The terrible history behind cluster munitions

Here's exactly why cluster munitions, which the US is sending to Ukraine, present such an enduring risk to civilians.
A US soldier holds a cluster bomb shell
A US soldier carries a 155mm Base Burn Dual Purpose Improved Conventional Munition round (a cluster munition) in 2016 in South Korea. Gabriel Jenko / US Army

On July 7, the White House announced the contents of its latest security assistance for Ukraine. These transfers of weapons and equipment have proceeded regularly over the last 18 months, since Russia launched a full-scale invasion of Ukraine in February 2022. The latest weapons include anti-air missiles, armored vehicles, anti-tank weapons, and a host of other systems. The most stand-out item, and the one that has attracted greater public response, is the inclusion of the Dual-Purpose Improved Conventional Munition (DPICM), otherwise known as cluster munitions.

A cluster bomb or cluster munition is a shell that, after it’s fired, opens and releases many smaller explosives, called submunitions. The ones being sent to Ukraine are rounds for 155m howitzers, an artillery piece that lobs shells at a high trajectory so they fly over obstacles and then descend to hit whatever is below. In a cluster bomb, the outer casing detonates away, allowing the spin of the shell to scatter cluster bomblets like so many deadly seeds. This dispersal means that the submunitions cover a larger area than the blast of a single conventional bomb would.

“With this announcement, we will be able to provide Ukraine with hundreds of thousands of additional artillery ammunition immediately. This decision will ensure we can sustain our support for Ukraine by bridging us to a point where we are producing sufficient artillery ammunition on a monthly basis across the coalition. We recognize the complexities here, which is why I want to quickly provide a few additional pieces of information on DPICM,” Colin Kahl, Under Secretary of Defense for Policy, said at a press conference after the announcement. 

The use of cluster munitions in Ukraine predates the 2022 invasion, with both sides using the weapons during the long Donbass war between Ukraine and Russia from 2014 until the 2022 invasion. Russia has used cluster bombs in its invasion of Ukraine, with reports indicating use against both military targets and cities. Ukraine is currently waging a counter-offensive against Russian forces entrenched in Ukraine, and has sought cluster munitions as a tool worth firing in their own country because of the desired military effect against defensive positions, like trenches.

That ability to cover an area with small explosives represents both the military potential and the biggest post-war concern from the use of cluster munitions. Bomblets are small, and while they are all designed to detonate on impact, some may not. These duds can either be truly inert, where they will never detonate, or they can be set off at some point in the future, by civilians in the area or by mine-clearing crews. There is a risk of leaving unexploded duds with all bombs, but because each cluster munition scatters many small bomblets, it makes the number of unexploded bombs much greater per shell than it is for single munitions.

The history of cluster munitions

During the Cold War, both the United States and the Soviet Union developed cluster munitions, alongside the development of precision-guided weapons. Like many Cold War weapons, they were originally designed for use in a massive ground war over Europe, and found use instead in the long running military campaigns, like the US in Vietnam and the Soviet Union in Afghanistan. Ukraine and Russia both inherited military equipment from the Soviet Union after the Cold War, including cluster munitions.

As a category, cluster munitions date back to World War II, and in a March 2022 report, the Congressional Research Service notes the weapons have been used by at least 21 countries since. These include use by the Soviet Union in Afghanistan, the United Kingdom in the Falklands War, by various factions in the Balkan wars of the 1990s, and others. The United States used cluster munitions extensively in Southeast Asia, as part of the Vietnam War, “and the International Committee of the Red Cross (ICRC) estimates that in Laos alone, 9 million to 27 million unexploded submunitions remained after the conflict, resulting in over 10,000 civilian casualties to date.”

The United States also used cluster munitions in the invasions of both Afghanistan and Iraq, but has reportedly not used the weapons since the first three weeks of the 2003 invasion of Iraq

Part of the challenge of making cluster munitions work is that potential for duds. From a human rights and laws-of-war perspective, duds are deadly because they pose a risk to people who are civilians—they’re not uniformed armed combatants, soldiers, or other members of the military. By threatening civilians, and by threatening them after a war is over, these weapons create an enduring risk; the small bomblets are costly to clean up and deadly to leave in place. The other reason duds are a problem for the military is that each dud fired in battle is a potential enemy left alive, making the weapon less effective than promised.

Dealing with deadly duds

There are a few ways countries have responded to the problems posed by cluster munitions and their duds. The first is the Convention on Cluster Munitions. This treaty, which is agreed to by more than 100 nations, entered into force in 2010.  The convention “bans the use of cluster munitions, as well as their development, production, acquisition, transfer, and stockpiling,” with two exceptions: if the cluster munition is designed to detect and hit a single target (like many small bombs hitting a tank) or if they are cluster munitions that include an electronic self-destruction or self-deactivating feature. That last feature lets munitions render themselves inert, reducing but not completely eliminating the risk to civilians posed by unexploded bombs.

Several nations have not signed the Convention on Cluster Munitions, including Russia, the United States, and Ukraine, among others. While some NATO allies, like Canada, France, and the United Kingdom are signatories, the treaty does not prevent general or military cooperation with non-signatory nations.

The other way to reduce the risk of unexploded submunitions is to ensure that more of the submunitions explode.

This is the tack that Kahl emphasized, saying that “compared to Russian cluster munitions, the DPICM rounds we will provide Ukraine have an extremely low failure, or dud rate. The DPICM ammunition we are delivering to Ukraine will consist only of those with a dud rate less than 2.35 percent. Compare that to Russia, which has been using cluster munitions across Ukraine with dud rates of between 30 and 40 percent. During the first year of the conflict alone, Russia fired cluster munitions deployed from a range of weapon systems have likely expended tens of millions of submunitions, or bomblets, across Ukraine.”

The aftermath 

Unexploded bombs from this fighting were already a major postwar concern for Ukraine, because safely clearing explosives is slow, painstaking work. While Kahl gave a failure rate of 2.35 percent, the New York Times reports that “the Pentagon’s own statements indicate that the cluster munitions in question contain older grenades known to have a failure rate of 14 percent or more.”

With 72 small grenades in each shell of cluster munitions, a 14-percent failure rate translates to just over 10 failures per shell. (The number of submunitions in a shell varies, with reports ranging from tens to hundreds.) These are stockpiled weapons that the United States stopped using in 2003, and stopped procuring in 2008 as the failure rate was deemed too high under Pentagon policy.

In a press conference July 7, National Security Advisor Jake Sullivan emphasized the nature of the war Ukraine is fighting as a justification for the weapons.

“The argument I’m making is that Russia has already spread tens of millions of these bomblets across Ukrainian territory,” said Sullivan. “So we have to ask ourselves: Is Ukraine’s use of cluster munitions on that same land actually that much of an addition of civilian harm, given that that area is going to have to be de-mined regardless?”

Kahl echoed that same sentiment, saying “Russia has been using cluster munitions indiscriminately since the start of this war in order to attack Ukraine. By contrast, Ukraine is seeking DPICM rounds in order to defend its own sovereign territory.”

These arguments anticipate and in part respond to the robust disagreement about the weapon’s transfer and use from allies and human rights organizations. On July 8, Canada’s government released a statement condemning the transfer, saying “We do not support the use of cluster munitions and are committed to putting an end to the effects cluster munitions have on civilians – particularly children.”

Legacy weapons—and the question of using them or not—are realities that present and future policy makers must grapple with. Like a submunition left undiscovered in a field until tragedy strikes, the decision to develop and field a weapon has implications in the immediate moments of the conflict, and in the long aftermath of a battle. The hastened end of a war may make the peacetime work of restoration and demining arrive sooner, but the way in which the war is fought will determine the scale of post-war repair needed.