Imagine swarms of undersea, surface, and aerial drones hunting submarines hidden in the vastness of the ocean. Or imagine hundreds of airborne drones darting through New York City, seeking out targets and dosing them with nerve agent.

These imaginary scenarios are not yet reality, but they are quickly becoming so.

Drone swarm technology could have a significant impact on every area of military competition, from enhancing supply chains to delivering nuclear bombs. This article examines the implications for chemical, biological, radiological, and nuclear (CBRN) weapons. Some applications are already possible, while others are futuristic, but plausible. Our broader study in the Nonproliferation Review on the applications of drone swarms to CBRN weapons offers additional analysis.

Drone swarms offer significant improvements to both nuclear offense, the ability to successfully deliver a warhead to a target, and defense, the ability to prevent successful delivery and mitigate consequences. When it comes to chemical and biological weapons, drone swarms can improve both defense and offense, but appear to strongly favor offense by addressing key challenges to delivery. In the future, this could weaken the norms against these weapons and encourage proliferation. U.S. national security agencies should act to combat the threat and take advantage of the opportunities this new technology offers for CBRN weapons.

Military Advantages of Drone Swarms

Precisely defined, drone swarms are “multiple unmanned platforms and/or weapons deployed to accomplish a shared objective, with the platforms and/or weapons autonomously altering their behavior based on communication with one another.”

The fact that components of the swarm can communicate with one another makes the swarm different from just a group of individual drones. Communication allows the swarm to adjust behavior in response to real-time information. Drones equipped with cameras and other environmental sensors (“sensor drones”) can identify potential targets, environmental hazards, or defenses and relay that information to the rest of the swarm. The swarm may then maneuver to avoid a hazard or defense, or a weapon-equipped drone (an “attack drone”) may strike the target or defense. Real-time information collection makes drone swarms well-suited for searching over broad areas for mobile or other hard-to-find units.

But swarming also adds new vulnerabilities. Drone swarms are particularly vulnerable to electronic warfare attacks. Because drone swarms are dependent on drone-to-drone communication, disrupting that signal also disrupts the swarm. As swarms become more sophisticated, they will also be more vulnerable to cyberattack. Adversaries may attempt to hijack the swarm by, for example, feeding it false information, hacking, or generating manipulative environmental signals. Although numerous counter-drone systems are in development, current defenses do not appear sufficient and even promising systems will face scalability challenges, from deployment allocation to training, in the system’s use.

Analysts are divided on whether drone swarms offer significant cost benefits. T.X. Hammes has posited in War on the Rocks that the future of warfare is “small, smart, and cheap platforms.” He highlights swarms of drones as one example, arguing the costs are already low and likely to become lower. But Shmuel Shmuel disagrees, arguing in a skeptical essay that this new technology will be more expensive to operationalize than most think.

Ultimately, the cost and its relevance depend in part on what role the swarm will play and what alternatives are available. Even multimillion-dollar drone swarms can be cost-effective on balance if they meaningfully increase the survivability of more expensive or particularly crucial platforms, such as aircraft carriers or nuclear deterrent forces. Simple, low-cost drones may also fill capability gaps, such as the Marine Corps’ interest in small, tactical drones and drone swarms to provide infantry organic close-air-support and reconnaissance.

Nuclear Deterrence

Drone swarm technology has significant implications for both the offensive and defensive sides of the nuclear deterrence equation.

Swarms offer new means of defeating traditional nuclear delivery systems — a defensive advantage. They could serve as novel missile defenses, potentially even against hypersonic missiles. Imagine 100,000 cheap, simple drones forming a dome over a high-value target. Any incoming missile, no matter how fast or maneuverable, would likely hit a drone (whether lightweight drones are enough to damage a reentry vehicle or throw it off course is an open question). The same drones could also serve effectively as air mines, colliding with or exploding in the vicinity of incoming bombers. Even small drones can significantly damage airplane wings. This could be especially effective against low-flying bombers because there is less airspace to cover and defenders can use short-range drones. Finally, multi-domain swarms of undersea, surface, and/or aerial drones could search the ocean for adversary submarines. The drones might locate, follow, relay information about, or attack the submarines. They also could draw information from broader sensor networks.

However, drone swarms also offer new means to improve nuclear delivery — that is, nuclear offense. States are already pursuing drone delivery systems for nuclear weapons, and drone swarms can also improve existing nuclear delivery systems without being armed with a nuclear weapon. Just as they may be able to serve as air and missile defenses, drone swarms can be used to defeat, disable, or trick those same defenses. While it’s true that air and missile defenses are highly mobile, creating significant challenges for locating and destroying them, drone swarms have the advantage of being able to spread out broadly to search for them. Along the same lines, Israel used drones as decoys to trick Syrian air defenses into believing they were Israeli aircraft. Drone swarms could do the same in larger, more distributed numbers to encourage defenses to hit the drones instead of the delivery systems carrying nuclear, biological, or chemical weapons. Drone swarms would move more effectively as a unit, akin to how groups of actual aircraft would behave.

Swarms may also improve nuclear targeting. Drones can be used to collect information to identify vulnerabilities or previously unknown defenses. Traditional delivery systems such as cruise missiles, while not technically drones, might incorporate drone swarm technology to adjust their approach en route, for instance based on other systems’ success or failure in striking targets. This is especially useful for counterforce strikes against an adversary’s military, which hinge on accurate and comprehensive target identification and precise strikes on those targets. Improved targeting is less important for second strikes and countervalue strikes, which target cities and civilians. Additionally, more accurate weapons mean fewer warheads and delivery systems would be needed. Targeting improvements may also lower upkeep or other costs.

In this way, drone swarm technology could make nuclear delivery systems either more or less survivable, depending on who uses the technology and how. Delivery system survivability is critical to nuclear stability. A nuclear threat is less credible if the threatened state believes it can reliably defeat the nuclear system. And on the other hand, if a state believes its nuclear delivery systems can be defeated, it may develop and deploy more nuclear weapons and novel delivery systems, as well as act more aggressively in crises and conflicts. Such concerns underlie Russia’s objections to U.S. ballistic missile defenses. This was also a key reason the United States and others have pursued multiple means of delivering nuclear weapons: to ensure nuclear weapons could always survive a first strike.

Will drone swarms ultimately improve nuclear offense more than they would improve nuclear defense? It’s unclear. But theoretically, emerging technologies that improve the ability to defeat nuclear weapons are more disruptive to overall nuclear competition than improvements to delivery. Nuclear weapons already inflict such significant damage that delivery improvements are unlikely to fundamentally alter the character of nuclear warfare. If North Korea can significantly deter the United States with a small, simple nuclear arsenal, for instance, delivery systems improvements seem unlikely to alter the fundamental dynamic. Therefore, while drone swarm technology could aid attacking states, the improvements for defenders are likely to matter more.

Chemical and Biological Weapons Proliferation

Drone swarm technology is likely to encourage chemical and biological weapons proliferation and improve the capabilities of states that already possess these weapons. Terrorist organizations are also likely to be interested in the technology, especially more sophisticated actors like the Islamic State, which has already shown interest in drone-based chemical and biological weapons attacks. Drone swarms may also aid counter-proliferation, prevention, and response to a chemical or biological attack, but those applications appear less significant than the offensive applications.

Indeed, swarms have the potential to significantly improve chemical and biological weapons delivery. Sensor drones could collect environmental data to improve targeting, and attack drones could use this information in the timing and positioning for release, target selection, and approach. For example, attack drones may release the agent earlier than planned based on shifts in wind conditions assessed by sensor drones.

Dispersed attacks also allow for more careful targeting. Instead of spraying large masses of agent, drones could search for and target individuals or specific vulnerabilities such as air ventilation systems. This also means the drones would not need to carry as much agent.

Moreover, drone swarms enable the use of combined arms tactics. Some attack drones within the swarm could be equipped with chemical or biological payloads, while others could carry conventional weapons. Chemical or biological attack drones might strike first to force adversary troops into protective gear that inhibits movement, then follow up with conventional strikes. Although combined arms tactics are possible with current delivery systems, drone swarms allow much closer integration between conventional and unconventional weapons.

These improvements in chemical and biological delivery could conceivably weaken both the military and moral justifications for the relative marginalization of weapons in international politics (with some key exceptions). As far as military utility goes, chemical and especially biological weapons are often unreliable modes of attack. Environmental and territorial conditions such as precipitation, wind, humidity, and vegetation reduce the efficacy of the agent, while protective gear may significantly or wholly mitigate the harm they cause. But drone-based environmental sensors could make these weapons much more reliable, while combined arms tactics could mitigate the impact of, or even gain advantage from, adversary use of protective gear.

The moral opposition to chemical and biological weapons has much to do with their indiscriminate nature and the consequential risk of collateral harm. In 1968, wind blew a cloud of VX nerve agent from the Dugway Proving Grounds in Utah into a nearby farm, killing thousands of sheep. Public opposition to the event helped catalyze the Nixon administration’s review of the U.S. chemical and biological weapons programs, culminating in an end to the bioweapons program. With improved targeting, including employing drone-based environmental sensors, it’s possible to imagine less error-prone, more discriminate chemical and biological weapon delivery systems that might be less morally objectionable.

Of course, just because these weapons are more usable does not necessarily mean they will reemerge. Modern chemical and biological weapons emerged in a different security environment. Various international laws may constrain rearmament and significant usage, as might popular opinion or political leadership. Still, it’s worth considering how advances in technology could make previously indiscriminate weapons more discriminate.

At the same time, drone swarms may also help prevent and respond to chemical and biological weapon attacks. Drone swarms could aid counter-proliferation efforts by, for example, coordinating searches for previously unknown chemical and biological facilities to secure stockpiles after a war. They could similarly coordinate searches along national borders to identify potential smuggling activity, including CBRN material smuggling, or searches through cities to search for gaseous plumes. Notably, swarms could serve as mobile platforms for chemical or biological detectors with different types of sensors to mitigate false positives. If an attack is successful, drones could coordinate mapping of affected areas to help guide responders. Drones could even have sprayers to help clean up after an attack, without risking harm to humans. But given the rarity of chemical and biological weapons attacks and the technical uncertainty of creating reliable, drone-based CBRN detectors, these applications appear less significant than the improvements to offensive capabilities.

Conclusion

How should the United States government address this still-nascent threat? Several agencies have clear equities in this area and should consider how to respond to the technology’s emergence.

First, the Commerce Department’s Bureau of Industry and Security should adopt new rules restricting the export of swarming-capable drones and related technologies. These rules should especially focus on technology with the potential to improve chemical and biological weapons delivery.

The Defense Department should expand its ongoing research and development into drone swarms to include CBRN-relevant uses. Current DoD research appears to focus on fundamental drone swarm capabilities, but not CBRN-specific applications. The department should also conduct red-team analysis to identify in which that drone swarms could support adversary capabilities in this area, especially chemical and biological weapons delivery.

The Department of Homeland Security should fund research and development into drone swarms for CBRN detection and response. This research should focus on three separate, but related lines of research: detectors, decontaminators, and platforms. Detectors and decontamination systems need to be small enough to effectively mounted on small drones. Drone swarm platforms need to effectively coordinate actions when broadly dispersed and require control systems for detectors and decontaminators.

The State Department should evaluate whether and to what extent existing international treaties are sufficient to discourage proliferation of CBRN-relevant drone swarm technology. Particularly, the department should consider whether and how to account for swarming technology in the Missile Technology Control Regime, which restricts individual drones.

Lastly, the intelligence community should collect information on adversaries’ interests in and experimentation with drone swarms, including those related to CBRN. The potential applications of drone swarms are extremely broad, and adversaries may identify novel, disruptive applications. The intelligence community should pay particular attention to China’s drone swarm research, as the Chinese have shown considerable interest in the technology.

As the technology underlying drone swarms matures and spreads, the barriers to entry will almost inevitably fall. After all, when reading about drones in 2010, how many readers would have thought that an organization such as Islamic State would have mounted hundreds of drone attacks in a single month or that commercial drones would shut down airports?

Zachary Kallenborn is an independent national security researcher/analyst specializing in CBRN terrorism, CBRN weapons, radical environmental terrorism, and drone swarms. His work has been published in Studies in Conflict and Terrorism, the Nonproliferation Review, Modern War Institute at West Point, Defense One, and other outlets.

Philipp C. Bleek is an Associate Professor in and Acting Program Chair of the Nonproliferation and Terrorism Studies Program, and a Fellow at the James Martin Center for Nonproliferation Studies, both at the Middlebury Institute of International Studies at Monterey. He previously served as Senior Advisor to the Assistant Secretary of Defense for Nuclear, Chemical and Biological Defense Programs. Kallenborn and Bleek are the authors of “Swarming Destruction: Drone Swarms and CBRN Weapons” in the Nonproliferation Review.

Image: Ars Electronica/Martin Hieslmair