Counter-Swarm: A Guide to Defeating Robotic Swarms


Editor’s note: This is the last article in a six-part series, The Coming Swarm, on military robotics and automation as a part of the joint War on the Rocks-Center for a New American Security Beyond Offset Initiative. Read the first, second, third, fourth, and fifth entries in this series.


Swarming with a large number of low-cost autonomous systems can be useful for a wide range of applications in warfare, and the U.S. military should move to harness the advantages of this approach. But so will others. While swarming provides numerous opportunities to expand U.S. combat effectiveness by enabling greater range, persistence, daring, mass, coordination, intelligence, and speed on the battlefield, it may be enemy swarms that are the real game-changer.

Many of the innovations that enable swarming – low-cost uninhabited systems, autonomy, and networking – are driven by the commercial sector, and thus will be widely available. Moreover, many states and non-state groups may be more eager to embrace them than the U.S. military, which is heavily invested in existing operational paradigms and the expensive and exquisite platforms they rely on. Swarms are more likely to be embraced by those who lack the institutional and cultural hurdles to their adoption that exist in the U.S. military.

Strategists should not be deceived by the cheap, unsophisticated drones currently in the hands of non-state groups like Hamas, Hezbollah, or the Islamic State. Fully autonomous GPS-programmable drones can be purchased online today for only a few hundred dollars. Large numbers of them could be used to field an autonomous swarm carrying explosives or even crude chemical or biological agents. Just as cheap improvised explosive devices wreaked havoc on U.S. forces operating in Iraq and Afghanistan, low-cost drones could similarly be extremely disruptive and cost-imposing – airborne improvised explosive devices that, instead of lying in wait, seek out U.S. forces. Think about the panic recently caused by one wayward drone mistakenly flown onto the White House lawn. Now imagine hundreds carrying explosives intentionally directed at the windows of the Oval Office, an open-air public event, or the deck of a carrier conducting freedom of navigation exercises. This is possible with today’s commercially available technology. The U.S. military and law enforcement must begin to think now about how to counter these threats and in cost-effective ways.

Swarms can be devilishly hard to target because they distribute combat capabilities across a wide number of dispersed assets and because they leverage mass to saturate and overwhelm defenses. That is, after all, one of their advantages. At the same time, nothing is invulnerable. Individual elements of a swarm can still be attacked directly, although cost-effective means are critical. Shooting down a thousand dollar drone with a million dollar missile is not a cost-effective strategy. Whole swarms can be targeted, however, through electronic warfare, high-powered microwaves, or cyber attacks. Furthermore, the cooperative nature of swarms can be used against them, by jamming a swarm to force it to “collapse” to individual uncoordinated elements, out-maneuvering a swarm to force it into a disadvantageous position, or even conceivably hijacking a swarm to take control of it.

Swarm warfare is only in the very earliest stages of development, but below are some of the innovative ideas being explored on how to counter enemy swarms.

Destroy the Swarm

Individual swarm elements are still vulnerable to destruction, although militaries will want to find cost-effective means of doing so. Possible approaches include low cost-per-shot weapons, counter-swarms, and wide area electronic attacks.

Low cost-per-shot weapons

Low cost-per-shot weapons consist of exotic technologies like lasers and electromagnetic rail guns as well as more traditional technologies like machine guns. The Navy is currently developing laser weapons and rail guns. It successfully tested a laser weapon at sea last year and will test a rail gun at sea in 2016. Lasers and rail guns are appealing counter-swarm weapons because they are electrically powered and therefore have relatively low costs for each shot – significantly lower than a missile – assuming power sources are available. The Navy has already demonstrated the ability of a laser to shoot down an enemy drone, although defeating an entire swarm of drones is a more significant challenge. Machine guns, such as the sea-based Phalanx and land-based counter-rocket, artillery and mortar (C-RAM) system, are also potentially cost-effective ways of defeating incoming projectiles or smart drones, provided the radars can successfully identify and track small, slow, low-flying objects.


One method of taking out a swarm could be with another swarm. As long as the counter-swarm is cheaper and/or more effective than the enemy swarm, it can be a relatively low-cost way to defend against enemy swarm attacks. The Naval Postgraduate School is currently researching swarm-on-swarm warfare tactics, with the intent of testing a 50-on-50 aerial swarm dogfight. Basic research in swarming tactics will be critical, as winning in swarm combat may depend upon having the best algorithms to enable better coordination and faster reaction times, rather than simply the best platforms.

High-powered microwaves

Low cost-per-shot weapons and counter-swarms are appealing, but still require targeting individual swarm elements. High-powered microwaves, on the other hand, could potentially blanket a wide area with electromagnetic energy to disrupt or destroy electronics, thus taking out an entire swarm in one move. While high-powered microwaves currently have limited range, they could be effective for terminal defense against some types of swarm attacks, or could be mounted forward on platforms that intercept and knock out swarms further away from the assets being defended.

Collapse the Swarm

Communications jamming can also be an effective means of disrupting a swarm by preventing coordination among individual elements, “collapsing” the swarm so that it disintegrates into many disparate, uncoordinated elements. Swarms that rely upon implicit communication techniques such as co-observation – as flocks of birds, schools of fish, or herds of animals do – are inherently resilient against direct communications jamming. Nevertheless, co-observation can still be jammed through the use of obscurants or other measures to create “noise” in whatever spectrum swarm elements observe one another. While such jamming wouldn’t destroy individual swarm elements, it would prevent swarm elements from fighting cooperatively, potentially making individual elements easier to the target and eliminate.

Trap the Swarm

Conversely, one could adopt the opposite approach and leave swarm coordination intact, but leverage it to one’s own advantage to force the swarm into a disadvantageous position. This could be done by trapping a swarm, canalizing it into unfavorable terrain, encircling it with another swarm, or otherwise compressing or dispersing the swarm to force it to fight in a way such that many of its advantages are negated. Native Americans, for example, used to leverage the herding behavior of buffalo to drive them off a cliff, killing whole herds at a time in a “buffalo jump.”

Hijack the Swarm

The ultimate tactic in counter-swarm warfare is to hijack the enemy’s swarm for one’s own purposes. There are many examples in nature of animals repurposing swarms for their own use, sometimes in ways that are not harmful to the swarm such as hiding within it for protection, but in other cases in ways that are absolutely destructive.

In a form of spoofing, or false data, attack, the West African Rubber Frog secretes a pheromone that prevents the normally aggressive stinging ant paltothyreus tarsatus from attacking it. The frog then lives inside the ant colony during the dry season, reaping the benefits of the nest’s humidity and protection from prey.

The slave-making ant polyergus breviceps, on the other hand, is less benign when it hijacks an entire colony of a rival ant species. The polyergus queen infiltrates a rival colony, kills the queen, and assumes control of the colony as its new queen. Her own offspring are then raised by the hijacked colony and its workers, thus taking control of an entire swarm and using it for her own purposes.

Similarly, in the military context, swarms could be hijacking by spoofing incoming data, generating signals in the environment to induce certain swarm behaviors, or by direct communications hacking.


As these examples demonstrate, swarm security will be essential in military operations. The increased degree of autonomy in swarming systems introduces novel risks. While autonomous systems may not be more susceptible to spoofing or cyber attacks, the consequences if an enemy were to gain control of a highly autonomous system – or an entire swarm – could be much greater. While an enemy might be able to ground a human-inhabited aircraft through a cyber vulnerability, an enemy could conceivably take control of an uninhabited system and no human would be physically present to disable the system. Actually controlling a remotely piloted aircraft today would require replicating the control data and would be quite onerous for even a single aircraft, much less a large number of them. But as uninhabited systems incorporate greater autonomy, an enemy, once in, could conceivably redirect it to turn on friendly forces with a few lines of code.

Decentralizing swarm command-and-control architectures can be one method to enhance resiliency. Perhaps paradoxically, requiring human authorization for some functions can also enhance resiliency against some forms of attacks. Armed with “common sense” and the ability to adapt to unanticipated situations, humans may be better at responding to some forms of spoofing attacks. Furthermore, requiring a human “in the loop” for some functions at least requires an adversary to replicate that command and control function in order to take control of a swarm, rather than simply being able to send false data or insert malware and allow automation to do the rest. “Human firewalls” can help build resilience against cyber attacks.

Rejecting all automation and relying entirely on human operators would give up the advantages of not only swarming but even basic vehicle autonomy for communications-degraded operations. Therefore, the best cognitive architecture will inevitably be a blend of human and machine decision-making. Militaries will want to harness automation for some tasks but keep humans “in the loop” for others, particularly high-consequence actions like the use of force.

The Enemy Gets a Vote on the Future of Swarming

Faced with some of the challenges in building and operating swarms – and keeping them operational in contested environments – it might be tempting to move slowly in experimenting with swarming concepts. But the enemy gets a vote. Cheap drones are proliferating worldwide, and they will incorporate increasing amounts of autonomy, enabling swarming with commercially-available technology. An ongoing revolution in information technology is generating a technology space that is flat and accelerating. New innovations are widely available to friend and foe alike, and the pace of innovation far outstrips the lumbering bureaucracies of governments and defense institutions. Moreover, because the technology behind increasing autonomy is software- not hardware-based, it can be easily copied, modified, and proliferated. It may be enemy swarms that first force the U.S. military to confront the challenges of swarm warfare, but the United States would be foolish not to also exploit its opportunities.

Swarming will require new concepts of operation and several paradigm shifts for the U.S. military. We must move from a paradigm of driving and piloting vehicles to mission-level command of a swarm. We must shift from waiting for “full autonomy” to seizing the opportunities afforded by operationally-relevant autonomy today. Instead of focusing on capability, we must focus on capability per dollar, and the advantages that mass may bring. We must shift our focus from survivability of individual platforms to resiliency of the swarm as a whole. We must think of not only payloads over platforms, but also software over payloads. Finally, instead of thinking about “unmanned” systems replacing people, we should think about robotic swarms as yet another tool to help warfighters adapt to a changing world to do their jobs – to fight and win.


Paul Scharre is a fellow and Director of the 20YY Warfare Initiative at the Center for a New American Security (CNAS) and author of CNAS’ recent report, “Robotics on the Battlefield Part II: The Coming Swarm.” He is a former infantryman in the 75th Ranger Regiment and has served multiple tours in Iraq and Afghanistan.


Photo credit: Official U.S. Navy Imagery