Vehicle armor

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

Military vehicles are commonly armored (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 armored. These vehicles include cars used by reporters, officials and others in conflict zones or where violent crime is common, and presidential limousines. Armored 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 specialized armor to protect them against impacts from micro-meteoroids or fragments of space junk. Modern aircraft powered by turbine engines usually have them fitted with a sort of armor 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.

The design and purpose of the vehicle determines the amount of armor plating carried, as the plating is often very heavy and excessive amounts of armor restrict mobility. In order to decrease this problem, some new materials (nanomaterials) and material compositions are being researched which include buckypaper, aluminium foam armour plates, ...

Materials

Metals

Steel

Rolled homogeneous armor 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.

Aluminum

Aluminum is used when light weight is a necessity. It is most commonly used on APCs and armored cars.

Iron

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

Titanium

Titanium has not seen much use due to its expense. It is however considered to be superior to most other metal armor types. 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

Because of its high density, depleted uranium can also be used in tank armor, sandwiched between sheets of steel armor plate. For instance, some late-production M1A1HA and M1A2 Abrams tanks built after 1998 have DU reinforcement as part of the armor plating in the front of the hull and the front of the turret, and there is a program to upgrade the rest.

Plastic

Plastic metal, was a type of vehicle armor 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 armor was highly effective at stopping armor piercing bullets because the hard granite particles would deflect the bullet which would then lodge between plastic armor and the steel backing plate. Plastic armor could be applied by pouring it into a cavity formed by the steel backing plate and a temporary wooden form.

Glass

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 armor.

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 behavior 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, aluminum oxynitride, is much lighter but at US$10–$15 per square inch is much more costly.

Ceramic

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

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

Composite armor is armor 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 armor. Composite armor 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 armor such as Chobham armor. Composite armor'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

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

Belt armor is a layer of armor-plating outside the hull of warships, typically on battleships, battlecruisers, cruisers and some aircraft carriers.

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 armor 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 armor 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 armor that was thinner or shallower than was desirable, to speed production and conserve resources.

Aircraft

Armour plating is usually not very common on aircraft, which generally rely on their speed and maneuverability to avoid ground fire, rather than trying to resist impacts. Additionally, any armor capable of stopping large-caliber 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 armor 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.

Armored fighting vehicles

The most heavily armored 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 armor to protect the crew. Outer armor is modular and enables quick replacement of damaged armor.

Technologies

T-34 with appliqué armor welded on.

For efficiency, the heaviest armor on an armored 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 defense or withdrawal operations.

Sloping and curving armor can both increase its protection. Given a fixed thickness of armor plate, a projectile striking at an angle must penetrate more armor 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.

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 armor

Vehicle composite add-on armor kit manufactured by Composhield

Appliqué armor 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 armor of the vehicle. An advantage of appliqué armor is the possibility to tailor the vehicle's protection level to a specific threat scenario.

Improvised armor

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

Vehicle armor 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. 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-armored in the field with glacis plates and other armor 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 armored with sandbags and locally fabricated steel armor plate. More recently, U.S. troops in Iraq armored Humvees and various military transport vehicles with scrap materials: this came to be known as "hillbilly armor" or "haji armor" by the Americans.

Spaced armor

Sturmgeschütz III with spaced armor plates.

Armour with two or more plates spaced a distance apart, called spaced armor, 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 armor, 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 armor in the form of armored skirts, to make their thinner side armor more effective against anti-tank fire.

The principle of spaced armor protects against high explosive anti-tank (HEAT) projectiles which create a focused jet of plasticized metal, very effective at the focus point, but much less so beyond there. Relatively thin armor plates or even metal mesh, much lighter than fully protective armor, can be attached as side skirts or turret skirts on tanks and other armored vehicles. This light armor detonates the warhead prematurely so that the jet of molten metal is focused well before the main armor, becoming relatively ineffective. Factory-made and improvised stand-off armor 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 armor was reintroduced in the 1960s on the German Leopard 1. There are hollow spaces inside this type of armor, increasing the length of travel from the exterior of the vehicle to the interior for a given weight of armor, 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 armor 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 armor plates increases the total volume covered by the armor, which by the Square-cube law increases the amount of armor needed for a given thickness by around the 2/3 power of the total volume. Also thinner sheets of armor can be more subject to damage by kinetic weapons than a single thicker layer of armor would be.

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

The Whipple shield uses the principle of spaced armor to protect spacecraft from the impacts of very fast micro meteoroids. 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 armor

The Merkava features extreme sloped armor on the turret

Sloped armor is armor that is mounted at a non-vertical and non-horizontal angle, typically on tanks and other armored fighting vehicles. For a given normal to the surface of the armor, its plate thickness, increasing armor slope improves the armor's level of protection by increasing the thickness measured on a horizontal plane, while for a given area density of the armor the protection can be either increased or reduced by other sloping effects, depending on the armor 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 armor in armored vehicles design. Another motive is the fact that sloping armor 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 armor

M60A1 Patton tank with Israeli Blazer ERA.

Explosive reactive armor, 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 armor, however, offers better protection. The only example currently in widespread service is Russian Kontakt-5. Reactive armor poses a threat to friendly troops near the vehicle.

Non-explosive reactive armor is an advanced spaced armor 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 armor

IDF

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

Slat armor 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. Slat armour can be defeated by tandem-charge designs such as the RPG-27 and RPG-29.

Electrically charged armor

Electrically charged armor is a recent development in the United Kingdom by the Defense Science and Technology Laboratory. 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 armored vehicles are considering this technology.

External links

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