Just as the United States is about to finish destroying its chemical weapons stockpile as mandated under the Chemical Weapons Convention and is implementing its new Civilian Harm Mitigation and Response Action Plan, the Biden administration has announced its decision to provide cluster munitions to Ukraine. This decision to accede to Ukraine’s longstanding request is highly controversial. Its supporters include many in the Pentagon and Congress, as well as some military experts. The State Department has expressed deep reservations, and it faces opposition from some members of Congress, a UN special rapporteur, human rights and arms control organizations, and several of our allies as well as Russia and China.
In Part I, I’ll first explain what cluster munitions are and why the Biden administration decided to give them to Ukraine. I’ll then address their failure rate and their potential impact on civilian populations. I’ll conclude this part with a discussion of the international law issues for Ukraine and the United States.
In Part II, I’ll move on to domestic law issues for the United States as well as international law issues for Cluster Ban Treaty party members, many of whom are allied with Ukraine. I’ll also address arguments about Ukraine losing the moral high ground and weakening the alliance.
In Part III, I’ll conclude with a discussion of how both the United States and the global community might reinforce the emerging norm against cluster munition use. The decision to supply cluster munitions to Ukraine will not be undone, but that need not spell doom for either the norm against cluster munitions or the more general move in favor of enhanced civilian protections.
What are cluster munitions?
First, what is a cluster munition (also known as a cluster mine)? It is a bomb that contains multiple explosive submunitions (also known as bomblets). After being fired, launched, or dropped, it breaks open at a specified height dispersing bomblets over a wide area. In turn, those bomblets are designed to explode close to or on impact with the ground or other solid objects, “spreading shrapnel that is designed to kill troops or take out armored vehicles.” For instance, one of the proposed models for transfer to Ukraine contains 88 bomblets (per single artillery canister) that could disperse over about eight acres.
Why did the U.S. say yes now?
Ukraine has been requesting the weapons since the start of the war with Russia. Military experts and administration officials have justified the transfer on a variety of related grounds: (1) cluster munitions, of which the U.S. has a large stockpile, would reduce Ukraine dependence on other artillery which is now in limited supply, (2) cluster munitions get more bang for the buck than current artillery, as fewer rounds are needed to destroy more targets, (3) cluster munitions allow Ukraine to save missiles for high-value targets, (4) cluster munitions are effective against trench lines as well as troop and armored formations, and (5) Russia is already using high dud rate cluster munitions against Ukraine and thus (a) Ukraine is not the first to introduce them into the battlefield and (b) Ukraine will already have to demine its territory. Ukraine offers an additional argument that they will “have an extraordinary psychological impact on already demoralized Russian occupation groups.” While the United States has dragged its feet on this issue, many believe there is a new sense of urgency created by what is seen as a “critical stage in the conflict” and the “slow pace of [Ukraine’s] long anticipated counteroffensive.” Reports suggest that Biden was ultimately swayed by the argument that Ukraine itself viewed the Russian occupiers as a much deadlier threat than the risk of unexploded ordnance and Ukraine ought to get to make the call as to which is riskier.
I cannot comprehensively speak to the overall empirical correctness or strength of these arguments, but given my work on landmines and civilian casualties more generally, I would like to note that states in conflict often overestimate the necessity and value of particular weapons they seek. For example, even if cluster munitions help Ukraine push through Russian trench lines, Ukrainian troops would still have to grapple with densely mined fields. And how much cluster munitions would act as a force multiplier is heavily debated. That said, I have no doubt cluster munitions would be of utility to Ukraine, potentially significant utility especially if the alternative is running out of or having to conserve conventional artillery. At the same time, they are not a silver bullet that guarantees the success of Ukraine’s counteroffensive. Even the Biden administration describes the transfer as “an extra arrow in [Ukraine’s] quiver” rather than a game changer. But if this were simply a question of how useful cluster munitions are, the decision to transfer would not be so fraught. So what’s on the other side of the ledger?
What are the objections?
The main objection is the civilian toll cluster munitions inflict. For instance, take the cluster munitions and other unexploded ordnance dropped by the U.S. in Laos during the Vietnam War. They have killed over 10,000 civilians, of which more than 30% were children who are often particularly attracted to them. Even decades after the war, millions of cluster munition bomblets remain continuing to kill Lao civilians as well as hindering farming and other economic development. Why such a deadly legacy? Unfortunately, cluster munitions do not always explode on contact with the ground or an object. If they fail to do so, they function similarly to landmines, creating significant risks for civilians and deminers—often long after the conflict has ended. For what it is worth, the Cluster Munitions Monitor reports that in 2021, civilians comprised a staggering 97% of cluster munitions fatalities.
The failure to explode rate is known as the dud rate. Historically, cluster munitions have suffered from high failure rates in the 20% and above. For instance, Russia is currently using cluster munitions in Ukraine with 40% dud rates. In order to combat this concern, the U.S. indicated that it would not send older munitions with dud rates higher than 2.35%, and Brigadier General Pat Ryan said that the U.S. “would be carefully selecting rounds with lower dud rates, for which we have recent testing data.” Human Rights Watch and other experts sharply contest this—concluding the actual dud rate will be much higher because of environmental factors and decrying the lack of transparency as to why the U.S. will be deviating from its normal below 1% dud rate transfer requirement (explained in Part II). Older Pentagon reports suggest the cluster munitions to be sent to Ukraine probably have an actual dud rate of somewhere between 6% about 14% and a recent Congressional Research Service report shows that in the past, manufacturers claiming low dud rates have often been between 10% and 30% in actual use.
Even if the U.S. is accurate about the 2.35% predicted dud rate, Ukraine would still need to conduct comprehensive demining efforts in order to protect its civilian population after ending attacks. In turn, Ukraine says it would “deploy the weapons judiciously given that it is fighting on its own land” and claims that it will be engaging in such demining anyway in order to pass through Russian landmines. To its credit, Ukraine has in fact demined other parts of liberated Ukraine in order to rid them of Russian anti-personnel landmines and cluster munitions and has strong incentives to continue demining as it is able.
Other objections, such as the illegality of cluster munitions, undermining the cluster munitions ban and the norm against their use, and undermining the alliance are all related to this concern about the potential interactions between cluster munitions and the civilian population. So we’ll turn to these next.
Is cluster munition transfer and use legal?
International law as governs Ukrainian use and U.S. transfer
The Convention on Cluster Munitions (also known as the Cluster Mine Ban), in force since 2010, bans the use, sale, transfer, and stockpiling of cluster munitions as well as any assistance, encouragement, or inducement to anyone (state party or not) to engage in any activity prohibited to a state party. 110 countries have ratified the treaty, but neither the United States nor Ukraine has (and for that matter, neither has Russia). Thus, they are not governed by its terms.
To the extent that one believes that per se use of cluster munitions is a violation of customary international law, the United States, Ukraine, and Russia have been persistent objectors. The United States vocally declined to join the Cluster Mine Treaty, maintaining that the use of low-dud rate cluster munitions remains lawful, and it has not abandoned that position even as it implemented policies to limit their use. While early in the Ukraine war, then Press Secretary Jen Psaki suggested the Russian use of cluster munitions “would potentially be a war crime,” the context of questioning seems to mean their use against civilians rather than their use at all. And while then U.S. ambassador to the UN Linda Thomas-Greenfield gave a UN General Assembly speech asserting, “We have seen videos of Russian forces moving exceptionally lethal weaponry into Ukraine, which has no place on the battlefield. That includes cluster munitions and vacuum bombs—which are banned under the Geneva Convention,” the Biden administration quickly retreated from this position, noting in the official transcript of the speech that “the Geneva Conventions ban the use of cluster munitions only against civilians.”
The prohibition that Biden referenced comes from Article 51 of the Additional Protocol I to the Geneva Convention. This provision, which does govern both the United States and Ukraine as customary international law, states, “The civilian population as such, as well as individual civilians, shall not be the object of attack.” Of course, any weapon could be unlawfully used against civilians, and Ukrainians seem unlikely to use cluster munitions directly against a civilian population. In fact, given the nature of the conflict and the occupation, it would make little sense for Ukraine to target civilians since we are largely talking about Ukraine’s own civilian population. (In contrast, for example, to Russia which has very likely been using significant amounts of cluster munitions against the Ukrainian population in Ukraine.) That said, some have expressed fear that Ukraine will dissemble cluster munition artillery and use them in drones against the Russian population. Such an action would violate Article 51, but I do not view it as a risk likely to materialize.
The greater concern for Ukrainian cluster munition use is possible indiscriminate attacks which are also prohibited under the Geneva Convention. Article 54(4)(a) of Additional Protocol I dictates:
Indiscriminate attacks are prohibited. Indiscriminate attacks are: (a) those which are not directed at a specific military objective; (b) those which employ a method or means of combat which cannot be directed at a specific military objective; or (c) those which employ a method or means of combat the effects of which cannot be limited as required by this Protocol; and consequently, in each such case, are of a nature to strike military objectives and civilians or civilian objects without distinction.
In other words, if the use of cluster munitions in a specific instance is in an area with both military objectives and civilians and cannot be directed only against the military targets, their use in that scenario would be unlawful. Think of fighting in an urban area where there are soldiers and tanks that would be legitimate military targets, but also many civilians in or near their residences. If a soldier deploying a cluster munition in that instance could not predict whether it would hit a civilian or a soldier, such an attack would be indiscriminate and unlawful. Some believe that a high dud rate renders cluster munitions per se indiscriminate weapons and thus, they could never be used consistently with Article 54. The United States and Ukraine both reject this interpretation and instead hold that low dud rate cluster munitions exist and can be used consistently with the Geneva Convention.
Article 51 also prohibits disproportionate attacks—that is, “an attack which may be expected to cause incidental loss of civilian life, injury to civilians, damage to civilian objects, or a combination thereof, which would be excessive in relation to the concrete and direct military advantage anticipated.” Cluster munitions can obviously be used in disproportionate attacks, but whether that illegal use is likely again depends on your priors about the dud rate and/or your belief in general Ukrainian compliance with the Geneva Convention. In other words, if you think the U.S. cluster munition dud rate is low and the Ukrainian military will undertake the necessary assessments to determine whether a specific use is problematic, then their use is not likely to be illegal even if they do ultimately cause some (lawful) civilian casualties. If you disagree with either of those priors, then the risk of illegal behavior is much more significant.
A related concern would be Article 57’s “take care” provision of Additional Protocol I. It reads:
1. In the conduct of military operations, constant care shall be taken to spare the civilian population, civilians and civilian objects. 2. With respect to attacks, the following precautions shall be taken: (a) those who plan or decide upon an attack shall: . . . (ii) take all feasible precautions in the choice of means and methods of attack with a view to avoiding, and in any event to minimizing, incidental loss of civilian life, injury to civilians and damage to civilian objects.
Again, Ukraine could use cluster munitions in such a way as to violate the take care article. It has likely committed some serious violations of the Geneva Conventions during the war, but even the human rights organizations documenting these violations have been careful to note that such violations generally appear to be one-offs as opposed to Russia’s much more systematic violations.
I want to conclude this part with a mention of Ukraine’s pledges regarding its use of U.S. cluster munitions. Ukraine has promised not to use cluster munitions in Russia, to track cluster munition use to facilitate demining, and it has provided written assurances to the U.S. to minimize any civilian casualties including not using the weapons in urban areas populated by civilians. The Ukrainian defense ministry also tweeted that “cluster munitions will be used only in open fields where there is a concentration of Russian servicemen.” While these assurances may not have any binding legal status, if Ukraine keeps them, they would significantly reduce the risk of civilian casualties and international law violations (again, assuming cluster mine use is not a per se violation). Stay tuned for part II in which I will get to domestic law issues and the policy arguments about Ukraine and the United States losing the moral high ground and weakening the alliance.