The future of armour: The armour strikes back

IN THE first few days of the Yom Kippur war in October 1973, Israeli armoured units were attacked by Egyptian forces armed with Soviet-made anti-tank missiles. The Israelis “suffered wholesale destruction”, according to an American Army manual written soon afterwards to help counter the weapon in question. There was not much that could be done. As the American guide noted, the missile system—called Sagger by Western forces—could be carried in a suitcase, launched and steered using a joystick to hit a target 3km (1.9 miles) away. It would then penetrate any vehicle armour in existence.
Tanks had been destroyed with weapons carried by foot soldiers before; America introduced its M1 Bazooka during the second world war. But never had infantry so decimated armoured vehicles. Of Israel's roughly 2,120 tanks, about 840 were destroyed during the 20-day war. The era when “the tank was king” had ended, says Keith Brendley, head of Artis, an American firm that develops protection systems for military vehicles. Since then anti-tank munitions have become even more powerful, but steel armours have improved little. Now, however, aided with new materials and advanced sensors, a promising and eclectic array of alternative and often ingenious new forms of armour is emerging. 

Anti-tank missiles and rocket-propelled grenades (RPGs) penetrate armour with a shaped charge. This explodes after the tip of the warhead has sunk into the target. The brunt of the blast is projected straight ahead, forcing a powerful spike of metal, usually copper, into and through the armour. Using steel alone, few vehicles today could carry enough armour to stop even an inexpensive RPG reliably. 
Armour that explodes? Yes, really
To provide added protection, engineers have developed explosive-reactive armour. This involves covering parts of a vehicle with bricks of plastic explosives sandwiched between metal plates. When a warhead hits the outer metal plate, the explosives underneath (also specially shaped) detonate and force the sandwich to rapidly bulge as the plates move apart. This can shear the armour-piercing spike into bits, which are then less likely to pierce the underlying armour.
The Israel Defence Forces, shaken by their losses during the Yom Kippur war, developed an early but effective explosive-reactive armour that kept tank losses exceptionally light during the 1982 Lebanon war. The innovation, however, created a new problem: the explosive bricks generate shrapnel which can kill nearby infantry or civilians. As a result, when America's Bradley and Stryker fighting vehicles are clad in explosive-reactive armour they are not used in civilian areas.
Dynamit Nobel Defence, based in Burbach, Germany, is marketing a new metal-free explosive armour, called CLARA, that limits the number of such flying fragments. (The replacement materials are secret.) But no army has purchased it. Defence officials with one western European government have expressed concern that the extra protection to their armoured-vehicle crews would come at too great a cost: even explosive armours that produce less shrapnel could unacceptably endanger people near vehicles. Peter Lehniger of Dynamit Nobel Defence concedes that the armour “may not be, from a moral point of view, a good trade-off”.

Engineers are finding ways to use less explosive material. OJSC NII Stali, a Russian manufacturer, claims that by 2008 its reactive armour required only a quarter of the amount of explosives used in its 1999 version, but provided just as much protection. The earlier model's explosives detonated three to five microseconds after a warhead strike. Such “sluggishness”, according to the firm, has been eliminated, reducing the penetrating power of the spike. A danger, however, is that faster-reacting, more-sensitive explosives might detonate accidentally if hit by a bullet or another vehicle.
OJSC NII Stali and others are now developing non-explosive reactive armour, known as NxRA. This uses “energetic” but non-detonating rubber-like materials. Sandwiched between hard plates, they discharge a rapidly expanding gas to absorb energy from a warhead. The gas pushes out the external layer of armour so that it encounters the emerging spike at a glancing angle. “Bulging armour”, as this system is sometimes called, also increases the distance a spike must travel to enter the crew compartment.
Non-explosive reactive armours typically provide less stopping power, but they have an advantage in countering “tandem charge” munitions from systems like America's shoulder-launched Javelin and aircraft-launched Hellfire missiles. Once a brick of explosive armour detonates, that spot becomes more vulnerable to a second charge carried towards the rear of the same munition and detonated about 500 microseconds later. Rubbery non-explosive armour, in contrast, often remains partially intact. So-called “cage” armour can provide additional protection against tandem charges: metal bars (or even a strong fabric-like material) can make a warhead's first charge detonate a couple of dozen centimetres away from the vehicle.
With a clean hit, the Russian-made RPG-7, the most widely used anti-tank weapon, can sometimes penetrate more than 25cm of solid steel. A more recent model, the RPG-29, is even more formidable. To counter it, some European Union countries are developing electric armour. This consists of two electrically charged metal plates separated by an insulating layer. The idea is that when hit, the metal in a projectile shorts the two charged plates together, forming a circuit and releasing a surge of electricity which can break the warhead up.

Antoine Vincent, in charge of electric armour for the European Defence Agency (EDA), says it has tested well against RPGs. A study by BMT Defence Services, a British firm, notes that electric armour, being lightweight, makes it easier to airlift vehicles. Even so, neither BMT nor the EDA think the technology will be deployed soon. It has proven difficult to rearm the metal plates from batteries fast enough to zap the second charge of a tandem warhead. Some of the power-management technologies being developed for electric vehicles may help on that front. But, says Mr Vincent, electric armour still does not deliver enough electricity to fry the metal in many kinetic-energy projectiles, which destroy armour with their impact. An RPG warhead may eject a copper spike weighing several hundred grams. Kinetic-energy projectiles can weigh several kilograms.
Another approach is to use new materials. Steel armour performs well against a powerful, broad blast, but if the energy is focused on a small spot the metal can “melt like butter”, says an engineer with an American manufacturer of armoured vehicles. To cope with that, scientists have developed hard ceramic composites made from rubber and epoxy resins. Unlike steel, they respond to tremendous pressure by snapping. This action can break up a projectile or a shaped charge. A ceramic armour called Dorchester Level 2, used on British Challenger 2 tanks, is reportedly at least three times as resistant to some strikes as the same weight of steel.
The shockwave from a buried “improvised explosive device” (IED) can tear into a vehicle or toss it over. SJH Projects, a small British company, has developed a so-called “stone sponge” material that, fixed to a vehicle's undercarriage, partially absorbs the blast. XPT, as it is called, is a roughly 2cm-thick sheet of silica particles glued together with a strong, heat-resistant resin. Small pores, visible with a magnifying glass, channel the blast into mazes of micro-chambers. As they are destroyed, the blast-energy is absorbed. It costs about $17,000 to protect a jeep-sized vehicle using XPT, and it only works once. Steve Holland, the owner of SJH Projects, says NATO trials with crash-test dummies show that the material dramatically reduces spine and skeletal injuries.
Does this mean armour is catching up with weapons technology? Hardly. Armour is getting better, but weapons are getting deadlier. Consider the Panzerfaust 3 (literally, “tankfist”), a shoulder-fired anti-tank guided missile that flies at more than 720kph (450mph). After striking its target, the exploding warhead shoots out a spike of copper at more than 7km a second (25,200kph) with enough energy to blast through a metre of steel, or any armoured vehicle used today, according to its manufacturer, Dynamit Nobel Defence. (Like many defence suppliers, it makes both weapons and anti-weapon systems.)
Moreover, some munitions can kill a tank crew without even penetrating the armour. A high-explosive munition known as “squash head”, fired by some British tanks, flattens a ball of plastic explosives against an armoured vehicle. It immediately explodes, transmitting a compression shock wave into the crew compartment, where it strips off “spall”—flakes of metal, some the size of a frisbee—that fly into occupants. Summing up the outlook for vehicle survivability, Stuart Wheeler, an armour expert at the Tank Museum in Bovington, England, says: “It looks grim.” Armour and vehicle designers, he says, are still looking for a comeback.
Fight fire with fire
It may be on the way. On March 1st an RPG was fired at an Israeli tank patrolling near the Gaza Strip security barrier. A radar system on the tank tracked the incoming warhead, feeding data to a computerised gun that shot it down with a small burst of projectiles. Israel plans to deploy the system, called Trophy, more widely. Daniel Klein, an armaments official at the EDA, reckons that the foiled attack, probably the first of its kind, bodes well for defending military vehicles. An additional benefit, he believes, is that Trophy and other so-called “active protection” systems are lightweight. Some modern military vehicles have become so heavy with armour that their manoeuvrability is impaired and they are unable to use certain roads and bridges.
The new Iron Curtain
Iron Curtain, another active-protection system, has been developed for American forces by Artis. It uses radar and optical sensors to calculate the trajectory of an incoming warhead, and then intercepts it with a projectile fired from a roof-rack (pictured). The impact causes the warhead to combust before it hits the armour. Mr Lehniger, of Dynamit Nobel Defence, says that Iron Curtain and similar systems might be able to defeat his firm's Panzerfaust 3 missile. If so, the achievement will be especially instructive to those who, decades ago, considered protecting vehicles to be a doomed endeavour.