of World War I and the Washington treaty put a temporary halt in the construction of new battleships. This hiatus was used to refine the protection for the next generation of battleships. It was at this time that the airplane and aerial bombs began to make an impact on naval warfare. With the signing of the Washington Treaty the Allies had an excess of old battleships, especially from the former Imperial German Navy. These were expended in gunnery and bombing trials. In the light of these experiments, it was believed that aerial bombs and the shells from the guns of enemy battleships would be fused to explode only after penetrating into a ship's vitals. If on its way through the ship there was nothing to activate the fuse, then the shell or bomb could pass through the ship without detonating, or if it did detonate, the blast would be outside of its armor. The ship would only sink if its own magazines were penetrated; thus the maximum thickness of armor would be around the magazine area, leading to the final manifestation of the ‘all or nothing’ scheme.

In practice
No navy built pure "all or nothing" battleships, although most navies put the theory into use to some degree. Designed and built within the full constraints of the Washington Treaty, the Royal Navy's and the French navy's  came closest to the ideal.

The misgivings of building a pure "all or nothing" ship was that these had areas still vulnerable to guns of even modest warships, small arms fire, and blast damage from a ship's own guns. For instance, blast damage was to plague the careers of the Nelsons, a situation aggravated by the positioning of her guns. It was also considered demoralizing for crew, for example those serving in the secondary batteries, to know that they had no protection. The superstructure, for instance, housed crucial command stations, communications, and radar equipment. Other critical areas such as the rudder, propellers, and bow could not be armored, so damage to these areas could reduce a ship's maneuverability and buoyancy.

From the on to its, the United States Navy pioneered the all or nothing approach without taking it to its logical conclusion. For example, the US designed its battleships to give the crew additional protection instead of relying only on the armored deck of the citadel. These vessels had three armored decks: a sacrificial armored top deck to decap and set off bombs and shells; a splinter deck between the top; and citadel decks to protect the majority of the crew from shell and bomb fragments. In World War II-era battleships and modernized Standard type battleships, the secondary armament was also in armored turrets, the same type of mounts also found in newer fleet carriers and cruisers, since this was a vital defense against enemy aircraft (particularly Kamikazes).

Regardless of armoring scheme used, battleships still had crucial areas that could not be protected such as the bow, rudder, and propellers; good examples include Bismarck and Prince of Wales. The superstructure housing command facilities, communications, and radar also remained vulnerable; for instance Tirpitz suffered extensive topside damage in Operation Tungsten.

In action
The battleship versus battleship showdown that all sides planned for never came about, so the benefits of the all or nothing ship's design were never fully tested.

There were few battleship-to-battleship encounters that took place in the Second World War. In the Atlantic, these included the Battle of Mers-el-Kébir in July 1940, Battle of Dakar in September 1940, the Battle of Denmark Strait and Last battle of the Bismarck in May 1941, the Battle of Casablanca in November 1942, and the Battle of North Cape in 1943. In the Pacific, there was the Second Naval Battle of Guadalcanal in November 1942 and the Battle of Surigao Strait in October 1944, part of the larger Battle of Leyte Gulf. In the Battle of Denmark Strait, HMS Prince of Wales (53) was hit repeatedly by 15 in (38 cm) AP shells, causing damage without seriously endangering the ship. HMS Hood (51) was built to an early standard and suffered a magazine explosion allowed by poor deck armor. A tilt of the ship towards Bismarck in her final turn exposed the deck armor when she made ready to unmask her rear battery. Using the older banded armor design that was geared towards shorter-range fire as in the Battle of Jutland, the Kriegsmarine's  was well-built and compartmentalised, and proved difficult to sink. Bismarck withstood tremendous punishment during her last battle, as an expedition later found out that almost no British heavy shells penetrated the Bismarck's citadel, although some main-turret barbettes were penetrated. Bismarck's sister ship Tirpitz suffered extensive topside damage from Royal Navy aerial strikes during Operation Tungsten but her vitals were relatively unharmed.

In the Second Naval Battle of Guadalcanal (also known as the fourth battle of Savo Island) USS South Dakota (BB-57) was hit by a 14 in (36 cm) armor-piercing round from the Japanese battleship Kirishima which shattered on a barbette without serious damage. Though South Dakota was in no danger of sinking, she was put out of action by faulty circuit breakers as well as damage from smaller caliber fire.

The Battle of Surigao Strait was the last battleship versus battleship encounter. Once the Japanese forces (after first being decimated by US destroyer torpedoes) reached the main US line, the deciding factor was the much greater numbers of the American forces, plus their superior radar, so the armor scheme of US battleships were not tested.