Cluster Bombs and Other Cluster Munitions: Dangers to Noncombatants

An Honest John missile warhead with sarin gas submunitions.

An Honest John missile warhead with sarin gas submunitions.

Since the end of the Cold War, many states have opted to remove certain munitions from their arsenals. Sometimes, states opted to decommission munitions because their operation and sustainment was costly. In other cases, munitions fell out of favor for humanitarian reasons. Cluster munitions, some of the most lethal and destructive conventional weapons currently in use, are a type of munition whose continued use is remarkably controversial because of the dangers they pose to civilian noncombatants.

What are cluster munitions?

A CBU-24 cluster bomb which failed to open and dispense its submunitions (the small metal spheres). Image from

A CBU-24 cluster bomb which failed to dispense its submunitions and subsequently broke apart upon impacting the ground. The submunitions are the small metal spheres. Image from

Cluster munitions were invented in the early 20th century as a way to increase the area damaged by bombing. Normal (unitary) bombs and warheads contain one large explosive charge. Cluster munitions, on the other hand, contain a number of small submunitions which are dispersed in mid-flight (see above). Each of these mini-bombs, or bomblets, has its own detonator and explosive charge. When the cluster munition opens, each submunition’s path is variably affected by wind and other factors, resulting in the submunitions dispersing over a relatively wide area prior to detonation.

Many cluster submunitions inflict damage through blast fragmentation. In other words, each submunition simply detonates like a small bomb. These types of cluster munition are often used against large installations such as surface-to-air missile (SAM) sites and military bases. Because of submunition dispersion, one cluster bomb or warhead can eliminate a large SAM site that would have required multiple unitary munitions to destroy.

A CBU-24 cluster bomb loaded on an F-105 Wild Weasel aircraft. These cluster bombs would have been employed primarily against SAM sites.

CBU-24 cluster bombs loaded on an F-105 Wild Weasel aircraft. These cluster bombs would have been employed primarily against SAM sites.

Of course, because each submunition is relatively small, the individual bomblets do not have a lot of explosive power. For this reason, simple fragmentation cluster bombs are only useful against soft (unarmored) targets. However, this does not mean that cluster munitions cannot be used against armor. Indeed, cluster bombs using explosively-formed penetrators (EFPs), such as the CBU-100 Rockeye II, are capable of defeating armored targets. Because the submunitions fall on the roof of the target, which is generally lightly armored, the small EFP can penetrate a tank.

While anti-tank and blast fragmentation cluster munitions are the most common, any payload which can be miniaturized can be packed into a bomblet. Thus, some cluster munitions contain incendiary submunitions, while others are used for minelaying or even pamphlet distribution.

What makes cluster munitions so dangerous for noncombatants?

An unexploded BLU-26 submunition in Laos.

An unexploded BLU-26 submunition in Laos.

Cluster munitions excel at eliminating certain types of targets. Yet, many militaries have vowed to end their use. Why is this? The answer is that cluster munitions pose a unique and devastating threat to noncombatants, even years or decades after their initial use. There are a few reasons for this, but the largest issue as that cluster munitions produce large amounts of unexploded ordinance (EXO).

To illustrate the EXO danger posed by cluster munitions, let us consider a hypothetical situation in which bomb (and bomblet) fuses have a universal 1/100 failure rate. In reality, cluster submunitions actually have higher failure rates than fuses for unitary bombs, but for simplicity’s sake that will be ignored.

If you drop five large bombs on a SAM site, the odds that any of them will fail to explode are fairly low assuming a 1/100 failure rate for each bomb. Now, consider an attack with cluster bombs, in which 500 submunitions are deployed. The odds are that multiple bomblets will fail to detonate, assuming this 1/100 failure rate.

This simple hypothetical illustrates the danger of cluster munitions: the more munitions (or submunitions) dropped, the more likely it is that a few will fail to explode. The massive number of bomblets stored in many cluster munitions essentially guarantees that a cluster munition employment will have a few duds and leave EXO.

Compounding this issue is the small size of cluster munition EXO. If a 250lb bomb fails to explode, it is relatively easy to identify and disarm the bomb because of its size. Cluster munitions, on the other hand, can weigh only a couple of pounds. While nobody would miss an unexploded 250lb bomb, submunitions can easily go overlooked for years or even decades when they fall into brush or become covered in dirt. Small submunition size combined with the potentially large number of unexploded bomblets make cluster munitions highly dangerous for noncombatants and costly to remove; a light jostle could be all it takes to detonate a years-old bomblet hiding in tall grass. Cluster bomb submunitions can also be easily mistaken for harmless toys or innocuous scraps of metal, especially by children. Lastly, submunitions can be defused and their explosives harvested by insurgents or terrorist groups.

Because of these dangers, a multitude of nations have signed or ratified the Convention on Cluster Munitions, which bans all signatory states from producing and employing cluster munitions. Others, however, refuse to sign. Many of the states which have not signed the convention possess powerful militaries (for example, Russia, China, and the United States are non-signatory). Others are in conflict areas – very few Middle-Eastern or Asian states have ratified the convention.

A map showing states which have agreed to the Convention on Cluster Munitions. Dark green=ratifications; light green=signatories.

A map showing states which have agreed to the Convention on Cluster Munitions. Dark green=ratifications; light green=signatories.

Many countries, such as the US, keep cluster munitions but use them sparingly. While the US maintains a stock of cluster munitions for use in high-intensity warfare, it avoids using them in most cases; precision munitions such as guided missiles and bombs are preferred.

Other nations, such as Russia, are less discriminating in their use of cluster munitions. In Syria, where the US has mostly employed precision munitions, Russia has used a number of unguided bombs, reportedly including cluster bombs.

In the end, each individual nation has to make tough choices regarding cluster munitions. On the one hand, pressure from NGOs and disarmament groups certainly influences militaries to dispose of their cluster munitions in order to avoid the associated noncombatant casualties and negative publicity. On the other hand, cluster munitions can be valuable in certain tactical situations, especially for the elimination of large area targets such as forward bases, staging areas, infantry formations, airfields, SAM sites, and artillery batteries. Surrendering the cluster munition capability could equate to a loss of combat effectiveness, and many militaries (such as the US) have stopped using cluster munitions regularly, which reduces unnecessary casualties.

Another solution is to field more advanced cluster munitions, such as the CBU-97 Sensor Fused Weapon, which contains only 10 submunitions. Each submunition dispenses four smaller units, which acquire targets individually and then fire kinetic penetrators. The design reduces unexploded ordinance rates and collateral damage significantly, but advanced cluster bombs  such as the CBU-97 are very pricey, and many nations could not afford to purchase them.

A model of the CBU-97 Sensor Fused Weapon.

A model of the CBU-97 Sensor Fused Weapon.

Thus far, the trend has been for African and European states to join the Convention on Cluster Munitions, while most of Asia remains non-signatory. The Americas are a more mixed bag; many states have ratified the treaty, but heavyweights Brazil and the US have not yet followed suit. Of course, disarmament debates remain lively, and if/when the dust settles in Syria and Iraq, new insights into the use of cluster munitions could inform future decisions. However, there are no real indications that Russia and the US will swear off cluster munitions anytime soon. Seeing as these two countries drop the majority of ordinance and have the largest stocks of cluster munitions, any efforts to end the usage of cluster munitions will require the acquiescence of both.

About the Author

Alex Hempel
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