Commonly known as a cluster bomb, the cluster bomblet unit (or CBU) is a single air-dropped bomb which ejects about 200 small bomblets. These are often stabilized with small parachutes or streamers. They may explode on contact with the ground or be fused with a delay. The bomblets have an anti-personnel function, and sometimes are designed to pierce tank armor as well. Cluster bombs are part of a family of weapons called 'submunitions' (i.e. a munition contained within another munition). The other type of submunition is known as a 'scatterable mine' (see entry on Landmine).
CBUs are designed to scatter over a specific area, referred to as its 'footprint', causing significant damage to buildings and people. One common type of bomblet - the Bomb Live Unit (BLU) 97, produced by the United States - has the shape and size of a soft drink can, is bright yellow, and weighs 1.5 kg. They are designed to fragment at high velocity into hundreds of pieces of shrapnel.
CBUs were developed in order to improve the efficiency of aircraft bombing raids, as aircraft carrying CBU can make an effect on a far larger footprint than an aircraft carrying an equivalent tonnage of conventional bombs.
CBUs are able to ignite combustible materials. Some types of CBU can pierce through 125 mm of armoured steel.
The use of these weapons is hotly opposed by many individuals and groups, such as the Red Cross and the United Nations, because about 10% of the bomblets do not explode on impact, and act like land mines for many years. The small size and bright colours of some bomblets make them attractive to passers-by, especially small children. CBUs are still a danger in Indochina, especially in Laos and southern Vietnam. More recently, in Afghanistan, several civilians including children have been killed by unexploded bomblets.
In the United States military action against Afghanistan in 2002, military forces faced an embarrassing problem in that humanitarian rations dropped from airplanes initially had the same yellow colored packaging as unexploded cluster bombs. The rations packaging was later changed first to blue and then to clear packaging.