Prof. Dr. T.D. Gill University of Amsterdam & Netherlands Defence Academy

 What are Unmanned Aerial Vehicles (UAVs) and Autonomous Weapons Systems (AWS)?  Are UAVs and AWS Inherently Incompatible with Existing Law?  Applicable Law ( Legal Bases and Regimes)  UAV Strikes and International Law: Main Controversies  AWS and the Main Challenges and (Legal) Questions Relating to their Potential Use  Conclusions

 UAVs are remotely piloted aircraft. They have been in use since the Vietnam War and have been used as weapons platforms for over a decade.  They have certain capabilities which distinguish them to some extent from manned aircraft, but are essentially no different than conventional manned aircraft.

 There is no generally agreed definition of AWS presently in use.  AWS should be distinguished from automated weapons systems such as CIWS which have been in use for decades.No fully autonomous weapons systems are presently in use.  AWS are usually distinguished from automated weapons by their envisaged ability to independently acquire, select and engage targets in an offensive mode and in a dynamic environment.

 A weapon which is incapable of being directed against a lawful military objective in the context of an armed conflict, which causes unnecessary suffering or superfluous injury to combatants, or whose effects cannot be controlled is illegal per se under IHL.  Outside the context of an armed conflict any weapon used must minimize risk both to the intended target and to surrounding persons and objects.  The use of lethal force under IHL is allowed within the limits laid down in the law. It is inherent to the conduct of hostilities.  The use of lethal force outside the context of an armed conflict and in certain circumstances within the context of an armed conflict is exceptional and subject to stringent conditions.

 Neither UAVs nor the automated weapons systems presently in use are inherently illegal under the law set out above.  Whether future designed AWS would be inherently illegal would depend upon a number of factors and potential modes of employment which will be considered below.  As no such weapons presently exist, any answer to this question must necessarily be contingent and speculative at present.

 In the absence of any general prohibition of such weapons systems, the question of their legality must be assessed on the basis of existing international law.  This includes the law relating to the use of force under the UN Charter and customary international law alongside rules of general international law relating to respect for State sovereignty (legal bases).  It also includes the applicable legal regimes for the conduct of hostilities within the context of an armed conflict and the rules relating to the application of (potentially) lethal force outside the context of hostilities.

 Within a legal perspective, the applicability of IHL and IHRL ratione materiae, ratione personae,ratione loci, & ratione temporis are of particular importance in determining which body of law is applicable and whether a given use of such weapons would be (in)compatible with the law.  Alongside legal considerations, there are moral or ethical and policy considerations which are also relevant. This is particularly true with regard to fully autonomous weapons systems as defined above.

 One main area of controversy is whether certain uses of UAVs have an adequate legal basis. These relate to whether a particular use of force can be justified as lawful self-defence or whether a particular State has validly consented to their use within its territory.  Another controversy is whether certain uses of UAVs ( targeted killings/signature strikes) are lawful under either IHL or IHRL and which of these regimes is applicable in the given circumstances.  Finally, there are widely diverging reports of the amount of incidental injury to civilians resulting from their use in particular situations.

A number of considerations are central to the debate on AWS:  The degree of human involvement in overseeing and employing the system ( “in, on or out of the loop”);  The mode of potential employment (offensive v. defensive tasks);  The type of targets to be engaged ( human/ objects ( military platforms, incoming missiles etc.);  The type of environment ( dynamic/static, urban/open);  Predictability of how the weapon will perform ( will the weapon have the ability to independently “learn”and modify its “behaviour” in ways not foreseen by its designer/employer)?

 UAVs can be used both legally and illegally: if a particular strike would be legal if carried out by a manned aircraft (e.g. F-16), it would be equally legal if conducted by a UAV ( and vice versa).  The legality of the (potential) use of AWS depends upon the answers to the previously mentioned questions: to the extent such weapons are used for tasks which allow for application of the IHL rules and principles relating to the targeting of persons and objects and the weapon is capable with more or less human involvement to comply with these, there are potential scenarios in which they could be lawfully used.

 However, even if this is the case, there may be reasons to forego or at least limit the potential use of such weapons, particularly in urban or dynamic environments.  Moreover, even if at some point in the future it was technically feasible to design a weapon which could lawfully perform even in such environments, there may be overriding ethical or policy considerations which militate in favour of caution in designing a machine which is independently capable of outhinking, outperforming and killing human beings.