The Drone Threat, the Laser Response, and the Law – Part II

The first part of this two-part post, described and explained the weapons law principles and rules that apply to suicide or kamikaze drones. It also set forth and explained applicable targeting law principles and rules and addressed the legality of mass attacks involving weapons of that kind. While various traditional anti-aircraft weapon systems are being used to counter the threat posed by these kinds of drone, during mass attacks significant numbers evade those defensive measures, causing death, injury, and damage.

While Sir Isaac Newton’s Third Law of Motion states that for every forceful action in nature there is an equal and opposite reaction, the weapon-countermeasure analogy is perhaps not identical. Maybe it would be correct to say that on each occasion when a new and effective way of conducting hostilities emerges, such as the employment of mass drone attacks, significant (but not always successful) efforts will be devoted to the development of effective countermeasures. There can be no doubt that the use of mass drone attacks has caused many casualties and serious destruction to critical infrastructure. Maybe we are now witnessing the emergence of effective countermeasures, in the form of a laser technology that, tests suggest, may provide a more successful defence against the drone threat.

Current Anti-Drone Technologies

Reference in this section will be made to experience in the Russia-Ukraine armed conflict. This is merely intended to illustrate the relevant issues, it being recognised that similar technologies have been employed in other armed conflicts with similar consequences.

Reports here, here, and here show that the techniques currently employed by Ukraine to shoot down Russian drones include the use of: the Avenger air defence system which employs Stinger missiles and machine guns; assault rifles; anti-aircraft guns mounted on tracked vehicles; heavy machine guns equipped with thermal scopes; and Patriot and Iris-T systems. Such anti-aircraft weapon systems are broadly similar to weapons which have been used in such roles for many years and which do not contravene the principles and rules of weapons law.

However, reports, for example here, show that while large numbers of Russian drones are shot down by these air defence capabilities, substantial numbers also get through and cause damage, injuries, and death. This is particularly the case when large numbers of drones are fired in what are sometimes described as swarms. If an intruding drone is successfully targeted, falling debris may also cause casualties, destruction, and damage. Unsurprisingly, therefore, States that are subject to these mass drone attacks are keen to acquire a capability that will successfully intercept higher proportions of these drone weapons, preferably at reduced financial cost. Ideally, the drone interceptions would take place in locations where the falling debris will not cause damage and injury to those on the ground. It is just possible that technological advances earlier this year may provide an appropriate solution.

Emerging Laser-Based Anti-Drone Systems

In December 2024, South Korea started the deployment of the Laser-Based Anti-Aircraft Weapon – Block-I. A recent report indicates that Block-I, also known as Skylight or Cheongwang, is a stationary 20 kW-class fibre laser system that can neutralise drones within a range of 2 to 3 kilometres. The cost of each shot is said to be U.S. $1.45. The intended targets are small, unmanned air vehicles and multi-copters. In live-fire tests, the system achieved 100% success in engaging the intended targets. Upgrades of the South Korean laser system in the form of Block-II and Block-III are apparently planned.

The United Kingdom’s first firing of a high-power laser against an aerial target was reported in January 2024. The firing took place in the Hebrides; information about the range of this weapon, named DragonFire, is classified, but it is stated to be a line-of-sight weapon that can engage any visible target. The level of required precision is stated to be equivalent to that of engaging a £1 coin at a distance of one kilometre. The engagement of a target takes place at the speed of light and uses an intense beam of light to cut through the target “leading to structural failure or more impactful results if the warhead is targeted.”

In December 2024, it was reported that a high energy laser weapon had been fired by the British Army from an armoured vehicle successfully destroying flying drones. The weapon directs “an intense beam of infra-red light in the form of energy towards its target using advanced sensors and tracking systems which maintain lock-on and accuracy in real time.” Integrated onto a Wolfhound troop-carrying vehicle, soldiers were able to track and bring down hovering targets at a range in Wales. Apparently, the weapon has been developed by a group of companies led by Raytheon.

Israel’s Iron Beam is a 100 kW class, mobile high energy laser system developed by Rafael Advanced Defense Systems. According to reports, the weapon demonstrator has successfully intercepted unmanned aerial vehicles (UAVs), mortars, rockets and anti-tank missiles at ranges up to 4.34 kilometres. It includes an air defence radar, a command and control unit, and two high energy laser systems. Adverse weather conditions can apparently impact the system’s performance with the laser beam underperforming in conditions of fog, dust, and cloud. The air defence radar is designed to detect an incoming projectile which a thermal camera then tracks concurrently with engagement by the two high energy lasers. According to open-source reporting,

The laser system of the Iron Beam features an optical director, which includes multiple channels, a multichannel HEL transmitter, a visible zoom wide or narrow field of view, and a laser range finder to measure distances precisely. In addition, it is equipped with a laser illuminator that indicates the target of interest using laser beams for detection by humans and a thermal cabin telecommunications unit.

Other countries are reported to have or be developing similar weapons, including Russia, China, and Iran.

Applying Weapons Law to Laser Anti-Drone Systems

The discussion in this section offers a few of the matters that the author considers acquiring States should consider when preparing a review of this sort of weapon technology. In this regard it should be remembered that States that are party to Additional Protocol I are required by Article 36 of that Treaty to determine whether the employment of a new weapon that they are studying, developing, or acquiring “would, in some or all circumstances, be prohibited by the[e] Protocol or by any other rule of international law applicable to [that State].” Where States that are not party to Additional Protocol I are concerned, the author has argued that they are subject to an implied legal obligation to review whether the intended use of new weapons that they acquire complies with the international law rules that bind that State.

The superfluous injury/unnecessary suffering principle as reflected in Article 35(2) of Additional Protocol I prohibits weapons that are of a nature to cause injury or suffering for which there is no corresponding military purpose. It is a customary principle of law, binding on all States, that is concerned with the effect that the reviewed weapon will inevitably have on combatants and on directly participating civilians of the adverse party. No issues under this principle are likely to arise from high energy lasers used against drones, missiles, rockets and mortars. The principle will not be considered further.

The indiscriminate weapon principle, derived from Article 51(4)(b) and (c) of Additional Protocol I, prohibits the use of weapons which are by nature indiscriminate. These are weapons which cannot be directed at a specific military objective or the effects of which cannot be limited as required by international law and which, as a result, are of a nature to strike military objectives and civilians or civilian objects without distinction. When a particular laser weapon of the sort discussed in this post is being reviewed, the results from test firings must be considered. Those test firings should reflect the kinds of target it is intended to engage and all of the intended circumstances in which it is intended to fire the weapon. These will include but will not be limited to various weather and atmospheric conditions, day and night firings, test firings to simulate urban and rural locations, firings against static, hovering, rapidly moving targets, and firings against targets in a swarm.

The laser weapon systems described in the previous section of this post are unlikely to be indiscriminate by nature, but their performance in tests may indicate particular ways in which they should not be used. If so, that should be explained in the weapon review. Likewise, based on the test results the weapon review may identify factors that need to be taken into account by users of the weapon in order to ensure that its use on specific occasions is discriminating, e.g. the presence of dust in the atmosphere, weather conditions such as the presence of fog or cloud, the presence in the relevant area of civilian aircraft and so on. In this regard, consideration may need to be given to matters discussed later in this post.

In accordance with Articles 35(3) and 55 of Additional Protocol I, States party must consider whether the laser weapon is either intended or may be expected to cause widespread, long-term, and severe damage to the natural environment. States that are not party to Additional Protocol I are required to consider whether the use of the weapon is consistent with the customary law obligation to have due regard to the natural environment. It is not considered that this rule will be of significant relevance to high energy laser weapons as such, so it will not be considered further.

The only rules of international law that specifically address laser weapons are to be found in Protocol IV to the Conventional Weapons Convention. Article 1 of that treaty prohibits the employment of laser weapons specifically designed as a combat function to cause permanent blindness to unenhanced vision. It is most unlikely that weapons of the kind being discussed in this post will be so designed. Article 2 of the treaty requires a State party, when using laser systems, to “take all feasible precautions to avoid the incidence of permanent blindness to unenhanced vision,” such precautions to include training and other practical measures. The weapons discussed in this post are likely to operate, under normal circumstances, at elevations such that the human eye is unlikely to be affected. The particular characteristics of the specific weapon and the way in which it is to be used must, however, be considered by reference to the Article 2 requirement. It should be noted that by virtue of Article 3 blinding as an incidental or collateral effect of the legitimate military employment of a laser system is not prohibited.

A full technical description of the particular laser weapon system will be required in order to support a legal review. This will include the intended and actual destructive range of the laser. Consider for example a laser with a destructive range of 4.3 kilometres, or 14,107 feet. It would be necessary to determine the range at which, for example, the laser weapon can be expected to have a damaging effect, say, on an aircraft in flight. It would seem to the author that the use of technology of this kind may render the use of airspace to a certain range from the source of the laser dangerous. While the operational purpose will be to engage the intended targets such as UAVs etc, Article 57(1) of Additional Protocol I requires that the parties to the conflict take constant care to spare civilians and civilian objects, and Article 57(2) requires that particular precautions be taken. In the author’s view, consideration should also be given to the Article 58 obligation to take necessary precautions to protect the civilian population, individual civilians and civilian objects under the control of the State using the laser weapon against the dangers resulting from such military operations.

Risk to Civilians and Civilian Aircraft

The danger to civilians on the ground as UAVs, kamikaze or suicide drones and other targets are shot out of the sky most obviously comes within the Article 58(c) provision mentioned at the end of the previous section. This would suggest that, to the extent practically possible, care is required in the positioning of the laser system and, in particular, in the piece of airspace in which it engages the inbound drones, missiles etc, with a view to avoiding or at least minimising the injury to civilians and damage to civilian objects beneath. The Article 58 obligation is caveated “to the maximum extent feasible,” which makes it clear, in the author’s view, that this requirement should not prejudice the successful engagement of the inbound weapons, but the Party to the conflict using the laser weapon will wish to do what it reasonably can to safeguard its own civilians. The other matter to be discussed in this section is whether the use of such laser systems poses risks to civil aviation.

Much will depend on whether the particular high energy laser system that is being reviewed employs a beam that can be directed at a specific object and that can limit its damaging effect to that target object. If that is the case, the discrimination rule discussed above is likely to be satisfied. If, however, the beam is such that it will have a damaging effect not just on the target object but also on any other object that is within range along the line of the beam, this may, depending on the location where the weapon is to be used, be problematic. These considerations are, however, unlikely to render the laser weapon indiscriminate by nature. Rather, it may be necessary that carefully articulated firing protocols and other precautions be developed and taken by the using State to address the potential risk to other air traffic in the area of use.

Rule 87(a) of the Oslo Manual reminds States that they are “entitled to restrict or prohibit entry into their national airspace.” Rule 91(b) stipulates that civilian airliners “are civilian objects and entitled to particular care in terms of precautions.” Rule 95(a) explains, in non-binding terms, that during an armed conflict, “States should—whenever necessary for the safety of civil aviation—restrict access to their national airspace (in whole or in part) by civilian airliners.” Rule 95(b) asserts, as a mandatory obligation derived from customary law, that States “must keep under review the level of danger to civil aviation under its air traffic control and inform the relevant foreign actors of any imminent dangers to aviation in the airspace for which it is responsible.” Operators of civilian airliners have, as a matter of non-binding best practice, a corresponding obligation under Rule 96 to “avoid areas of potentially hazardous military activity, even if civil aviation has not been restricted or prohibited in the respective airspace.”

As noted earlier, much will depend on where the high energy laser weapon is to be used, whether civilian aircraft would normally use airspace within its destructive range, whether the laser beam can and will be directed only at lawful targets, whether when so directed the beam’s destructive effect is limited to the lawful target and so on. It seems to the author that these are matters that must be carefully tested and that the results of those tests must be considered fully in the weapon review. That review document should specify any circumstances in which the weapon should not be used and should give the precautionary measures that should be taken to seek to obviate the risks discussed here, and any other such risks identified in the review. In the author’s view, those precautionary measures should, where relevant, include the measures discussed in the previous paragraph.

States where hostilities are taking place, including hostilities involving the laser weapons discussed in this post, should be forthcoming in notifying the associated risks to civilian users of the affected airspace, e.g. through the issue of Notices to Airmen. Equally, operators of civilian airliners and, in the final analysis, pilots should seek to ensure that hazardous airspace is avoided.

Conclusion

This post has sought to identify some of the legal issues that should be considered when the legal implications of high energy laser weapons are being considered. It must be stressed that, as with the review of the drone systems addressed in my preceding post, it is the characteristics, performance and data associated with the particular weapon that will inform the legal review, and it is the law as it applies to the reviewing State that will be relevant.

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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.

Photo credit: UK MOD, Crown copyright 2024