Vehicle armour
Military vehicles are commonly armoured to withstand the impact of shrapnel, bullets or shellss, protecting the soldiers inside from enemy fire. 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.
Spaced armour, introduced in the 1960s on the German Leopard 1 tank, uses the fact that a shaped charge makes a jet of molten metal and plasma that dissipates after it travels a meter or two. There are hollow spaces inside the armour, increasing the length of travel from the exterior of the vehicle to the interior, in hopes of reducing the shaped charge's penetrating power; in some cases the interior surfaces of these hollow cavities are sloped, presenting angles to the anticipated path of the shaped charge's plasma jet in order to further dissipate its power. Thus instead of having a single 30cm layer of steel armour, it is possible to have two 15cm layers half a meter or more apart, giving far greater protection against shaped charges at no penalty in weight.
Composite (aka Chobham) armour was developed in the 1970s by the British and first used on the German Leopard 2. It consists of layers of steel, ceramic, and plastic honeycomb, sometimes with layers of depleted uranium added. Composite is effective against both kinetic and shaped charge munitions. Against kinetic penetrators, the brittle ceramic blunts the projectile while the softer steel layers absorb its kinetic energy. Still, it is significantly less effective against shaped charge munitions, so sometimes depleted uranium layers are added to provide extra protection against these warheads.
An alternate description of Chobham is that it combines spaced armour with composites. Supposedly the exterior layer is a cast aluminum slab with rods of tungsten or depleted uranium running horizontally through it, intended to cause the points of high-velocity long-rod penetrator armour-piercing projectiles to bend, which sometimes causes the projectile to tip and strike the armour at an angle, presenting far greater surface area to the armour and therefore greatly increasing the resistance. Other layers in the armour are steel, with hollow spaces serving the same function that they do in spaced armour, often filled with layers of Kevlar or similar material to trap and reduce fragmentation.
Reactive armour, initially developed by 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 charge's plasma flow. It is less effective against kinetic penetrators.
Sloping and curving armour both increase the effective thickness, as a projectile striking at an angle must cut through more armour than one impacting perpendicularly. They also increase the chances of deflecting projectiles. The sloping front armour of a tank is often called the glacis, and provides the best protection as it is assumed to be the easiest part of the tank to hit. It is also made the thickest because the tank is usually considered an inherently offensive weapon, and it is has been assumed by designers since before the Second World War that a tank will be moving directly towards the enemy almost all the time; even on the defensive, a tank will be deployed in such a way as to have the glacis oriented in the direction from which the enemy is expected to attack.
Recently, many manufacturers have added a spall liner to the inside of the armour, which is designed to absorb fragmentation (spallation) released from the impact of an enemy shell, protecting soldiers and equipment inside. They tend to be made from kevlar or similar materials.
See also: Shield, Military history, Armoured fighting vehicle and Main Battle Tank
The novel "Armor"
Armor is also a military science fiction novel by John Steakley. It has some superficial similarities with Robert Heinlein's Starship Troopers (such as the military use of exoskeletons and insect-like alien enemies.) but this novel has more to do with the psychological effects of violence on human beings than with the political aspects of the military, which were the focus of Robert Heinlein's novel.
It was first published in december 1984.
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