A cluster munition is a military weapon, such as a artillery shell, unguided rocket or guided missile warhead, or a gravity bomb, which releases submunitions that actually cause the desired weapon's effects. The munition may be delivered using precision-guided munitions technology, or may be a "dumb" ballistic projectile. 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.
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. Others carry munitions that are landmines, but that can be detonated only by the weight of a tank or other military armored vehicle. Some could be electronic jammers.
Yet other submunitions are independently guided to attack tanks, and have little danger to personnel not on the tank.
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. Especially the antitank submunitions have done away with perceived need for tactical nuclear weapons to stop large tank formations. There is the question, of course, of how common large tank formations may be.
The purpose conceived as legitimate for using antipersonnel cluster munitions is to attack a spread-out group of soldiers and lightly protected equipment, as might be found with an infantry unit, at an air defense or artillery position, or a supply dump. If it could be assured that the submunitions could either immediately detonate or render themselves safe, these might be considered militarily appropriate, but there is little trust that the "dud" unexploded but hazardous submunition problem will be completely solved in the near term.
Many nations have, for this reason, taken potential antipersonnel submunitions out of their ammunition stockpiles, and others are seeking treaties to ban them. Even if a completely reliable fail-safe mechanism were demonstrated today, that would not account for weapons already in stockpiles. It is simply not certain, however, if the replacements might have even worse unexpected consequences.