Cunning new UK technology will see British troops' vehicles in Afghanistan protected from armour-piercing rocket warheads - by cloth.

The MoD was pleased yesterday to unveil its new TARIAN "textile based" vehicle protection system, which will see lightweight cloth attached to the sides of military vehicles in Afghan combat. TARIAN is expected to resist strikes from RPGs*, shoulder-fired antitank rockets in common use among the Taliban.

That might seem to be impossible, as an RPG warhead can blast a hole through thick armour plate. But in fact TARIAN, already on trial in Afghanistan, apparently works well.

That's because it's actually a replacement, not for armour plate, but for so-called "bar" or "slat" RPG protection. An RPG warhead pierces heavy armour using the shaped-charge effect, in which a hollow cone of explosive - usually lined with copper - is detonated. The effect is to form the copper into a pencil-thin slug of incredibly hot, high-velocity molten metal which can burn its way through armour which would have shrugged off an ordinary explosive charge.

But a shaped charge only works if it's detonated at the correct stand-off distance from the surface of the armour. This is done by having the detonator mounted ahead of the cone; in the case of an RPG at the tip of the streamlined nose put on the end of the warhead in order to make it fly straight.

Bar armour is basically a heavy wire fence mounted a few inches out from a vehicle's normal plating. It's just strong enough that hitting it makes an RPG warhead go off early. The copper jet blasts through the flimsy cage with ease, but by the time it reaches the real armour it has spread, cooled and slowed and it can't penetrate.

While bar protection is light compared to the main plates of a fighting vehicle, however, it's still noticeably cumbersome and reduces the load a vehicle can carry. That's where TARIAN comes in, replacing metal bars or slats with super-strong, tough textile. The TARIAN cloth is stretched taut enough that it can, apparently, trigger an RPG just as well as a bar kit.

Cunning indeed - quite literally a bit of out-of-the-box thinking by Dorset firm AmSafe, TARIAN's maker. Provided the RPG-proof cloth is durable and reliable enough for field use - which the Afghan trials would seem to have confirmed - TARIAN should enable our boys and girls' vehicles to carry more or have more protection elsewhere, without losing any protection. ®

*Rocket Propelled Grenade, or more correctly Raketniy Protivotankoviy Granatomet