Cluster bomb: what it is and how it works

Cluster weapons are a staple of both NATO and Warsaw Pact armed forces. Delivered as cluster bomb units (CBUs) or artillery shells, they can be designed as anti-armor, incendiary, or chemical weapons.

The United States has sold two types of air-dropped CBUs to Israel, the last shipment made in 1975. These are:

* The CBU-58. No longer produced, this bomb-shaped canister opens like a clamshell when dropped at low altitude and high speed and disperses 650 golf ball-sized bomblets. These are activated by spinning and explode on impact.

* The MK-20 Rockeye. This newer CBU contains 247 dart-like bomblets about 8 inches in length and explodes after piercing the outer shell of armored vehicles.

Both are designed to immobilize lightly armored military targets such as truck convoys, communications vans, personnel carriers, and radar sites. They can be particularly effective against surface-to-air missile sites, since such sites depend on relatively vulnerable radar dishes.

''It's designed to saturate a fairly limited area with a number of small explosions which would render ineffective the mobility of whatever your target is,'' says a US Air Force spokesman. ''We consider them to be built for anti-materiel purposes, but obviously if one drops them on troops, they're anti-personnel.''

The US in Vietnam used CBUs designed specifically to be dropped on enemy troop concentrations, but such weapons are no longer produced.

The exact dispersal pattern of CBUs depends on altitude and airspeed at delivery and is classified. But the effective coverage area for a single CBU is reported by James Dunnican in ''How to Make War: A Comprehensive Guide to Modern Warfare'' to be 50 meters wide by 200 meters long. Therefore they are difficult to deliver with pinpoint accuracy in areas where military targets are close to civilian populations.

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