Leaflets dropped 45 minutes before airstrikes targeting ISIL oil tankers. Image credit: US Defense Department

Editor’s Note: This is the second in a two-part post discussing how the law of war applies to airstrikes against oil tanker trucks. You can read Part One here.

In Part 1 of this post, I set out the facts, as they have been revealed in open sources, of recent airstrikes against tanker trucks in ISIL territory and discussed under what circumstances the tankers can be deemed military objectives under customary international humanitarian law (IHL). This post will focus on the rationale behind the dropping of leaflets in advance of the strikes. It will also address the civilian status of the truck drivers and how their actual or hypothetical actions might shade this analysis.

So Why Drop Leaflets?

Under IHL, and as a corollary to the principle of distinction, commanders are under an obligation to take precautions on a continuous basis to avoid harm to civilians or civilian objects. When there is a choice of means and methods for conducting a particular attack, the parties must choose a course of conduct that will minimize incidental injury to civilians. And they must give the civilian population advance warning of attacks, unless not permitted by the circumstances (e.g., when the element of surprise is paramount or if notice would endanger the attacking troops). This is where the leaflets come in.

The relevant rules state:

  • Rule 15: In the conduct of military operations, constant care must be taken to spare the civilian population, civilians and civilian objects. All feasible precautions must be taken to avoid, and in any event to minimize, incidental loss of civilian life, injury to civilians and damage to civilian objects.
  • Rule 17: Each party to the conflict must take all feasible precautions in the choice of means and methods of warfare with a view to avoiding, and in any event to minimizing, incidental loss of civilian life, injury to civilians and damage to civilian objects.
  • Rule 20: Each party to the conflict must give effective advance warning of attacks which may affect the civilian population, unless circumstances do not permit.

These rules are derived from Article 57 of Additional Protocol I (API) to the 1949 Geneva Conventions, which says that parties to a conflict shall “take all reasonable precautions to avoid losses of civilian lives and damage to civilian objects” in accordance with their rights and duties under IHL. (Remember that API governs conduct in international armed conflicts — generally, those between states — so it isn’t strictly binding in the Syria context.) API, in turn, no doubt drew inspiration from Article 19 of the Lieber Code, which governed the conduct of Union Forces during the US Civil War. With similar caveats on practicability, the Code required military commanders to

inform the enemy of their intention to bombard a place, so that the noncombatants, and especially the women and children, may be removed before the bombardment commences.

There is no analog on precautions in Additional Protocol II, which governs contemporary non-international armed conflicts (NIACs) — those between states and non-state actors or among non-state actors. But the International Committee of the Red Cross (ICRC) considers the rule on precautions to be inherent to the principle of distinction, which applies regardless of conflict classification. So does the UN General Assembly, as expressed in Resolution 2675 (1970).

Given these obligations, leafletting has been used in prior military operations to warn the civilian population of an impending attack on a nearby military objective. Some states use other techniques. Israel has several, including the use of phone calls and text messages, as well as the more controversial “roof knocks” (i.e., dropping a minimal-impact munition on a building before destroying it to allow the civilian population time to vacate the premises). During the humanitarian intervention in Kosovo in 1998, there was some question as to whether NATO troops had adequately warned the civilian staff of a Serbian television station that was later destroyed, although blame was also laid on the Yugoslav authorities for not evacuating the building when it became known that it was on NATO’s target list.

This latter incident reveals that the rule on precautions applies to both the attacking and the defending party. In particular, IHL places a duty on all parties to avoid collocating military objectives near civilians or civilian objects:

  • Rule 23: Each party to the conflict must, to the extent feasible, avoid locating military objectives within or near densely populated areas.
  • Rule 24: Each party to the conflict must, to the extent feasible, remove civilian persons and objects under its control from the vicinity of military objectives.

Derived from Article 58(a) of API, these rules place obligations on the defending party to protect its own civilian population from the effects of armed conflict.

The dropping of leaflets brought the coalition into compliance with the duty to take precautions, not least because — notwithstanding the precision-guided assets at the coalition’s disposal — targeting the trailer while avoiding the cab would be near impossible, given the trucks’ combustible contents.

What if the Drivers Were Killed in the Strikes?

Statements about the strikes on the tankers indicate that the truck drivers are considered to be civilians. Under IHL, civilians are defined in contradistinction to combatants:

  • Rule 5: Civilians are persons who are not members of the armed forces. The civilian population comprises all persons who are civilians.

Combatants, by contrast, are defined as members of the armed forces of a party to the conflict:

  • Rule 3: All members of the armed forces of a party to the conflict are combatants, except medical and religious personnel.
  • Rule 4: The armed forces of a party to the conflict consist of all organized armed forces, groups and units which are under a command responsible to that party for the conduct of its subordinates.

Note that the law of armed conflict does not recognize the concept of “combatant” — someone entitled to prisoner-of-war status upon capture — when it comes to non-state actors engaged in NIACs. That said, and not surprisingly, the various IHL provisions addressed to NIACs do contemplate the existence of non-state armed actors as distinct from civilians.

Assume for the moment a counterfactual: that some truck drivers were killed in the strikes. Civilians who are present in the vicinity of military objectives (e.g., civilian workers in a munitions plant) may be immune from being directly targeted, but they are not necessarily protected against attacks directed at those objectives.

However, the presence of civilians near a military objective fundamentally alters targeting decisions because it requires a consideration of the principle of proportionality in designing and implementing the attack:

  • Rule 14: Launching an attack which may be expected to cause incidental loss of civilian life, injury to civilians, damage to civilian objects, or a combination thereof, which would be excessive in relation to the concrete and direct military advantage anticipated, is prohibited.

This rule finds expression in Articles 51(5)(b) and 57 of API. The principle of proportionality states that when military force is used against a proper military objective, and there is a risk of harm to nearby civilians or civilian objects, only force that is proportional to the military advantage to be gained may be deployed. If a choice of weaponry or tactics is available, the commander should choose a course of action that will cause the least incidental harm. The rule is flexible, meant to cover a whole range of contingencies related to target conditions, weaponry employed, the proximity and number of civilians, prevailing weather conditions, the skill of the operators, etc.

As a doctrinal matter, no proportionality calculus is required when the target is a “pure” military objective and there is no risk of harm to civilians or civilian objects. That said, additional rules limit the means and methods of war that may be employed against military objectives, including the rule against causing “superfluous injury or unnecessary suffering,” the rule against wanton destruction not justified by military necessity, or the rule against launching an attack that is “intended, or may be expected, to cause widespread, long-term and severe damage to the natural environment.”

While tragic, civilian casualties in and of themselves are thus not necessarily unlawful if they are incidental to an otherwise lawful attack. And, the greater the military advantage anticipated, the more “collateral damage” is tolerated under customary IHL. However, attacks that cause damage to civilians and civilian objects that is excessive in relation to the anticipated military advantage are unlawful and can be prosecuted as war crimes by a court with jurisdiction.

As applied to the operations in question, and assuming a driver is not a “military objective” as discussed below, if one died as a result of an attack on his truck, the rule of proportionality would apply and the incidental harm to the civilian would be weighed against the military advantage gained from eliminating the tanker. Obviously, this can be a subjective determination, and the weight to be accorded to the military advantage to be gained versus the risk to civilians might differ depending on who is undertaking the analysis.

What if the Drivers Had Disregarded the Leaflets and Refused to Abandon Their Trucks?

There is little positive law on this contingency, although there are any number of scenarios in which civilians, despite warnings of an impending strike, might assume the risk of an attack by remaining in the vicinity of a military objective (e.g., if an informal weapons depot had been established near a family home). It has been argued — not without controversy — that the voluntary presence of civilians near a known military objective might alter the proportionality calculus and render such military objectives more amenable to direct attack.

This is, however, a minority view, and Article 57 makes clear that the issuance of warnings does not diminish the legal obligations that otherwise constrain an attacker:

No provision in this article may be construed as authorizing any attacks against the civilian population, civilians or civilian objects.

The ICRC has thus taken the position that all obligations — including the duty to launch only proportionate attacks — endure even if civilians remain in the zone of operations after a warning has issued. An attack must still, in the language of Article 57 of API, be:

cancelled or suspended if it becomes apparent that the objective is not a military one or is subject to special protection or that the attack may be expected to cause incidental loss of civilian life, injury to civilians, damage to civilian objects, or a combination thereof, which would be excessive in relation to the concrete and direct military advantage anticipated.

It is not permissible to threaten remaining civilians with attack. Article 51(2) of API and Rule 2 of the ICRC’s Customary International Law Study state that “Acts or threats of violence the primary purpose of which is to spread terror among the civilian population are prohibited.”

As discussed below, this analysis may be different, however, if it were determined that the drivers were directly participating in hostilities by virtue of their involvement in the system of oil production and distribution or if their decision to remain with their trucks was a deliberate effort to render the trucks immune from attack.

Under What Circumstances, if Any, Would the Drivers (Apart From Their Trucks) Be Directly Targetable?

Much of the commentary opposed to the issuance of warnings has posited that the drivers are “jihadis” who should have been targeted rather than warned. Like civilian objects that are misused for military purposes, civilians lose their immunity from attack if they directly participate in hostilities:

  • Rule 6: Civilians are protected against attack, unless and for such time as they take a direct part in hostilities.

This formulation appears in both API (at Article 51(3)), governing international armed conflicts, as well as Additional Protocol II (in Article 13(3)), governing NIACs.

In the late 2000s, ICRC undertook a consultative process to develop interpretive guidance around what it means to take a direct part in hostilities. The results have not been universally accepted, to be sure, but the guidance provides a useful place to start in understanding the concept of direct participation in hostilities (DPH).

According to this guidance:

In order to qualify as direct participation in hostilities, a specific act must meet the following cumulative criteria:

  1. the 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 (threshold of harm), and
  2. 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 (direct causation), and
  3. 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 (belligerent nexus).

The DPH doctrine is thus conduct-based. In addition, and as a corollary, some posit that members of organized armed groups who undertake a continuous combat function are targetable at any time. For these actors, the doctrine is status-based and the temporality requirement (“for such time”) becomes irrelevant. Both inquiries are highly fact-specific, which has been a source of criticism in light of the difficulty of gleaning these facts in many real-world targeting scenarios.

To exemplify the debate around the concept of DPH, the ICRC regularly cites the case of someone driving an ammunition truck to the front lines as the easy case. By contrast, it posits that transporting ammunition to a port for onward shipment to the front would be too far removed from any particular military operation to satisfy the causation requirement (and perhaps the threshold of harm element as well). Any number of scenarios may exist between these two fact patterns.

If these particular drivers are deemed to be directly participating in hostilities, a direct attack against both the truck and its driver would be lawful. If the drivers are not directly participating in hostilities, they may not be directly targeted, although they may be subject to other forms of sanction. And, the truck remains a military objective, regardless of the status of the driver. So, the targetability of the drivers hinges in part on whether operating the vehicles constitutes DPH.

Even under the most expansive interpretation of DPH, the drivers at issue here have not lost their immunity from direct attack. To be sure, the drivers’ actions, while non-violent, are “likely to adversely affect the military operations or military capacity of a party to an armed conflict” — the first element of the ICRC’s DPH formulation. But activities that merely support a war effort do not generally satisfy the causation element, which requires that the conduct be “an integral part” of a military operation. Here, absent specific intelligence to the contrary, it is not clear that the drivers’ conduct is connected to any phase — preparatory through return — of any particular military engagement or deployment.

Moreover, the DPH doctrine requires that the conduct in question be specifically designed to support a party to a conflict to the detriment of another party to the conflict. While some of drivers may in fact be “members” of ISIL intent on furthering the organization’s goals, others are likely merely trying to support their families or are little more than war profiteers. The conduct of the latter two groups may lack a belligerent nexus. It will, of course, be impossible to tell from the air which is which. So by operating their trucks, the drivers may be breaking domestic law, or running afoul of a sanctions regime, but they likely cannot be directly targeted with lethal force absent additional intelligence about their relationship with ISIL or their destination.

This is where the presumption of civilian status is at its most potent. With this presumption in place, IHL rules demand that these drivers be considered civilians until proven otherwise, particularly when the mission can be accomplished without engaging the drivers directly. As such, while the truck itself remains a military objective, the driver would retain his or her protected status. Any attack on an occupied truck would have to treat the driver as a civilian and adhere to the rules of proportionality and precaution.

It should be noted that there is another way that these drivers may be deemed to be directly participating in hostilities: If they are deliberately attempting to protect their trucks from attack and thus acting as so-called voluntary human shields in violation of IHL. Whether voluntary human shields are directly participating in hostilities marks another area of sharp debate in IHL. To be sure, and in violation of IHL, civilians have been used as involuntary human shields to attempt to render military objectives immune from attack, as posited by the Israeli Defense Forces (IDF) in Gaza. The Israeli Supreme Court has distinguished these two categories as follows:

What is the law regarding civilians serving as a “human shield” for terrorists taking a direct part in the hostilities? Certainly, if they are doing so because they were forced to do so by terrorists, those innocent civilians are not to be seen as taking a direct part in the hostilities. They themselves are victims of terrorism. However, if they do so of their own free will, out of support for the terrorist organization, they should be seen as persons taking a direct part in the hostilities.

Other commentators have argued that even the presence of apparently voluntary human shields does not alter the proportionality analysis. Given the difficulty of determining whether human shields are voluntarily or involuntarily present, armed forces often — as a matter of policy — continue to apply proportionality to any attack on the underlying military objective, even if the party does not consider itself legally bound to do so. (See our prior commentary on human shields more generally here.)

So Where Does This Leave the Analysis?

The above discussion reveals that the operative legal framework offers some guidance, but leaves much ambiguity and room for alternative courses of conduct. And, in addition to these legal rules, there are likely many other non-legal considerations at play.

For one, commanders will be motivated by the economy-of-force imperative, which directs commanders to use only the force necessary to attain the sought-after military advantage. Likewise, the law of armed conflict answers only the “can we” question. The “should we” question is the province of commanders and policymakers, who must be cognizant of reputational harm, concerns about reprisals and reciprocity, potential “CNN Effects,” and the perceptions and attitudes of the local populace and of constituencies back home. Finally, although the United States has not conceded this, certain coalition partners may be moved by emerging restraints on the deployment of kinetic force that require that least restrictive means be employed where possible (e.g., individuals should be captured rather than killed if feasible).

All told, the approach taken to targeting the tankers reflects a fealty to the law-of-war principles of distinction, proportionality, precaution, and humanity. The use of leaflets as a precaution respects the humanitarian concerns inherent in the law of armed conflict. Targeting the trucks, while sparing the drivers, offers a compromise position, one that reflects the presumption of civilian status — even if it is not considered binding — while stretching the treaty definition of military objective to reach an outcome that few would fault.