Brig. Gen. (ret.) David Wallace, Col. Shane Reeves, and Maj. Trent Powell [*]
[Full text of this Article in PDF is available at this link]
Civilians contribute to nearly every war effort, and always have. Throughout history, non-military personnel have supplied logistic, economic, administrative, and political support to parties in armed conflicts. When civilian contributions are indirect and away from battlefields, there has historically been little concern about those participants jeopardizing their protected status under the Law of Armed Conflict (LOAC). More recently, however, belligerents have begun using civilians in capacities that involve greater or more direct participation in hostilities. Some commentators have referred to this phenomenon as the “civilianization of armed conflict.”
Prior studies have identified at least four developments that contribute to civilians’ growing participation in hostilities: (1) the privatization of warfare, (2) a long-term shift toward non-international versus international armed conflicts, (3) the greater use of civilian proxies by States, and (4) the expanding role civilians play in high-technology warfare. At the individual level, the consequences of civilians directly participating in hostilities are significant and several. Such civilians lose their immunity from attack during the period of time that they take a direct part in hostilities. Additionally, civilians who directly participate in hostilities are subject to prosecution and punishment to the extent that their activities, their membership, or the harm they caused is criminal under domestic law.
In the context of the LOAC, the protection of civilians is one of its underlying and primary goals. The civilian population and individual civilians enjoy general protections against dangers arising from military operations. In that regard, the LOAC explicitly provides that the civilian population, as well as individual civilians, shall not be the object of an attack and that civilians retain their protections against attack unless and for such time as they take a direct part in an attack. Critically important to the protection of civilians is the rule against taking direct part in hostilities. In other words, the protections afforded individual civilians during an armed conflict is subject to an overriding condition, i.e., that they refrain from all hostile acts. This principle is well grounded in both international treaties, including Additional Protocols I and II, and through State practice where it has developed into a generally accepted norm of customary international law applicable to both international and non-international armed conflicts.
Despite its seeming simplicity and straightforwardness, the notion of taking a direct part in hostilities—which is inextricably linked to the core LOAC principle of distinction—is one of the most vexing provisions under the LOAC. Its application raises many challenging and thought-provoking issues. For example, who precisely is considered a civilian under the law of armed conflict? What conduct amounts to taking a direct versus indirect part in hostilities? What does “for such time” and “direct part” mean in practice? At what point does taking a direct part in hostilities begin and end?
In some instances, it is abundantly clear when a civilian is taking a direct part in hostilities. For instance, a civilian that engages an enemy soldier with a weapon during an international armed conflict is taking a direct part in hostilities and loses his or her protection under the LOAC. Other circumstances are less obvious, including a situation where a civilian drives an ammunition vehicle during an armed conflict in support of a party to the conflict. The LOAC supports the proposition that the vehicle is a targetable military objective, but a question remains whether the civilian driver is independently targetable for his or her actions. Did the driver lose the LOAC protections during the period he or she was operating the vehicle?
As complicated as this question may seem, the notion of taking a direct part in hostilities presents even greater difficulties when applied to cyber operations. LOAC applies to cyber operations during armed conflicts, and therefore, as Michael Schmitt notes, “[t]hose who qualify as combatants enjoy the belligerent right of engaging in hostilities; no reason exists to distinguish cyber from kinetic military operations in this regard.” Similar to kinetic situations, there are cyber actions that are obviously taking a direct part in hostilities and others that are not so clear. For example, if a civilian conducts a Distributed Denial of Service (DDoS) operation against an enemy’s external computer systems during an armed conflict, that civilian is taking a direct part in hostilities and becomes targetable while he or she is engaged in the DDoS attack. By contrast, it is far less clear whether a civilian is taking a direct part in hostilities when he or she develops malware and provides it to others knowing that the malicious software will be used to attack an enemy at some unknown time.
Determining when a civilian cyber operator in armed conflict is directly participating in hostilities is often even more challenging than the two examples provided above. In most circumstances, the battlefield status of the individual remains unclear. Yet, as cyber space has become a decisive battleground, it is important to provide clarity in how the LOAC applies in this domain as legal ambiguity “in no way relieves commanders or the lawyers advising them” of their obligations. Therefore, this article attempts to address this issue by first providing a short background section on the dangerous trend towards increased civilian participation on modern battlefields. An overview of the legal concept “direct participation in hostilities” follows. The article then considers Tallinn Manual 2.0 on the International Law Applicable to Cyber Operations (Tallinn Manual 2.0) rules and commentary as this resource pointedly addresses the notion of taking a direct part in hostilities in cyber operations. Finally, the article concludes by outlining several important fault lines highlighted by the group of experts behind Tallinn Manual 2.0 in hopes of strengthening “the implementation of the principle of distinction” and, consequently, ensuring greater accountability in warfare.
[*] Brig. Gen. (Ret.) David Wallace is a Professor Emeritus, Department of Law, United States Military Academy at West Point, New York. Col. Shane Reeves is a Professor and Head, Department of Law, United States Military Academy at West Point, New York. Maj. Trent Powell is an Army judge advocate currently assigned as a LL.M. candidate at the University of Virginia Law School. The opinions, conclusions, and recommendations in this article do not necessarily reflect the views of the Department of Defense, the United States Army, or the United States Military Academy. The authors thank the editors of the Harvard National Security Journal for their assistance, including Sam Cohen, Philip Chertoff, Jon DeWitt, Mikhaila Fogel, Christopher Gorman, David Hogan, Annie Kapnick, Matthew Kahn, Anastasia Pyirinis, Sam Rebo, Diego Negron-Reichard, Kathryn Reed, and Avery Smith.
 See, e.g., Shane R. Reeves & Ronald T.P. Alcala, Five Legal Takeaways from the Syrian War, Harv. Nat’l Sec. J. Online, 3–4 (Sept. 30, 2019), https://harvardnsj.org/wp-content/uploads/sites/13/2020/04/Reeves-Alcala_Five-Legal-Takeaways-from-the-Syrian-War_FINAL.pdf [https://perma.cc/2DPL-GAEK] (last visited Nov. 14, 2020) (discussing the trend towards using private military contractors for offensive operations).
 See, e.g., Andreas Wegner & Simon J.A. Mason, The Civilianization of Armed Conflict: Trends and Implications, 90 Int’l Rev. Red Cross 835, 836 (2008) (cataloguing factors that contribute to civilian-participants’ changing role in hostilities).
 Most notably, recruiting and using private military and security companies to undertake certain traditional functions performed by members of armed forces illustrates this concept of “privatization of warfare.”
 Wenger & Mason, supra note 2, at 835–52.
 Protocol Additional to the Geneva Conventions of 12 August 1949, and Relating to the Protection of Victims of International Armed Conflicts (Protocol I), art. 51(3), adopted June 8, 1977, 1125 U.N.T.S 3 [hereinafter AP I] (“Civilians shall enjoy the protection afforded by this Section, unless and for such time as they take a direct part in hostilities.”).
 Int’l Comm. of the Red Cross, Interpretive guidance on the Notion of Direct Participation in Hostilities Under International Humanitarian Law (Nils Melzer ed., 2009), 83–85, available at https://www.icrc.org/eng/assets/files/other/icrc-002-0990.pdf [https://perma.cc/63A5-FCBJ] (last visited Oct. 28, 2020) [hereinafter ICRC Interpretive Guidance].
 AP I, supra note 5, art. 51(2)–(3).
 Id. art. 51(3).
 See Yves Sandoz et al., Commentary on the Additional Protocols of 8 July 1977 to the Geneva Conventions of 12 August 1949 ¶ 1942–45 (1987) [hereinafter Commentary].
 AP I, supra note 5, art. 51(3); Protocol Additional to the Geneva Conventions of 12 August 1949, and Relating to the Protection of Victims of International Armed Conflicts (Protocol II), art. 13(3), adopted June 8, 1977, 1125 U.N.T.S 609 [hereinafter AP II].
 Jean-Marie Henckaerts & Louise Doswald-Beck, Customary International Humanitarian law: Volume I: Rules, 19–24 (2005) [hereinafter Rules]. But see U.S. Dep’t of Def., Law of War Manual §5.9.1-.2, at 236–37 (2016) [hereinafter DoD Law of War Manual] (noting that the United States does not agree these rules as a matter of customary international law).
 Gary D. Solis, The Law of Armed Conflict: International Humanitarian Law in War 693 (2d ed. 2016).
 See, e.g., DoD Law of War Manual, supra note 11, § 126.96.36.199 (listing examples where an individual is taking a direct part in hostilities). See also Stephen Pomper, Toward a Limited Consensus on the Loss of Civilian Immunity in Non-International Armed Conflict: Making Progress Through PRactice, 88 Int’l L. Stud. 181, 190 (2012) (“The period during which an individual can be deemed to be directly participating in hostilities is generally viewed to include the period during which that individual is deploying to and returning from the hostile act . . . .”).
 See, e.g., DoD Law of War Manual, supra note 11, § 188.8.131.52 (listing examples where an individual is not taking a direct part in hostilities).
 See Tallinn Manual 2.0 on the International Law Applicable to Cyber Operations 375 (Michael N. Schmitt & Liis Vihul eds., 2017) [hereinafter Tallinn Manual 2.0]. In 2017, states including Cuba and, reportedly Russia and China, backtracked on earlier recognition that the law of armed conflict applied in cyberspace. See Michael Schmitt & Liis Vihul, International Cyber Law Politicized: The UN GGE’s Failure to Advance Cyber Norms, Just Sec. (June 30, 2017), https://www.justsecurity.org/42768/international-cyber-law-politicized-gges-failure-advance-cyber-norms/ [https://perma.cc/3QGA-AX2S]. However, the vast majority of the international community agrees that “international law applies to State-conducted or State-sponsored activities in cyberspace” and believe this is a settled question. See, e.g., DoD Law of War Manual, supra note 11, § 16.1; Gary P. Corn, “Cyber National Security: Navigating Gray-Zone Challenges in and through Cyberspace,” in Lieber Series Vol. 1 Complex Battlespaces: The Law of Armed Conflict and the Dynamics of Modern Warfare 399–400 (Ford & Williams 2019).
 Michael N. Schmitt, Cyber Operations and the Jus in Bello: Key Issues, 87 Int’l L. Stud. 89, 97 (2011).
 Tallinn Manual 2.0, supra note 15, at 565 (A Distributed Denial of Service (DDoS) is a “technique that employs multiple computing devices (e.g., computers or smartphones), such as the bots of a ‘botnet’…, to cause a ‘denial of service’…to a single or multiple targets.”).
 Id. at 430.
 Schmitt, supra note 15, at 97.
 “On a battlefield no one is without some status.” Solis, supra note 12, at 187. This “battlefield status” determines the associated rights, duties, and responsibilities of both warfare participants and other persons not engaged in the hostilities. See Sean Watts, Combatant Status and Computer Network Attack, 50 Va. J. Int’l L. 392, 414–14 (2010).
 See e.g., Summary of the 2018 National Defense Strategy of the United States of America, 3 available at https://dod.defense.gov/Portals/1/Documents/pubs/2018-National-Defense-Strategy-Summary.pdf [https://perma.cc/4PJX-SYKF] (last visited Oct. 28, 2020) (“Today, every domain is contested—air, land, sea, space, and cyberspace.”).
 Corn, supra note 15, at 365.
 See generally Tallinn Manual 2.0, supra note 15.
 ICRC Interpretive Guidance, supra note 6, at 5.