Cluster Munitions: What Are They, and Why Is the United States Sending Them to Ukraine?

The United States has announced that it will send cluster munitions to Ukraine after weeks of internal debate and public speculation. Ukraine has asked for these munitions, which are highly effective against area targets such as infantry, artillery, and truck convoys. However, the munitions are controversial because of high dud rates and the resulting danger to civilians. The munitions will help Ukraine’s armed forces as they continue their counter-offensive, but they will not be a game changer.

Q1: What are cluster munitions?

A1: The international Convention on Cluster Munitions defines cluster munition as “a conventional munition that is designed to disperse or release explosive submunitions, each weighing less than 20 kilograms.” Thus, cluster munitions consist of a dispenser and submunitions loaded onto it. Submunitions are essentially grenades with tail fins or a streamer to help them land in the right orientation.

Photo: Scott Peterson/Getty Images

An unexploded cluster munition identified by members of the Mine Advisory Group in a backyard garden in Yohmor, Lebanon on August 21, 2006.

Photo: Scott Peterson/Getty Images

The dispenser releases the submunitions above the target, and the submunitions spread out as they fall. The submunitions explode when they hit the ground affecting a much larger area than a single, concentrated explosion. The picture below shows a dispenser that has stuck in the ground after dispersing its submunitions. The submunitions would be stacked in the rails.

Photo: Yasuyoshi Chiba/AFP via Getty Images

Internal components of a cluster munition remains in a grass field near Lysychansk, eastern Ukraine, amid the Russian invasion of Ukraine on May 10, 2022.

Photo: Yasuyoshi Chiba/AFP via Getty Images

The most common alternative to a cluster munition is a “unitary” warhead that has a single explosive package. As an illustration, a Multiple Launch Rocket System (MLRS) rocket can carry 518 bomblets (M26A1/A2) or a single 200-pound warhead.

Cluster munitions can be in the form of artillery shells, rockets, or air-delivered munitions. The United States has produced all three. However, the Department of Defense’s announcement mentioned only artillery munitions. The United States is unlikely to provide air-delivered cluster munitions because strong Russian air defenses over the battlefield make delivery of munitions by aircraft extremely dangerous. It might provide MLRS rockets with cluster munitions though it is unclear whether any are still available. Thousands were produced, but many have been converted to other uses.

The standard U.S. submunition is called dual-purpose improved conventional munition, or DPICM. It is dual-purpose because it has effects on both vehicles and personnel. The most recent version, the M77, has a penetrating charge for attacking vehicles and a fragmentation element for attacking personnel. A155 mm artillery shell carries 88 submunitions (M483A1) or 76 in the longer-range M864.

During the Cold War and into the 1990s, cluster munitions were the U.S. standard ammunition. Hundreds of thousands of artillery shells remain.

Q2: Why are cluster munitions controversial?

A2: They are controversial because the submunitions have high dud rates. They often land wrong, so the fuse does not function. Dud rates vary from 2 percent to 40 percent, with U.S. submunitions on the lower end and Russian submunitions on the higher end. Duds act like landmines and can injure civilians. For this reason, the Convention on Cluster Munitions was established. Signed by 123 nations, it came into effect in 2010. The convention prohibits using, developing, producing, acquiring, stockpiling, or transferring cluster munitions.

Russia, Ukraine, and the United States have not signed the convention. The United States has not signed because it wants to retain the right to use such munitions in combat emergencies.

Although the United States did not sign the convention, it stopped producing cluster munitions in 2008 and has produced only unitary warheads since then. It has gradually converted inventories to convention-compliant configurations. For example, it has replaced the cluster munition warhead on many MLRS rockets with an inert warhead appropriate for training.

The United States tried to develop submunitions with dud rates under 1 percent. However, this was not technically feasible. Before ceasing production in 2008, DOD was able to produce submunitions with dud rates under 2.35 percent, and these are the cluster munitions being sent to Ukraine.

Q3: Why does Ukraine want cluster munitions?

A3: Ukraine wants cluster munitions because they are highly effective against area targets such as infantry, artillery, and vehicle convoys. Indeed, cluster munitions got the nickname “steel rain” because of their intense and widespread effects. Because cluster munitions spread bomblets out over a wide area, a single munition can cover the same area as many unitary projectiles. Thus, to get the same effect, the Ukrainians would need to fire multiple projectiles with unitary warheads, reducing stockpiles and exposing the firing batteries to Russian counterfire for a longer time.

Analysis of cluster munition use during the Vietnam War found it to be eight times as effective in producing casualties as standard high explosive projectiles. In peacetime testing against vehicles, cluster munitions were 60 times as effective.

Cluster munitions do not have increased effectiveness against all targets. Unitary warheads are more effective against point targets like buildings.

Ukraine’s counteroffensive is now one month old, and although it is still moving forward, it has not achieved the rapid advance hoped for. Thus, adding a weapon with this additional combat power might help sustain the offensive.

Q4: Why did the Biden administration decide to provide these munitions now?

A4: The administration cited two reasons―the lack of alternatives and the Ukrainian request. There was likely a third, unstated reason―political pressure.

The lack of alternatives occurred because the United States has committed over 2 million artillery shells to Ukraine. As a result, the inventory of standard (high explosive) artillery shells is now very low. Although the United States continues to provide some shells as new production becomes available, the numbers are not sufficient to meet Ukraine’s artillery needs. Cluster munitions will fill that gap. The United States has implied that cluster munitions will not be necessary when production of standard munitions is sufficient. However, that could take years.

The second reason is that the democratically elected Ukrainian government has made a judgment that this is in the best interests of the nation and its people. As National Security Adviser Jake Sullivan stated, “Ukraine would not be using these munitions in some foreign land. This is their country they're defending. These are their citizens they're protecting. And they are motivated to use any weapons system they have in a way that minimizes risk to those citizens.” It would be presumptuous for the United States and Europe to say that they know better than elected Ukrainian officials what is good for the Ukrainian people.

The third reason, political pressure, arises because Ukrainian president Zelensky has been very vocal in pressing for new weapons, including cluster munitions. Many national security opinion leaders and members of Congress have picked up that advocacy. In the past, the dynamic on controversial new systems has been that the United States resists, pressure builds from both domestic sources and the Ukrainians, and the United States eventually relents. This was the experience with Patriot air defense missiles, M1 Abrams tanks, and F-16 aircraft. That is now the case with cluster munitions.

Q5: Are there alternatives to cluster munitions?

A5: Yes, but none that are readily available. For cannon artillery, an alternative is a standard high explosive projectile with a proximity fuze that causes it to detonate in the air. That airburst spreads effects over a wide area, like a cluster munition. However, the supply of regular high-explosive projectiles is low, and the effect of airbursts, while substantial, is not as great as that of a cluster munition.

For MLRS rockets, the alternative is the alternative warhead. When the United States was unable to produce cluster munitions with an acceptable dud rate, it took a different approach. The alternative warhead explodes in the air and spreads a pattern of 160,000 preformed tungsten fragments. This gives it a shotgun-like effect. Because these are fragments, not bomblets, there is no dud problem. The airburst and large number of fragments provide an area effect similar to a cluster munition, though not covering as large an area. However, this warhead only went into full-rate production in 2019, so there are probably about 5,000-10,000 now available. It appears that many of these have been sent to Ukraine already.

Q6: Will this increase the postwar demining problem?

A6: Yes, but that challenge is already huge. With a 2 percent dud rate, a U.S. 155 mm DPICM projectile will produce 1.9 duds. Thus, 10,000 projectiles would produce 19,000 duds that would need to be removed or deactivated. However, there are already hundreds of thousands of pieces of unexploded ordnance in Ukraine from cluster munitions, regular artillery shells that failed to function, and landmines that both sides have employed.

Q7: Will opposition derail the transfer?

A7: Probably not. Most U.S. allies, including most NATO members, have signed the cluster munition convention. Because the convention also bans state parties to “assist, encourage or induce anyone to engage in any activity prohibited,” many feel uncomfortable with the U.S. transfer. Although there may be some discussion at this week’s NATO summit in Vilnius, Lithuania, it is unlikely that any allies will act to block the transfer. In general, they have strongly supported aid to Ukraine and will not want to be seen opposing a potentially effective weapon that Ukraine has asked for. NATO secretary general Jens Stoltenberg has said that NATO will not take a position, thus, in effect, allowing the United States to go ahead.

The Republican national security leadership has strongly supported the transfer of cluster munitions. Progressives in Congress have stated their opposition to the transfer. However, they will not be able to impose their will on a Democratic White House. Last fall, the same progressives signed a letter expressing reservations about the cost of aid to Ukraine, but the White House put an end to that effort within 24 hours. Although Democratic opposition might be broadening, it is unlikely to be strong enough to overcome the president’s policy, especially with Republican support.

Q8: Will cluster munitions be a "game changer"?

A8: Unfortunately, no single weapon or munition will bring victory. Ukrainian victory will result from the cumulative effect of the weapons and munitions provided by the United States, NATO, and global allies, training provided to the Ukrainian troops, and the determination of the Ukrainian people. That said, cluster munitions are very effective against certain targets and will add to Ukrainian military capabilities.

Mark F. Cancian (Colonel, USMCR, ret.) is a senior adviser with the International Security Program at the Center for Strategic and International Studies in Washington, D.C. In the U.S. Marine Corps, he was an artillery officer and fire support planner, during which time he employed cluster munitions.