Today, drones have become omnipresent and are widely used throughout society. Not only are they popular products for recreation, but they are also more and more used in the commercial sector. At present, the number of drones used in Germany is estimated at more than half a million units. In addition, the portion of drones used for commercial purposes continues to increase steadily.1 The fact that drones are spread throughout society is what makes them a challenge that reaches far beyond the military sector, and, hence, falls under the sphere of competence of national regulatory authorities – at least in peacetime.
This chapter serves to show the limitations of the individual capabilities and powers of both police and military, where civilian and military agencies can and where they must complement one another. This chapter has been written with a view to general applicability to the extent possible. However, various national legal provisions, powers, and competences for the domestic employment of military resources, in particular, may deviate from the perspective represented within this document.
Law Enforcement Authorities and Military Powers in the Homeland and in Peacetime
Whereas International Humanitarian Law (IHL), the Law of Armed Conflict (LoAC) and, where necessary, an associated UN mandate form the legal foundation for the employment of military force between nations, the use of military assets and resources in the home country during peacetime is subject to distinctly different regulations in most NATO nations. Often, the lowest common denominator when using force of arms is the right to self-defence only.
Military Aid to the Civil Authorities
In general, the constitutions of the Western democracies allow the domestic employment of regular armed forces within a strictly limited legal framework only. However, many NATO nations have either amendments to their constitutions in effect or particular legislation that enables so-called ‘Military Aid to the Civil Authorities (MACA)’, ‘Military Aid to the Civil Power (MACP)’ or ‘Defense Support of Civil Authorities (DSCA)’. As a rule, all terms denote the employment of armed forces in support of the civil authorities of a state.2, 3 The armed forces do not, in general, operate autonomously under military command but are assigned for mission performance under operational command of the police forces to be supported or at least ordered to cooperate with them. Based on such arrangements, many countries have employed military forces in response to national crises after the SARS-CoV-2 coronavirus breakout.4
Military-organized Police Forces (Gendarmeries)
Many NATO nations also have military-organized police forces, so-called Gendarmeries, which belong to the military. However, in peacetime, these forces are assigned to the Home Office and assume various police responsibilities in their home countries. Gendarmeries can be found, for example, in France (Gendarmerie Nationale), Italy (Carabinieri), the Netherlands (Koninklijke Marechaussee) or Spain (Guardia Civil). In 2004, the European Gendarmerie Force (EGF) was established on the initiative of France as an autonomous supranational gendarmerie unit. Besides France, present EGF member states are Italy, the Netherlands, Poland, Portugal, Romania, and Spain.5
Domestic Military Operations
To counter an already increased threat situation in peacetime, several nations have established their own domestic ‘operations’ for their armed forces.
Operation Sentinel is a French military operation with 10,000 soldiers and 4,700 police and gendarmes deployed6 since the aftermath of the January 2015 Île-de-France attacks, with the objective of protecting sensitive ‘points’ of the territory from terrorism. It was reinforced during the November 2015 Paris attacks, and is part of an ongoing state of emergency in France due to continued terror threats and attacks.7, 8
Operation Temperer is a British government plan to deploy troops to support police officers in key locations following a major terrorist attack. It was put into effect for the first time on 22 May 2017 following the bombing of an Ariana Grande concert at Manchester Arena9 and for a second time following the Parsons Green bombing.
Operation Vigilant Guardian was a Belgian army operation following the January 2015 Île-de-France attacks and the dismantling of a terrorist cell in Verviers10 having foiled attacks imminent, to deal with the terrorist threat and protect the ‘points’ of sensitive territory. The operation was put in place 16 January 2015 and significantly strengthened during the same year, after the attacks of 13 November, notably through the implementation of an absolute emergency in the Brussels area from 21 to 26 November 2015 and after the attacks of 22 March 2016 in Brussels.11, 12
Military Assistance – The ‘New Normal’?
As a conclusion, one can say that the employment of armed forces at home and in peacetime can be an option for protection against threats to public safety when resources and assets of the civil regulatory authorities do not suffice. For such a purpose, the established and proven approaches described above already exist and may serve as an example for potential implementation in other nations.
On the other hand, based on the lessons learned in recent history, in particular the two world wars, the separation of police and military, as well as the separation of powers in Western democracies in general, has proven to be purposeful and sensible over many decades. With a view to past crisis situations, such as natural disasters or terrorist attacks, it can also be seen that the domestic deployment of armed forces is an increasingly recurring necessity.
It should be assured, however, that these operations will not become the new standard, so that the separation of police and the military mentioned above remains clearly defined.
With regard to drone defence, it must be clarified in a timely manner at which threat level, with which military resources and under which hierarchy, military force should or may be used.
The Applicability of Military Countermeasures against Drones in the Homeland and in Peacetime
As mentioned above, the use of military force is subject to fundamentally different legal provisions in peacetime and in case of war. However, despite national differences, it can be generally concluded that domestic military operations in peacetime are subject to considerable restrictions. For this reason, the military options for drone defence and their limitations in peacetime and at home will be discussed in the following paragraphs.
Employment of Weapons
The most obvious military resource in drone defence is the use of force of arms. These assets may be, for example, air defence systems to engage the drone itself or firearms employed against the drone’s operator.
The principles of the distinction between civilians and combatants and the proportionality of the resources used, as laid down in international humanitarian law (IHL), do not constitute the legal foundation in peacetime, but can by their very nature also be found in various national legislations on the use of sovereign force. For this reason, it must generally be assumed that within the NATO community of shared values, the protection of its population has priority over all other considerations. This is in direct contrast to IHL, which allows balancing the military advantage against the collateral damage anticipated. In peacetime and at home, such balancing is not admissible and the protection of the health and life of uninvolved persons must always be given priority.
This issue places the use of potentially lethal force of arms under considerable reservations, unless other legal foundations, such as the right to self-defence, explicitly allow this use of force. For this reason, the employment of weapons in or near urban areas can be regarded as largely unwarranted, as it is not possible to exclude with certainty that uninvolved persons will not be jeopardized. In individual cases, this issue may be assessed differently with regard to the protection of remote military installations or critical civilian infrastructure that is not located in immediate proximity to the population.
Defence action that has become a de-facto standard in both the military and police sectors in recent years is the jamming or spoofing of radio communications between drone and operator as well as drone and satellite. This ‘jamming’ has already proven itself in military operations against the threat of ‘improvised explosive devices’ (IEDs) by preventing the attacker from detonating IEDs by interrupting radio contact. Within drone defence, depending on the model, the interruption of radio contact usually results in the drone remaining in its current position, returning to its starting point, or even in the crash of the drone itself.
Wireless networks. Commercial drones use various frequency bands for their data links, including the range between 2.4 and 5.8 gigahertz (GHz). The two frequency bands are used, among other things, for wireless network connections, which are also used by many civil authorities, industrial plants, or hospitals. For this reason, jamming measures in the vicinity of such facilities have the potential to cause considerable problems and possibly economic costs, unless very directional or localized omnidirectional radiation is being employed.
Mobile radio networks. Recent drone models are capable of using mobile radio networks to establish data connections. Electronic countermeasures in this area will presumably cause at least local communication failures in the mobile radio network affected. Since many private homes and smaller companies no longer have landline connections, emergency calls may no longer be made in the event of a mobile radio connection failure, which could indirectly jeopardize human lives.
Navigational systems. Usually, many drones use the ‘Global Positioning System’ (GPS) to determine their altitude and position. Due to the relatively weak GPS signal strength, the system can easily be jammed or spoofed. However, GPS does not only transmit position details but also extremely accurate time information. A variety of military and civilian applications take advantage of this. For this reason, jamming the GPS signal presumably has the most far-reaching consequences of all electronic countermeasures. Depending on the range of the GPS jammer, interference with air traffic may also be expected. Hence, cooperation with the national aviation authorities is essential in this area, since the authorities must alert manned aviation to GPS failures in cases of the compelling need to jam GPS frequencies. This procedure has already been successfully tested by the police in operational situations.
Typically, domestic frequency jamming in peacetime is subject to strict conditions and licensing requirements imposed by national telecommunications or regulatory authorities to avoid the aforementioned implications with other users of the networks. For this reason, large-scale and continuous jamming measures in the vicinity of other network users must always be assessed with regard to the proportionality of the measure and possible failures must be communicated to the bodies concerned. If used in a target-oriented manner, limited in time and space, and above all coordinated with the civil authorities, these electronic countermeasures are an adequate means, for drone defence. It should be noted, however, that the effects of jamming are often only indirect and it is, therefore, often difficult to assess the benefit of their use.
Electronic jamming – as described above – always requires an intervention in the civilian network structure, and negative impacts on other network users must always be anticipated. Countermeasures in cyberspace, on the other hand, can be employed in a much more target-oriented manner and possibly allow taking over and controlling the drone in question. One civilian manufacturer of drones already offers a system exclusively to regulatory authorities that is capable of tracking its own drones.13 In most cases, such systems also allow locating the remote control so that measures against the operator can be taken as well. Military developments in this sector are based on either the voluntary disclosure of data protocols or reverse engineering of such protocols without consent provided by the drone manufacturers. Some of the latest systems are capable of filtering radio signals of known drones in a radius of more than 10 km, identify the model, read out stored details (such as the serial number), and – depending on the model – take over these drones fully automatically to, for instance, keep them outside of a perimeter, fly to a particular position or turn off the rotors and, thus, cause them to crash.
Cyber-attacks against and the takeover of drones always involves infringing on the property rights of the operator. Moreover, reading out the data memory may violate national data protection regulations. Reverse engineering of decrypted radio communication protocols will most likely violate patent rights. However, the higher precedent right to protect the health and life of the population should presumably justify such interventions. This weighing of the proportionality must, however, always be carried out with regard to the individual situation of the operations, and may require a court order or authorization.
If legally assessed and admissible, the above measures in cyberspace offer the advantage of causing the least possible impairment to uninvolved persons and the public space in general.
Potential Police Actions and Powers for Drone Defence
The basic pillars of police responsibilities include the protection against threats to public safety, monitoring compliance with applicable laws, and law enforcement. These responsibilities are also part of drone defence.
Protection against threats to public safety. An essential element of police work is the protection of life and limb of the population. With regard to the threat posed by drones, this responsibility has most often priority in the protection of events. These may be public events, such as concerts, sports events, or demonstrations, but also closed events, such as summit meetings, expert meetings or conferences. Also, critical infrastructure and facilities that are currently in the public focus always represent potential targets for an attack and must be protected from the threat of drones as well. Since the scope of responsibilities of the protection against threats to public safety can be compared very well with military installation defence (force protection), synergies between police and military concepts of operation and technical equipment should be identified to learn from one another and provide mutual support, where required.
Monitoring compliance with applicable law. In drone defence, this responsibility includes monitoring compliance with the relevant regulations, such as the European drone regulation, or compliance with the conditions for drone flights under national aviation law. However, in contrast to the long-established monitoring of civil air traffic, comprehensive monitoring of drone flights can only be performed in smaller areas at the moment since there is neither pertinent legislation nor general technical implementation by the drone manufacturers. At present, only one larger manufacturer offers appropriate antenna systems capable of identifying their own drones within a radius of up to 50 km.14
Law enforcement. Following the measures taken to protect public safety against threats and in the event of violations of, among others, the laws mentioned above as an example, the police are responsible for criminal prosecution. As a precondition for all further criminal prosecution activities, it is first of all essential to identify the owner or user of the drone. For this purpose, registration of the owner would be helpful, similar to the licensing of a vehicle by its owner. However, at present, it is usually necessary to locate the position of the drone’s remote control, since the drone itself rarely bears identification marks of its owner or does not even come into the possession of the police.
Potential Drone Defence Systems in Police Operations
Not every available drone defence system is suitable or admissible for police operations. Some systems that may be used or that are already in service use are briefly described in the following paragraphs.
Radio bearing. The direction of a radio signal can be determined by means of radio bearing. Using several direction-finding facilities results in cross bearings, which can be used to determine the position of the radio transmitter. Since the drone and its remote control both act as transmitter and receiver, this technology can be used to locate the signals transmitted. From the perspective of the police, special focus is on the drone’s launch preparation activities. The signals resulting from the remote control’s coupling with the drone when the devices are switched on can inform the emergency services of the possible location of the drone operator, even before the drone takes off.
Radiofrequency detection. In addition to the aforementioned radio bearing, the monitoring of radio frequencies received can also be used to filter out and decode typical communication signals transmitted by drones. This allows the readout of position details and other data of the drone and its remote control. The system by DJI mentioned above is partly based on this principle but uses an additional ID signal transmitted by DJI drones. Future developments might also decrypt signals transmitted by uncooperative drones and read out this information. This might be endorsed by appropriate legislation on the disclosure of encryption and communication protocols for governmental purposes.
Primary radar. In contrast to the secondary radar (see below), the primary radar actively transmits signals and is capable of locating objects in the airspace based on the reflections received. Modern radar systems with several radar panels arranged in a circle can thus achieve coverage of 360 degrees all around and 180 degrees upwards with a range of up to 5 km. These so-called 3D radar systems have the advantage that not only the direction but also the altitude of approaching flying objects is determined. By software analysis of the radar energy reflected and the object’s flight path, these radar systems are capable of distinguishing quite reliably between drones and other naturally occurring objects, such as birds or leaves.
Secondary radar. As a rule, manned aircraft are equipped with a transponder that, if available, must be used. In some areas of the airspace, such as airports and their surroundings, aircraft may only fly using an active transponder.15 At present, there is no obligation for drones to use a transponder, and there is a general ban on flying in areas where a transponder is required. If future regulations stipulate the installation and use of a transponder or make it a precondition for the licensing of drones, secondary radars might be capable of providing a pertinent air picture to aviation and regulatory authorities. In conjunction with primary radars, uncooperative air traffic participants might be filtered out to enable further target-oriented countermeasures.
Laser-based video reconnaissance. The normal ambient lighting may not be sufficient for visual verification of objects in the airspace, in particular, for the identification of smaller drones, depending on the local conditions, e.g. in case of heavy clouds, rain, twilight, or at night. In such cases, laser-illuminating the flying object to be verified can still enable identification using a high-resolution electro-optical camera at a distance of more than 2,000 m. A precondition for this so-called laser-gated viewing is, however, target location and tracking by more traditional means of, for example, radar.
Laser defence. High-energy lasers can be used to blind the sensitive electro-optical sensor of a drone camera and if necessary, destroy it. For this purpose, the laser is scattered to generate a correspondingly wide laser field in the direction of the drone or sensor. On the other hand, a laser can also be focused on the drone in order to heat its electronics in fractions of a second to such an extent that the electronics eventually fail and the drone is destroyed. However, it should be noted that the use of a high-energy laser always involves a risk to the affected areas of the airspace, and its scattered light can be dangerous to the human eye. For this reason, the use of lasers always requires local conditions to be taken into account and cannot be realized by the police under the current circumstances.
Hunter drones. Destroying drones always entails the risk of jeopardizing uninvolved parties, e.g. through falling components or the release of hazardous substances. Hunter drones solve this problem by tracking, capturing, and transporting the drone to be repelled, usually by using a net, which can be ejected by the hunter drone. The captured drone is then transported to a predetermined position, which is typically defined in such a way as to eliminate the hazard to personnel and material. Here, further measures can then be taken, e.g. defusing of explosives, evaluation of the data memory, or determination of identification features.16
Due to the legal restrictions to military and police operational resources within drone defence, but also with regard to technical and operational differences, the problematic issues briefly discussed in the following paragraphs can be derived.
Protection of Domestic Military Facilities
The guarding and securing of military facilities against unauthorized entry and espionage is usually the responsibility of the military. However, traditional measures of installation defence usually aim at only securing the immediate area of the military site. In legal terms, too, the use of military force is usually limited to this area. Outside military installations, only the police are responsible for the protection against threats to public safety. However, this strict separation is not helpful in the defence against drones, as drones can easily operate both inside and outside military installations. So when it comes to the defence against drones, the question arises as to the extent to which police forces are allowed to act inside military installations, or military forces may act and possibly engage drones outside the installation. In addition, there is also the question of coordinating the measures in order not only to avoid jeopardizing uninvolved parties but, above all, to avoid jeopardizing their own personnel.
Resources Required for the Protection of Critical Infrastructure and Major Events
Even when combining all currently procured police and military defence systems, the present capacities would not nearly be sufficient for comprehensive protection against the threats posed by drones. Drone defence measures are therefore only performed selectively and based on careful threat analysis. In the event of a general increase of the threat situation and the resulting increased need for protection of civilian and military facilities, the capacity limits of all available state resources for drone defence will be exhausted quickly. For this reason, it is imperative to effectively coordinate and deploy the defence systems, which are available to only a limited extent. This raises the question of the command relationships and directive powers among the authorities involved. There is also the question as to what extent defence systems and measures can be placed under the responsibility of state or commercial operators of critical infrastructure, and how these can be integrated into a holistic approach to drone defence.
Interoperability of the Police and Military
In order to enable joint operations, if necessary, technical interoperability of the systems used on the one hand and mutually agreed-upon procedures on the other hand are essential.
Technical interoperability. Police and military reconnaissance and defence systems are generally optimized for use under their own command and within their own network infrastructures. For security reasons, the police and military usually operate these system structures as separate and self-contained systems. For example, frequency ranges are reserved for the individual police or military use and, if necessary, secured by their own discreet encryption protocols. Some radio sets are not even designed to transmit or receive in the frequency range of the other authority. Since drone defence is still at a relatively early stage of development in both the police and the military, these interoperability issues should be taken into account in the planning phase of procurement projects. It will also be helpful to use widespread file formats for audio, image, and video files to ensure the possibility of mutual data exchange.
Mutually agreed procedures. In accordance with the military principle of ‘train as you fight, fight as you train’, joint measures for drone defence can only be successful if police and military operational procedures are coordinated and successfully tested together in exercises. This includes even the simplest but most essential training contents, such as the common understanding of appropriate operational terminology.
Mutual Legal Foundations
As briefly outlined at the beginning of this chapter, the police and military operate under different legal prevailing conditions. As a rule, this also applies if the military is deployed at home on special occasions. Whereas different legal provisions do not stand in the way of joint operations, they can complicate planning and implementation. If this conflict cannot be resolved by special legislation, a jointly agreed upon regulation of competences, subordination and responsibility is imperative in order to create security of action and clarity of the available options for all parties involved.
Summary and Recommendations
Due to the widespread proliferation of drones, they must be expected to fly into military installations and critical civilian areas at anytime and anywhere – whether it be intentionally or accidentally. The number of areas in potential need of protection exceeds the resources available to the police by a considerable amount. The military can provide temporary and local support in the event of an increased hazard situation. However, the rules of engagement of soldiers and their military defence systems must be modified to reflect the legal prevailing conditions for operations in peacetime and in their home country. To improve joint drone defence between the police and the military, or in some cases to achieve it in the first place, it is necessary to procure equipment that is interoperable on a technical basis, and practice coordinated operational principles.