Breaking the Shield: Countering Drone Defenses

By Zachary Kallenborn and Marcel PlichtaJoint Force Quarterly 113
Breaking the Shield: Countering Drone Defenses > National Defense University Press > News Article View (ndu.edu)

Marine Corps Sergeant Jacqueline Peguero-Montes, combat videographer with 24th Marine Expeditionary Unit, operates SkyDio unmanned aircraft system during fire support team exercise on Camp Lejeune, North Carolina, November 29, 2023 (U.S. Marine Corps/Ryan Ramsammy)

Zachary Kallenborn is a Policy Fellow in the Schar School of Policy and Government at George Mason University. He is also a Research Affiliate in the Unconventional Weapons and Technology Division, START (Study of Terrorism and Responses to Terrorism), at the University of Maryland. Marcel Plichta is a Ph.D. Candidate in the School of International Relations at the University of St. Andrews.

Unmanned systems will help save Taiwan.¹ At least, that is what some recent war games suggest. A 2020 RAND study conducted and analyzed a series of U.S.-China war games and simulations and found that a preponderance of interconnected and attritable unmanned aerial vehicles (UAVs) would prove a decisive part of a near-peer conflict against China.² Similarly, a Center for a New American Security war game held in August 2022 recommended that the United States should invest in unmanned underwater vehicles (UUVs) and that Taiwan should invest in UAVs to give it an edge.³ Beyond hypotheticals, conflicts in Ukraine, Nagorno-Karabakh, and Yemen show that drones are quickly becoming a central area for development and innovation in warfare at all levels of technological sophistication.

Drone defenses are moving fast, too. The Department of Defense (DOD) planned to spend over $700 million on counter UAVs (c-UAVs) in fiscal year 2023 alone, almost all going to research and development.⁴ The global c-UAV market is forecast to grow to about $5 billion in 2029.⁵C-UAV and drone defense may minimize the effects of drones in high-intensity conflict; however, if counters to drone defenses are developed that mitigate their ability to threaten, drones could retain their utility. The evolving interaction among drones, drone defenses, and counters to drone defenses will be critical in determining the net effect of drones on global security.

The article begins with an overview of drone defenses, with an emphasis on how they operate and the trade-offs involved. The article then looks at countermeasures to drone defenses, surveying 11 different approaches to breaking the drone shield. The emphasis is on an overview to understand the scope of the possibilities and the potential trade-offs associated with each approach. Countering drone defenses depends entirely on which ones are employed and prove most effective, so the value of specific counter-countermeasures will change over time. We next present policy recommendations that emphasize understanding adversary drone defenses; developing, assessing, and fielding counter-countermeasure approaches tailored to adversary defenses; and carefully understanding trade-offs in counter-countermeasure development and deployment.

First, a brief note on scope and language. This article includes an analysis of drones operating across every domain of warfare. The article uses the termdroneto refer to the generic category of unmanned system. When analysis focuses on a specific domain, the appropriate variation of unmanned aerial vehicle is used. Adrone swarmrefers to multiple drones with integrated communications rather than a simple preponderance of systems. Finally, the phrasescounter drone defensesandcounter-countermeasuresare used interchangeably for lexical variety.

Drone Defenses

A basic drone defense consists of detection/ identification and interdiction systems. Detectors and identifiers allow defenders to identify incoming drone threats and relevant attributes, such as the number of systems, speed, size, and whether the drone is friendly, while interdiction systems allow defenders to disable, damage, or defeat the drone. Ideally, a drone defense should include multiple sensor and interdiction options to accommodate trade-offs among them. In practice, high-value fixed assets may have robust defenses, while mobile or ad hoc assets may have limited to no specialized drone defenses.

Interdiction methods include traditional kinetic weapons, jamming drone connections to the operator or navigational satellites, manipulating drone autonomy, employing directed energy to degrade and destroy drone frames or electronics, and using intelligence to attack staging areas in offensive antiair operations. The viability of interdiction systems may vary within domains. Lasers are expensive (though may have a low cost-per-shot) and have long acquisition times: although small UAVs can easily be given protective coatings or adopt new tactics, upgrades to larger and more exquisite systems may be costlier and more difficult. Some existing interdiction technologies apply regardless of domain. This is especially true of jammers, as most drones rely on some kind of signal, though the frequency and type of signal may depend on domain, with UUVs using more acoustic than electromagnetic signals. Directed-energy and kinetic weapons designed for countering UAVs are also being tested against unmanned surface vessels (USVs) and unmanned ground vehicles (UGVs). New and economical kinetic systems such as the United Kingdom’s Martlet (or Lightweight Multirole Missile) can target unmanned platforms on land, at sea, and in the air.⁶

Despite the potential for c-UAV technologies to be used against unmanned platforms on land and at sea, we found minimal open-source research analyzing the challenge. Open sources provide limited references to DOD work in the area: the Navy sought to improve the Mk 38 Mod 3 machine gun system’s ability to counter USVs, and it also had a procurement program to improve USV situational awareness for the I-Stalker/North Atlantic Treaty Organization (NATO) Seasparrow missile system. Furthermore, DOD held a Counter Unmanned Ground Vehicle Working Group in 2018, though the outcomes are unknown.⁷

Improvised and purpose-built USVs and UGVs, however, are increasingly used. In the Red Sea, Iranian-backed Houthi forces conducted multiple attacks against the Saudi-led coalition with simple explosive-laden USVs.⁸ In Ukraine, UGVs are used on a small scale for support functions such as mine clearing and casualty evacuation, while Ukraine also used mass kamikaze USV attacks against Russia’s Black Sea Fleet.⁹ Likewise, states are developing drone swarms that operate in multiple domains at once, such as Russian UGVs whose targeting is guided by several small UAVs. As drone swarms are developed on massive scales and become weapons of mass destruction, the counter-drone challenge becomes even greater.¹⁰ Full-spectrum drone warfare across every domain may define the socalled Third Drone Age.¹¹

Detection and Identification

There are a few ways to detect incoming drones. Radar can detect most UAVs at long range, though they will have difficulties with low-flying UAVs, especially those doing nap-of-the-earth flying.¹² The start-up costs for radars and operators are steep, but most militaries already operate radars to detect aircraft and incoming projectiles. Radio-frequency scanners are cheaper, can detect and triangulate the location of a drone, and can detect drones before their launch (if the system is emitting signals in the spectrum the scanners are designed to detect), but there are limitations to range and ability to track multiple targets at once. Acoustic sensors are useful to detect UUVs but struggle to provide location and speed data for UAVs and have limited utility for detecting UGVs. Finally, visual detection requires a direct line of sight and provides limited information about the number, type, and distance of UAVs. For this article, detection also includes identification of the incoming drone to assess whether it is a friend or a foe.

Interdiction

Kinetic Weapons.The most obvious way to counter a drone is to use existing kinetic counter-vehicle weapons for the appropriate domain. The slow speed and lack of countermeasures on most UAVs leave them vulnerable to most antiaircraft systems, if they are in range. Start-up costs are also lower, as militaries field various antiaircraft guns, machine guns, missiles, snipers, and man-portable systems that could destroy a UAV with sufficient warning. For example, Ukraine has found some success using old World War II–style automatic antiaircraft cannons.

The drawback of kinetic c-UAV is that the most capable air defenses are often not economical to use against drones. Many UAV systems are cheaper than missiles launched by the Patriot or S-300, and if facing a sustained threat from drone swarms, strategic air defense platforms may face a shortage of missiles. RAND’s study on using drone swarms against China argues that Chinese air defense batteries would run out of missiles attempting to combat a drone swarm at sea.¹³ The United States and others are working on more economical solutions, such as the VAMPIRE c-UAV missile system, but the range is short (less than 8 kilometers). Similarly, conventional antitank or antiship missiles might work fine against a UGV or USV, but the approach is unlikely to be economical, except for large, more exquisite systems.¹⁴

Directed-Energy Weapons.The other major avenue of counter-drone development is a range of directed-energy weapons.¹⁵ These technically refer to anything that focuses electromagnetic energy on a target, but for drone defense, the focus is jammers, global navigation satellite system (GNSS) spoofing, high-energy lasers, and high-powered microwaves. Each is discussed in turn, although it is worth noting that larger electronic warfare systems have combined interdiction elements and therefore can employ more than one of these.¹⁶ When compared to kinetic weapons, some electronic warfare platforms are less likely to cause collateral damage if used near a populated area, and nearly all have a “reduced logistics trail,” as users would not need to store a large number of munitions to keep the system operating.¹⁷ Of course, the exact risk depends on the type of weapon and its proximity to vulnerable civilian systems.

Directed-energy weapons also tend to have much cheaper costs-per-shot than kinetic systems, as the cost is measured by the electricity needed to power it. However, given the speed at which drone technology and countermeasures are evolving, investing heavily in directed energy may be risky if inexpensive countermeasures are developed.

Radio frequency and GNSS jammersare the most common directed-energy method for interdicting drones.¹⁸ Jammers work either by severing the connection between the drone and its operators or increasing interference to make it difficult for the drone to locate the correct signal. Depending on the drone’s programming, jamming its connection to the satellites can force its return to base or reduce the drone’s accuracy.

Hand-portable jammers can protect a small area from a single UAV. In 2017 the Air Force acquired portable jammers for about $30,000 per unit.¹⁹ More capable jammers are often incorporated into electronic warfare and signals intelligence suites that also intercept and process enemy communications, which often climb into the low millions of dollars.²⁰ Vehicle-mounted electronic warfare suites can be placed on naval vessels; groundbased, like the Army’s Electronic Warfare Tactical Vehicle; and attached to aircraft via pods like on the EA-18 Growler. Although jammers may be useful for nonaerial drones, the drones may use different frequencies for signals or not use the electromagnetic spectrum at all.

GNSS spoofingis another option for drone defenses.²¹Instead of blocking the system’s connection to a satellite, a spoofing attack sends competing signals that disrupt or override satellite navigation services. GNSS spoofing may lead to attack misses, drone crashes, or even fratricide. Unmanned systems navigating with GNSS waypoints are particularly vulnerable to spoofing. Conversely, drones that do not use GNSS or have backup systems may not experience significant effects. If a drone is in spoofing range, it may be more advantageous to the defender to jam or destroy the system.

High-energy lasersfocus a beam of light onto a drone, which can blind its sensors, weaken its structural integrity, and eventually defeat the system. The time required for the laser to cause damage is dwell time and may require the laser to maintain focus for several seconds. Lasers cannot fire over the horizon, and there is currently a big size/range trade-off. The most advanced lasers are large, static, and intended for degrading enemy satellites and intercepting hypersonic missiles rather than intercepting a UAV at range. Additionally, researchers and manufacturers tend to overpromise the capabilities of lasers, making uncertain how quickly lasers will be a standard feature of modern militaries.²²

Whereas lasers designed for satellites and hypersonic missiles measure their power in megawatts, most c-UAV lasers measure it in kilowatts (kW), which increases mobility at the cost of range. Mobile and lower powered lasers for drone defense such as China’s LW-30 and proposed upgrades to the U.S. military’s M-SHORAD are in the range of 30kW to 50kW and are therefore limited in their range and power.²³They can, however, still damage or destroy sensors on a drone at a greater range than they can damage the actual airframe. Meanwhile, larger systems like the Army’s new Indirect Fire Protection Capability are the size of a large truck and use 300kW+ lasers to down small- to medium-sized UAVs as well as traditional indirect munitions.²⁴

High-powered microwavesoperate similarly to lasers by directing microwaves at a target. What sets microwaves apart is that they are especially damaging to electronic components and have a wider cone of effect than a laser, which reduces its effective range but allows the platform to engage several UAVs if they are grouped. Microwaves may also operate at different frequencies. High-powered microwaves currently in development for military use are about the size of a small trailer, but some firms are designing high-powered microwaves small enough to be mounted on large rotary-wing drones.²⁵

Autonomy Manipulation.As drone functions become more autonomous, adversary manipulation becomes more plausible. For example, hackers used small stickers to trick a Tesla auto-pilot into driving into an oncoming traffic lane.²⁶Although autonomous military drones operate in different environments and the Tesla manipulation required a specific, limited angle of view, the same approach could work. If a drone uses machine vision to detect and engage targets without human supervision, an adversary could paint, for instance, a picture of a tank on the side of a school bus. When the autonomous drone destroys the school bus, the adversary may win an information warfare victory in decrying violence against civilians and fielding of error-prone technology. As drones scale into massive drone swarms, they must become more autonomous, which means more opportunities for such manipulation. Using a swarm’s intelligence against it may be far more effective than shooting down thousands of drones or blasting them with electromagnetic energy.²⁷Of course, any autonomy manipulation requires a strong and precise technical understanding of how the drone’s autonomous features operate.


Marine with 2nd Battalion, 1st Marines, assigned to Special Purpose Marine Air-Ground Task Force–Crisis Response–Central Command, participates in counter–unmanned aircraft system training in U.S. Central Command area of operations, May 21, 2021 (U.S. Marine Corps/Melissa Marnell)

Offensive Antiair Operations.With strong intelligence, some militaries may not need to develop a bespoke solution for drones. Militaries facing a drone attack could attack the airfields or storage facilities before an attack is launched, anticipate the target, and move point defense to the area or locate the origin of a drone attack to forestall future attacks. Some NATO officials think targeting operators and the industrial base should be the focus rather than relying on any specific technology.²⁸Saudi Arabia frequently claims to target Houthi USVs while in port before they can be used in attacks.²⁹Likewise, Ukrainian and Russian forces increasingly target adversary drone operators because trained operators are much harder to replace than cheap drones.³⁰Intelligence agencies, however, seldom have the assets to identify the location and intent of every drone threat, and even when they do, it is hard to guarantee that every hostile drone has been located with enough time to strike the site or prepare defenses.

Breaking the Drone Shield

Just as militaries seek ways to destroy enemy drones, they will also seek ways to prevent adversaries from destroying their drones. As nonstate actors increasingly field drones, they will seek these ways also. The following section examines existing and emerging technologies and tactics to undermine an adversary’s counter-drone capabilities. Counter- countermeasures may enable the drone to avoid an attack, mitigate harm if a defender is successful, or launch counter-attacks to damage or destroy adversary defenses. The value of any countermeasure is necessarily dependent on the types of drone defenses that are fielded and how effective they prove in combat. Currently, most drone defenses are radiofrequency or GNSS jammers, so approaches that counteract jamming are likely to be quite effective. Virtually all counter-countermeasures apply to jamming, so another drone defense may replace them as the dominant mode. Counter-countermeasures may also emerge from normal developments in drone technology; drone autonomy reduces the dependence on external commands using the electromagnetic spectrum. At least 11 types of counter- countermeasures exist (see table).


Amphibious assault ship USS America test-fires rolling airframe missile launcher to intercept remote-controlled drone during exercise to test ship’s defense capability, April 6, 2017 (U.S. Navy/Demetrius Kennon)

Native Counter-Weapons.Native counter-weapons are integrated into the drone platform and designed to counter drone defenses. Drones could be equipped with anti-radiation missiles designed to target drone defenses. Although normal anti-radiation missiles might be fine for typical air defenses, modifications may be required to home in on the frequencies those weapons use. Drones may also incorporate bespoke counter-munitions, such as the Helios counter-laser system for drones, which senses incoming lasers, infers the location’s source, then uses the drone’s lasers to confuse the defense.³¹Alternatively, drones might just use directed-energy sensors to triangulate the source and fire back with other munitions.

Attritable drones could be used as decoys to activate camouflaged countermeasures or force countermeasures to focus on the more proximate unmanned threat while the missile or aircraft strikes the target. A variation of this occurred in the Iraq War when Firebee drones built in the 1960s flew over Baghdad to pull antiaircraft fire away from strike aircraft.³²

Supporting Weapons and Units.Supporting weapons and units are systems or units external to the drone platform that carry out strikes against drone defenses. This first requires an intelligence apparatus capable of locating drone defenses. The difficulty depends on the form the drone defenses take and the type of signatures they emit. Finding and fixing a soldier carrying a hand-held jammer is likely to be extraordinarily difficult. However, finding and fixing a relatively large microwave weapon such as THOR that requires 3 hours to set up and has a relatively short range may be much easier.³³Even easier would be a nonstealthy airborne laser system like a future variation of the Boeing YAL-1 that is mounted inside a 747-400F, which is likely quite detectable to ordinary air defense radar.³⁴

Of course, once the drone defense is found and fixed, it must be disabled, damaged, or destroyed. Commanders have any number of options from artillery and missiles to infantry or special operations forces. The challenge and opportunity costs are real, though they will be highly context-dependent. Using highly trained special operations forces to eliminate a single soldier with a handheld jammer is almost certainly a waste of operator skills. But eliminating an expensive high-powered microwave or laser before a massed drone attack on a high-value target may be worth it. It also depends on the type and quantity of drones available to the commander—accepting high attrition may be just fine.

Material Hardening.Material hardening involves the addition of materials or changes to existing drone materials that protect the drone against external harm. Materials may absorb or reflect incoming energy, protecting sensitive drone electronics. The Air Force is researching spray-on coatings that could absorb high-energy lasers.³⁵Research is ongoing to develop various meta-materials that are more effective at reflecting or absorbing the energy. One challenge is that the effectiveness of new materials may be dependent on the frequencies the directed-energy weapons use. That is, the material may only be effective in protecting against a narrow band of frequencies.³⁶This means understanding defender capabilities will be critical as well as rapidly changing materials or favoring wideband materials.³⁷Of course, it will also be important to understand any potential effects the materials have on drone components and resilience. For example, how might hardened materials affect communication systems?


Stealth.Stealth involves changes to the drone platform that decrease the likelihood of an adversary detecting the drone. In general, drones have small radar signatures but that depends a lot on drone size, which varies considerably by domain. A small aerial quadcopter will naturally have a much smaller signature than an MQ-9 Predator–size drone. Of course, stealth is likely to come with a trade-off in cost because the drone must be shaped to accommodate it. Although improved computing is reducing the costs of stealth, drones are quite cost-sensitive because much of their military value depends on affordability.³⁸Some forms of stealth may not be too difficult, though, such as reducing the often quite distinctive buzzing sound small drones emit, especially when operating in swarms.

Communication Upgrades.Communication upgrades are changes to the operations of the communication system onboard the drone platform or the ground control station. At the simplest end, this involves basic electronic protection. Devoting more power to drone communications or frequency- hopping may allow drone operators to mitigate jamming signals. But drones may also use different types of communication systems. Fifth-generation wireless technology is harder to jam while providing greater data transfer and a greater likelihood of detecting adversary electronic warfare equipment.³⁹

As multiple drones integrate into drone swarms, communications become critical. The essence of a drone swarm is communication, which enables complex behaviors.⁴⁰However, that communication is also a potential vulnerability if adversaries attempt to jam or manipulate it.⁴¹The drone swarm architecture may be modified to accommodate that. A drone swarm may incorporate dedicated communication drones to provide backup signals, emphasize decentralized communications to minimize single points of failure, or incorporate external systems to provide alternative communication relays.⁴²Drone swarms also may use indirect approaches to communication, such as stigmergy, in which digital pheromones are used to mark targets or areas of interest.

Navigation Upgrades. Navigation upgrades are changes to the navigational system onboard the drone platform or supporting navigational infrastructure. Most current drones rely on GNSS, either directly or indirectly (for example, some UUVs use GNSS surface buoys since the GNSS signals do not penetrate the water well). Drones might also use multiple, redundant methods for position, navigation, and timing, such as using GPS, GLONASS (Globalnaya Navigatsionnaya Sputnikovaya Sistema, global navigation satellite system), and INS (inertial navigation system) at once. Navigation redundancy would mitigate the jamming of a single navigation source and recognize spoofing attacks if position data differs drastically. A drone could use integrity monitoring to detect GNSS spoofing attempts. The Iranian Shahed 131s reportedly have multiple GNSS antennae, raising the possibility that existing drones are already capable of simple integrity monitoring.⁴³

Alternatively, new approaches to drone navigation may not require GNSS signals. For example, drones might use onboard visual sensors and preloaded satellite imagery data to determine their locations.⁴⁴Advancements in visual odometry and other nonjammable navigation methods will limit the utility of jamming or spoofing satellite navigation.⁴⁵

Drone Technology Enhancements.
Drone technology enhancements are general technical changes to the drone platform and its operations that are not necessarily intended to counter drone defenses. Increasing the ability of drones to operate autonomously would reduce the requirements to receive external commands using the electromagnetic spectrum. If the drone could operate entirely without external commands, radio frequency jamming would have no use. This is particularly the case for one-way attack drones not intended for multiple attacks. However, there are likely to be practical upper bounds on autonomy. Artificial intelligence is not yet capable of complex mission planning, so humans are likely to provide high-level mission command and support even if drones can execute autonomously. The window for useful jamming would be limited to when drone operators provide mission updates. Likewise, DOD or foreign military policy may require humans to make decisions on target engagement, either in that specific context or in general.<sup>46

Similarly, improving and developing autonomous systems and artificial intelligence used for machine vision and other functions will improve drone resilience. Current machine vision systems are quite brittle, capable of being fooled by a single pixel. Although military machine visions are unlikely to be so brittle, they still face the challenges of error and manipulation. Improved testing and evaluation, and more reliable machine vision systems in general, would make adversary manipulation much harder. Likewise, improvements that allow machine vision systems to be updated easily would allow militaries to quickly recover from a discovered vulnerability. Understanding mechanisms for fooling vision systems might also uncover other counter-countermeasures: the single pixel attack example is highly dependent on the camera angle, so simply maneuvering the drone off the glide path would mitigate the risk.

Cybersecurity.Cybersecurity involves improvements to the drone platform and supporting systems. This requires a broad range of activities, such as identifying potential vulnerabilities that may be exploited, understanding how malware might affect drone systems and operations, measuring the ability of an adversary to persist in using the drone, and seeking opportunities to protect the drone.47Cybersecurity must be considered across all elements of the drone system including the platform, the control system, and any supporting systems such as external sensors or communication relays that may be vulnerable to cyberattack. General drone cybersecurity is unlikely to look drastically different than normal cybersecurity, except for the need to protect all the systems involved with drone operation and assess vulnerabilities in systems like flight controllers. Cybersecurity vulnerabilities might also be mitigated through increased human control because the drones are less reliant on computer code.48Of course, this implies a greater degree of human control, which also makes the drone more susceptible to jamming attacks.

Massing.Current drone defenses are not well equipped to handle multiple drones at once. Interdiction systems would need to shoot fast enough and have enough ammunition to take down each drone.49Detection products may also not be able to account for multiple drones at once.50A 2012 Naval Postgraduate School study found that in a modeled eight-drone attack on a U.S. naval destroyer, half would typically hit the ship.51Even if most drones get shot down, some leakers will make it through. Saturation attacks also create dilemmas for positioning drone defenses, particularly if the adversary relies on directional systems or lacks full radar coverage.

Massing assumes a willingness to accept losses, so the value of the drone counter-countermeasure will depend on the values of the drone, the attacked target, and the overall conflict context. A major strategic objective may be worth sacrificing a lot of cheap, easily replaceable drones, but a narrow objective may not be worth risking lots of higher end platforms, especially in a protracted conflict where sustainment will be a challenge. In practice, massing is likely to be most effective against slower kinetic weapons with limited areas of effect, while least effective against directed-energy weapons that affect a broad area like microwave weapons.

Maneuver.Maneuver involves the positioning and movement of drones to create an advantage. The easiest way to protect drones from countermeasures is to identify and avoid a hostile system. However, avoidance works best when radar coverage and air defenses are widely distributed, creating gaps for drones to penetrate, and when there are enough targets that the adversary cannot provide point defense at every potential site. Some gaps are inevitable because drone defenses will likely run out before lists of defended assets do. If drone defenses are thetargetof the attack, they cannot be evaded without calling off the mission, unless they are inactive or in storage. Locating adversary countermeasures also requires significant intelligence, especially if these are mobile.

Even if the defender is aware of an impending drone attack and has some countermeasures, attacking a site from multiple directions with attritable systems increases the chance of causing harm. If a drone defense can only engage one drone at a time and requires a small amount of time to destroy the system outright, then deploying many systems attacking at multiple angles would be able to strike or overwhelm the defense before it could defeat the drones. A successful maneuver, however, requires substantial mission planning and the acknowledgment that some or all the drones will be destroyed. This depends on the commander’s willingness to tolerate risk and the cost and value of the drones. Losing many cheap, one-way attack drones may be no great loss, but large, expensive platforms may be better served to provide situational awareness out of range of enemy drone defenses or waiting until defenses are degraded to attempt a strike.


German soldier uses shoulder-mounted drone jamming device to jam fixed-wing unmanned aerial vehicle during Counter-Unmanned Aerial System Technical Interoperability exercise in Vredepeel, Netherlands, November 9, 2021 (NATO)

Drones might also maneuver to make directed-energy weapons harder to use. Particles in the air (water droplets, dust, aerosols) can have significant effects on all directed-energy weapons.52The particles may absorb some of the energy, cause scattering effects, or create lensing effects that bend the beam.53Even marginal changes to laser wavelength may drastically change the amount of power generated.54Drones may take advantage to operate at longer distances with more opportunities for atmospheric impediments or at higher altitudes with higher densities of particles.55Or drone operators might just take advantage of smoke screens designed to obscure other troop movements or smoke that occurs naturally as part of the fighting. Or drone operators may fly directly at a high-energy laser to create thermal blooming effects in which the air heats up and defocuses the laser.56Of course, atmospherics may create trade-offs in system reliability, since the atmospherics may also impede drone sensors or machine vision systems that now must handle obscured objects.57

Drone maneuver coupled with some technological enhancements might also manipulate adversary drone identification. A drone may comply with adversary airspace coordination measures and predetermined routing, and even emit signals of friendliness. Of course, this approach requires a sophisticated understanding of an adversary’s procedures to identify drones, and deceptions may be revealed with simple measures such as observing the type of incoming drone.

Decoys. In the same way drones can act as cheap and attritable systems to support missiles or manned aircraft, cheap and attritable platforms could accompany operational drones to complicate interdiction efforts. Decoys absorb hits from long-range kinetic systems, which may lack sufficient munitions to engage every target and make it difficult for short-range systems such as lasers to engage every drone in the limited time window before they reach the intended target. The line between the decoy and offensive drone may be blurry, though, as the Air Force’s Miniature Air-Launched Decoy is also capable of jamming and attacking. The critical part is that the decoy lights up adversary detection systems and absorbs hits while still being highly expendable.</sup>

Policy Recommendations

With numerous options for defeating drone defenses, what should the United States do? First, it must assess adversary drone defenses. Second, it should calibrate counter-countermeasure development and acquisition based on adversary countermeasures. Third, it should continually judge what trade-offs exist with counter-countermeasures and how they affect overall drone vulnerabilities and military value.

Understand the Adversary.Because counter-countermeasures are about breaking down enemy defenses, intelligence and analysis of adversary defenses, tactics, and operations are critical. What drone defenses are adversary states developing? What are their specific technical parameters, limitations, and overall readiness? Are there any common emphases? Efforts such as the Directed Energy Lethality Intelligence Initiative, a DOD and Intelligence Community collaboration, would help provided the intelligence requirements account for directed-energy weapons specific to drones.⁵⁸

Develop, Test, Acquire, and Deploy Counter-Countermeasures.Countercountermeasures should be developed, tested, acquired, and deployed based on an established understanding of adversary behavior. For instance, if microwaves became a popular and common type of drone defense, then counter-countermeasures research and development should take advantage of its limited range or its need for large volumes of electricity. Of course, because dominant drone defense approaches may change over time and may vary by domain and drone type, research and development should experiment with a broad range of counter-countermeasures. Plus, having a range of options to threaten drone defenses compels adversaries to develop complex and expensive layers of defenses to mitigate the threat. One specific area worth exploring is designing anti-radiation weapons for use against drone defenses. Existing anti-radiation sensors might work fine with some modification, but open-source documents are unclear and do not provide any indication of existing research.

Understand Trade-Offs.DOD needs to understand trade-offs between counter-countermeasures as they relate to drone vulnerabilities and military value. Any counter-countermeasure necessarily requires research and development costs and almost always will increase drone system cost and complexity. Increased costs are particularly important because the value of drones largely stems from their relatively low cost. If counter- countermeasures significantly reduce, or even remove, the relative drone cost advantage, that would greatly reduce their overall military value. Maneuvering and supporting fires, however, do not entail new platform costs, but those still require exercises and modeling to understand opportunity costs and commander and operator training. Likewise, employing some counter-countermeasures may make drones vulnerable to other types of drone defenses. This is particularly acute around autonomy and artificial intelligence, where more autonomy reduces radio frequency jamming vulnerabilities but increases cybersecurity and autonomy manipulation vulnerabilities. Plus, any form of onboard countermeasure may increase drone weight, reduce payloads, and reduce range. Thus, countermeasures should be considered holistically. As the United States and its allies field drones in larger numbers operating across more domains, adversaries will inevitably field countermeasures. If drones prove decisive on the battlefield, then the United States must consider how to maintain that decisive edge despite those countermeasures. The United States must break the drone shield.JFQ

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