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

On November 16, US war planes destroyed 116 fuel trucks in in oil-rich eastern Syria, the source of a solid portion of ISIL’s oil revenue. In a statement, the US Defense Department indicated that in addition to the tankers, airstrikes also hit a number of tactical units, fighting positions, storage depots, vehicles, and staging areas in Syria and Iraq as part of Operation Inherent Resolve. In subsequent operations, the number of tankers destroyed reached 238. Not to be outdone, the Russian press reported last week that Russia has destroyed more than 1,000 (or maybe it was 500) tankers, although the Pentagon is “skeptical” of this assertion.

The decision to target the trucks, which were parked at an oil collection point, was apparently made before the Paris attacks. Although a Pentagon spokesman indicated that this was the coalition’s first strike against tankers, the DOD (with the Gulf coalition) has struck a number of oil-producing facilities and other energy assets in the past, and a handful of tankers were destroyed in October 2014. (Ken Watkin covered these strikes on Just Security at the time; his excellent paper on the topic was later published here.) The most recent strikes are apparently part of a new stepped-up campaign to further degrade ISIL’s energy infrastructure that has been dubbed “Tidal Wave II” after a World War II effort to destroy oil refineries in Ploieşti, Romania that supplied up to a third of Nazi Germany’s fuel needs. The new operation is also reminiscent of the so-called Tanker Warslargely naval — between Iran and Iraq. (Incidentally, according to the US Air Force historian, production resumed quickly in Ploieşti; it remains to be seen if ISIL’s oil production capability will also recover quickly or if there will be long-term incapacitation of ISIL’s war economy as is hoped.)

The Pentagon warned truck drivers in advance of the planned strike with leaflets dropped over the site as well as show-of-force overflights. The leaflet messaging was unambiguous:

Get out of your trucks now, and run away from them. Warning. Airstrikes are coming, oil trucks will be destroyed. Get away from your oil trucks immediately. Do not risk your life.

The coalition did not attack drivers fleeing from their trucks, and it appears that no drivers were killed.

The Treasury Department has estimated that ISIL now earns between $1 million and $1.5 million a day from illegal oil sales generated by a sprawling production system that rivals many state-owned oil companies in terms of organization and scope. A recent Rand Corporation study ranks oils as third on the list of ISIL’s sources of revenue, behind extortion/taxation extracted from people within its vast territory and funds stolen from Iraqi banks; other sources of income include ransoms, selling antiquities, human trafficking, and wealthy donors.

At its peak, ISIL has controlled up to 80% of Syria’s oil production — so much so that the Syrian government and rebel groups must, at times, purchase fuel from them, which may explain why these tankers have not been targeted in the past by the regime. It has been reported that lines of trucks can extend 5 miles, with tanker drivers waiting up to a month for their turn to fill up. Drivers, mostly independent traders, generally transport the crude to formal and informal refineries. Some petrol is consumed internally; the rest is exported across the border into Turkey or Iraq.

The delay in adding ISIL’s pipeline-on-wheels to the coalition strike list and the use leaflets to give ISIL a “45 minute warning” before attacking have left many in the right-wing blogosphere incensed. Is this rancor justified?

While these airstrikes raise a number of international law issues, I’m going to consider two sets of questions: First, what legal framework applies to the strikes and what sorts of objects can be targeted, and second, questions related to the duty to warn civilians and the actual or counterfactual actions of the tanker drivers.

Below, I cover the first set of issues, concluding that the definition of military objective can be expanded to cover the tankers themselves, but not without accepting the legality of targeting war-sustaining elements of an enemy force. 

The Framework

These inquiries will generally be guided by customary international humanitarian law (IHL) given that none of the relevant IHL treaties is fully in force in the territory at issue. While many of the rules addressed to the means and methods of warfare are found in Additional Protocol I (API) to the 1949 Geneva Conventions, this treaty applies only to international armed conflicts (IACs), as idiosyncratically defined by that treaty. Most IACs involve conflicts between states. In 2012, the International Committee of the Red Cross (ICRC) publically classified the conflict in Syria as a non-international armed conflict (NIAC) — i.e., one between states and non-state actors or among non-state actors. Notwithstanding the participation of various foreign powers in the conflict, it likely remains so given that — for the moment anyway — the foreign forces are engaged militarily against non-state actors and not against the Assad regime. In any case, API does not formally govern the United States’ actions because the United States has not ratified it (though Syria and a number of the United States’ European and Gulf coalition partners have).

Even the most relevant treaty addressing the conduct of hostilities in NIACs (Additional Protocol II) has little binding guidance to offer here. While this treaty is well subscribed to, neither the United States nor Syria has ratified it.

As a result, we must look to customary international law (CIL) to evaluate the coalition’s approach to targeting the tanker trucks. For this, I will refer to the ICRC’s tremendous study of the topic, which tracks the two essential elements of CIL: state practice and opinio juris (a subjective belief that state conduct conforms to a legal obligation).

What Makes an Object a Lawful Military Objective?

The first big question in evaluating the airstrikes against ISIL tankers implicates the principle of distinction, which is foundational to IHL. This principle requires all parties to a conflict to distinguish between lawful and unlawful targets. Per the ICRC CIL Study:

  • Rule 1: The parties to the conflict must at all times distinguish between civilians and combatants. Attacks may only be directed against combatants. Attacks must not be directed against civilians.
  • Rule 7: The parties to the conflict must at all times distinguish between civilian objects and military objectives. Attacks may only be directed against military objectives. Attacks must not be directed against civilian objects.
  • Rule 10: Civilian objects are protected against attack, unless and for such time as they are military objectives.

The principle of distinction thus hinges upon the definition of “military objectives.” Article 52(2) of API indicates that for objects to be military objectives, they must “by their nature, location, purpose or use make an effective contribution to military action” and their “total or partial destruction, capture or neutralization, in the circumstances ruling at the time, [must] offer[] a definite military advantage.”

The definition of “military objective,” as confirmed by Rule 8 of the ICRC CIL Study, thus has two components:

  1. They must make an effective contribution — through their nature, location, purpose, or use — to military action by the party under attack, and
  2. Their destruction must offer a definite (as opposed to speculative or indeterminate) military advantage to the attacker in the circumstances at the time.

Article 57 of API requires that commanders “do everything feasible to verify that the objectives to be attacked are neither civilians nor civilian objects.” Rule 10 clarifies that civilian objects lose their protection against attack when they are used for military purposes, i.e., to make an effective contribution to military action. Today’s hostilities reveal that almost any civilian object can become a military objective by virtue of its use in military operations.

API contains the additional rule at Article 52(3) that

in case of doubt whether an object normally dedicated to civilian purposes … is being used to make an effective contribution to military action, it shall be presumed not to be so used.

Although generally well established, this presumption of civilian status is not necessarily universally accepted. For example, the new DOD Law of War Manual, which has been covered extensively on Just Security, does not accept that this presumption is a rule of CIL (see §

The principle of distinction is relatively simple when it comes to obvious military assets, such as a weapons system, munitions factory, or barracks. Applying these rules becomes more fraught with respect to what some have deemed to be “dual-use objects,” such as transportation systems (like those the tankers travel on), energy sources (like oil fields), communications systems, and manufacturing plants. (Note that some commentators, including the Law of War Manual at §, consider all objects to fall into one of two buckets — military objectives or civilian objects — and reject any notion that there is an intermediate category).

In 1956, the ICRC drew up Draft Rules for the Limitation of the Dangers Incurred by the Civilian Population in Time of War whose Annex contained a proposed list of categories of legitimate military targets applicable in all conflicts, international and non-international. In addition to obvious targets (the opponent’s armed forces, military installations, supply depots, airfields), the list included the following more generic objectives, with some caveats:

(6) Lines and means of communications (railway lines, roads, bridges, tunnels and canals) which are of fundamental military importance.

(7) The installations of broadcasting and television stations; telephone and telegraph exchanges of fundamental military importance.

(8) Industries of fundamental importance for the conduct of the war:

(a)        industries for the manufacture of armaments such as weapons, munitions, rockets, armoured vehicles, military aircraft, fighting ships, including the manufacture of accessories and all other war material;

(b)       industries for the manufacture of supplies and material of a military character, such as transport and communications material, equipment of the armed forces;

(c)        factories or plants constituting other production and manufacturing centres of fundamental importance for the conduct of war, such as the metallurgical, engineering and chemical industries, whose nature or purpose is essentially military;

(d)       storage and transport installations whose basic function it is to serve the industries referred to in (a)–(c);

(e)        installations providing energy mainly for national defence, e.g. coal, other fuels, or atomic energy, and plants producing gas or electricity mainly for military consumption.

Introduced during the Cold War, these Draft Rules were never formalized, in part because states were reticent about concretizing a discrete list that might not accommodate future contingencies. Two decades later, the drafters of API codified a set of abstract principles to govern targeting. Nonetheless, the Draft Rules continue to inform subsequent analyses.

The targetability of objects based upon their war-sustaining capability alone — without a direct nexus to any concrete military operation — remains open to debate. The ICRC CIL Study notes that some states consider economic targets that effectively support military operations to be military objectives, provided that their destruction offers a definite military advantage. The United States’ position in favor of such targetability is derived in part from the Civil War-era cotton blockades, erected to account for the fact that cotton was used by the Confederacy to purchase of weapons, ammunition, and ships from British manufacturers. It now finds expression in the Military Commission Act at § 950p(a).

At the same time, commentators have suggested that even attacks on legitimate military objects may be unlawful if they cause excessive long-term damage to an enemy’s economic infrastructure. This concern was acknowledged by a DOD spokesperson, who stressed that the goal was to disable rather than completely destroy the facilities, which will be vital to a new regime in the event of a (hoped for) political transition.

So Are the Tankers Lawful Military Objectives?

Turning to the facts, the contribution made by ISIL’s system of oil production and distribution to the group’s military activities seems clear. It provides ISIL with an indigenous energy source, a vital raw material for its operations, a tool for controlling the populations in the territory it holds, and a steady source of hard currency to fund its military aims and terrorist activities. Indeed, if stationary elements of ISIL’s oil producing and refining system are directly targetable, it is hard to see why tankers are not also proper military objectives, since the oil produced is of little use to military operations unless it is transported to where it is needed or is otherwise monetized. Hindering ISIL’s ability to exploit these resources will offer an immediate advantage to the coalition — thwarting any ISIL operations that are dependent on oil — in addition to longer-term advantages emanating from a reduction in ISIL’s purchasing/bartering power.

That said, targeting the tankers does stretch API’s definition of “military objective” considerably. This is particularly so given the fungability of oil and the fact that the tankers may have been dispersing to multiple locations, from ISIL military installations to the Turkish border. Tankers carrying oil designated for military use is an easier case than tankers carrying oil for export or, even easier, for civilian consumption. And it is impossible to know which tankers are which from the air absent extremely granular intelligence.

Whether the tankers are lawful military objectives will thus hinge on the validity of targeting war-sustaining objects and whether CIL is moving, or has moved, in this direction. There has, as yet, been no major public outcry about this expanded target set, although protests — by US coalition partners, other states, or the ICRC — may have been lodged behind-the-scenes. Whether this public silence can be deemed acquiescence, or even a demonstration of opinio juris, remains a doctrinal controversy in international law. That ISIL is an odious regime, committing its resources to death and destruction, no doubt makes certain legal licenses more palatable.

The fear in stretching these abstract concepts too far, of course, is that the entire distinction framework will collapse — to the ultimate detriment of the civilian population — and we will regress to the point at which “total war” is countenanced and the entire civilian infrastructure is considered a legitimate target. Moreover, any rule advanced in one conflict will be fair game for other parties to that conflict and may be picked up by belligerents in future conflicts as well.

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In Part 2 of this post, I will focus on the leaflets as well as the legal status of the drivers of the trucks.