The U.S. Army's M1 Abrams MBT with TUSK upgrade uses composite, reactive, and slat armour

Military vehicles are commonly armoured (or armored) to withstand the impact of shrapnel, bullets, missiles, or shells, protecting the personnel inside from enemy fire. Such vehicles include tanks, aircraft, and ships.

Civilian vehicles may also be armoured. These vehicles include cars used by reporters, officials and others in conflict zones or where violent crime is common, and presidential limousines. Armoured cars are also routinely used by security firms to carry money or valuables to reduce the risk of highway robbery or the hijacking of the cargo.

Armour may also be used in vehicles to protect from threats other than a deliberate attack. Some spacecraft are equipped with specialised armour to protect them against impacts from micrometeoroids or fragments of space junk. Modern aircraft powered by turbine engines usually have them fitted with a sort of armour in the form of an aramid composite kevlar bandage around the fan casing or of debris containment walls built into the casing of their gas turbine engines to prevent injuries or airframe damage should the fan/compressor/turbine wheel disintegrate.^[1]

The design 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 include buckypaper,^[2] aluminium foam armour plates,^[3] ...

Materials[link]

This section requires expansion.

Metals[link]

Steel[link]

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 processing cast steel billets of appropriate size and then rolling them into plates of required thickness. 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. Rolling also elongates the grain structure in the steel to form long lines, which enable the stress the steel is placed under when loaded to flow throughout the metal, and not be concentrated in one area.

Aluminium[link]

Aluminium is used when light weight is a necessity. It is most commonly used on APCs and armoured cars.

Iron[link]

Wrought iron was used on ironclad warships. Early European iron armour consisted of 10 to 13 cm of wrought iron backed by up to one meter of solid wood.

Titanium[link]

Titanium has not seen much use due to its expense. It is however considered to be superior to most other metal armour types.^{[by whom?]} However, some notable examples of its use include USAF A-10 Thunderbolt II and the Soviet/Russian-built Sukhoi Su-25 ground-attack aircraft, utilizing a bathtub-shaped titanium enclosure for the pilot, as well as the Soviet/Russian Mil Mi-24 attack helicopter.

Uranium[link]

Because of its high density, depleted uranium can also be used in tank armour, sandwiched between sheets of steel armour plate. For instance, some late-production M1A1HA 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 (see Chobham armour).

Plastic[link]

Plastic metal, was a type of vehicle armour originally developed for merchant ships by the British Admiralty in 1940. The original composition was described as 50% clean granite of half-inch size, 43% of limestone mineral, and 7% of bitumen. It was typically applied in a layer two inches thick and backed by half an inch of steel.

Plastic armour was highly effective at stopping armour 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.

Glass[link]

Ballistic test of a bullet-resistant glass panel

Bulletproof glass is a colloquial term for glass that is particularly resistant to being penetrated when struck by bullets. The industry generally refers to it as bullet-resistant glass or transparent armour.

Bullet-resistant glass is usually constructed using a strong but transparent material such as polycarbonate thermoplastic or by using layers of laminated glass. The desired result is a material with an appearance and light-transmitting behaviour of standard glass but offers varying degrees of protection from small 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 with polyvinyl butyral, polyurethane or ethylene-vinyl acetate. This type of bullet-resistant glass has been in regular use on combat vehicles since World 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[link]

Ceramic's precise mechanism for defeating HEAT 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 the hollow charge, greatly diminishing the penetration.

Composite[link]

Plasan Sand Cat light (5t) military vehicle featuring integrated composite armoured body

Composite armour is armour consisting of layers of two or more materials with significantly different chemical properties; steel and ceramics 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 as Chobham armour. Composite armour's effectiveness depends on its composition and may be effective against kinetic energy penetrators as well as shaped charge munitions; heavy metals are sometimes included specifically for protection from kinetic energy penetrators.

Ships[link]

Diagram of common elements of warship armour. The belt armour is denoted by "A".

Belt armour is a layer of armour-plating outside the hull of warships, typically on battleships, battlecruisers, cruisers and some aircraft carriers.^[4]

Typically the belt covered from the deck down someway below the waterline of the ship. If built within the hull, rather than forming the outer hull it could be fitted at an inclined angle to improve the protection.

When struck by a shell or torpedo, 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 the shell or torpedo. Often, the main belt armour was supplemented with a torpedo bulkhead spaced several meters 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 adds buoyancy. Several wartime vessels had belt armour that was thinner or shallower than was desirable, to speed production and conserve resources.

Aircraft[link]

Armour plating is usually not very common on aircraft, which generally rely on their speed and manoeuvrability to avoid ground fire, rather than trying to resist impacts. Additionally, any armour capable of stopping large-calibre antiaircraft fire or missile fragments would be simply too heavy and overtax the powerplant. Still, this is one area where titanium is used extensively as armour plating. For example, in the USAF A-10 Thunderbolt II ground-attack aircraft and the Soviet-built Sukhoi Su-25 Frogfoot ground attack jet, as well as the Mil Mi-24 Hind ground-attack helicopter, the pilot sits in a titanium enclosure known as the "bathtub" for its shape. In addition, larger aircraft's cockpit glazing is generally made of impact-resistant, laminated materials, even on civilian craft, to prevent damage from striking birds or other debris.

Armoured fighting vehicles[link]

The most heavily armoured vehicles today are the main battle tanks, which are the spearhead of the ground forces, and are designed to withstand anti-tank missiles, kinetic energy penetrators, NBC threats and in some tanks even steep-trajectory shells. The Israeli Merkava tanks were designed in a way that each tank component functions as additional back-up armour to protect the crew. Outer armour is modular and enables quick replacement of damaged armour.

Technologies[link]

T-34 with appliqué armour welded on.

For efficiency, the heaviest armour on an armoured 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 in defence or withdrawal operations.

Sloping and curving armour can both increase its protection. Given a fixed thickness of armour plate, a projectile striking at an angle must penetrate more armour than one impacting perpendicularly. An angled surface also increases the chance of deflecting a projectile. This can be seen on v-hull designs, which direct the force of an Improvised explosive device or landmine away from the crew compartment, increasing crew survivability.^[5]

Beginning during the Cold War, many AFVs have spall liners inside of the armour, designed to protect crew and equipment inside from fragmentation (spalling) released from the impact of enemy shells, especially high explosive squash head warheads. Spall liners are made of Kevlar, Dyneema or similar materials.

Appliqué armour[link]

Vehicle composite add-on armor kit manufactured by Composhield

Appliqué armour ^[6] 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 which can penetrate the original armour of the vehicle.^[7][8] An advantage of appliqué armour is the possibility to tailor the vehicle's protection level to a specific threat scenario.

Improvised armour[link]

A Humvee equipped with the Marine Armor Kit in post-invasion Iraq

Vehicle armour is sometimes improvised in the midst of an armed conflict by vehicle crews or individual units. In World War II, British, Canadian and Polish tank crews welded spare strips of tank track to the hulls of their Sherman tanks.^[9] 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 create Improvised Jumbos, named after the heavily armored M4A3E2 assault tank. In the Vietnam War, U.S. "gun trucks" were armoured with sandbags and locally fabricated steel armour plate.^[10] More recently, U.S. troops in Iraq armoured Humvees and various military transport vehicles with scrap materials: this came to be known as "hillbilly armor" or "haji armor" by the Americans.^[9]

Spaced armour[link]

Sturmgeschütz III with spaced armour plates.

Armour with two or more plates spaced a distance apart, called spaced armour, when sloped reduces the penetrating power of bullets and solid shot as after penetrating each plate they tend to tumble, deflect, deform, or disintegrate, when not sloped reduces the protection offered by the armour, and detonates explosive projectiles before they reach the inner plates. It has been in use since the First World War, where it was used on the Schneider CA1 and St Chamond tanks. Many middle and late-World War II German tanks had spaced armour in the form of armoured skirts, to make their thinner side armour more effective against anti-tank fire.

The principle of spaced armour protects against high explosive anti-tank (HEAT) projectiles which create a focused jet of plasticised metal, very effective at the focus point, but much less so beyond there. Relatively thin armour plates or even metal mesh, much lighter than fully protective armour, can be attached as side skirts or turret skirts on tanks and other armoured vehicles. This light armour detonates the warhead prematurely so that the jet of molten metal is focussed well before the main armour, becoming relatively ineffective. Factory-made and improvised stand-off armour was introduced in the Second World War to defend against the new Bazooka, Panzerfaust, and other HEAT weapons.

In response to increasingly effective HEAT warheads, integral spaced armour was reintroduced in the 1960s on the German Leopard 1. There are hollow spaces inside this type of armour, increasing the length of travel from the exterior of the vehicle to the interior for a given weight of armour, to reduce the shaped charge's penetrating power. 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. For example, a given weight of armour can be distributed in 2 layers 15 cm (6 inch) thick instead of a single 30 cm (12 in) layer, giving much better protection against shaped charges.

Adding space between the armour plates increases the total volume covered by the armour, which by the Square-cube law increases the amount of armour needed for a given thickness by around the 2/3 power of the total volume. Also thinner sheets of armour can be more subject to damage by kinetic weapons than a single thicker layer of armour would be.

Today light armoured vehicles mount panels of metal rods, known as slat armour or cage armour, and some main battle tanks carry rubber skirts to protect their relatively fragile suspension and front belly armour.

The Whipple shield uses the principle of spaced armour to protect spacecraft from the impacts of very fast micrometeoroids. 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[link]

The Merkava features extreme sloped armour on the turret

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.

Reactive armour[link]

M60A1 Patton tank with Israeli Blazer ERA.

Explosive reactive armour, initially developed by German researcher Manfred Held while working in Israel, uses layers of high explosive sandwiched between steel plates. When a shaped-charge warhead hits, the explosive detonates and pushes the steel plates into the warhead, disrupting the flow of the charge's liquid metal penetrator (usually copper at around 500 degrees Celsius; it can be made to flow like water by sufficient pressure). Traditional "soft" ERA is less effective against kinetic penetrators. "Hard" reactive armour, however, offers better protection. The only example currently in widespread service is Russian Kontakt-5. 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[link]

IDF Caterpillar D9 armoured bulldozer with slat armour (in addition to armour plates and bulletproof windows). The D9 armour deflected RPG rockets and even 9K11 Malyutka (AT-3 Sagger) ATGMs.

Slat armour is designed to protect against anti-tank rocket and missile attacks, where the warhead is a shaped 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. ^[11] Slat armour can be defeated by tandem-charge designs such as the RPG-27 and RPG-29.^[12]

Electrically charged armour[link]

Electrically charged armour is a recent development in the United Kingdom by the Defence Science and Technology Laboratory.^{[13][14][15][16][17][18][19]} A vehicle is fitted with two thin shells, separated by insulating material. The outer shell holds an enormous electrical 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. Developers of the Future Rapid Effect System (FRES) series of armoured vehicles are considering this technology.^{[citation needed]}

See also[link]

• Active protection system
• Armoured fighting vehicle
• Armoured forces
• Main battle tank
• Non-military armoured vehicles
• Personal armour
• Plastic armour

References[link]

External links[link]

• Electrically charged armour
• Defense Systems - Idaho National Laboratory
• [1] - New Light Armor
• Modern armoured vehicles