Ukraine Symposium – Are Civilians Reporting With Cell Phones Directly Participating in Hostilities?

As Russia continues to pummel electric grids and other critical infrastructure from the air, Ukraine is creatively developing methods to defend its skies. One new tool is “ePPO,” a new mobile application (“app”) that Ukrainian civilians can download on their cell phones to report the locations of incoming missiles or other air threats (see, e.g., here and here). It appears to be working. For instance, on 22 October, Ukrainian forces reportedly used data from the app to successfully shoot down a Kalibr cruise missile with a mobile air defense system. Such cruise missiles and explosive-laden unmanned aerial vehicles (commonly called “drones”) are among Russia’s key weapons for targeting critical infrastructure.

Use of the app raises the issue of whether Ukrainian civilians who download and use it to report enemy threats are “directly participating in hostilities” and, therefore, targetable by Russian forces under international humanitarian law (IHL). Moreover, if users qualify as direct participants, Russian forces need not consider any incidental harm to them in the proportionality analysis required before an attack or when assessing feasible precautions to avoid harming civilians. In this post, we examine whether, and if so when, the IHL rule regarding direct participation in hostilities applies to the use of the ePPO app. Our conclusion is that it does – sometimes. We also point out that directly participating in the hostilities, as such, does not violate IHL.

The ePPO App

The use of civilians to identify enemy movements is not new to warfare. In the Second World War, for example, the British employed volunteers as part of the Royal Observer Corps to identify incoming German aircraft and V1 and V2 rockets. Similarly, Somali civilians burned tires to report the approach of U.S. forces in advance of the “Black Hawk Down” raid. Nor is the practice even novel in this conflict. Prior to the renewal of Russia’s invasion in February of this year, for instance, videos posted to social media were used to confirm the staging movements of Russian troops and equipment (see, e.g., here). But the ePPO app makes such civilian involvement possible on an unprecedented scale and with unparalleled effectiveness.

The app is simple to use. An authenticated user opens it on their cell phone and toggles the applicable category from a menu of options: airplane, helicopter, drone, rocket, or explosion. The user then points the phone in the direction of the incoming object and presses a single button. Using its internal GPS and compass, the phone reports location and trajectory data to nearby air defense units, which use the information to supplement their targeting radars. The additional data is especially useful to defend against Iranian-made Shahed-136 drones, which are difficult to detect by radar due to their low altitude, small size, and largely non-metallic construction. However, their slow speed and loud signature make them vulnerable to detection by observers using the ePPO app.

A Ministry of Defense website contains easy-to-use instructions for the app. Downloaded more than 180,000 times since its release, ePPO is currently available only on Google Android devices. An Apple iOS version is forthcoming. One of the app’s developers has asserted that the “aim [is] to enlist ‘the entire population’ in helping to spot incoming attacks.” And in a statement by its Strategic Communications Department, the Office of the Commander-in-Chief of the Armed Forces of Ukraine noted, “Now every citizen of Ukraine can join the anti-missile and anti-aircraft defense of our skies.”

The Law of Direct Participation

The app’s intended use raises challenging questions regarding participation in the conflict by Ukrainian civilians. According to the 1977 Additional Protocol I to the 1949 Geneva Conventions, to which both Russia and Ukraine are Parties, civilians enjoy protection from direct or indiscriminate attacks (Article 51(2), (4)). When civilians are at risk during an attack on combatants or a military objective, an attacker must consider any harm likely to befall them in the requisite proportionality analysis (Article 51(5)(b)), which forbids attacks that are expected to cause injury or death that is excessive relative to the concrete and direct military advantage the attacker expects to gain by conducting the operation. Even when civilians are not being directly or indiscriminately attacked, and the anticipated military advantage is such that an attack may continue despite the likelihood of civilian harm, an attacker must consider alternative weapons, tactics, and weapons that might minimize civilian harm (Article 57). These rules reflect customary law (Customary IHL study, rules 1, 11, 14, 15).

Yet in an international armed conflict such as that occurring in Ukraine, these protections cease to apply to civilians “for such time as they take a direct part in hostilities” (Article 51(3); see also Article 13(3)) of Additional Protocol II for non-international armed conflict). The rule reflects customary law, and all current U.S. military manuals set forth similar guidance (DoD Law of War Manual § 5.8; Army/Marine Corps Commander’s Handbook, ¶ 2-2; Navy/Marine Corps/Coast Guard Commander’s Handbook, ¶ 5.4.3).

The exception’s significance, therefore, is that the loss of these protections means direct participants may be attacked (ICRC Commentary to AP I, ¶ 1942). Additionally, they are not treated as civilians when assessing whether an attack is indiscriminate, they do not factor into proportionality calculations, and there is no requirement to try to avoid harming them when attacking a military objective or lawfully targetable individuals. For example, if the app’s use amounts to direct participation, and assuming users can be identified, Russian forces can lawfully attack them and would not need to consider their presence if targeting nearby military objectives.

There are three determinative questions when applying the rule of direct participation – to whom does the rule apply, what is direct participation, and for what period does the rule apply? They are issues that animated the ICRC’s five-year project leading to the publication of its The Interpretive Guidance on the Notion of Direct Participation in Hostilities. As will be explained, the use of the ePPO app poses significant interpretive challenges when answering the third question.

To whom does the rule apply?

The rule only applies to civilians who participate on an individual, ad hoc, or unorganized basis, as opposed to combatants and members of organized armed groups (OAGs), who are targetable around the clock. Concerning the latter, the ICRC suggested in its Interpretive Guidance that only OAG members with a “continuous combat function,” such as those responsible for the group’s finances, are targetable in the same manner as combatants. According to this approach, members who do not meet this criterion should be treated like civilians, i.e., targetable only if and when directly participating in hostilities. The ICRC’s assertion has been challenged, however, and rightly so. (Dod Law of War Manual, § 5.8.2.1; Watkin; Schmitt, Harvard). Thus, for the purposes of our analysis, the use of the ePPO app issue is only relevant for civilians who are not members of an OAG.  But based on the app’s intended audience, most users are likely to fall into this category.

What is Direct Participation?

The next question is whether users to whom the rule applies are engaged in “direct participation in hostilities.” The Interpretive Guidance offers three “constitutive elements” of direct participation (at 46; see also Schmitt, NYU; Melzer). Although there is some disagreement over their scope (see NYU Forum), they amount to fair criteria with which we agree.

Threshold of Harm:  First, “[t]he act must be likely to adversely affect the military operations or military capacity of a party to an armed conflict or, alternatively, to inflict death, injury, or destruction on persons or objects protected against direct attack”  (Interpretive Guidance at 46; see also ICRC Commentary to AP I, ¶ 1944). There is no question that use of the app would satisfy this element.

To begin with, note that the action need only be likely to affect Russian operations. Direct participation does not require that an adverse effect occur. Thus, it would encompass situations in which the threat has already been reported to air defense units or where Ukrainian forces lack the means to attack it.

Moreover, the action must affect enemy military operations or capacity. Qualifying acts are not limited to those that kill or wound the enemy or damage or destroy military facilities and equipment. Rather, they need only adversely affect enemy operations or capacity, as in “providing or relaying information of immediate use in combat operations, such as acting as a…spotter or member of a ground observer corps or otherwise relaying information to be used to direct an [attack]” (DoD Law of War Manual, § 5.8.3.1). Given that the app’s primary purpose is to frustrate Russian attacks by enabling Ukrainian air defenses, its use undoubtedly satisfies this element.

Causation: The second element of direct participation is that “there must be a direct causal link between the act and the harm likely to result either from that act, or from a coordinated military operation of which that act constitutes an integral part” (Interpretive Guidance at 52). This element has been the source of significant disagreement.

As the ICRC has noted, “[f]or a specific act to qualify as ‘direct’ rather than ‘indirect’ participation in hostilities there must be a sufficiently close causal relation between the act and the resulting harm” (at 52). The question is how close is close enough. For instance, the ICRC suggested that “the assembly and storing of an improvised explosive device (IED) in a workshop” or serving as a voluntary human shield does not amount to direct participation (at 54, 56), assertions with which we and others disagree (Schmitt, Fleck Festschrift).

With respect to the app, the causal relationship is far from attenuated, even by the ICRC’s more demanding approach. As the Interpretive Guidance further clarifies, “where a specific act does not on its own directly cause the required threshold of harm, the requirement of direct causation would still be fulfilled where the act constitutes an integral part of a concrete and coordinated tactical operation that directly causes such harm (at 54–55).” During Ukraine’s first reported combat use, a Russian missile “invisible to radars” was targeted “a few seconds” after receiving data from the app. As this example illustrates, the causal relationship is necessarily direct because of the limited time available to engage a threat following identification.

Belligerent Nexus: Finally, to amount to direct participation, “the act must be specifically designed to directly cause the required threshold of harm in support of a party to the conflict and to the detriment of another” (Interpretive Guidance at 46). Satisfaction of this element is self-evident, for the app was designed as a countermeasure to Russian aerial attacks.

For What Period Does the Rule Apply?

Although answering the first two determinative questions is relatively clear-cut, doing so for the third is more challenging because the rule, and its resultant loss of protections, only applies “for such time” as direct participation endures. There are two facets of this question – the points at which direct participation begins and ends and the temporal scope of involvement (see generally Boothby).

Beginning and End of Participation: Obviously, protections are lost while a civilian uses the app. The more challenging questions are, does a user lose protection before that point, and for how long after the app has been used is the user still directly participating? For instance, does the period of direct participation begin when the app is downloaded? When the user is authenticated? When it is opened? Or used? Does it end when the report is made? When the app is closed? Only when it is deleted?

There is consensus that the period of direct participation includes preparatory measures (see ICRC Commentary to AP I, ¶ 1943). The ICRC, for instance, asserts that such measures “are of a specifically military nature and so closely linked to the subsequent execution of a specific hostile act that they already constitute an integral part of that act” (Interpretive Guidance at 65–66). Yet, agreement on what preparation encompasses is lacking.  The ICRC takes a narrow approach, explaining that “it could be said that preparatory measures aiming to carry out a specific hostile act qualify as direct participation in hostilities, whereas preparatory measures aiming to establish the general capacity to carry out unspecified hostile acts do not” (at 66; see also ICRC Commentary to AP I, ¶ 1943). Although we would leave it to the ICRC to apply this analysis, the standard would presumably not apply to civilians who are merely prepared to report, such as those who simply download the app or leave it running in the background in the off chance that a Russian system might be spotted. Instead, the individual must be at least actively looking for Russian threats, if not in the process of actually reporting one. This is because only in those cases are the individuals acting to carry out the specific act of reporting instead of merely being prepared to report.

It could be argued that the “for such time” period should be interpreted more broadly.  Yoram Dinstein, for instance, has suggested that “in demarcating the relevant time span in the course of which a civilian is directly taking part in hostilities, it is necessary to go as far as is reasonably required both ‘upstream’ and ‘downstream’ from the actual engagement” (Conduct of Hostilities at 176; see also Boothby). Although we agree with the approach in principle, we would reserve it for the (likely rare) case of an individual who downloads the app for the specific purpose of later setting out on a “mission” of spotting Russian systems. In such a scenario, we would not wait until the civilian has physically left to do so before characterizing him as a direct participant.

At the other end of the process, the ICRC opines that direct participation includes a return from where the action was executed if such movement is an “integral part” of the operation (Interpretive Guidance at 67; see also DoD Law of War Manual, § 5.8.4.1). By this approach, which we find reasonable, once the individual is no longer actively looking for Russian systems to report or has finished reporting one just seen, the period of direct participation would end.

The Revolving Door: The remaining question is how to characterize an individual who repeatedly engages in acts of direct participation. For instance, when can we say that a civilian who repeatedly identifies Russian systems is “directly participating?”

Focusing on the “for such time” restraint, the Interpretive Guidance suggests that it “necessarily entails that civilians lose and regain protection against direct attack in parallel with the intervals of their engagement in direct participation in hostilities” (at 70). In other words, civilians are entitled to protection between each act of participation. By this approach, users of the ePPO app would only forfeit their protections while actively searching for Russian systems or, should they spot one, reporting it. The ICRC claims “the ‘revolving door’ of civilian protection is an integral part, not a malfunction, of IHL” (at 70).

This claim has long been disputed, perhaps most memorably by the late Hays Parks. In our view, the revolving door is operationally unworkable and unfounded in law. Instead, as one of us has explained, “[t]he better approach is one whereby a civilian who directly participates in hostilities remains a valid military objective until he or she unambiguously opts out of hostilities through extended non-participation or an affirmative act of withdrawal. He or she may be attacked between episodes of participation” (Schmitt, Harvard at 38; see also DoD Law of War Manual, § 5.8.4.2). In a scenario where a civilian establishes a pattern of using the app, that individual would be targetable from the moment the first act began (see discussion above) until definitively and permanently ceasing participation.

But what if an individual decides to stop reporting but fails to signal this intent by, for example, deleting the app? Direct participation would end when the civilian decides to desist altogether. But in such a case (discussed by Schmitt, Harvard at 38), the direct participant bears the risk associated with any misunderstanding regarding status, not the adversary. After all, the direct participant had no right to engage in hostilities in the first place under IHL, and its rules are largely based on the premise that civilians do not participate directly in the armed conflict.

Lawfulness of Direct Participation

The preceding analysis raises the issue of whether Ukrainian civilians who use the app to report Russian systems are violating international law. In this regard, it is sometimes asserted that direct participation in hostilities violates international law. Indeed, some Guantanamo defendants were charged with violating the law of the war by attacking U.S. soldiers (see, e.g., Hicks charge sheet).

They are not. While civilians do not enjoy a privilege to engage in hostilities, engaging in activities that IHL does not otherwise prohibit is not a violation of that body of law. Thus, providing information that enables Ukrainian forces to damage or destroy military objectives, or even kill Russian soldiers, is lawful under international law.

This conclusion may not extend to domestic law. Whether a civilian may be tried for the act(s) which amounted to IHL direct participation depends on whether a prosecuting state has properly exercised prescriptive jurisdiction over the offense and is appropriately exercising adjudicatory jurisdiction over the individual. This depends on many factors, such as the extent of extraterritorial jurisdiction in the domestic legal system and the application of international human rights law; it is a subject well beyond the scope of this post.

Finally, we should also point out that there is some disagreement regarding the treatment of civilian direct participants upon capture, a complex issue that is also beyond this post’s scope. Suffice it to say that some experts argue that they are unlawful combatants who neither enjoy protection as prisoners of war under Geneva Convention III nor as civilians under Geneva Convention IV except in occupied territory (Dinstein, ILS). Instead, they are protected only by certain minimal safeguards reflected in Article 75 of Additional Protocol I. This is, broadly speaking, the position adopted by the United States (DoD Law of War Manual, § 10.3). By contrast, the ICRC and many other experts suggest that they continue to qualify as detained civilians entitled to the relevant protections of Geneva Convention IV, a position with which at least one of us (Schmitt) agrees (see discussion in Pejic).

Conclusion

Operationally, the development and distribution of the ePPO app make great sense. It has already resulted in successful defensive operations against Russian attacks. And those employing the app to report Russian systems are violating no rule of international law.

But it must be understood that one consequence of Ukraine instituting a modern-day “observer corps” is that the civilian volunteers involved lose the essential protections against attacks and their effects that they would otherwise enjoy. Moreover, depending on the approach taken with the revolving door issue, they may lose that protection for an extended period. This not only places them at risk but could even render Russian attacks lawful that would otherwise be precluded through operation of the proportionality and feasible precaution rules.

Accordingly, suggestions that the ePPO could be used across the entire civilian population should raise particular concerns. Such risks may well be worth taking, particularly when facing an enemy that has shown nothing but disregard for the civilian population. However, Ukraine should assess the practice with eyes wide open, fully sensitive to the practical consequences of the IHL on point.

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Michael N. Schmitt is the G. Norman Lieber Distinguished Scholar at the United States Military Academy at West Point. He is also Professor of Public International Law at the University of Reading; Professor Emeritus and Charles H. Stockton Distinguished Scholar-in-Residence at the United States Naval War College; and Strauss Center Distinguished Scholar and Visiting Professor of Law at the University of Texas.

Major William C. Biggerstaff is a military professor at the Stockton Center for International Law at the U.S. Naval War College, where he co-teaches a course on the Law of Armed Conflict.

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