Cluster Munitions and the Ukraine War

by | Feb 28, 2022

Cluster Munitions

There are reports that cluster munitions have been used by both sides during the Ukraine Wars. Is such use lawful?

Cluster munitions can, in general terms, be defined as “weapons that open in mid-air and disperse smaller sub-munitions—anything from a few dozen to hundreds—into an area. They can be delivered by aircraft or from ground systems, such as artillery, rockets and missiles.” The sub-munitions, which are generally explosive in nature, are usually designed to detonate on impact with the ground or with some other solid object. They may also be fuzed to detonate or air-burst at a prescribed height from the ground. The damaging or injurious purpose is achieved by a combination of blast and fragmentation. Blast and fragmentation are not, from a weapons law perspective, controversial methods of warfare.

The footprint of effect of a cluster munition will be determined by the area of land within which the sub-munitions, or bomblets fall. The fact that a weapon is directed at an area of land as opposed to a specified person or object does not, per se, render the weapon indiscriminate. Military objectives, whether persons or objects, may be concentrated within the footprint of the cluster munition such that the area of land where they are located becomes a military objective.

Weapons law includes, however, a principle of law that prohibits weapons that are, by nature, indiscriminate. This is a principle of customary law that is therefore binding on both Russia and Ukraine. Likewise, the prohibition of indiscriminate attacks is customary and binding on both sides in the conflict.

Cluster munitions have been regarded as militarily effective ways of engaging wide area or dispersed targets, such as soft-skinned vehicles, concentrations of troops, military vehicles and other military objects and some kinds of armour. They were used by the Soviet Union and Germany during WWII, by the United States in Laos, during Operation Desert Storm in Iraq, by Sudan in Equatoria, by Russia in Chechnya[1] and by NATO during the Kosovo Conflict. Large numbers of the sub-munitions used during some of these conflicts, however, failed to explode as intended leaving dangerous explosive sub-munitions strewn around the battlefield, a persistent danger to civilians returning after the conclusion of hostilities.

Moreover, use of cluster munitions, indeed the use of any weapon during an armed conflict, must be in accordance with the law of targeting, and the principle of distinction is the cornerstone of that body of law. Indiscriminate attacks are prohibited. To determine whether an attack breached this prohibition, however, it will be necessary to establish what the target of the attack was, what military advantage was anticipated to accrue from the successful prosecution of the attack, what civilian deaths, injury and/or damage was expected to result and whether the latter was expected to be excessive in relation to the former.

States party to the Conventional Weapons Convention recognised in the early 2000s the problems posed by what came to be known as “explosive remnants of war,” and on 28 November 2003 the Protocol on Explosive Remnants of War (ERW) was adopted. The Russian Federation and Ukraine are both parties to the treaty.

The main focus on the Protocol is on clearance, removal and destruction of explosive remnants of war, including bomblets lying around on the former battlefield and abandoned munitions. There are additional provisions on recording, retaining and transmitting information about such remnants, the taking of feasible precautions to protect civilians from them, protection of humanitarian missions from ERW and cooperation and assistance. Parties to an armed conflict have specified responsibilities with regard to ERW on territory they control.  Moreover, users of ordnance that become ERW on enemy territory where the user does not control the territory have assistance obligations to facilitate clearance, removal and destruction of the ERW.

Having addressed ERW by the adoption of the Protocol, humanitarian concern then focused more specifically on cluster munitions. That concern related to the apparently indiscriminate employment of such weapons and on the humanitarian consequences of high failure rates, so-called dud bomblets.

The States party to the Conventional Weapons Convention agreed mandates for discussion of the relevant issues in November 2006 and in succeeding years. Having failed to achieve a Protocol by 2011, a group of concerned States initiated an ad hoc process which in due course led to a diplomatic Conference, and the adoption of the Convention on Cluster Munitions.[2] This is an arms control treaty that prohibits not just use of cluster munitions, but also development, acquisition, stockpiling, retention and a variety of other activities associated with cluster munitions. At the time of writing, there are 110 States that are party to the Convention, but these do not include the Russian Federation or Ukraine. Accordingly, the Convention’s provisions do not bind either Russia or Ukraine as a matter of treaty law. Moreover, it is not yet possible to find a general practice among States, accepted as law, supporting a conclusion that the Convention’s provisions bind at the customary law level.

It is, however, well established in IHL that if there is no specific provision of international law dealing with a particular matter, “the inhabitants and the belligerents remain under the protection and the rule of the principles of the law of nations, as they result from the usages established among civilized peoples, from the laws of humanity and the dictates of the public conscience” (Hague Convention IV, 1907, preamble, para. 8).

The customary principles that are of most relevance would seem to be the principle of distinction, the principle prohibiting indiscriminate attacks, and the principle prohibiting weapons that are by nature indiscriminate, as discussed above.

Therefore the following legal conclusions with respect to cluster munitions are clear:

    • There is in international law no prohibition on the use of cluster munitions as such by the Russian Federation or by Ukraine.
    • If a particular kind of cluster munition is so designed that it cannot be directed at a specific target or that its effects cannot be limited to a specific target and if it is therefore of a nature to strike military objectives and civilians and/or civilian objects without distinction, it is prohibited by weapons law.
    • If a sufficient proportion of the individual bomblets fail to detonate and cause civilian death or injury such that the use of the weapon can properly be described as indiscriminate, the weapon per se would be prohibited under the indiscriminate weapons principle.
    • If the particular kind of cluster munition is found not to be indiscriminate by nature, its use on a specific occasion may nevertheless breach the prohibition of indiscriminate attacks. Assessing whether that rule has been broken involves a careful application of targeting law.  The information that was available to the attacking commander when making the attack decision, the steps taken by that commander to obtain further relevant information, the expected injury to civilians and damage to civilian objects, the anticipated military advantage from the attack, the precautions taken by the attacking commander and the precautions taken by the opposing authorities against the effects of attacks are among the numerous factors to be considered.
    • States that employ explosive weapon systems with high failure rates need to be mindful of the important ERW clearance, removal, destruction and assistance obligations imposed by Protocol V to CCW.


Air Commodore William H. Boothby retired as Deputy Director of Royal Air Force Legal Services in July 2011. He is Honorary Professor at the Australian National University and also teaches at the University of Southern Denmark and at the Geneva Centre for Security Policy.



[1] See the entry relating to BL755 in Janes’ Air Launched Weapons (1998) and V Wiebe, Footprints of Death: Cluster Bombs as Indiscriminate Weapons under International Humanitarian Law, 2000 22 Mich JIL 85, 91-5.

[2] Convention on Cluster Munitions, adopted in Dublin on 30 May 2008.


Photo credit: Stéphane De Greef, Landmine and Cluster Munition Monitor