Naval armour

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Naval armor refers to the various protections schemes employed by

Naval armour consists of many different designs, depending on what the armour is meant to protect against. Sloped armour and belt armour are designed to protect against shellfire; torpedo belts, bulges, and bulkheads protect against underwater torpedoes or naval mines; and armoured decks protect against air dropped bombs and long-range shellfire.

The materials that make up naval armour have evolved over time, beginning with simply wood, then softer metals like lead or bronze, to harder metals such as iron, and finally steel and composites.

Early ship armour probably had its origins in applying thin sheets of metal to ship undersides for preservative reasons.

The first

Ironclads were designed for several roles, including as high seas battleships, coastal defence ships, and long-range cruisers. The rapid evolution of warship design in the late 19th century transformed the ironclad from a wooden-hulled vessel which carried sails to supplement its steam engines into the steel-built, turreted battleships and cruisers familiar in the 20th century. This change was pushed forward by the development of heavier naval guns (the ironclads of the 1880s carried some of the heaviest guns ever mounted at sea)^{[citation needed]}, more sophisticated steam engines, and advances in metallurgy which made steel shipbuilding possible.

The rapid pace of change in the ironclad period meant that many ships were obsolete as soon as they were complete, and that naval tactics were in a state of flux. Many ironclads were built to make use of the

In turn the modern

The turn of the 20th century saw a development towards battleships, with large guns and copious armour. In previous eras, large caliber guns had been able to fire on the order of minutes, and were unwieldy to aim. But the development of powered aiming systems and ammunition hoists increased the rate of fire up to twice a minute, which combined with other developments, made battleships a finally useful force. The increasing calibers and muzzle velocity of guns required increasingly protective armor to stop projectiles. The development of new, more effective gunpowders also increased the length of guns, and the effective range of engagement. This meant that plunging fire became a serious concern, and lead to the strengthening of deck armor. Belt armor also became much thicker, surpassing 300 mm (12 in) on the largest battleships.^[8][9] One of the most heavily armored ships of all time, the Yamato-class battleship, had main belt of armour up to 410 millimetres (16.1 in) thick.^[10]

The development of the torpedo and effective naval mines required further considerations for underwater armor, which had not been given much thought in prior eras. The World War era also saw the emergence of the armoured cruiser, which traded some armor in exchange for speed as compared to a battleship.^[9]

Since World War II, naval armour has been less important, due to the development of

Armoured citadel

An

Simply sloping a piece of armour inherently increases its effectiveness by increasing the distance a projectile must travel to penetrate it. It also increases the odds that a projectile will ricochet off the target without causing damage.^[12]

Torpedo bulkhead

A

After the lessons learned during World War I, many capital ships were refitted with double, triple, or even quadruple torpedo bulkheads, as well as anti-torpedo bulges to the exterior of the hull.^[13]: 185 For example, the last US battleship designs during World War II had up to four torpedo bulkheads and a triple-bottom.^[13]: 185 The innermost bulkhead is commonly referred to as the holding bulkhead, and often this bulkhead would be manufactured from high tensile steel that could deform and absorb the pressure pulse from a torpedo hit without breaking. If the final bulkhead was at least 37 mm thick, it may also be referred to as an armoured bulkhead, as it would be capable of stopping splinters and shells with low striking velocities.^{[citation needed]}

Torpedo belt

The torpedo belt was part of the armouring scheme in some warships between the 1920s and 1940s. It consisted of a series of lightly armoured compartments, extending laterally along a narrow belt that intersected the ship's waterline. In theory this belt would absorb the explosions from torpedoes, or any naval artillery shells that struck below the waterline, and thus minimize internal damage to the ship itself.

Torpedo belts are also known as Side Protection Systems or SPS, or Torpedo Defense System or TDS.

Torpedo bulge

The development of aircraft carriers necessitated new forms of protection. An armoured flight deck is an aircraft carrier flight deck that incorporates substantial armour in its design.

Composition

Iron armour

Early experiments showed that wrought iron was superior to cast iron, and wrought iron was subsequently adopted for naval use. British efforts at perfecting iron armour were headed by a government Special Committee on Iron, formed in 1861 by War Secretary Lord Herbert for the continued research into naval armour. Among its members was Sir William Fairbairn, a noted civil and structural engineer who had also built over 80 iron vessels before retiring from shipbuilding. Other members included metallurgist John Percy, civil engineer William Pole and representatives of the Royal Engineers, Royal Artillery and Royal Navy. This committee worked four years, between 1861 and 1865, during which time it formulated the best performing armour with the metallurgy as then known, suggested ways for improving its production and quality and helped develop more effective shot against ironclad vessels.^[19]

For instance, two processes were used in constructing iron armour. In the first, hammering, large lumps of iron of scrap or puddled iron were heated to welding temperature and placed under heavy steel hammers. Repeated blows welded these lumps into one solid plate and shaped it to the required form and dimensions. Hammered iron plate was the armour used in the earliest ironclad vessels, including HMS Warrior. The second method, rolling, involved stacking iron lumps atop one another, heating them to welding temperature and passing them between two iron rollers to become one plate of the required size. Rolled iron was difficult to produce initially, as it required machinery of immense size and great power. However, when the Special Committee tested both types of plate in 1863, it found that rolled iron was superior to hammered due to greater uniformity in quality. The committee and iron manufacturers worked together on how to more easily produce rolled plate, which became standard use in warships beginning in 1865.^[20]

The committee addressed the use of wooden backing with iron armour. Early European iron armour consisted of between four and five inches (roughly 10 to 13 cm) of wrought iron backed by between 18 and 36 inches (roughly one-half to one metre) of solid wood. After considerable testing, the committee found that wood prevented spalling, cushioned the shock of a hit from damaging the structure of the ship and distributed the force over a larger area, which prevented penetration. The drawback of using wood and iron was extreme weight. Experiments with reducing or eliminating wooden backing to save weight proved unsuccessful. The committee also tested steel as potential armour as its members felt that the harder the armour, the better it might deflect or resist shot. However, the steel being produced at that time proved too brittle to be effective. Iron, being softer, bent, dented and distorted but held together and remained an effective means of protection.^[21]

Experiments were also carried out with

Due to the ever increasing thickness of the armour, and the associated weight, proposals were made from an early date to

By the mid-to-late 1870s, iron armour started to give way to steel armour, which promised to reduce the thickness, and therefore the weight, of the armour.

Harvey armour

Main article:

Hayward Augustus Harvey. The Harvey United Steel Company was a steel cartel whose chairman was Albert Vickers. The year 1894 would see the ten main producers of armor plate, including Vickers, Armstrong, Krupp, Schneider, Carnegie and Bethlehem Steel

, form the Harvey Syndicate.

Krupp armour

Krupp Arms Works in 1893 and quickly replaced Harvey armour

as the primary method of protecting naval ships, before itself being supplanted by the improved "Krupp cemented armour". 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%

quenching first the superheated side 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 in (260 mm) of Krupp armour offered the same protection as 12 in (300 mm) of Harvey armour.

Krupp cemented armour

By the early twentieth century, Krupp armour was rendered obsolete by the development of Krupp cemented armour (also "Krupp cemented steel", "K.C. armour" or "KCA"), an evolved variant of Krupp armour.[22] The manufacturing process remained largely the same, with slight changes in the alloy composition: in % of total – carbon 0.35, nickel 3.90, chromium 2.00, manganese 0.35, silicon 0.07, phosphorus 0.025, sulfur 0.020.^[23][24]

KCA retained the hardened face of Krupp armour via the application of carbonized gases but also retained a much greater fibrous elasticity on the rear of the plate. This increased elasticity greatly reduced the incidence of

spalling and cracking under incoming fire, a valuable quality during long engagements. Ballistic testing shows that KCA and Krupp armour were roughly equal in other respects.^[22]

Homogeneous Krupp-type armour

Developments in face-hardened armour in the late nineteenth and early to mid-twentieth centuries revealed that such armour was less effective against glancing oblique impacts. The hardened face layer's brittleness was counterproductive against such impacts. Consequently, alongside face hardened armour such as KCA, homogeneous armour types that combined ductility and tensile strength were developed to protect against glancing impacts.^[22] Homogeneous armour was typically used for deck armour, which is subject to more high-obliquity impacts and, on some warships such as Yamato class and Iowa class battleships, for lower belt armour below the waterline to protect against shells that land short and dive underwater.

Ducol steel

Ducol or "D"-steel is the name of a number of high-strength low-alloy steels of varying composition, first developed from the early 1920s by the Scottish firm of David Colville & Sons, Motherwell.

Applications have included warship hull construction and light armouring, road bridges, and pressure vessels including locomotive steam boilers and nuclear reactors.

Ships

Ducol has been used for bulkheads in both

Italian navies.^[25] After WW2 the highest grades of the commercial shipbuilding steels were based on this type of steel.^[26]

Royal Navy

Welded Ducol was used in HMS Nelson and HMS Rodney (1927), and may have contributed to initial structural damage when the big guns were fired.^[27] A solution was found by using rivets to attach the welded Ducol substructures to the hull rather than the original all-welded construction, allowing for some 'give'.^{[citation needed]}

It was used in British anti-torpedo-system design practice in its last battleships. The internal hull and torpedo bulkheads and internal decks were made of Ducol or "D"-class steel, an extra-strong form of

HTS. According to Nathan Okun, the King George V-class battleships had the simplest armour arrangement of all post-WWI capital ships. "Most of the load-bearing portions of the ship were constructed of British Ducol ("D" or "D.1") extra-high-strength silicon-manganese high-tensile construction steel, including the weather deck and the bulkheads."^[28]

HMS Ark Royal's fully-enclosed armoured hangar and the armoured flight deck which it supported were constructed of Ducol.^{[citation needed]}

Other types of armour used on Navy ships:

• HTS = High-tensile steel
• STS = Special treatment steel = homogenous armour

Imperial Japanese Navy

The

Hokkaidō, Japan: the company was set up with investment from Vickers, Armstrong Whitworth and Mitsui.^[29]

The Mogami-class cruisers were originally designed with all-welded Ducol bulkheads which were then welded to the ship's hull. The resultant faults caused by electric welding used in the structural portions of the hull resulted in deformation, and the main gun turrets were unable to train properly. They were re-built with riveted construction, and the other two were redesigned.^[30][31][32]

All of the following ships or classes (the list is not complete) used Ducol in structural bulkheads and protective plating:

• Japanese aircraft carrier Kaga (1928)
• Japanese cruiser Takao^[a][34]
• Mogami-class cruisers (x2, 1931), (x2 1933–34)
• Nagato-class battleships x2, (1920, upgraded 1934–36)
• Japanese aircraft carrier Shōkaku (1939)^[b]

Lengerer differs considerably as to what was made of Ducol, perhaps because of the extensive refit in 1934-36? "The lower strake of the armour was backed by 50 millimeters (2.0 in) of Ducol steel. The magazines were protected by 165 millimeters (6.5 in) of New Vickers Non-Cemented (NVNC) armour, sloped at an inclination up to 25° and tapered to thicknesses of 55–75 millimeters (2.2–3.0 in). The flight and both hangar decks were unprotected and the ships' propulsion machinery was protected by a 65-millimeter (2.6 in) deck of CNC armour.

The Shōkakus were the first Japanese carriers to incorporate a torpedo belt system. The torpedo bulkhead itself consisted of an outer Ducol plate 18–30 millimeters (0.71–1.18 in) thick that was riveted to a 12-millimeter (0.47 in) plate."^[36]

• Japanese battleship Yamato (1940)^[28][c]
• Japanese battleship Musashi (1940)
• Japanese aircraft carrier Hiyō (1941)^[38]
• Japanese cruiser Oyodo (1941)^[39]
• Agano-class cruisers x4, (1941–44)
• Japanese aircraft carrier Shinano (1944)

In addition, the IJN's '25-ton' type river

motor gun boat

had an all-welded hull, protected by 4-5mm Ducol steel.

Italian Navy

The Italian Navy used a similar type of steel to Ducol in its Pugliese torpedo defence system. This underwater "bulge" system was introduced in the Italian Littorio-class battleships, and in the completely rebuilt versions of the Italian battleship Duilio and the Conte di Cavour-class battleships. The inboard-facing side was consisted of a layer of silicon-manganese high-tensile steel from 28–40 mm (1.1–1.6 in) thick called "Elevata Resistenza" (ER) steel, which was probably somewhat similar to the British Ducol ("D" or "Dl") Steel used for light armour and torpedo bulkheads in WWII.^[40]

"However, the power of the torpedoes used during WWII rapidly outclassed even the best bulge protection systems and the magnetic pistol, when finally perfected, allowed the torpedo to completely bypass the bulge by detonating under the keel of the ship."^[40]

Plastic armour

Plastic armour (also known as plastic protection) was a type of vehicle armour originally developed for merchant ships by Edward Terrell of the British Admiralty in 1940. It consisted of small, evenly sized aggregate in a matrix of bitumen, similar to asphalt concrete. It was typically applied as a casting in situ in a layer about two inches (51 mm) thick on to existing ship structures made from one-quarter-inch-thick (6.4 mm) mild steel or formed in equally thick sections on a one-half-inch-thick (13 mm) steel plate for mounting as gun shields and the like. Plastic armour replaced the use of concrete slabs which, although expected to provide protection, were prone to cracking and breaking up when struck by armour-piercing bullets. Plastic armour was effective because the very hard particles would deflect bullets which would then lodge between the plastic armour and the steel backing plate. Plastic armour could be applied by pouring it into a cavity formed by the steel backing plate and a temporary wooden form. Production of the armour was by road construction firms and was carried out in a similar way to the production of road coverings, the organization of the armouring being carried out by naval officers in key ports.^{[citation needed]}

Electric armour

Electric armour is a type of armour proposed for the protection of ships and armoured fighting vehicles^[41] from shaped charge weapons. Electric armour uses a strong electric field to disrupt the jet of ionized gas produced by a warhead.^[42]

Electrically charged armour is a recent development in the United Kingdom by the Defence Science and Technology Laboratory.^{[43][44][45][46][47][48][49][needs update]} This functions by installing two conductive plates either side of an air gap or solid insulator with the plates attached to a capacitor holding a very high electrical charge, when a round or shell pierces the insulation and completes the circuit between the two plates the energy stored in the capacitor is discharged through the projectile vaporizing it.

Notes

Footnotes

1. ^ Japanese heavy cruiser Takao, along with Japanese battleship Nagato and the aircraft carrier Kaga and subsequent designs used torpedo bulges - inner curves formed by bulkheads made up of two 29mm plates providing 58mm of protetction. Also on Takao, Ducol was used on the conning tower (middle bridge deck). Torpedo warheads were also protected by a Ducol steel casing.^[33]
2. ^ "As already noted, in comparison with the preceding Hiryu, Shōkaku's armour protection was considerably improved. 25mm Ducol Steel (DS) steel plates protected her magazines and 132mm New Vickers non-cemented (NVNC) deck. Belt armour consisted of 16mm NVNC plates."^[35]
3. ^ The main portion of the central longitudinal structure was made with Ducol - rivetted, not welded, after problems with the Mogami-class cruisers. Also given 9mm deck plating.^[37]

References

1. ^ ^{a b} Samuel Hawley, The Imjin War. Japan's Sixteenth-Century Invasion of Korea and Attempt to Conquer China, The Royal Asiatic Society, Korea Branch, Seoul 2005, pages 193-199
2. ^ Stephen Turnbull, Fighting ships of the Far-East (2), page 18
3. ^ J. Rudloff (1910) "Die Einführung der Panzerung im Kriegschiffbau und die Entwicklung der ersten Panzerflotten", Beiträge zur Geschichte der Technik und Industrie, Vol. 2, No. 1 (1910), pages 2-3
4. ^ Robert Henry Thurston, "The Earliest Iron-Clad" in Cassier’s Magazine. vol. 6, 1891, pages 313-314
5. ^ Joseph Needham, Science, and civilization in China: Vol. 4, Physics and physical technology. Pt. 3, Civil engineering and nautics. Cambridge University Press (1971), pages 682-684 and 697
6. ^ Sondhaus, pp. 73–74
7. ^ Sondhaus, p. 86.
8. ^ "JDR Military Service - Battleship Service". web.mst.edu. Retrieved 2020-07-10.
9. ^ ^{a b c} "Naval ship - Armour". Encyclopedia Britannica. Retrieved 2020-07-10.
10. ^ Johnston and McAuley, p. 123
11. ^ Raven and Roberts, p. 9
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25. ^ Okun, Nathan. "Armor Profection of the Battleship KM Bismarck". Retrieved 14 August 2019.
26. ^ Okun, Nathan. "Table of Metallurgical Properties of Naval Armor and Construction Materials: Average Post-WWI Extra-High-Strength "D" Silicon-Manganese HT Steels". Retrieved 15 July 2019.
27. ^ Jordan 2011, p. 80. sfn error: no target: CITEREFJordan2011 (help)
28. ^ ^{a b} Okun, Nathan. "Armor protection of the battleship KM Bismarck". Retrieved 15 August 2019.
29. ^ "JSW Corporate Guide" (PDF). JSW: The Japan Steel Works, Ltd. October 2018. p. 1. Retrieved 15 August 2019.
30. ^ Caruana 1966, p. 58. sfn error: no target: CITEREFCaruana1966 (help)
31. ^ Lacroix 1981a, pp. 323–367. sfn error: no target: CITEREFLacroix1981a (help)
32. ^ Lacroix 1984, pp. 246–305. sfn error: no target: CITEREFLacroix1984 (help)
33. ^ Skulski 2004, p. 19. sfn error: no target: CITEREFSkulski2004 (help)
34. ^ Lacroix 1983, pp. 232–282. sfn error: no target: CITEREFLacroix1983 (help)
35. ^ Parry, Allan (ed.). "Warships of the Imperial Japanese Navy, Vol. 6 - Shokaku class, Soyru, Hiro, Unryu class, Taiho" (PDF). CombinedFleet.com. English Translation of Kojinsha Photo File. Retrieved 15 August 2019.
36. ^ Lengerer 2015, pp. 100–101, 102–106, 107–9. sfn error: no target: CITEREFLengerer2015 (help)
37. ^ Skulski 2017, pp. 12–13. sfn error: no target: CITEREFSkulski2017 (help)
38. ^ Lengerer & Rehm-Takahara 1985, pp. 9–19, 105–114, 188–193. sfn error: no target: CITEREFLengererRehm-Takahara1985 (help)
39. ^ Lengerer 2018, pp. 102, 104, 198. sfn error: no target: CITEREFLengerer2018 (help)
40. ^
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41. ^ "The armour strikes back". The Economist. 2011-06-02. Retrieved 2015-08-31.
42. ^ "Surface Forces: Electromagnetic Armor". Strategypage.com. 2007-08-14. Retrieved 2015-08-31.
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44. ISSN 0261-3077
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45. ^ "News". March 15, 2016. Archived from the original on December 17, 2008 – via www.telegraph.co.uk.
46. ^ MoD Develops 'Electric Armour' Archived April 10, 2010, at the Wayback Machine
47. ^ "New Age Electric Armour – Tough enough to face modern threats". Armedforces-int.com. Archived from the original on 2009-05-02. Retrieved 2012-01-29.
48. ^ "Add-On – Reactive Armor Suits". Defense-update.com. 2006-04-25. Archived from the original on 2012-01-26. Retrieved 2012-01-29.
49. ^ "Advanced Add-on Armor for Light Vehicles". Defense-update.com. 2006-04-25. Archived from the original on 2007-10-15. Retrieved 2012-01-29.