March 26, 2023

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The Russian Intercept of the U.S. Reaper and International Law

The Russian Intercept of the U.S. Reaper and International Law

On March 14, two Russian Su-27 “Flanker” fighters intercepted a U.S. Air Force MQ-9 “Reaper” in international airspace over the Black Sea. The remotely-piloted aircraft (RPA) was unarmed and conducting an ISR (intelligence, surveillance, and reconnaissance) mission. The intercept reportedly lasted 30-40 minutes.

According to U.S. European Command (EUCOM), the Flankers dumped fuel on the Reaper and repeatedly flew in front of it. The dumping of fuel was likely meant to interfere with its sensors, while “zooming” in front of an aircraft can create dangerous “jet wash.” Eventually, one of the Flankers hit a propeller on the Reaper (denied by Russia), which led to the decision by U.S. forces to ditch it in international waters. The Russian aircraft may have been damaged but landed safely.

EUCOM labeled the Russian intercept “reckless and unprofessional,” demonstrating a lack of competence on the part of the pilots. Department of Defense spokesperson, Brigadier General Patrick Ryder, echoed that characterization, adding that the intercept was “unsafe.” Ned Price of the State Department went furthest, calling the Russian actions a “brazen violation of international law” and noting that the United States was “conveying in strong terms our objections.” He stopped short, however, of stating what law had been violated by Russia’s actions, which I will turn to below. As will be explained, I see two possibilities, failure to exercise due regard and the unlawful use of force.

There have been prior incidents resembling the Reaper downing, most recently the 2019 Iranian shoot-down of a US Navy RQ 4A Triton in the Persian Gulf. And during the Cold War era, the “Black Sea Bumping Incident” involving a U.S. Navy cruiser and destroyer on the one hand and two Soviet Navy frigates on the other drew global attention; it continues to be studied by students at the U.S. Naval War College.

But the Reaper downing is different, for it took place during an international armed conflict and involved neutral and belligerent platforms. In light of that context, the U.S. contention that the intercept was unlawful merits examination. I first explain why, despite Russian contentions to the contrary, the U.S. operations should themselves be understood as lawful. I then examine Russia’s actions, asking whether they violated any rule of international law and, if so, whether any legal justification exists. Finally, based on these assessments, I conclude with a brief assessment of international law response options available to the United States.

The US ISR Mission

According to EUCOM, “U.S. Air Forces in Europe – Air Forces Africa routinely fly aircraft throughout Europe over sovereign territory and throughout international airspace in coordination with applicable host nation and international laws. In order to bolster collective European defense and security, these missions support Allied, partner, and U.S. national objectives.”

To assess this particular operation, it is necessary to consider the Reaper’s location and mission. At the time of the intercept, it was flying approximately 75 miles southwest of the Crimean Peninsula, Ukrainian territory that Russian unlawfully claims to have annexed in 2014. In this regard, the Russian Ambassador to the United States, Anatoly Antonov, declared, “American aircraft have no business being near the Russian border.” But even if Crimea was Russian territory (which it is not), the incident occurred over the “high seas” and, therefore, international airspace.

It is universally accepted that aircraft, including military platforms, enjoy the right of high seas overflight. This right is codified in Article 2 of the 1958 Convention on the High Seas, to which the United States is Party, and Article 87(1)(b) of the 1982 Law of Sea Convention (UNCLOS), to which it is not. Russia is Party to both. Despite UNCLOS non-Party status, the United States recognizes its navigational provisions as reflecting customary international law. Indeed, the DoD Law of War Manual and the U.S. Navy/Coast Guard/Marine Corps Commander’s Handbook on the Law of Naval Operations both emphasize the right of military aircraft to conduct operations over the high seas (§ and § 2.6.3, respectively).

As to the mission, Ambassador Antonov correctly noted that the Reaper is “a multipurpose [drone], with strike capabilities of up to a 1,700 kilograms explosive payload.” Yet as he acknowledged, the platforms are also used for reconnaissance. Indeed, this was a routine ISR mission, which Russia surely understood, and by which it could not have been surprised.. Espionage, as such, violates no rule of international law. And with respect to espionage, it must be pointed out that the United States has been engaging in ISR operations in the Black sea for decades. Thus, it is not necessarily the case that this mission was to gather information harmful to Russia in its conflict with Ukraine.

But there is some question as to whether the law of neutrality is a fly in the ointment. If the intelligence gathered by the drone was meant to be shared with Ukraine for use in military operations, some may understand the mission to have been an “internationally wrongful act” (Articles on State Responsibility, art. 2) in the form of a neutrality law violation. For example, the DoD Law of War Manual states that, during an international armed conflict, “[t]he principal duties of a neutral State are to abstain from any participation in the conflict and to be impartial in conduct towards contending parties” (§15.3.2). Intelligence sharing with one of the belligerents can certainly run afoul of this principle.

Yet, there is an ongoing debate over whether this principle applies fully in the Ukraine conflict (see here, here, here, and here). Some observers, including me, support the notion of “qualified neutrality,” by which the rules requiring impartiality are relaxed when one State is the clear aggressor. This is most apparent in cases of UN Security Council authorization of enforcement action against a State (as in the 1990-91 Gulf War, UNSC Res.678 (1990)). But it can extend to situations in which the aggressor is obvious.

The United States supports the qualified neutrality approach, which is sometimes labeled non-belligerency (DoD Law of War Manual, § 15.2.2). By it, assistance to Ukraine in the form of intelligence sharing is lawful, just as collective-self defense of Ukraine would be lawful, although it raises the separate question of the point at which assistance could constitute an indirect use of force or render the United States a Party to the conflict (see my thoughts here).

Both views are reasonable and enjoy ample support in State practice and doctrine. Yet, it is only if the intelligence the Reaper was gathering was intended to be shared with Ukraine for military use in the armed conflict, and only with the strict application of neutrality law, that the U.S. operation could have been unlawful. The better position is that the operation complied with international law.

The Russian Intercept

 As Brigadier General Ryder noted in his press briefing, aircraft intercepts are common but typically conducted safely. National Security Council spokesperson John Kirby also pointed out that there had been Russian intercepts in recent weeks, albeit not as unsafely. That the Flankers intercepted the Reaper does not alone violate international law. Indeed, they enjoyed the same right of overflight of international waters as the Reaper. But this is not the end of the analysis.

International law prohibits one State’s threat or use of force against another (UN Charter, art. 2(4) and customary law). However, while there is no question that the Russian actions endangered the Reaper, it seems that the intent was to discourage its flight, not to down it. Along these lines, State Department spokesperson Price declined to speculate on the Russian motivations for the intercept. Without knowing more about Russian intentions, can the action nevertheless qualify as a use of force?

There is an ongoing discussion among international law experts as to whether “intent” is required for a breach of the prohibition. Marko Milanovic dealt with the subject of whether a mistake of fact can preclude wrongfulness in his three-part EJIL:Talk! series. He noted that only the United States had invoked the doctrine in the jus ad bellum context, and, even then, “it did not attract widespread acceptance” (the shootdown of Iran Air 655 1988 by USS Vincennes). Milanovic concluded that while “one cannot categorically exclude that such a rule could exist…it seems unlikely that it does.” But in his comprehensive study of armed attacks in the law of self-defense, Tom Ruys finds significant support for the requirement of “animus aggressionis” (§ 3.2.2). Although the issue of intent remains unsettled in international law, it is easier to make the use of force case in situations of recklessness, as seems to be the case in the Russian intercept, than those involving a mistake of fact, even a reasonable one. Assuming that the acts were indeed reckless but unintentional, an assertion that the Russian action amounted to a use of force is colorable but not unassailable.

The more straightforward characterization of the Russian actions is as a violation of the international law obligation of “due regard.” The requirement, which was presaged in Article 2 of the High Seas Convention, is codified in UNCLOS, Article 87(2): high seas “freedoms shall be exercised by all States with due regard for the interests of other States in their exercise of the freedom of the high seas.” The customary character of the provision is reflected in the Commander’s Handbook acknowledgment that “the aircraft of all States are free to operate in international airspace with due regard for the safety of other aircraft and without interference by other States” (§ 1.9; see also DoD Law of War Manual § As an aside, it merits mention that the Chicago Convention‘s due regard obligation does not apply in this situation because the instrument does not govern “State aircraft” (art. 3(d)).

Note that mere interference with lawful flight operations suffices to breach the obligation. But even where a State’s aircraft is responding to a breach of international law (as in refusal to depart national airspace following unconsented-to entry), there are common techniques for conducting an interception to dissuade the offending aircraft from persisting. These include “zooming” past the offending aircraft and hitting afterburners while doing so; flying close enough to it to cause the pilot concern either by dashing at or slowly turning into it; and creating jet wash across which the offending aircraft would have to fly, thereby making it difficult to control (as in this case). The point is that an aerial intercept must be one of very controlled and cautious escalation. The fact that one of the Flankers hit the Reaper demonstrates that it was flying without due regard. It is, therefore, difficult to avoid the conclusion that the interception, or at least the method used to conduct it, was an internationally wrongful act.

Possible justifications for the Russian actions

There are three possible justifications for the Russian action, none of which hold up under examination. The first is self-defense under Article 51 of the UN Charter and customary law. Clearly, the U.S. operation does not qualify, standing alone, as an “armed attack,” the threshold at which the right to engage in a defensive use of force (and any lesser action) is triggered. This being so, the only possible way self-defense could apply would be to treat the Reaper mission as an integral component of Ukrainian attacks on Russian forces. Under the law of State responsibility, “where several States are responsible for the same internationally wrongful act, the responsibility of each State may be invoked in relation to that act (Articles on State Responsibility (ASR), art. 47(1)). The glaring problem with this argument is that the operation in question must be unlawful. But Ukrainian operations are lawful exercises of the right of self-defense. It is well established that under the law of State responsibility, there is no self-defense against a lawful exercise of self-defense.

Even if that were not the case, it is doubtful that the Russians knew what the Reaper was collecting and how it would be used by Ukrainian forces, if at all. Moreover, any assistance must be integral to the operation in question for an operation to be considered joint as a matter of law; more than mere aid and assistance (see ASR, art. 16) is required. Again, there is no indication that was the case here.

The second possible justification is self-help in the face of a neutrality law violation. As noted above, I believe there has been no such violation. But assuming for the sake of analysis that the Reaper flight violated the United States’ obligations of abstention and impartiality, was Russia entitled to take measures to end the violation?

Neutrality law does include a right of self-help for aggrieved belligerents, including the right to engage in forcible actions. But that right applies only to situations where the opposing belligerent is violating its neutrality law obligations.  The DoD Law of War Manual explains, “[s]hould the neutral State be unable, or fail for any reason, to prevent violations of its neutrality by the forces of one belligerent entering or passing through its territory (including its lands, waters, and airspace), the other belligerent State may be justified in attacking the enemy forces on the neutral State’s territory” (§ 15.4.2). Here, it is the neutral State that is alleged to have engaged in an internationally wrongful act.

Nevertheless, if, and only if, the Reaper operation violated neutrality law (which it did not), Russia would be entitled to take countermeasures – acts or omissions that would be unlawful but for the fact that they are designed to put an end to another State’s unlawful action or secure any reparations due for harm suffered (ASR, art. 49). This would preclude the wrongfulness of Russia’s breach of its due regard obligation. Yet, because countermeasures may not be forcible (ASR, art. 50(1)(a)), the Russian response was unlawful if, as discussed above, it amounted to a use of force. To qualify as a lawful countermeasure, then, the U.S. operation must have violated international law (it did not), and Russia’s interception and downing must not have constituted a use of force (it might have).

The third justification is the trickiest. During an armed conflict, belligerents may create “operational zones” to prevent interference with their operations. In fact, this is the claimed justification for the Russian intercept. According to Ambassador Antonov, the Reaper “was moving deliberately and provocatively towards the Russian territory with its transponders turned off [and] violated the boundaries of the temporary airspace regime established for the special military operation, which was communicated to all the concerned users of international airspace in accordance with international norms.” Because the United States is the “victim” State in the incident, it is appropriate to apply its own interpretation of the law governing operational zones to any characterization it might offer of the incident.

United States legal doctrine recognizes operational zones for both aerial and naval operations. For instance, the DoD Law of War Manual (§ 14.7) provides,

During armed conflict, States may establish airspace zones and associated procedures intended to prohibit aircraft from entering or flying in designated areas, including areas in international airspace. Such zones may be established for a variety of purposes, including to decrease the risk of inadvertent attack of civil or neutral aircraft, to control the scope of the conflict, or to enhance the predictability and effectiveness of ongoing operations.

The United States is of the view that a belligerent may establish such a zone in the “immediate area or vicinity” of naval operations “to ensure the security of its forces and its right to conduct hostilities without interference from neutrals” (id.). Some other States active in maritime operations expressly agree (see, e.g., U.K. Law of Armed Conflict Manual, §13.8; Australia, Law of Armed Conflict, ¶ 6.16; Germany, Commander’s Handbook, ¶ 303). The “immediate” area or vicinity “is that area within which hostilities are taking place, or belligerent State forces are actually operating” (§ 13.8.1). As to the consequence of violation, the DoD Manual cautions that “[a]ny transmission to an opposing belligerent State of information concerning military operations or military forces is inconsistent with the neutral State’s duties of abstention and impartiality and renders the neutral State’s vessel or aircraft making such a communication liable to capture or destruction (§ 13.8.2; see also Commander’s Handbook, § 7.8). This would apply if the Reaper was transmitting intelligence to Ukrainian forces.

In the Reaper downing incident, therefore, the key questions are whether there were ongoing Russian naval operations in the area and whether the Reaper was engaged in operations placing them at risk. If so, by the U.S. approach, the intercept arguably would be lawful. But, beyond that area, as explained by Professor Pete Pedrozo in his comprehensive survey of the Ukraine conflict at sea, “Russia may only establish temporary warning areas to advise ships and aircraft that it is conducting activities at sea that may pose a hazard to navigation and overflight.” Given what we know, the latter scenario is the more likely one.

One red herring merits discussion. If the Reaper was supporting Ukrainian operations, it would seem to qualify as a “military objective” (see Additional Protocol I, art. 52(2), which reflects customary law). But the United States and Russia are (probably, see here) not involved in an international armed conflict to which IHL applies. And even if the Russian action triggered one due to the occurrence of hostilities between the U.S. and Russian armed forces, as explained above, there is no self-defense basis under the jus ad bellum for Russia taking the action.

Possible U.S. Responses

U.S. responses to the incident under international law are relatively limited. To begin with, even if the Russian intercept rose to the level of a use of force, it was not at the armed attack level, which, according to the International Court of Justice and the majority view among States, is the “most grave form” of the use of force (Paramilitary Activities, ¶ 191). Admittedly, the United States is of the view that there is no “gap” between the use of force and armed attack thresholds (DoD Law of War Manual, § However, even if the incident is characterized as an armed attack, it is over. As a result, justifying a forcible (or any other) response on the basis of self-defense would not satisfy the temporal aspect of self-defense’s “necessity” criterion (Paramilitary Activities, ¶ 194), at least not unless the downing was but the first in an ongoing campaign at that level. Responsive uses of force that are not necessary at the time are mere retaliation, not self-defense.

The more viable option is the taking of countermeasures. While countermeasures are not permissible once an incident is over, they are to secure any reparations that might be due (ASR, arts. 31, 34). If the Russian action qualifies as an internationally wrongful act, which, as explained above, it likely does, the United States may engage in proportionate, non-forcible countermeasures until Russia provides reparations for the downed Reaper.

In this regard, it is important to note that countermeasures need not be in-kind. For instance, the United States could mount cyber operations that violate Russian sovereignty until Russia makes good the loss it has suffered, at least so long as those operations have a reasonable chance of succeeding at inducing Russia to pay. Another possibility would be to close U.S. territorial waters to the transit of certain Russian-flagged vessels, such as warships.

Finally, the United States may engage in acts of “retorsion,” a term that denotes unfriendly but lawful actions. The paradigmatic example in the context of the Ukraine conflict is economic sanctions.

Concluding Thoughts

Legal conclusions are fact-dependent, and many facts needed to assess the Reaper downing are unavailable. They are likely to remain so due to their classified nature. Nevertheless, based on those appearing in open sources, the Russian operation almost certainly violated the international law obligation of due regard and, perhaps, the prohibition on using force. And there would appear to be no definitive legal justification for its action. It would follow that the United States is entitled to reparations for the loss of the Reaper and enjoys the right to take countermeasures to secure them. For practical reasons, however, this is an unlikely scenario. Instead, any responses are likely to lie in the realm of retorsion – as has been the case throughout the latest phase of Russia’s aggression against Ukraine, during which the Biden administration has made great efforts to avoid escalation even while offering steadfast support to Ukraine. The same is likely to be its approach here.

IMAGE: An MQ-9 Reaper remotely piloted aircraft (RPA) is prepared for training mission. A Russian fighter jet had collided with an MQ-9 Reaper drone, causing the unmanned aircraft to crash into the Black Sea, on March 14, 2023. (Photo by Isaac Brekken/Getty Images)