Military vehicles are commonlyarmoured (or armored;see spelling differences) to withstand the impact ofshrapnel,bullets,shells,rockets, andmissiles, protecting the personnel inside from enemy fire. Such vehicles includearmoured fighting vehicles liketanks,aircraft, andships.
Civilian vehicles may also be armoured. These vehicles include cars used byofficials (e.g.,presidential limousines),reporters and others in conflict zones or where violent crime is common. Civilianarmoured cars are also routinely used by security firms to carry money or valuables to reduce the risk ofhighwayrobbery or thehijacking of the cargo.
Armour may also be used in vehicles to protect from threats other than a deliberate attack. Somespacecraft are equipped with specialised armour to protect them against impacts frommicrometeoroids or fragments ofspace debris. Modern aircraft powered byjet engines usually have them fitted with a sort of armour in the form of anaramidcompositekevlar bandage around the fan casing or debris containment walls built into the casing of theirgas turbine engines to prevent injuries orairframe damage should the fan, compressor, orturbine blades break free.[1]
Thedesign and purpose of the vehicle determines the amount of armour plating carried, as the plating is often very heavy and excessive amounts of armour restrict mobility. In order to decrease this problem, some new materials (nanomaterials) and material compositions are being researched which includebuckypaper,[2] andaluminium foam armour plates.[3]
Rolled homogeneous armour is strong, hard and tough (does not shatter when struck with a fast, hard blow). Steel with these characteristics is produced by processingcast steel billets of appropriate size and then rolling them into plates of required thickness.[4] Rolling and forging (hammering the steel when it is red hot) irons out the grain structure in the steel, removing imperfections which would reduce the strength of the steel.[5] Rolling also elongates thegrain structure in the steel to form long lines, which enables the stress the steel is placed under when loaded to flow throughout the metal, and not be concentrated in one area.[4]
Cast homogenous armour orcast steel armour is produced by directlycasting steel into the desired shape.[6] It tends to be softer as heat treatment is difficult or impossible. Nevertheless, the flexibility in shape has made it popular as the structural hull in modern tanks.[7]
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Aluminium is used when light weight is a necessity. It is most commonly used onAPCs andarmoured cars. While certainly not the strongest metal, it is cheap, lightweight, and tough enough that it can serve as easy armour.
Wroughtiron was used onironclad warships. Early European iron armour consisted of 10 to 12.5 cm of wrought iron backed by up to one metre of solidwood. It has since been replaced by steel due to steel being significantly stronger.
Titanium has almost twice the density of aluminium, but can have a yield strength similar to high strength steels, giving it a highspecific strength. It also has a high specific resilience and specific toughness. So, despite being more expensive, it finds an application in areas where weight is a concern, such aspersonal armour andmilitary aviation. Some notable examples of its use include theUSAFA-10 Thunderbolt II and the Soviet/Russian-builtSukhoi Su-25 ground-attack aircraft, utilising a bathtub-shaped titanium enclosure for the pilot, as well as the Soviet/RussianMil Mi-24 attack helicopter.
Because of its high density,depleted uranium (DU) can also be used in tank armour, sandwiched between sheets of steel armour plate. For instance, some late-productionM1A1HA and M1A2 Abrams tanks built after 1998 have DU reinforcement as part of the armour plating in the front of the hull and the front of the turret, and there is a program to upgrade the rest (seeChobham armour).
Plastic metal was a type of vehicle armour originally developed formerchant ships by theBritish Admiralty in 1940. The original composition was described as 50% cleangranite of half-inch size, 43% oflimestone mineral, and 7% ofbitumen. It was typically applied in a layer two inches thick and backed by half an inch ofsteel.
Plastic armour was highly effective at stoppingarmour piercing bullets because the hard granite particles would deflect the bullet, which would then lodge between 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.
Some main battle tank armour utilises polymers, for example polyurethane as used in the "BDD" appliqué armour applied to modernizedT-62 andT-55.
Bulletproof glass is a colloquial term forglass that is particularly resistant to being penetrated when struck bybullets. The industry generally refers to it asbullet-resistant glass ortransparent armour.
Bullet-resistant glass is usually constructed using a strong buttransparent material such aspolycarbonatethermoplastic or by using layers oflaminated glass. The desired result is a material with the appearance and light-transmitting behaviour of standard glass, which offers varying degrees of protection fromsmall arms fire.
The polycarbonate layer, usually consisting of products such as Armormax,Makroclear, Cyrolon,Lexan or Tuffak, is often sandwiched between layers of regular glass. The use of plastic in the laminate provides impact-resistance, such as physical assault with a hammer, an axe, etc. The plastic provides little in the way of bullet-resistance. The glass, which is much harder than plastic, flattens the bullet and thereby prevents penetration. This type of bullet-resistant glass is usually 70–75 mm (2.8–3.0 in) thick.
Bullet-resistant glass constructed of laminated glass layers is built from glass sheets bonded together withpolyvinyl butyral,polyurethane orethylene-vinyl acetate. This type of bullet-resistant glass has been in regular use oncombat vehicles sinceWorld War II; it is typically about 100–120 mm (3.9–4.7 in) thick and is usually extremely heavy.
Newer materials are being developed. One such,aluminium oxynitride, is much lighter but at US$10–15 per square inch is much more costly.
Ceramic's precise mechanism for defeatingHEAT was uncovered in the 1980s. High speed photography showed that the ceramic material shatters as the HEAT round penetrates, the highly energetic fragments destroying the geometry of the metal jet generated by thehollow charge, greatly diminishing the penetration. Ceramic layers can also be used as part of composite armour solutions. The high hardness of some ceramic materials serves as a disruptor that shatters and spreads thekinetic energy of projectiles.
Composite armour is armour consisting of layers of two or more materials with significantly different physical properties;steel andceramics are the most common types of material in composite armour.Composite armour was initially developed in the 1940s, although it did not enter service until much later and the early examples are often ignored in the face of newer armour such asChobham armour. Composite armour's effectiveness depends on its composition and may be effective againstkinetic energy penetrators as well asshaped chargemunitions;heavy metals are sometimes included specifically for protection from kinetic energy penetrators.
Composite armour used on modern Western and Israeli main battle tanks largely consists of non-explosive reactive armour (NERA) elements - a type ofreactive armour. These elements are often a laminate consisting of two hard plates (usually high hardness steel) with some low density interlayer material between them. Upon impact, the interlayer swells and moves the plates, disrupting heat 'jets' and possibly degrading kinetic energy projectiles. Behind these elements will be some backing element designed to stop the degraded jet or projectile element, which may be of high hardness steel, or some composite of steel and ceramic or possibly uranium.
Soviet main battle tanks from theT-64 onward utilised composite armour which often consisted of some low density filler between relatively thick steel plates or castings, for exampleCombination K.[8] For example, the T-64 turret had a layer of ceramic balls and aluminium sandwiched between layers of cast steel armour,[9] whilst some models of theT-72 features a glass filler called "Kvartz". The tankglacis was often a sandwich of steel and some low density filler, either textolite (afibreglass reinforced polymer) or ceramic plates.[10] Later T-80 and T-72 turrets contained NERA elements, similar to those discussed above.[11][12]
Belt armour is a layer of armour-plating outside thehull of warships, typically onbattleships,battlecruisers,cruisers and someaircraft carriers.[13]
Typically, the belt covers from the deck down some way below thewaterline of the ship. If built within the hull, rather than forming the outer hull, it can be fitted at an inclined angle to improve the protection.
When struck by ashell ortorpedo, the belt armour is designed to prevent penetration, by either being too thick for the warhead to penetrate, or sloped to a degree that would deflect either projectile. Often, the main belt armour was supplemented with atorpedo bulkhead spaced several metres behind the main belt, designed to maintain the ship's watertight integrity even if the main belt were penetrated.
The air-space between the belt and the hull also addsbuoyancy. Several wartime vessels had belt armour that was thinner or shallower than was desirable, to speed production and conserve resources.
Deck armour on aircraft carriers is usually at theflight deck level, but on some early carriers was at thehangar deck. (Seearmoured flight deck.)
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Armour plating is not common on aircraft, which generally rely on their speed and maneuverability to avoid attacks from enemy aircraft and ground fire, rather than trying to resist impacts. Additionally, any armour capable of stopping large-calibre anti-aircraft fire or missile fragments would result in an unacceptable weight penalty. So, only the vital parts of an aircraft, such as theejection seat and engines, are usually armoured. This is one area where titanium is used extensively as armour plating. For example, in the AmericanFairchild Republic A-10 Thunderbolt II and the Soviet-builtSukhoi Su-25 ground attack aircraft, as well as theMil Mi-24 Hind ground-attack helicopter, the pilot sits in a titanium enclosure known as the "bathtub" for its shape. In addition, the windscreens of larger aircraft are generally made of impact-resistant,laminated materials, even on civilian craft, to prevent damage frombird strikes or other debris.
The most heavily armoured vehicles today are themain battle tanks, which are the spearhead of the ground forces, and are designed to withstandanti-tank guided missiles,kinetic energy penetrators,high-explosive anti-tank weapons,NBC threats and in some tanks even steep-trajectory shells. TheIsraeliMerkava tanks were designed in a way that each tank component functions as added back-up armour to protect the crew. Outer armour is modular and enables quickly replacing damaged parts.
For efficiency, the heaviest armour on anarmoured fighting vehicle (AFV) is placed on its front. Tank tactics require the vehicle to always face the likely direction of enemy fire as much as possible, even indefence orwithdrawal operations.
Sloping and curving armour can both increase its protection. Given a fixed thickness of armour plate, a projectile striking at anangle must penetrate more armour than one impactingperpendicularly. An angled surface also increases the chance of deflecting a projectile. This can be seen onv-hull designs, which direct the force of animprovised explosive device orlandmine away from the crew compartment, increasing crewsurvivability.[14]
Beginning during theCold War, many AFVs havespall liners inside of the armour, designed to protect crew and equipment inside from fragmentation (spalling) released from the impact of enemy shells, especiallyhigh-explosive squash head warheads. Spall liners are made ofaramids (Kevlar,Twaron),UHMWPE (Dyneema,Spectra Shield), or similar materials.
Appliqué armour,[15] or add-on armour, consists of extra plates mounted onto the hull or turret of an AFV. The plates can be made of any material and are designed to be retrofitted to an AFV to withstand weapons that can penetrate the original armour of the vehicle.[16][17] An advantage of appliqué armour is the possibility to tailor a vehicle's protection level to a specific threat scenario.
Vehicle armour is sometimes improvised in the midst of an armed conflict by vehicle crews or individual units. InWorld War II, British, Canadian and Polish tank crews welded spare strips of tank track to the hulls of theirSherman tanks.[18] U.S. tank crews often added sand bags in the hull and turrets on Sherman tanks, often in an elaborate cage made of girders. Some Sherman tanks were up-armoured in the field with glacis plates and other armour cut from knocked-out tanks to createImprovised Jumbos, named after the heavily armouredM4A3E2 assault tank. In theVietnam War, U.S. "gun trucks" were armoured with sandbags and locally fabricated steel armour plate.[19] More recently,U.S. troops in Iraq armouredHumvees and various military transport vehicles with scrap materials: this came to be known as "hillbilly armour" or "haji armour" by the Americans.[18] Moreover, there was theKilldozer incident, with the modified bulldozer being armoured with steel and concrete composite, which proved to be highly resistant to small arms.
Armour with two or more plates spaced a distance apart, called spaced armour, has been in use since theFirst World War, where it was used on theSchneider CA1 andSaint-Chamond tanks. Spaced armour can be advantageous in several situations. For example, it can reduce the effectiveness ofkinetic energy penetrators because the interaction with each plate can cause the round to tumble, deflect, deform, or disintegrate. This effect can be enhanced when the armour issloped. Spaced armour can also offer increased protection againstHEAT projectiles. This occurs because theshaped charge warhead can detonate prematurely (at the first surface), so that the metal jet that is produced loses its coherence before reaching the main armour and impacting over a broader area. Sometimes the interior surfaces of these hollow cavities are sloped, presenting angles to the anticipated path of the shaped charge's jet in order to further dissipate its power. Taken to the extreme, relatively thin armour plates, metal mesh, orslatted plates, much lighter than fully protective armour, can be attached as side skirts or turret skirts to provide additional protection against such weapons. This can be seen inmiddle and late-World War II German tanks, as well as many modernAFVs. Taken as a whole, spaced armour can provide significantly increased protection while saving weight.
The analogousWhipple shield uses the principle of spaced armour to protect spacecraft from the impacts of very fastmicrometeoroids. The impact with the first wall melts or breaks up the incoming particle, causing fragments to be spread over a wider area when striking the subsequent walls.
Sloped armour is armour that is mounted at a non-vertical and non-horizontal angle, typically on tanks and other armoured fighting vehicles. For a given normal to the surface of the armour, its plate thickness, increasing armour slope improves the armour's level of protection by increasing the thickness measured on a horizontal plane, while for a given area density of the armour the protection can be either increased or reduced by other sloping effects, depending on the armour materials used and the qualities of the projectile hitting it. The increased protection caused by increasing the slope while keeping the plate thickness constant, is due to a proportional increase of area density and thus mass, and thus offers no weight benefit. Therefore, the other possible effects of sloping, such as deflection, deforming and ricochet of a projectile, have been the reasons to apply sloped armour in armoured vehicles design. Another motive is the fact that sloping armour is a more efficient way of covering the necessary equipment since it encloses less volume with less material. The sharpest angles are usually seen on the frontal glacis plate, both as it is the hull side most likely to be hit and because there is more room to slope in the longitudinal direction of a vehicle.
Explosive reactive armour, initially developed by German researcher Manfred Held while working in Israel, uses layers ofhigh explosive sandwiched between steel plates. When a shaped-charge warhead hits, the explosivedetonates and pushes the steel plates into the warhead, disrupting the flow of the charge's liquid metal penetrator (usuallycopper at around 500 degrees Celsius;[citation needed] it can be made to flow like water by sufficient pressure). Traditional "light" ERA is less effective against kinetic penetrators. "Heavy" reactive armour, however, offers better protection. The only example currently in widespread service is RussianKontakt-5. Explosive reactive armour poses a threat to friendly troops near the vehicle.
Non-explosive reactive armour is an advanced spaced armour which uses materials which change their geometry so as to increase protection under the stress of impact.
Active protection systems use a sensor to detect an incoming projectile and explosively launch a counter-projectile into its path.
Slat armour is designed to protect againstanti-tank rocket and missile attacks, where the warhead is ashaped charge. The slats are spaced so that the warhead is either partially deformed before detonating, or the fuzing mechanism is damaged, thereby preventing detonation entirely. As shaped charges rely on very specific structure to create a jet of hot metal, any disruption to this structure greatly reduces the effectiveness of the warhead.[20] Slat armour can be defeated bytandem-charge designs such as theRPG-27 andRPG-29.[21]
Electric armour is a recent development in theUnited Kingdom by theDefence Science and Technology Laboratory.[22][23][24][25][26][27][28] A vehicle is fitted with two thin shells, separated by insulating material. The outer shell holds an enormouselectric charge, while the inner shell is at ground. If an incoming HEAT jet penetrates the outer shell and forms a bridge between the shells, the electrical energy discharges through the jet, disrupting it. Trials have so far been extremely promising, and it is hoped that improved systems could protect against KE penetrators. The developers of theFuture Rapid Effect System (FRES) series of armoured vehicles are considering this technology.[citation needed]
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