At the present time, political pundits and activists are arguing about President Biden’s decision to send cluster munitions to Ukraine for use against the invading Russian forces. The discourse often starts from a basic proposition that cluster bombs are inherently evil and that their use is always immoral. This has led some supporters of Ukraine to opine that Ukraine will lose “the moral high ground” in its struggle against the Russian invasion. Much is made of the fact that many countries have banned the use of cluster munitions, noting that they have done so to protect civilians, alluding to the modern consensus on the conduct of war that efforts to avoid “collateral damage”, the euphemism for the killing or wounding of non-combatants (civilians), must be undertaken by the belligerent states.

But, are cluster munitions inherently immoral weapons of war? Does their substantial destructive power place then in a category apart from other weapons of war that are regarded as legitimate tools for resisting armed aggression? Or, does the possibility that some might harm civilians as a result of delayed detonation make their use immoral?  

Customary law of war proscribes the direct targeting of civilians. Likewise, it prohibits the use of weapons that have an indiscriminate impact, foreseeably affecting non-combatants in like manner as combatants. Opponents of the use of cluster munitions argue that their use is prohibited because of the high likelihood that innocents will be wounded or killed by their use. But, likelihood, even a high likelihood, of innocent victims due to the use of a particular weapon is not the same as foreseeable inevitability of many innocent victims from the use of a particular weapon. We must assess to what degree large number of non-combatant casualties from Ukraine’s use of US supplied cluster munitions is nearly inevitable.

Cluster munitions are designed for use against concentrations of enemy combatants or their resources. If used in this way, avoiding the targeting or foreseeable impact on civilians, they are no more immoral than non-cluster munitions are. But what about the situation of cluster munitions that fail to detonate (duds) when used against combatants, but can detonate later harming or killing civilians?

If a large number of duds likely to harm civilians is foreseeable, then the use of cluster munitions would be an immoral use. Just as a foreseeable high inaccuracy rate of precision-guided munitions being used against terrorists in congested urban areas renders them an illegitimate means of counter-terrorist operations, a foreseeable high ‘dud rate’ among cluster munitions would render them an illegitimate instrument of war. The foreseeable inevitability of many non-combatant casualties renders intentionality a moot point for making a moral analysis of a weapon’s use.

In a July 7 press briefing, National Security Advisor Jake Sullivan stated that the US cluster munitions being sent to Ukraine have a dud rate below 2.5%. He also stated that the dud rate for the cluster munitions already in use by the Russians was between 30 and 40 percent. Such a high rate of initial failure renders the Russian cluster munitions an indiscriminate weapon as they lead to many foreseeable deaths of civilians. Several press outlets and Human Rights Watch have reported that several hundred Ukrainian civilians have been harmed or killed by Russian bomblets that failed to detonate when first used. 

Does a dud rate of no more than 2.5% render the use of cluster munitions acceptable? It is not possible to eliminate all possibility of collateral damage in modern warfare. That said, by deploying only cluster munitions with a dud rate of less than 2.5%, in conjunction with careful targeting to avoid their use in areas with a high concentration of civilians, cluster munitions can be a legitimate weapon for national defense.

A vital detail in determining the ethical use of a weapon is its purpose. Russia is using cluster munitions in an unjust war of aggression against a sovereign neighbor. Ukraine is using cluster munitions as part of its efforts to dislodge and drive out the numerically superior and better-armed forces of an invader. While the particular circumstance of being the victim of unwarranted aggression does not justify the use of any and all weapons available to the defending state (for example, chemical and biological weapons are always prohibited), its status as the aggrieved party allows it greater leeway in determining the weapons to be used in its sovereign territory to defend its people.

Throughout its military campaign against Ukraine, Russia has targeted civilians. It has committed numerous atrocities, including imprisonment, rape, torture, and summary executions. Yet, even with all these provocations, the Ukrainian armed forces have, in the main, respected the customary rules of war as well as the Geneva Convention, including scrupulously avoiding attacking non-combatants. 

Why such circumspection? In large part, because the civilians being harmed in this war are overwhelmingly Ukrainians. As flawed as the government of Ukraine may be, there is no evidence it would use a weapon with indiscriminate impact because that weapon would risk harming its own citizens as much as the personnel of the invading forces. Even with the apparent need to use these weapons against well dug-in Russian forces to foster success of their current counter offensive, the evidence to date is that Ukrainian government would not use cluster munitions if such use were likely to result in significant casualties among the civilian population.

Whether it is with armed drones, precisely targeted missiles, or cluster munitions, Ukraine is defending itself with legitimate weapons against an aggressor that has repeatedly demonstrated contempt for international norms regarding the protection of non-combatants. Its use of cluster munitions is not immoral, for it does not target innocents, only uses munitions with a low dud rate, and uses them only in a defensive posture not as an aggressor, and that on its own sovereign territory.  

In conclusion, cluster munitions, properly designed and deployed, can be a morally licit instrument of prosecuting a state’s legitimate defense of its sovereignty and its people, but only by meeting certain conditions:

First, cluster munitions must only be used against enemy combatants and neither target nor be used in close proximity to a concentration of civilians.

Second, cluster munitions with a high dud rate must not be used if there is a strong likelihood that soon after their use, a large number of civilians will occupy the area where they were used.

Third, careful records of the areas in which they are used must be maintained so that once fighting has ended, the area can be scoured for any duds.

Fourth, efforts should be made to monitor the dud rate of the cluster munitions used and to stop their use if the dud rate becomes so high as to preclude the possibility of recovering most undetonated munitions once the fighting has ended.

Fifth, if the Russian invaders refrain from the use of cluster munitions, the Ukrainian side must refrain from using cluster munitions.

In conclusion, Ukraine has met or is meeting the conditions listed above, and will not lose the “moral high ground” by using cluster munitions to prosecute its legitimate war aim of defending its people and sovereignty.