Composite armour

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Composite armour is a type of vehicle armour consisting of layers of different material such as metals, plastics, ceramics or air. Most composite armour are lighter than their all-metal equivalent, but instead occupy a larger volume for the same resistance to penetration. It is possible to design composite armour stronger, lighter and less voluminous than traditional armour, but the cost is often prohibitively high, restricting its use to especially vulnerable parts of a vehicle.

The most common type of composite armour today is Chobham armour, first developed and used by the British in the experimental FV 4211 tank, which was based on Chieftain tank components. Chobham sandwiches a layer of ceramic between two plates of steel armour, which was shown to dramatically increase the resistance to high explosive anti-tank (HEAT) rounds. HEAT had posed a serious threat to armoured vehicles since its introduction in WWII, and Chobham was such an improvement that it was soon used on the new U.S. M1 Abrams main battle tank (MBT) as well. It is the fabrication of the ceramic in large tiles that gives the Challenger and Abrams their "slab sided" look.

Chobham's precise mechanism for defeating HEAT was something of a mystery until 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. The effectiveness of the system was amply demonstrated in Desert Storm, where not a single British Army Challenger tank was lost to enemy tank fire. Chobham-type armour is currently in its third generation and is used on modern western tanks such as the American M1A2 SEP Abrams, the British Challenger 2 and the German Leopard 2A5/A6.

The first widespread use of a composite armour appears to have been on the Soviet T-64. It used an armour known as Combination K, which apparently is glass reinforced plastic sandwiched between inner and outer steel layers. Through a mechanism called thixotropy, the resin changes to a fluid under constant pressure, allowing the armour to be moulded into curved shapes. Later models of the T-64, along with newer designs, used a boron carbide-filled resin aggregate for greatly improved protection. However the quality of the tanks produced during this era varied widely; if the boron carbide was not available in time to meet production quotas, the tank would be shipped with any filler that could be found, and sometimes nothing at all. In order to deal with these problems, the Soviets invested heavily in reactive armour, which allowed them some ability to control quality.

Composite armour has since been applied to smaller vehicles, right down to jeep-sized. Many of these systems are applied as upgrades to existing armour, which makes them difficult to place around the entire vehicle. Nevertheless they are often surprisingly effective; ceramic upgrades to Canadian M-113s were carried out in the 1990s, after it was realized that it would offer more protection than newly built APCs like the M2 Bradley.