Wreckage of an Iranian-made UAS recovered after an attack on the Al Tanf Garrison, a U.S. base in Syria, in 2021. (Photo courtesy of authors)

Practice Notes

Expanding the Inherent Right to Self-Defense in a Counter-UAS Environment

By Major Jeremy S. Watford and Captain Ashley R. Jesser

On 20 October 2021, hostile forces launched five fixed-wing unmanned aircraft systems (UAS) at the Al Tanf Garrison (ATG), a U.S. base in southeastern Syria.1 The weapons were on a one-way path into the base, loaded with “ball bearings and shrapnel with a ‘clear intent to kill.’”2 While no group took immediate responsibility for the attack, the UAS matched others used previously by Iranian-backed militias against U.S. bases in Iraq.3 Since that attack, Iranian-made Shahed-131 and Shahed-136 UAS have been a fixture of the conflict in Ukraine.4 Ukraine’s Main Intelligence Directorate claims Russia has launched as many as 660 Shahed-type UAS in similar one-way attacks against Ukrainian targets, including over eighty such launches during a concerted attack spanning 1 and 2 January 2023.5

The UAS attack against ATG in 2021 is not unique.6 Militia groups continue to employ similar one-way UAS attacks against U.S. forces in the region, with lethal effects.7 Simultaneously, the Ukrainian conflict has highlighted the effectiveness of one-way UAS attacks in conventional conflicts.8 Attacks utilizing UAS are now one of the most common threats to U.S. bases in the region and will continue to be a persistent threat in the modern operational environment. Commanders, and their legal counsel, must learn to interpret and respond to this new threat within mission requirements and the law of armed conflict (LOAC) principles. Because of their size and flight patterns, UAS are often difficult to detect and difficult to engage once in flight. Accordingly, to best protect U.S. forces, commanders require the flexibility to engage hostile UAS while still on the ground, or “left of launch.” Developing a self-defense framework that gives commanders maximum maneuver space in response to identified hostile UAS will best ensure mission success while adhering to LOAC principles.

Background

Class I UAS include quadcopters (rotary wing) and other types of small-sized fixed-wing “hobbyist drones.” (Credit: Repina Valeriya)

Unmanned Aircraft Systems Classification

The umbrella term UAS refers to a wide variety of weaponized unmanned aerial systems. The North Atlantic Treaty Organization classifies UAS into three classes based on size and flight capabilities: Class I, II, and III.9 All three categories are capable of intelligence, surveillance, and reconnaissance (ISR) in addition to their capabilities for offensive targeting operations.10

Class I UAS include quadcopters (rotary wing) and other types of small-sized fixed-wing “hobbyist drones.”11 Widely available at affordable prices within recent years, Class I UAS are easily accessible to non-state actors for modification into weapons systems.12 However, they possess a short flight range of five to fifty kilometers and restricted payloads.13

Class II UAS are mid-sized, traditionally fixed wing crafts.14 Both military and non-state actors prefer Class II for actions in the modern operational environment, such as the recent attack on ATG and other U.S. operating bases.15 These systems have an average range of about 200 kilometers.16 Class II UAS often conduct kamikaze-style missions with a large attached explosive payload on a one-way path to its target, similar to traditional vehicle-borne improvised explosive devices.17 They also frequently perform mid-range surveillance missions, armed or unarmed.18 Fixed-wing, armed Class II UAS can carry larger payloads over longer distances than Class I rotary-wing UAS.19 They fly at lower altitudes than their larger Class III counterparts, which consist of larger, almost exclusively fixed-wing, drones.20 Class III UAS are expensive, may possess stealth and complex operating capabilities, and are almost exclusively used by advanced state military forces.21

While the higher price tag for Class II systems generally prohibits their use by individual malign actors, some state actors, such as Iran, have transferred mid-sized UAS to non-state actors.22 The proliferation of Class I and II UAS among a wide range of non-state actors has significantly expanded the kinetic capabilities of these groups. Non-state actors now use Class I and Class II UAS for unauthorized reconnaissance, conveying illicit materials, conducting kinetic kamikaze-style attacks, and conducting chemical, biological, or radiological attacks.23

A V-2 rocket, like the ones that struck Britain in the final stages of World War II, stands on display at the Historical Technical Museum in Peenemunde, Germany. (Credit: travelview - stock.adobe.com)

Historic Parallels

Operationally, many of the challenges presented by modern UAS are analogous to those posed by early ballistic missile systems. During World War II, Germany struck Britain with over 1,100 V-2 rockets during a seven-month span, killing over 2,800 people.24 Because of their speed, the rockets arrived with little to no warning.25 Lacking effective countermeasures once the rockets were airborne, Britain’s best defensive option was targeting the launch sites across the English Channel.26 However, the rockets were highly mobile and could be launched from virtually any flat ground.27

While the context of the conflict and legal basis for the use of force differ, many of the technical challenges presented by UAS are the same. The point of origin of UAS are difficult to predict in advance; once airborne, the systems’ intended destination and time on target are often unclear; and their size, speed, and flying altitude can inhibit detection and countermeasures. But unlike early ballistic missiles, modern UAS (particularly Class I and II) are widely accessible at relatively low cost to both state and non-state actors.28 The conflict in Ukraine has demonstrated the effectiveness of one-way UAS as cheap loitering munitions, available at a lower cost and better able to fly below radar than analogous missile systems, capable of potentially overwhelming and depleting air defense assets through sheer numbers.29 Unmanned Aircraft System launches can be quick and easy. Users can launch Class I and some smaller Class II UAS by hand or by handheld devices from any location close to the intended target.30 Larger, Class II UAS are often launched using trucks driving down roadways or from easily assembled fixed-rail systems.31 Post-launch, UAS can be difficult to accurately detect. Radar is the most common form of detection for flying objects, but it is less effective in detecting UAS because of their slower speed and lower flight profile compared to traditional aircraft.32 Finally, base radar systems may not register an incoming UAS threat until there are mere minutes remaining to engage base defense systems and move personnel to shelter. Reduced reaction time impedes commanders’ abilities to effectively engage base countermeasures and protect the force.33

Class II or Class III UAS are less likely to have non-military uses but ascribing “hostile intent” to such a system pre-launch still requires supporting intelligence. (Credit: Jamal Wilson)

Law of Armed Conflict and UAS

As commanders refine responses to developing UAS threats, they must consider the foundational principles of LOAC.34 The four basic principles of LOAC that frame a commander’s use of force are: distinction, military necessity, proportionality, and the duty to cause no unnecessary suffering.35 Concurrently, the inherent right to self-defense, delineated in Article 51 of the Charter of the United Nations,36 is a core principle of international law. The right to self-defense includes the right to anticipatory self-defense: protection of oneself from an imminent attack when alternative peaceful means are not available.37

To comply with law of war principles, commanders engaging in strikes against UAS in self-defense must clearly understand when it is appropriate to engage.38 The key challenges that engaging a UAS left of launch present are (1) distinguishing hostile from civilian non-combatant systems, and (2) properly assessing the threat as imminent.

Distinction

Of the four basic principles of LOAC, maintaining distinction in UAS strikes before said UAS is launched is the most challenging. Class I rotary-wing UAS are common, commercially-available items equally accessible to civilian hobbyists and to non-state hostile actors. However, a civilian UAS may immediately become a valid military target because of its use.39 Class II or Class III UAS are less likely to have non-military uses but ascribing “hostile intent” to such a system pre-launch still requires supporting intelligence. A stationary UAS parked on a runway could be intended for terrain mapping or aerial photography within an actor’s own territorial bounds.

Likewise, it can be difficult to determine whether individuals in the proximity of a UAS are hostile forces themselves, owing to the challenges of achieving positive identification of forces in non-international armed conflicts.40 The loss of innocent lives from target engagement is extensively debated in both news media and scholarly dissertations about how the United States executes strikes.41 Numerous commentators have argued that justifying UAS strikes pre-launch could lead to a degradation of the legitimacy of law of war principles and hard-won protections for non-combatants under human rights law.42

A commander’s decision-making process while responding to an imminent threat includes multiple levels of built-in requirements, analysis, oversight, and review designed to ensure that pre-launch strikes in self-defense align with LOAC principles.43 The Department of Defense has established the Joint Counter-small UAS Office (JCO) to develop specific criteria for when striking a UAS pre-launch complies with military necessity and distinction.44 The Secretary of Defense recently directed military leadership to scrutinize and provide an in-depth assessment of the root causes and lessons learned from unnecessary civilian harm caused by U.S strikes.45 Rules of engagement provide specific, fact-based criteria to assess hostile intent for commanders and warfighters at all levels.46 Finally, expertly trained legal advisors directly advise commanders on LOAC in strike scenarios, ensuring firm adherence to civilian protections.47

Ultimately, LOAC seeks to strike a balance between the opposing military necessity and humanitarian considerations, aiming to “minimize[e] human suffering without undermining the effectiveness of military operations.”48 Adopting a permissive approach to self-defense strikes on UAS pre-launch is consistent with these aims. As UAS are unmanned, there is a decreased risk of loss of human life associated with their destruction, particularly in comparison to the potential physical destruction and loss of life that UAS attacks can inflict.49 Military commanders must take feasible precautions to protect civilians based on the information they have available at the time, but they do not have to “discard considerations of military necessity or . . . forget their mandate to accomplish the mission.”50 As always, commanders and their legal advisors should rely upon vetted and reliable intelligence reporting to assess “hostile intent” of pre-launch UAS and take appropriate actions in self-defense. Pre-launch strikes of appropriately assessed hostile UAS are a legitimate military objective justifiable as self-defense.51

Conclusion

Because of the unique problem set that surrounds countering hostile UAS systems, commanders must be afforded the decision-making space to react as far left of launch as possible. Preserving the option to strike a UAS system pre-launch is necessary to retain the inherent right to self-defense. Nonetheless, assessing grounded UAS as hostile and neutralizing them pre-launch presents risks. Commanders, and their legal advisors, must be mindful of the distinction between civilian and military targets and the potential for dual-use systems, must closely examine the specific factors that support a reasonable certainty of hostile intent, and be cognizant of the impact that a misinformed strike could have on the operational environment.52

The guardrails of the rules of engagement, combined with principled legal counsel that is well integrated into the strike process, will keep pre-launch UAS strikes in line with LOAC. Ultimately, evaluating emerging UAS threats must not only comply with LOAC, but also be tailored to preserve commanders’ operating space—without imposing unnecessary restrictions—to protect U.S. and coalition forces and fulfill the mission.53 A permissive approach to pre-launch strikes of hostile UAS is consistent with these aims. TAL

MAJ Watford is a national security law Attorney at the National Counterterrorism Center, at the Office of the Director of National Intelligence in McLean, Virginia.

CPT Jesser is a trial counsel for the 11th Corps Signal Brigade at Fort Hood, Texas.

Notes

1. Eric Schmitt & Ronen Bergman, Strike on U.S. Base Was Iranian Response to Israeli Attack, Officials Say, N.Y. Times (Nov. 18, 2021), https://www.nytimes.com/2021/11/18/world/middleeast/iran-drone-al-tanf-syria.html.

2. Id.

3. Id.

4. Ellie Cook, Ukraine Details Key Weapon Used to Shoot Down Shahed Drones, Newsweek (Apr. 3, 2023), https://www.newsweek.com/unkraine-weapons-shoot-iranian-shahed-drones-russia-1792098.

5. Ellie Cook, How the West Can Help Thwart Russia’s Drone Assault, Newsweek (Feb. 8, 2023), https://www.newsweek.com/how-west-thwart-shahed-drone-kamikaze-assault-gepard-anti-aircraft-1779524 (discussing 660 total unmanned aircraft systems (UAS) attacks); How Are “Kamikaze” Drones Being Used By Russia and Ukraine?, BBC News (Jan. 3, 2023), https://www.bbc.com/news/world-62225830 (discussing specific attack of 1-2 January 2023).

6. U.S. Dep’t of Def., Counter-Small Unmanned Aircraft Systems Strategy 6 (2021). (“[N]ation states are improving performance, reliability, and survivability of UAS. Low-cost systems are increasingly available around the world.”).

7. Eric Schmitt, American Contractor Killed in Drone Attack on U.S. Base in Syria, N.Y. Times (Mar. 23, 2023), https://www.nytimes.com/2023/03/23/us/politics/syria-drone-attack-us-base.html.

8. See Cook, supra note 4.

9. N. Atlantic Treaty Org., ATP-3.3.8.1, Minimum Training Requirements for Unmanned Aircraft Systems (UAS) Operators and Pilots 2-2 fig.2-1 (2019) [hereinafter ATP-3.3.8.1]; Andreas Schmidt & Berry Pronk, Defensive Counter-Air Operations, in A Comprehensive Approach to Countering Unmanned Aircraft Systems 102, 108 (Matthew Willis et al. eds., 2021).

10. See Raul Pedrozo, Use of Unmanned Systems to Combat Terrorism, in 87 Naval War Coll., International Law Studies: International Law and the Changing Character of War 217, 217 (Raul Pedrozo & Daria P. Wollschlaeger eds., 2011).

11. See Andreas Schmidt & André Haider, The Differences Between Unmanned Aircraft, Drones, Cruise Missiles and Hypersonic Vehicles, in A Comprehensive Approach to Countering Unmanned Aircraft Systems 27, 30-31 (Matthew Willis et al. eds., 2021).

12. Kelley Sayler, Ctr. For a New Am. Sec., A World of Proliferated Drones: A Technology Primer 11-13 (2015).

13. ATP-3.3.8.1, supra note 9, at 2-2 fig.2-1.

14. See André Haider, Introduction to A Comprehensive Approach to Countering Unmanned Aircraft Systems 14-15 (Matthew Willis et al. eds., 2021); Joint Air Power Competence Centre, A Comprehensive Approach to Countering Unmanned Aircraft Systems 523 (Matthew Willis et al. eds., 2021) (depicting Russian Forpost Class UAS).

15. See Associated Press, Attack Hits Syria Base that Houses U.S. Troops; No U.S. Injuries, NBC News (Oct. 21, 2021, 9:16 AM), https://www.nbcnews.com/news/world/attack-hits-syria-base-houses-us-troops-no-us-injuries-rcna3466 (discussing use of one-way UAS in 20 October 2021 attack on ATG); Chris Gordon, Coyote Air Defense Weapon Shoots Down Drones Attacking US Outpost, Air & Space Forces Mag. (Jan. 20, 2023), https://www.airandspaceforces.com/coyote-air-defense-weapon-shoots-down-drones-us-syria/ (discussing use of Shahed UAS in 2017 attack on ATG).

16. ATP-3.3.8.1, supra note 9, at 2-2 fig.2-1.

17. Joshua L. Cornthwaite, Can We Shoot Down That Drone? An Examination of International Law Associated with the Use of Territorially Intrusive Aerial and Maritime Surveillance Drones in Peacetime, 52 Cornell Int’l L.J. 475, 482 n.37 (2019); Sayler, supra note 12, at 18.

18. See Sayler, supra note 12, at 18.

19. See ATP-3.3.8.1, supra note 9, at 2-2 fig.2-1.

20. See Sayler, supra note 12, at 20.

21. Sayler, supra note 12, at 23.

22. See Sayler, supra note 12, at 17.

23. Bradley Wilson et al., RAND Corp., Small Unmanned Aerial System Adversary Capabilities, Homeland Security Operational Analysis Center xii-xiii (2020).

24. Charlie Hall, ‘Flying Gas Mains’: Rumour, Secrecy, and Morale during the V-2 Bombardment of Britain, Twentieth Century British Hist., Mar. 2022, at 52, 54.

25. Id.

26. Id.

27. Id. at 66.

28. Jason Sherman, Drone-on-Drone Combat in Ukraine Marks a New Era of Aerial Warfare, Sci. Am. (Apr. 2, 2023), https://www.scientificamerican.com/article/drone-on-drone-combat-in-ukraine-marks-a-new-era-of-aerial-warfare.

29. Dominika Kunertova, The War in Ukraine Shows the Game-Changing Effect of Drones Depends on the Game, 79 Bull. of the Atomic Scientists 95, 97 (2023).

30. See UAV Launch & Recovery Systems, Unmanned Sys. Tech. (Sept. 28, 2022), https://www.unmannedsystemstechnology.com/category/supplier-directory/ground-control-systems/launchers-recovery-systems (providing an overview of launch capabilities available on the market for larger fixed-wing, small, and medium UAS).

31. Id.

32. U.S. Dep’t of Def., supra note 6, at 6; see also Schmidt & Pronk, supra note 9, at 112.

33. See John Parachini & Peter Wilson, Drone-Era Warfare Shows the Operational Limits of Air Defense Systems, The Rand Blog (July 2, 2020), https://www.rand.org/blog/2020/07/drone-era-warfare-shows-the-operational-limits-of-air.html. Syrian regime forces often operate Russian-manufactured short-range air defense systems (SHORADS) defense from UAS. Id. The SHORADS were unable to effectively counter Israeli UAS attacks, in part due to the Syrian regime force’s reaction time. See id. Syrian personnel lacked the reaction time and training to operate defense systems fast enough upon recognition of the incoming threat. See id.

34. See U.S. Dep’t of Def., Dir. 2311.01, DoD Law of War Program para. 1.2 (2 July 2020); “Applying the Law of Targeting to the Modern Battlefield” – Full Speech Given by DOD General Counsel Jennifer O’Connor, Just Sec. (Nov. 28, 2016), https://www.justsecurity.org/34977/applying-law-targeting-modern-battlefield%E2%80%8E-full-speech-dod-general-counsel-jennifer-oconnor [hereinafter O’Connor] (“We follow the law because it reflects our core values, the very principles that we are fighting to protect and preserve—in short, it reflects who we are.”).

35. Off. Of Gen. Couns., U.S. Dep’t of Def., Department of Defense Law of War Manual para. 2.1 (12 June 2015) (C2, 13 Dec. 2016) [hereinafter Law of War Manual]; Nat’l Sec. L. Dep’t, The Judge Advoc. Gen.’s Legal Ctr. & Sch., U.S. Army, Operational Law Handbook ch. 3, sec. V (2022) [hereinafter Operational Law Handbook].

36. U.N. Charter, art. 51.

37. See Law of War Manual, supra note 35, para. 1.11.5.1 (“Under customary international law, States had, and continue to have, the right to take measures in response to imminent attacks.”); see also John Bassett Moore, A Digest of International Law 409–14 (1906) (describing The Caroline incident, a seminal international conflict surrounding the theory of anticipatory self-defense).

38. See Law of War Manual, supra note 35, para. 1.11.5 (“To constitute legitimate self-defense under customary international law, it is generally understood that the defending State’s actions must be necessary. For example, reasonably available peaceful alternatives must be exhausted. In addition, the measures taken in self-defense must be proportionate to the nature of the threat being addressed.”).

39. See Law of War Manual, supra note 35, para. 5.6.1.2.

40. See John Cherry & Michael Rizzotti, Understanding Self-Defense and the Law of Armed Conflict, the Lieber Inst. West Point: Articles of War (Mar. 9, 2021), https://lieber.westpoint.edu/understanding-self-defense-law-armed-conflict.

41. See, e.g., Azmat Khan, Hidden Pentagon Records Reveal Patterns of Failure in Deadly Airstrikes, N.Y. Times (Dec. 18, 2021), https://www.nytimes.com/interactive/2021/12/18/us/airstrikes-pentagon-records-civilian-deaths.html (“The promise was a war waged by all-seeing drones and precision bombs. The documents show flawed intelligence, faulty targeting, years of civilian deaths—and scant accountability.”).

42. See, e.g., Thomas Michael McDonnell, Sow What You Reap? Using Predator and Reaper Drones to Carry Out Assassinations or Targeted Killings of Suspected Islamic Terrorists, 44 Geo. Wash. Int’l L. Rev. 243 (2012); Hitomi Takemura, Unmanned Aerial Vehicles: Humanization from International Humanitarian Law, 32 Wis. Int’l L.J. 521 (2014); Julie Deisher, UN Concludes First Multilateral Meeting on Lethal Autonomous Weapons Systems, JURIST (May 18, 2014), https://www.jurist.org/news/2014/05/un-concludes-first-multilateral-meeting-on-lethal-autonomous-weapons-systems.

43. See generally Law of War Manual, supra note 35, ch. V (discussing LOAC principles and the conduct of hostilities).

44. See U.S. Dep’t of Def., supra note 6, at 11.

In 2019, the . . . JCO was established to lead, synchronize, and direct C-sUAS activities. In this role, the JCO will support the development and oversight of joint C-sUAS doctrine, requirements, materiel, training standards, and capabilities to establish joint solutions with a common architecture to address current and future emerging sUAS threats.

U.S. Dep’t of Def., supra note 6, at 11.

45. Eric Schmitt, Charlie Savage & Azmat Khan, Austin Orders U.S. Military to Step Up Efforts to Prevent Civilian Harm, N.Y. Times (Jan. 27, 2022), https://www.nytimes.com/2022/01/27/us/politics/us-airstrikes-rand-report.html.

46. Operational Law Handbook, supra note 35, ch. 5 (explaining that rules of engagement provide a framework that encompasses the left and right limits of national policy goals, mission requirements, and the law); Joint Chiefs of Staff, Instr. 3121.01B, Standing Rules of Engagement/Standing Rules for the Use of Force for U.S. Forces (13 June 2005).

47. Lieutenant General Charles Pede & Colonel Peter Hayden, The Eighteenth Gap: Preserving the Commander’s Legal Maneuver Space on “Battlefield Next,” Mil. Rev., Mar.-Apr. 2021, at 6, 19.

48. Yoram Dinstein, The Conduct Of Hostilities Under The Law Of International Armed Conflict 9 (3d ed. 2016); see also Declaration Renouncing the Use in Time of War of Explosive Projectiles Under 400 Grammes Weight, Dec. 11, 1868, 138 Consol. T.S. 297, https://ihl-databases.icrc.org/assets/treaties/130-IHL-6-EN.pdf (renouncing the use of specific weapons by weighing “the necessities of war” with “the requirements of humanity”).

49. See Cornthwaite, supra note 17 at 478 (analyzing how removing human operators from the equation changes the way that actors respond to UAS territorial incursions); United Nations Off. of Counterterrorism, Protecting Vulnerable Targets from Terrorist Attacks Involving Unmanned Aircraft Systems, UAS 6-7 (2022) (providing examples of the various forms of destruction that UAS are capable of causing).

50. Pede & Hayden, supra note 47, at 10.

51. See Operational Law Handbook, supra note 35, at 6.

A requirement that an attack reach a certain level of gravity before triggering a right of self-defense would make the use of force more rather than less likely . . . . [I]f States were required to wait until attacks reached a high level of gravity before responding with force, their eventual response would likely be much greater, making it more difficult to prevent disputes from escalating into full-scale military conflicts.

Id.

52. See Cherry & Rizzotti, supra note 40 (“There is nothing wrong with an operational commander limiting engagement authority for operational or policy reasons, but this must be done in a manner that does not imply nonexistent international law limitations.”).

53. Pede & Hayden, supra note 47, at 19 (analyzing how counterinsurgency and counterterrorism rules of engagement developed over time to tighten commanders legal maneuver space, and the need to preserve a commander’s ability to respond to real-time threats by adhering to the four basic principles of the law of armed conflict).