Chobham armour is a composite armour developed at the British tank research centre on Chobham Common. Although the exact composition of Chobham armour remains a secret, it appears to be a combination of ceramic layered between armour steel plating, a combination that is excellent at defeating high explosive anti-tank (HEAT) rounds. Possible ceramics for such armours are: Boron carbide, Silicon carbide, Aluminium oxide (Sapphire), or Titanium boride.

The exact nature of the protection offered by this layering remained a mystery for some time, but it was eventually revealed that Chobham armour works in a manner somewhat similar to reactive armour. When the armour is hit by a HEAT round the ceramic layer shatters under the impact point, forming a dust under high pressure. When the HEAT round "burns through" the outer layers of armour and reaches the ceramic, the dust comes flying back out the hole, slowing the jet of metal.

Modern tanks also have to face KE-penetrator rounds of various sorts, which the ceramic layer is not particularly effective against. For this reason many modern designs include additional layers of heavy metals to add more density to the overall armor package. The metal used appears to be either tungsten or, in the case of later M1 Abrams tanks, depleted uranium.

The effectiveness of Chobham armour was demonstrated in the first Gulf War, where no Coalition tank was destroyed by the obsolete Iraqi armor. In some cases the tanks in question were subject to multiple point-blank hits by both KE-penetrators and HEAT rounds, but the old Russian ammunition used by the Iraqis, in their Polish licence built T-72's, their old T-55's bought from Russia and upgraded with "enigma" type armour, and T-62 tanks left them completely incapable of penetrating coalition armour. It's also worth noting that the Iraqis rarely actually hit the coalition tanks, because of lack of training and inferior optics. To date, only 5-10 Chobham-protected tanks have been defeated by enemy fire in combat, including an M1 that was hit by an RPG-7 in the Second Gulf War.

The latest version of Chobham armour is used on the Challenger 2 (called Dorchester armour), and (though the composition most probably differs) the M1 Abrams series of tanks. Though it is often claimed to be otherwise, the Leopard II does not in fact use Chobham armour.