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On the occasion of the Third Review Conference of the Convention on Cluster Munitions in Vientiane, Lao PDR, we spoke with Paul Heslop, Senior Mine-Action Adviser at the UN Resident Coordinator's Office in Ukraine. He shares his experience and perspective on a weapon system designed for the massed tank formations of the Cold War, and now evolving in real time on Ukraine's front lines. A warning from VientianeI am in Vientiane this week for the Third Review Conference of the Convention on Cluster Munitions, often known as the Oslo Convention. Adopted in Oslo, Norway, and opened for signature more than 16 years ago, the convention brought countries together to prohibit the use, stockpiling, production and transfer of cluster munitions.Every five years, states parties meet to assess progress, advance universal adherence and agree on the next steps. More than 100 countries have ratified the convention.I am here to present what we are seeing in Ukraine. Laos, however, is far more than a backdrop to this discussion. It is probably the country most heavily affected by unexploded ordnance from the Vietnam War. Ukraine is already on course to become one of the world's most heavily contaminated countries. If we are not careful, it could eventually surpass Laos in the scale of its contamination. We need to understand the consequences before that happens. What Cluster Munitions Actually AreCluster munitions are a distinct weapons system. They can be delivered by artillery, multiple-launch rocket systems or aircraft. A canister is fired or dropped and, at a predetermined height or distance, opens to release multiple submunitions, or bomblets. Under the convention's definition, a cluster munition contains multiple submunitions, typically eight or more.These submunitions can serve very different purposes. Some are anti-personnel weapons designed to produce lethal fragmentation. Others are anti-armour weapons, using shaped charges to pierce a vehicle's relatively thin roof armour and destroy its crew, engine or weapons systems. Some contain incendiary components intended to ignite ammunition depots or fuel storage areas.They may be effective against military targets, but they are an exceptionally hazardous weapons system. They are indiscriminate when deployed against civilians. An Area-Effect WeaponAt its core, a cluster munition is an area-effect weapon. A single canister dropped from an aircraft can cover an area equivalent to one or two football pitches. A battery of multiple-launch rocket systems can blanket an entire one-kilometre grid square, over one million square metres.Before the widespread use of precision-guided munitions, cluster munitions were designed primarily to destroy large, massed formations of Soviet or Warsaw Pact tanks and infantry advancing into Western Europe. That was the scale for which they were developed.Since the Falklands War in the 1980s, they have been used in nearly all major state-on-state conflicts, including Afghanistan, Iraq, Lebanon in 2006, and, extensively, Ukraine. Their use has also been reported in other contemporary conflicts. The Long Tail of Unexploded OrdnanceThe central problem is their failure rate. If a canister containing 100 submunitions is used and 10 to 20 per cent fail to detonate, then between 10 and 20 live explosive devices may remain on the ground after a single strike. These remain live and dangerous for decades.These weapons are typically used in dynamic environments against moving targets such as convoys and armoured patrols, but can also be used against static defence positions or harbour areas. Their use is often poorly recorded. A battlefield today may be a farmer's field tomorrow. In an urban area, it may become a school, health post, hospital, playground, or residential neighbourhood.That is when the long-term danger begins. Civilians often return soon after fighting moves on. Many submunitions, in effect, become victim-activated. Their arming mechanisms may depend on forces such as centrifugal spin or parachute drag, but are always incredibly sensitive to external forces. As a result, a device may appear inert while remaining one disturbance away from detonation.A farmer ploughing a field may tilt a shaped-charge submunition just enough to trigger it. A weapon designed to penetrate a tank can pass through a tractor, and the person operating it. A child who picks up a fragmentation submunition may, in effect, be holding a live hand grenade.Such a device may not technically meet the definition of a victim-operated mine. The consequences, however, can be much the same. This is why cluster munitions are treated as indiscriminate weapons under international humanitarian law. From Laos to UkraineThis is the throughline that brought me to Vientiane. Cambodia, Laos and Vietnam have lived with cluster-munition contamination for decades. Their experience offers lessons that Ukraine must absorb while the war is still active.At present, many areas targeted by cluster munitions in Ukraine are military positions that civilians cannot easily access. The real test will come after a ceasefire or peace agreement, and people begin returning to land they may not have seen for years.The indiscriminate nature of these weapons means that civilians, and especially children, could be most vulnerable precisely at that moment.  A Dangerous New EvolutionWhat concerns me most is the way the technology is evolving.Cluster munitions once required relatively sophisticated delivery systems, generally available only to states. That largely confined their use to conventional, state-on-state warfare. This is changing rapidly.In Ukraine, we are seeing non-standard submunitions manufactured using 3D printers and delivered by drones. The combination of inexpensive, decentralised production and widely accessible delivery platforms dramatically lowers the barrier to entry. Both the quantity deployed and the areas contaminated are growing by the day.It moves the weapon system towards something capable of producing effects on a mass scale, arguably a weapon of mass destruction, and certainly towards consequences for civilians that are indiscriminate in character.Over the past six months, we have observed a shift from battlefield and frontline use towards reports of drone-delivered, 3D-printed submunitions being used against civilian areas. The pattern was initially reported in eastern Ukraine and is now spreading westward.Winter makes the danger even harder to manage. A submunition covered by snow becomes invisible while remaining lethal to anyone who steps on it or drives over it. When spring arrives and the snow melts, another wave of hazards is exposed. The Importance of DataNone of this is inevitable, but preventing a larger crisis requires reliable information.When strike locations, quantities used, weather and ground conditions, and soil types are not recorded, clearance becomes slower, more costly and more dangerous. With accurate data, clearance operations can be targeted and conducted far more efficiently. Without it, communities may live with the risk for years longer than necessary. Looking AheadWhy send a UN representative to a review conference in Vientiane?Partly, it is to demonstrate that the United Nations sees genuine value in the Convention on Cluster Munitions. The treaty has almost certainly helped save thousands of civilians from death and life-changing injury by reducing the use of an inherently indiscriminate weapon.But above all, I am here to argue against complacency.The world remembers the dangers posed by landmines, but people often forget how closely cluster munitions are linked to the same problem. A submunition can become victim-activated in practice, even when it does not meet the technical definition of a landmine.If we fail to address the evolution now under way, in technology, delivery systems and tactics, the civilian cost will be felt first in Ukraine. It could then spread as other armed actors, both state and non-state, learn from the conflict and adopt similar methods.My priority in Vientiane, and beyond, is to ensure that the lessons of Vietnam, Cambodia and Laos reach Ukraine before that happens, not afterwards.