A cluster munition is a military weapon, such as a artillery shell, unguided rocket or guided missile warhead, or a gravity bomb, which carries and releases cluster submunitions that actually cause the desired weapon's effects. The carrrier munition may be delivered using precision-guided munitions technology, or may be a "dumb" ballistic projectile; it may be a guided missile or unmanned aerial vehicle capable of flying to, and attacking, several locations.
Some submunitions are antipersonnel, designed to injure or kill people, or are "dual-purpose" and thus able to damage light construction or vehicles, and also hurt or kill people. These are the types of greatest humanitarian concern.
Other submunition types are not a significant threat to individual people. They may be lethal threats to tanks and other large armored vehicles, but will only detonate when they sense specific characteristics of such a massive object.
Yet other types are not intended to do permanent damage of any type. They may conduct electronic warfare for a short period of time, or be designed to disable electrical power transmission lines without destroying the power plants or substations.
There are a variety of carrying munitions for cluster submunitions. The simplest are bombs or shells that burst open, and, using motors, springs, or small explosive charges, scatter them in circular or ovoid patterns.
At the next level of delivery sophistication are bombs and missile warheads that can release the bomblets in batches. Such a weapon could follow a road, runway, or trench and disperse the submunitions in an efficient linear pattern.
Even more sophisticated dispensers can maneuver, and deliver submunitions to multiple targets. They may be able to transmit damage assessments, and be commanded to reattack, or be completely reprogrammed to fly to a target not known at the time the carrier was launched.
From a pure military standpoint, antipersonnel, dual purpose, and antitank cluster submunitions spread out over a larger area than would the effect of a conventional bomb, shell, or warhead, so that excessive explosive force is not "wasted" in a small area. For certain dispersed targets, such as a group of artillery pieces, it may not be practical to use precision guided weapons against the cannons themselves, which are made of very strong metal. If submunitions kill the crew or set off the ammunition, the cannon is neutralized. Bluntly, for other types of targets, such as a military headquarters, the only effect desired is kiling skilled personnel.
Antipersonnel and dual purpose submunitions were not intended to remain active and thus become minefields, but existing technology is insufficient to ensure all submunitions either explode immediately, which is the intended effect, or to render themselves harmless. There has been considerable international pressure generically directed at cluster munitions, but really at those that dispense antipersonnel or dual purpose submunitions. These two classes, if they are dispensed in populated areas, form antipersonnel minefields that result in unacceptable civilian casualties.
Not all types of submunitions are intended to injure people. Some emit thin carbon filaments, intended to short out power lines and temporarily cause blackouts. Some could be electronic jammers.
Various antitank submunitions are independently guided to attack tanks, and present little danger to personnel not on the tank. There are antitank submunitions that are intended to create temporary minefields, which are not considered significant risks because they will not detonate if stepped upon or handled; the weight or magnetic field of a tank is required to set them off.