Conflict is characterized by the quest for competitive advantage.[1] Throughout history, combatants have sought weapons that delivered surprising, disruptive, and ultimately overwhelming effects upon their adversaries. Effects are measured not only in body counts, but also—and perhaps more importantly—by their impact on the enemy’s sustained will and ability to fight. Unmanned systems, more popularly known as drones, have become the most ubiquitous and enthusiastically applied emergent technologies to overmatch and overwhelm adversaries across the conflict spectrum. The author contends that drones have revolutionized conflict and introduced novel operational, ethical, and legal considerations. For this article, a drone is defined as any unmanned vehicle or device that can be remotely controlled, inertially guided, or capable of executing dynamic, autonomous, or pre-programmed tasks.[2]

Scholars debate whether drones constitute a true game-changer, a so-called “revolution in military affairs.” Some academics argue that unmanned systems are nothing more than a novel delivery option for previously existing surveillance, communications, and weapons systems.[3] The counterargument contends that delivery systems themselves can be exemplars of revolutionary change when coupled with innovative application. Genghis Khan’s marauding horse-mounted hordes, Britain’s empire-spawning naval armadas, and nuclear-capable intercontinental ballistic missiles are just a few illustrations. Whether revolutionary or evolutionary, drones provide an asymmetric and readily available capability that has fundamentally changed the calculus for competitive advantage. This is evident in even a cursory examination of recent conflicts, including the Israel-Hamas war, Russia’s war on Ukraine, and the Nagorno-Karabakh conflict between Armenia and Azerbaijan.

Until recently, combat-capable drones were primarily fielded by powerful state actors. Indeed, the United States arguably has been the greatest innovator and user of weaponized drones in combat, dating back to the Vietnam War.[4] Unfortunately, the United States and its allies’ dominance in drone technology is now hotly contested. Widespread and underregulated drone weaponization has stimulated a scramble to develop and impose norms for self-constraint. Much of this initiative to rein in the unfettered use of drones stems from the United States’ own introspection. From targeted killings of US citizens abroad to unintended civilian casualties on the battlefield, the United States’ own loose applications of armed drones have led both domestic and international authorities to belatedly realize that we should soberly consider both how weaponized drones are used and who should use them.

Perhaps the most studied and cited case of constitutionally and ethically questionable drone attacks are the unmanned aerial system (UAS) strikes that killed four Americans in Yemen and Pakistan between 2009-2011. Then-Attorney General Eric Holder openly admitted in Congressional testimony that three of the killings—among them a sixteen-year-old minor—were unintentional. All of the targets were suspected terrorists whose names were listed on a covert government-sanctioned kill list known as the “distribution matrix”; all were also unapologetically executed without due process.[5] Both domestic and international apprehension regarding the legal parameters of high-frequency drone strikes like these stimulated internal investigation, a measure of self-imposed strike discipline, and ultimately, an executive order that clearly outlined the parameters for use of force in counterterrorism activities outside of declared conflict zones.[6] This executive order was repealed in 2019, and the ethical and legal debate over targeted killings continues.

Israel currently faces similarly intense scrutiny for its widespread and, critics argue, indiscriminate use of combat drones against Hamas militants. Israel is among the first to use lethal autonomous drones to clear insurgent-constructed tunnels and engage in close-quarters urban combat.[7] Moreover, Israel has determined that traditional government-to-government arms procurement channels are too sluggish to meet its urgent requirements, and has purchased self-piloting and kamikaze drones directly from US vendors. While tactically expedient and previously adopted by Ukraine, this eyebrow-raising practice sets a disturbing precedent that disincentivizes self-constraint and complicates the regulation and monitoring of weaponized drone capabilities.[8]

These examples and others have galvanized ethicists to demand coherent policies for combat drone proliferation and use. Responsible state actors recognize the need to judiciously apply the existing international legal framework for lawful conflict, or jus in bello, to drones and other developing technologies. However, many nations stop short of advocating for binding regulations that are based on legal abstractions and that might pre-emptively limit the use of emerging high-tech weaponry whose full range of applications are not yet fully understood.[9] This resistance to externally imposed constraints is rationalized in tandem with the awareness that non-state actors will respect no such fetters and are becoming more capable by the day. On 28 January 2024, three US service members were killed in Jordan by a drone attack, the first recorded instance of US deaths by enemy drones. Perhaps more troubling, the deadly attack was carried out by a non-state actor, Kataib-Hezbollah.[10]

Unmanned systems are an especially attractive option for armed non-state actors who aim to level the playing field against better-armed, resourced, and protected state adversaries. Many non-state actors prefer drones that are low-cost, readily available and, in a pinch, easy to manufacture.[11] Moreover, many non-state actors enjoy access to higher-end unmanned systems via state proxies; Iran is a particularly generous benefactor. Drones have become strategically significant in persistent insurgent and hybrid attacks on Israel and US forces in the region. Iran provides ample supplies of unmanned systems to its Hezbollah, Hamas, and Houthi proxies, resulting in almost daily drone attacks on US assets, allies, and partners in the Middle East, on land and at sea, since the onset of the October 7 Israel-Hamas war.[12]

Vulnerability to Non-State Threats

A wide range of malign non-state actors leverage drone technology to achieve their aims. Organized criminal groups have used airborne and seaborne drones as non-attributional and expendable courier vehicles to traffic drugs and other illicit goods.[13] Drones provide increasingly disturbing options for terrorists, by creating opportunities to produce strategic effects with limited investments. In addition to attacks on opposing militaries, non-state actors have utilized drones against a variety of non-military targets. Malevolent factions have already experimented with attacks capable of high-level disruption and systemic shock. With emerging technological advances, these attack modalities could rapidly escalate from highly disruptive to catastrophic.[14]

Assassinations

Democratic nations apply an outwardly rational, politically popular, and carefully legalized logic for why certain killings outside of combat zones are “necessary” to combat terrorism. From an ethical standpoint, assassinations and targeted killings are a particularly slippery slope, despite their operational effectiveness. By creating rules and norms for targeted killings, we tacitly concede that assassination is an acceptable mode of conflict, at least for powerful state actors. US leaders across the political spectrum tout their counterterrorism successes by name: bin Laden, Soleimani, al-Masri. Some state actors even approach assassination with macabre showmanship. Russia certainly plays up the theatrics; as Putin’s political rivals expire due to “freak accidents” and mysterious afflictions, the Kremlin dutifully issues half-hearted denials with a knowing wink. More disturbingly, targeted killings are no longer the exclusive purview of powerful state agencies with sophisticated UAS technology and legally sanctioned targeting criteria. Rogue states, insurgents, terrorists, and criminals also recognize that drone-enabled assassinations have a certain mystique, shock effect, and even a ghoulish allure.

For non-state actors, targeted killings remain murder or terrorism according to the rules-based international order, but legality is hardly a deterrent. Nearly all non-state armed groups employ assassination as a tactic; more than twenty high-profile assassination attempts were recorded from 2000 to 2024, and over half of them were successful.[15] Terrorists and other non-state actors continue to experiment with using drones for targeted killings. For example, in August 2018, two GPS-guided drones armed with explosives were used in a failed attempt to assassinate Venezuelan President Nicolás Maduro. While Maduro accused the Colombian government of carrying out the attack, it was also attributed variously to a coordinated effort by political dissidents in Venezuela, Colombia, and the United States, and as a possible diversionary ruse by the Maduro regime itself.[16] Regardless of the source, this attack clearly demonstrated that drone-enabled assassination attempts are a difficult-to-attribute and readily available option for malicious actors of all sorts. In 2021, Iraq’s Prime Minister Mustafa Al-Khadhimi narrowly escaped a drone assassination attempt; in the same year, a Taliban drone successfully targeted and killed Uzbek warlord Abdul Rashid Dostum.[17]  

Drone-enabled assassination attempts are a difficult-to-attribute and readily available option for malicious actors of all sorts

Chemical, Biological, Radiological, Nuclear, and Explosives Attacks

Though most infamous for its 1995 Tokyo subway attacks, the Japanese Aum Shinrikyo cult also attempted to murder the head of a rival organization in 1994 with a remote-controlled helicopter armed to spray sarin gas.[18] Aum Shinrikyo’s rudimentary application of drones over thirty years ago underscores the unsettling potential for today’s sophisticated drones to deliver deadly chemical, biological, radiological, nuclear, and explosives (CBRNE) payloads that could impact much larger populations. Legal and humanitarian concerns over unintentional civilian casualties impose a degree of self-constraint for future drone attacks by state actors in civilian-dense environments. However, the potential for non-state actors unfettered by legal or ethical constraints to deliberately target civilians presents an acute vulnerability.

Indeed, there have been a few reported instances of drones armed with CBRNE agents over the last ten years. According to the Global Terrorism Index 2023, “in 2015, a drone with radioactive sand targeted the roof of the Japanese Prime Minister’s office. In 2019, France’s UCLAT [interagency counter-terrorism unit] alerted about a possible terrorist attack on a football stadium by a drone carrying lethal chemicals.”[19] Each of these instances involved single drones with a limited scope of impact. CBRNE-capable UAS swarms pose a much more disturbing and currently viable scenario. A sufficiently large CBRNE-toting swarm could very well be considered a weapon of mass destruction.[20]

Critical Infrastructure Attacks

Russia’s illegal and relentless attacks on Ukraine’s energy networks and dams are certainly the best-known contemporary cases of drone attacks on critical infrastructure, but they are hardly unique. Drones have become an ever-present threat near critical US infrastructure, including nuclear facilities, electrical grids, and even the White House, prompting new legislation and counter-UAS authorities and tools for the Department of Homeland Security and other domestic security agencies. July 2020 marked the first publicized drone attack attempt on a US facility, when a DJI Mavic 2 drone narrowly failed in an attack that appeared to be aimed at short-circuiting a Pennsylvania electrical substation. This is likely to be the first of many future attempts, as US critical infrastructure remains an attractive, vulnerable, and almost inevitable target.[21]

As drones evolve the capability to autonomously navigate, carry larger payloads, and operate across domains, they become ideal tools for malicious actors. Deep-diving unmanned underwater vehicles are becoming more sophisticated and more readily available, making undersea cables and offshore infrastructure increasingly attractive targets. Hamas is known to possess drone submarines that it uses to target Israel’s offshore gas platforms, and Houthi rebels are confirmed to have added unmanned underwater vehicles to their arsenal.[22] The effects of critical infrastructure attacks are potentially devastating and may include power blackouts, supply chain disruptions, and telecommunication system interruptions.

Beyond the apparent and immediate physical damage, the psychological impact of a drone attack cannot be overstated.

Beyond the apparent and immediate physical damage, the psychological impact of a drone attack cannot be overstated. Drone attacks on critical infrastructure induce a shocking sense of vulnerability, stoking fear and uncertainty that dissolves public trust in government security institutions and potentially leading to social turmoil and economic disruption as access to essential goods and services is disrupted or denied. Even isolated drone attacks can exact their economic and emotional tolls. One poignant example is the drone incident at the Gatwick, UK airport during the 2018 Christmas holiday season. Between December 19 and 21, sophisticated operators piloted a pair of drones in synchronized sorties apparently aimed at disrupting airport operations and endangering travelers. Although no one was injured, the drone sorties halted all air traffic at one point and forced the cancellation of more than 1,000 flights over 33 hours, impacting 150,000 holiday travelers and costing the airline industry more than 50 million British pounds. The perpetrators were never caught.[23] Gatwick is one of several incidents that has created what one pilot dubs a “drone panic” among airline industry professionals, government regulators, and common citizens. Successful drone attacks on civil aviation assets are extremely rare, but media hype and slow, inadequate government counter-drone policies feed public and industry unease regarding vulnerability to drone attacks.[24]

Attacks on Strategic Resources

Adversaries employ hybrid tactics to target strategic resources, obliquely or overtly. Despite prohibitions under international law, strategic denial of access to essential goods, including food, water, and energy, is becoming distressingly commonplace and generates global consequences.[25] Russia’s deliberate destruction of Ukraine’s agricultural production capacity and blockade of Ukrainian wheat exports created a global food crisis that has particularly affected South Asian and African nations far away from the battlefield. The United States destroyed ISIS-controlled oil fields in Syria and Iraq in 2015 and 2016, while both Russia and Ukraine have targeted each other’s energy resources since Russia’s invasion began.

Non-state actors certainly recognize the shock effect of strategic resource disruption and have successfully carried out drone-enabled attacks to produce it. In September 2019, for example, the Aramco Abqaiq oil facilities in Saudi Arabia were hit by a combined swarm attack consisting of 18 drones and seven cruise missiles. Houthi insurgents claimed responsibility for the attack, although given the level of sophistication and precision, most Western analysts at the time assumed some level of Iranian government involvement. Regardless of the source, the attack achieved devastating outcomes by temporarily shutting down five percent of the world’s oil supply, which led to as much as a 20 percent increase in global oil prices. This swarm attack was especially disturbing because it defeated a robust, state-of-the-art air defense system that had been installed by the United States and Saudi Arabia; the system included Patriot missile batteries, and was intended to protect the facility and surrounding oil fields.[26] Combined swarms of drones and missiles appear to be emerging as a favored mode of attack for Iran and so-called Iran-affiliated “resistance forces,” as further evidenced by the massive swarm attack aimed at Israel on 13 April 2024 and regular Houthi-initiated volleys targeting maritime traffic in the Red Sea.[27]

This swarm attack was especially disturbing because it defeated a robust, state-of-the-art air defense system that had been installed by the United States and Saudi Arabia.

Attacks on Commercial Vessels and Civilian Aircraft

Commercial ships are some of the most vulnerable and frequent drone attack targets. Even when protected by the US Navy, commercial vessels in the Red Sea and Arabian Gulf have fallen victim to successful combined swarm attacks by both state and non-state actors. Almost daily, Houthi missiles and drones harass both military and commercial ships in the Red Sea and Gulf of Aden. A swarm attack on 3 December 2023 showcased an unusual level of sophistication by a non-state actor, simultaneously targeting the guided-missile destroyer USS Carney and three commercial vessels. Although the Carney was undamaged and thwarted several drone attacks, two commercial vessels were hit by ballistic missiles at the same time.[28] These persistent attacks, carried out with impunity, essentially fix US naval assets in the region, and necessitate the employment of disproportionately expensive and increasingly scarce countermeasures. These attacks are also having an increasingly costly effect on global trade, as ships travel longer, more difficult routes to avoid the Red Sea.[29]

Similarly, civilian aircraft are among the highest-profile high-impact targets for malign actors, a tragic lesson forever etched on the collective memory on 11 September 2001. No one has forgotten the airline hijackings and subsequent suicide attacks on the World Trade Center and the Pentagon that sparked two subsequent decades-long wars. However, static commercial aircraft on the tarmac are also targets, amounting to aluminum-clad sitting ducks, even when co-mingled with military assets on dual-use, protected airfields. While state actors with sophisticated, long-range weapons systems have identified airfields as strategic targets since the dawn of air power, armed insurgents are now empowered to test these waters with simpler tools and at closer range. In February, Rwanda-backed M23 rebels launched a limited-range drone armed with explosive projectiles toward the Goma International Airport in the eastern Democratic Republic of the Congo (DRC). The attack hit its mark, causing substantial damage to both military and civilian aircraft. Goma’s airport is Eastern Congo’s commercial nucleus and serves a population of over two million citizens. It is also the primary military operations hub for the DRC Air Force and UN peacekeeping forces.[30] These types of attacks, ranging from targeted to spectacular, underscore the inherent vulnerability of static or unprotected air and maritime commercial transport.

Drones have become organized crime’s tool of choice for “dull, dirty, or dangerous” jobs.[31] Air and sea drones serve as drug mules across the globe, smuggling methamphetamines from Syria, heroin between Pakistan and India, and of course traversing the robust smuggling networks between the United States and Central America with all manner of illicit cargo. The most capable undersea drones can deliver shipments of several hundred pounds of contraband. Drones provide additional capabilities for the enterprising cartel, including reconnaissance of smuggling routes, promising farm sites, and rival producers’ operations. Perhaps the most attractive UAS feature is that they can be used with impunity: if intercepted, drones can’t be arrested, and drones tell no tales. Drones are also used on a more limited basis for arms trafficking. India’s border security forces regularly intercept drones laden with small arms, ammunition, and explosive cargo along the border with Pakistan.[32] Mexico has expressed outrage at the proliferation of small arms originating from the United States in recent years, a trade supported by a robust drone-enabled weapons-trafficking enterprise.[33]

Drones provide additional capabilities for the enterprising cartel, including reconnaissance of smuggling routes, promising farm sites, and rival producers’ operations.

Propaganda and Disinformation

Creative uses for drones appear to be limitless. Enterprising neo-Nazi Tracy Mapes provided one nefariously clever application. In 2017, drones were used in an airborne propaganda campaign, dropping white supremacy- and conspiracy-themed leaflets on NFL stadiums, and in 2019, drone-delivered leaflets bearing swastikas and hate messages were dropped during an outdoor Farm-to-Fork fundraising dinner at Sacramento State University and an Ariana Grande concert at Sacramento’s Golden 1 Center.[34] Although both incidents were largely written off and underreported, the potential for drone-delivered messages to incite widespread panic is very real. Imagine drones distributing a message that bombs were set to go off inside a packed sports arena to provoke a deadly stampede of terrified sports fans charging for the exits. These instances demonstrate how easy it is for drones to infiltrate mass gatherings, whether laden with notes or explosives.

Drones themselves are powerful propaganda and disinformation tools. Non-state access to armed drones tangibly refutes the state’s exclusive prerogative to conduct surveillance, control air space, and legitimize violence in the name of security. In its heyday, the Islamic State certainly understood the symbolic power of drones and their application as a tool of propaganda. Despite limited tactical utility, ISIS’s prolific use of drones constituted a non-state air force that contested US and coalition air superiority and kept air defensive systems on constant high alert. ISIS also employed drones to film its most shocking exploits to terrorize enemies, subdue civilian populations under its control, and reinforce its allure to prospective recruits.[35]

Countering the UAS Threat

While armed drones may be distressing and ubiquitous, they are far from invincible. Indeed, UAS and other unmanned systems are susceptible to traditional defenses. The most common combat-capable drones employed today are an order of magnitude slower than manned jet aircraft. With a top speed of about 115 miles per hour, Iran’s Shahed-136 drones, which are globally distributed to both state and non-state actors, are exceedingly slow when compared to, say, a MiG-29 jet fighter, which can approach 1,500 miles per hour. Spectacularly expensive and effective counter-rocket, artillery, and mortar (C-RAM) systems such as Israel’s Iron Dome, as well as directed energy weapons and precision counter-battery munitions, have been used to defend against drones. Although they tend to receive the most attention, they are not the only means to stop most drones. UAS’s slower speeds make them vulnerable to field-expedient air defense tools such as machine guns, as Ukraine has demonstrated capably against Russian drones.[36] Simple and inexpensive passive measures such as anti-drone nets can also be effective for protecting key facilities and critical infrastructure against smaller drones.[37]

Since drones rely on remote control and communications to operate, they are highly susceptible to jamming. Electronic warfare (EW) may be the most promising and cost-effective countermeasure against drone swarms, since it does not rely on expensive or scarce munitions, and even relatively low-tech jamming techniques have proven effective.[38] There are drawbacks to jamming, of course. Low-end electronic warfare systems and methods can be indiscriminate. Friendly communications, targeting systems, and precision-guided weaponry also rely on distinguishable radio signals; blanket jamming techniques may disable both. Many jamming devices also broadcast a tell-tale signal that may reveal their location, leaving EW units vulnerable to counterattack. Moreover, a disabled drone may still be a threat. Airborne systems, when disabled, must fall somewhere. UAS laden with explosive or CBRNE-capable munitions that are hovering over civilian-dense areas or strategically important facilities must be eliminated with care.[39]

Conclusion

The convergence of emergent drone technology and the rising power of the non-state actor is changing the character of conflict. Drones are a commercially available technology that is easily adapted for combat application, terrorism, or sophisticated criminal enterprise. They are the ideal tool for the malign non-state actor: difficult to attribute, easy to use, cheap, and highly accessible. Drone payloads and range are increasing rapidly. They can be deployed en masse, and they enable an array of tactics from assassinations to critical infrastructure attacks. Countermeasures can be expensive, and may be rapidly exhausted when responding to adversary swarms.

Drones are the ideal tool for the malign non-state actor: difficult to attribute, easy to use, cheap, and highly accessible.

We are already in the midst of the next drone evolution; advances in artificial intelligence have now made it possible to remove the “human-in-the-loop” safety mechanism that keeps the drones themselves from “going rogue.” Indeed, it is not too fanciful to imagine autonomous unmanned systems becoming among the most dangerous and unpredictable non-state actors of the future.

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Scott Moreland is the Functional Lead for the Emergency Management and Resilience team and a lecturer at the Defense Security Cooperation University.

This is a work of the US federal government and is not subject to copyright protection in the United States. Foreign copyrights may apply.