The Kettering Bug, the world’s first unmanned aerial vehicle (UAV), began development in 1917 as a prototype for an unmanned flying bomb at the request of the US Army.^{Reference Hunt1} Also referred to as drones, unmanned aircraft, or remotely piloted vehicles, UAVs today are considered an integral part of many modern militaries’ arsenals, both as an intelligence, surveillance, and reconnaissance tool, as well as a combat instrument.^{Reference Urcosta2,Reference Sayler3}

Like many technologies borne out of military applications, modern day UAVs have evolved beyond their wartime origins and made the leap into both civilian and commercial sectors, with a wide range of applications from aerial photography and building safety inspections to locating survivors using body heat surveillance to the delivery of medical and other supplies to remote locations.^{Reference Joshi4,Reference Court, Edwards, Issa, Voskanyan and Ciottone5}

Specialists in Counter-Terrorism Medicine (CTM), an emerging sub-specialty of disaster medicine focusing on the health care related mitigation, preparedness, and response demands of increasingly more complex and asymmetric terrorist attacks, have also identified UAVs as a potential and concerning mass-casualty attack platform.^{Reference Court, Edwards, Issa, Voskanyan and Ciottone5} There is precedent. In the early 1990s, the Aum Shinrikyo cult explored the use of UAVs to deliver chemical weapons before the Tokyo Subway attack, and in 2019, the Houthi movement in Yemen launched a UAV attack on oil processing facilities in Saudi Arabia, something that continues today with on-going, sporadic attacks.^{6,Reference Hubbard, Karasz and Reed7} While these examples represent the use of UAVs as a novel platform for both conventional and non-conventional weapons rather than a novel attack methodology, per se, their ease of use, coordination, scalability, and potential to create a compounding disaster can exploit current vulnerabilities in the health care sector.^{Reference Tin, Hart and Ciottone8}

The mass proliferation and increasing affordability of UAVs in recent years has given rise to weaponized UAV use by terrorists, leading to mounting and credible concerns this attack methodology will be the next terrorism modus operandi.^{Reference Braun and Fleiss9–12} Low acquisition costs and the availability of multiple low-profile purchase pathways, along with the potential for high-accuracy targeting, operational flexibility, inadequate defenses, and low levels of infrastructure and training needs to support the use of simple UAVs, all add to their appeal.^{Reference Emil and Yannick13}

Alarmingly, UAVs can disrupt air traffic, and amateur/unsophisticated modification of civilian, off-the-shelf UAVs could enable them to carry explosives, creating a significant risk to mass-gathering events.^14,15 Agricultural UAVs designed to spray pesticides could be reappropriated as highly-effective delivery systems for chemical weapons attacks.^{Reference Lambert16,Reference Koblentz17} Increasingly sophisticated technologies, from autonomous behavior to collaborative swarming, are further enhancing UAV capabilities and creating new opportunities for terrorists to carry out complex, coordinated, multi-modality attacks with the potential of inflicting proportionally more harm.^{Reference Kallenborn and Bleek18,Reference Kallenborn19}

Existing government technology, funding, and policies do not appear sufficient to reduce the risk. The Center for the Study of the Drone at Bard College (New York USA) identified 537 counter-UAV systems available on the commercial market in December 2019. However, limited operational data are available to assess their efficacy, and few appear designed to handle multiple UAVs at once.^{Reference Michel20} Likewise, a recent Office of the Inspector General (US Department of Health and Human Services; Washington, DC USA) review found the US Department of Homeland Security (Washington, DC USA) had limited capabilities to counter UAVs and has not adequately funded counter-UAV operations.^{Reference Cuffari21} Current US law only allows federal authorities to operate counter-UAV systems, which may require the US government to adopt novel strategies to protect numerous, geographically dispersed critical infrastructure facilities.^{22,Reference Kallenborn23} While major international efforts, like United Nations Security Council Resolution 1540, seek to limit non-state actor access to traditional weapons of mass destruction, unfortunately, these efforts do not apply to conventionally-armed UAVs.²⁴

Specialists in CTM need to consider how UAVs alter or create new mass-casualty scenarios that can further exploit existing medical preparedness vulnerabilities. Larger-scale incidents from more effective chemical or biological weapon delivery systems, health care facilities as primary or secondary targets, and dispersed victim spread in multiple and fluctuating warm or hot zones from simultaneous, timed, and coordinated attacks all add to an already complex disaster response to terrorist attack matrix.

Exactly how UAVs change medical response requires further investigation and necessitates regular multi-agency discussions with disaster and CTM specialists, security, intelligence, and law enforcement experts, as well as counter-terrorism and counter-UAV specialists, to explore risk mitigation strategies to this extremely real and dangerous threat.^{Reference Kallenborn25} Focus should emphasize how UAV incidents differ from traditional terrorist incidents in terms of geographic dispersion of casualties, the distribution and type of injuries, and other factors.^{Reference Heszlein-Lossius, Al-Borno and Shaqqoura26} With an opportunity to be proactive in disaster prevention, mitigation, and preparedness, it is imperative this gathering storm be acknowledged and stakeholders bolster response capabilities that include updated and practiced CTM measures.