Vehicle armour

• 1. Introduction

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  Vehicle armour is the system of materials and engineering decisions that stands between a crew and whatever is trying to kill them. Picture a Sherman tank in the final years of World War II: its crew has welded spare track links to the hull and piled sandbags into the turret, improvising extra protection with whatever was at hand. That image captures something essential about armour. It is never static. It evolves in direct response to the weapons arrayed against it, and the contest between the two has shaped military technology for generations. How does armour stop a bullet, a shaped charge, or a fragment of space debris? Why does the angle of a steel plate matter as much as its thickness? And how did engineers go from wrought iron backed by solid wood to depleted uranium sandwiched inside a main battle tank? Those are the questions this documentary will trace.

• 2. Metals Under Fire

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  Rolled homogeneous armour begins as a cast steel billet, which is then hammered and rolled while the steel is still red hot. Forging and rolling iron out the grain structure, eliminating the microscopic imperfections that would allow a crack to run through the metal on impact. Rolling also elongates the grains into long lines, so that stress can flow throughout the plate rather than concentrating in one vulnerable spot. The result is a material that is simultaneously strong, hard, and tough enough not to shatter under a fast, hard blow.

  Cast steel armour takes a different path. Instead of rolling, the molten steel is poured directly into the desired shape. Heat treatment of a fully formed casting is difficult or impossible, which makes cast armour softer than rolled plate. What it loses in hardness it gains in geometric flexibility, and that trade-off has made it a popular choice for the structural hull of modern tanks.

  Aluminium sits at the other end of the weight spectrum. It is not the strongest of metals, but it is cheap, lightweight, and sufficiently tough for armoured personnel carriers and armoured cars where keeping the vehicle mobile matters as much as keeping it protected. Titanium presents a more exotic option. It has nearly twice the density of aluminium, yet it can achieve a yield strength close to high-strength steels, giving it what engineers call a high specific strength. That combination of lightness and toughness has made it the material of choice in personal armour and military aviation. The USAF A-10 Thunderbolt II, the Soviet and Russian Sukhoi Su-25, and the Soviet and Russian Mil Mi-24 attack helicopter all seat their pilots inside a bathtub-shaped titanium enclosure specifically designed to absorb hits.

  At the heavy end of the density scale sits depleted uranium. Some late-production M1A1HA and M1A2 Abrams tanks built after 1998 incorporate depleted uranium reinforcement in the front of the hull and the front of the turret, sandwiched between layers of steel plate. Wrought iron, the material that once clad ironclad warships, rounds out the historical spectrum. Early European iron armour ran to between 10 and 12.5 centimetres of wrought iron, backed by up to a metre of solid wood. Steel rendered it obsolete by being significantly stronger at comparable weight.

• 3. Glass, Plastic, and Ceramics

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  Bullet-resistant glass reaches its stopping power not from a single thick pane but from a laminate. Layers of regular glass are bonded together with polyvinyl butyral, polyurethane, or ethylene-vinyl acetate to form a composite that has been in regular use on combat vehicles since World War II. That laminated type runs roughly 100 to 120 millimetres thick and is typically very heavy. A second design sandwiches a polycarbonate layer, products such as Armormax, Lexan, or Tuffak, between sheets of ordinary glass. The polycarbonate provides impact resistance against physical assault, while the glass itself, being much harder, flattens a bullet on contact and prevents penetration. That polycarbonate-glass type is usually 70 to 75 millimetres thick. A newer candidate, aluminium oxynitride, is significantly lighter but costs between ten and fifteen US dollars per square inch.

  Plastic armour has a stranger origin. The British Admiralty developed it in 1940 to protect merchant ships. Its original formula was 50 percent clean granite in half-inch pieces, 43 percent limestone mineral, and 7 percent bitumen, applied in a layer two inches thick and backed by half an inch of steel. The hard granite particles would deflect an armour-piercing bullet on contact, causing it to lodge harmlessly between the plastic layer and the steel backing. The material could be poured directly into a cavity formed by the steel plate and a temporary wooden form, which made it practical to fit to ships without a drydock.

  Ceramic armour works by a different mechanism, one that only became fully understood when high-speed photography became available in the 1980s. When a high-explosive anti-tank round strikes ceramic armour, the ceramic shatters on penetration. The highly energetic fragments destroy the geometry of the metal jet that a hollow-charge warhead depends on to penetrate steel. By disrupting that jet before it can concentrate, the ceramic layer greatly diminishes the round's penetrating power. Some main battle tanks use polyurethane in their applique armour as well, as seen in the BDD package applied to modernised T-62 and T-55 tanks.

• 4. Composite and Reactive Designs

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  Composite armour was initially developed in the 1940s, though it did not enter service until considerably later. Its defining feature is the combination of two or more materials with sharply different physical properties. Steel and ceramics are the most common pairing, though heavy metals are sometimes added specifically to counter kinetic energy penetrators.

  Soviet main battle tanks from the T-64 onward used a variety of fillers. The T-64 turret incorporated a layer of ceramic balls and aluminium sandwiched between castings of steel. Some models of the T-72 used a glass filler called Kvartz. Tank glacis plates were often a sandwich of steel and either textolite, a fibreglass-reinforced polymer, or ceramic plates. Later T-80 and T-72 turrets incorporated non-explosive reactive armour elements, the same general family used on modern Western and Israeli tanks.

  Explosive reactive armour was initially developed by German researcher Manfred Held while he was working in Israel. The principle places layers of high explosive between steel plates. When a shaped-charge warhead strikes, the explosive detonates and drives the steel plates into the incoming warhead, disrupting the flow of its liquid metal penetrator, typically copper heated to around 500 degrees Celsius. Russian Kontakt-5 is the only example of heavy reactive armour currently in widespread service. Explosive reactive armour does pose a risk to friendly troops standing near the vehicle when it activates.

  Non-explosive reactive armour takes a related but distinct approach. Rather than detonating, it uses materials that change their geometry under the stress of impact, deflecting or disrupting an incoming jet. Electric armour, developed in the United Kingdom by the Defence Science and Technology Laboratory, goes further still. Two thin shells separated by insulating material wrap the vehicle. The outer shell carries an enormous electrical charge; the inner shell is grounded. If a HEAT jet bridges the two shells, the stored electrical energy discharges through the jet and disrupts it. Trials of the technology have been described as extremely promising, and the developers of the Future Rapid Effect System were considering it for that vehicle family.

• 5. Geometry as Defence

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  Sloped armour exploits a geometric truth: a projectile striking a plate at an angle must pass through more material than one striking it head-on. For a fixed plate thickness, increasing the slope raises the effective depth the projectile must traverse. The sharpest angles on any tank are almost always found on the frontal glacis plate, both because the front is most likely to face enemy fire and because there is more room to slope steel in the longitudinal direction of the vehicle.

  Spaced armour carries that logic a step further by placing two or more plates with a gap between them. The principle has been in use since the First World War, when the Schneider CA1 and Saint-Chamond tanks employed it. Against kinetic energy penetrators, the interaction with the first plate can cause the round to tumble, deflect, deform, or disintegrate before it reaches the main armour. Against shaped-charge warheads, the benefit is different: the first plate triggers detonation prematurely, so the metal jet loses coherence and strikes the main armour spread across a broader area rather than focused to a point. The interior surfaces of the cavities are sometimes sloped as well, to catch the jet at an angle that further dissipates its energy. Taken to the lightest extreme, metal mesh or slatted plates attached as side skirts can achieve a meaningful version of this effect at a fraction of the weight.

  Slat armour applies the same idea to rocket-propelled grenades and anti-tank missiles with shaped-charge warheads. The slats are spaced so that the warhead either deforms before detonating or the fuze mechanism is damaged outright. Tandem-charge designs, such as the RPG-27 and RPG-29, were developed specifically to defeat slat armour by firing a precursor charge to clear the slats before the main warhead fires.

  V-hull designs transfer the geometry principle to mines and improvised explosive devices. Rather than stopping the blast, a v-shaped hull directs the force away from the crew compartment, channelling the energy to the sides and improving the odds that the people inside survive.

• 6. Beyond the Battlefield

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  Civilian armoured cars serve a range of functions that have nothing to do with organised warfare. Officials, journalists, and others working in conflict zones or high-crime environments rely on armoured vehicles for personal protection. Security firms use them routinely to carry money or valuables, reducing the risk of highway robbery or cargo hijacking.

  Spacecraft face a threat that has no analogue on Earth: micrometeoroid impacts and fragments of space debris travelling at velocities that would defeat most conventional armour. The Whipple shield addresses this by applying the logic of spaced armour. When a high-speed particle strikes the shield's first wall, it melts or breaks apart, scattering fragments over a wider area. Those dispersed fragments then strike subsequent walls with far less concentrated energy, greatly reducing the risk of penetrating the spacecraft hull.

  Jet aircraft face their own internal threat. If a fan, compressor, or turbine blade breaks free inside a gas turbine engine, the resulting fragments can destroy the airframe or injure people nearby. Modern jet engines are fitted with an aramid composite kevlar bandage around the fan casing, or with debris containment walls built into the casing, to catch and contain those fragments. Windscreens on larger aircraft, civilian as well as military, are made of laminated impact-resistant materials to handle bird strikes and debris.

  Researchers are exploring materials that might resolve the fundamental tension between protection and weight. Buckypaper and aluminium foam armour plates are among the candidates currently under investigation. The Israeli Merkava tank points toward a different approach: each component of the tank is designed to function as supplementary armour for the crew, and the outer armour is modular so that damaged sections can be replaced quickly in the field.