The proliferation of drones to violent nonstate actors

1. Though others exist, we use the terms drone and unmanned aerial vehicle (UAV) interchangeably in this article.

2. Bunker (Citation2015) and Abbott et al. (Citation2016) report the death toll at 23, Almohammad and Speckhard (Citation2017) at 32, and Rossiter (Citation2018) at “dozens.”

3. This followed an attack in October 2015 on a separate ammunition depot that destroyed 3,000 tons of ammunition and damaged 1,700 homes in the vicinity.

4. We executed searches in Lexus Nexus, Web of Science, Google Scholar, and generic search engine queries with relevant Boolean operators. We also located primary sources for all empirical instances featured in our literature list, tabulating for each instance of VNSA drone use the date, group, location, action, outcome, type (intent, attempt, success), number of drones involved (when known), and indicators for key patterns. In addition, we pioneered a data collection project on the determinants of VNSA drone adoption. Using the Global Terrorism Database (GTD) for case selection, we collected information on group characteristics, drone use being a key one, across 997 VNSAs from 1995 to 2019. In addition to the GTD, our primary sources included the Mapping Militant Organizations dataset run by Stanford’s Center for International Security and Cooperation; the Big, Allied, and Dangerous dataset; the Terrorism Research and Analysis Consortium; the South Asia Terrorist Portal; the Counter Extremism Project; Rand Corporation; the Council on Foreign Relations; the Center for Strategic and International Studies; the Brookings Institution; the Jihad Identifiers Database; the Combating Terrorism Center at West Point; and the Long War Journal.

5. See Mandelbaum et al. (Citation2005); Miasnikov (Citation2005); Hammes (Citation2013), Hammes (Citation2016); Bunker (Citation2015); Abbott et al. (Citation2016); Horowitz et al. (Citation2016); Friese et al. (Citation2016); Rassler (Citation2016, Citation2018); Ball (Citation2017); Barsade and Horowitz (Citation2017); Tallis et al. (Citation2017); Rossiter (Citation2018); Jackman (Citation2019); Archambault and Veilleux-Lepage (Citation2020a, Citation2020b); and Rogers Citation2019, not to mention work produced by the Center for a New American Security and Bard College’s Center for the Study of the Drone.

6. These include Hezbollah, Hamas, and Houthi rebels.

7. We recognize that drones are best conceptualized as a spectrum, running the gamut from a child’s toy to the Beast of Kandahar. For simplicity and comparison, we divide that spectrum into three categories based on accessibility and technical/infrastructural requirements to operate.

8. The data on technical parameters were collected by consulting manufacturer specifications, mechanical manuals, consumer tests and reviews, and other miscellaneous open-source reports. It features information on wingspan/rotor diameter, weight, range, speed, altitude, endurance, and cost for 62 military-grade platforms, 48 commercial models, and 48 hobbyist drones. This represents approximately 33% of the universe of current drone technologies. To maximize coverage and variation in current technologies, the dataset features drones from 90 manufacturers spread throughout 20 nations. Due to the evolving nature of the civilian drone market, our data reflects a timestamped snapshot of the industry in the first half of 2019.

9. For example, the MQ-9 Reaper is estimated to cost $64 M per unit, well above the average for military-grade models and well outside most VNSAs’ budgets.

10. Speaking of the manned Lockheed Martin F-35 fighter jet, Gilli and Gilli (Citation2016, 57) cite that it “features seventeen miles of copper wiring while its software contains eight million lines of code.”

11. A drone suicide mission involves programming an armed UAV to crash into a target, exploding upon impact, versus dropping a munition from above and returning intact to a user. “Loitering munitions” are explicitly designed for this approach, but many VNSA suicide drones are adapted using low-cost consumer UAVs (Gettinger and Michel Citation2017).

12. This catalyzed a nationwide database search for drone-related incidents at sensitive nuclear facilities, which returned 42 reports since 2016 (Rogoway and Trevithick Citation2020).

13. It has been reported that a Shahed-129 drone was used by a VNSA against US forces. While the operator has not been positively identified, some sources suggest that ISIL obtained and successfully fielded the machine following a crash and recovery.

14. We define success in this context as execution of the VNSAs’ goal in deploying a given drone. Since UAVs can be used for a variety of purposes, from passive surveillance to lethal bombings, success constitutes carrying out one’s intended agenda for the inferred individual drone use.

15. Interestingly, Army investigators determined that some of the mortars, leaving noticeable impact craters, were made with a 3D printer.

16. The four expos include AUVSI Xponential, the Commercial UAV Expo, Drone Days Belgium, and the International Drone Expo. Data collection was performed by research assistants under the supervision of the authors.

17. Consider the demand growth of any toy fad, for instance, as evidence that increasing sales do not automatically imply increasing sophistication (i.e., Hatchimals, TickleMeElmo, or Pet Rocks).

18. Data collection was performed by research assistants under the supervision of the authors.