Composite armour is a type of armour consisting of layers of different material such as metals, plastics, ceramics or air. Most composite armours are lighter than their all-metal equivalent, but instead occupy a larger volume for the same resistance to penetration. It is possible to design a composite armour both 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 by the British in the 1970s for their new Challenger tank. Chobham sandwiches a layer of ceramic between two plates of steel armor, which was shown to dramatically increase the resistance to high explosive anti-tank (HEAT) rounds. HEAT had posed a serious threat to armored vehicles since its introduction in WWII, and Chobham was such an improvement that it was soon copied on the new US M1 Abrams main battle tank (MBT) as well (although there it is referred to as Special Armor). 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, blowing up to a huge volume which then expands back out the hole and pushes the metal jet of the HEAT with it. The effectiveness of the system was amply demonstrated in Desert Storm, where not a single British Army Challenger tank was lost. Newer versions of Chobham include open spaces, depleted uranium and other layers in addition to the original steel/ceramic layering. The uranium layers are included primarily to increase the total mass of metal while not being larger physically.

The first widespread use of a composite armor appears to be on the Soviet T-64. It used an armour known as Combination K , which apparently is glass reinforced plastic sandwitched 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 armor, which allowed them some ability to control quality.

The T-90 introduced Kontakt-5, effective both against HEAT warheads and APFSDS. It also carried an applique armour pack which is composed of a frontal steel plate about 60mm thick backed by an insert of three layers of inert interlayer reactive armour, composed of steel plates and penapolyurethane filler.

Composite armors have since been applied to smaller vehicles, right down to jeep-sized. Many of these systems are applied as upgrades to existing armors, which makes them difficult to place around the entire vehicle. Nevertheless these upgrades are often surprisingly effective; ceramic upgrades to Canadian M-103 's were carried out in the 1990s after it was realized that it would offer more protection than new-build APCs like the M-2 Bradley .

External link

• Defense Update/Advanced Armor Concepts