Lieber Papers Series – The United States and (Most of) the Rest: A Legal Interoperability Primer
Editors’ Note: Articles of War previously published two longer works on the subjects of States’ responses to malicious or hostile actions and besieged forces’ legal obligations as both posts and as Lieber Institute White Papers. The post below addresses the subject of U.S. legal interoperability. With this work, we add a third entry to our Lieber Papers series. Look for other Lieber Papers in the future to appear initially as posts that will later be organized separately at the Lieber Institute website and available for download as formatted documents. We will offer Lieber Papers as focused studies of subjects of enduring relevance to our field. Lieber Papers will differ somewhat from our routine offerings in their length, thoroughness, and relative independence from events of the day. But they will share our dedication to careful, informed, and relevant scholarship.
Since its inception, the United States has been a foundational pillar of the NATO Alliance. Its involvement in NATO and other coalition operations has been, and will remain, indispensable. Yet, the law of armed conflict (LOAC) obligations of many NATO Allies and other potential coalition partners (hereinafter “partners”) are often more demanding than those governing U.S. forces. This is because likely partners of the United States sometimes shoulder treaty obligations that it does not or have adopted more restrictive interpretations of customary law. Such differences can strain interoperability, often necessitating a complex division of labor or creative legal interpretation of national positions. The situation is particularly challenging for combined force commanders, who must avoid putting coalition partners at legal risk and adjust coalition operations when they play the so-called “red card.”
Despite these challenges, the situation is more manageable than it may seem at first glance. The Alliance has considerable experience accommodating different legal frameworks during joint and combined exercises and operations with its NATO Allies and other close partners. Indeed, next week, U.S. Army Europe-Africa’s Staff Judge Advocate will convene a conference of partner legal advisers in the ongoing effort to build greater legal interoperability.
This Lieber Paper offers a primer on key points of divergence between U.S. legal obligations and those of some partners (see also Matheson; Richard; Cadwalader). In this regard, it is essential to emphasize that the paper cannot capture every difference between the United States and other States. Nor can it explore every nuance of those it addresses. Instead, the objective is to introduce readers to some of the key LOAC issues that distinguish the United States from (most of) the rest in the hope of further minimizing their operational impact.
As noted, two core reasons drive the legal gap between the United States and many partners. Most importantly, the United States has deliberately chosen not to ratify certain international agreements that regulate military operations during armed conflict. Most significantly, it has not become a party to the 1977 Additional Protocol I to the 1949 Geneva Conventions (AP I), which contains most of the treaty-based rules governing the conduct of hostilities during international armed conflict. Within NATO, only Turkey joins the United States in this regard.
In addition to Additional Protocol I, the United States has refrained from becoming a party to Additional Protocol II, which deals with certain forms of non-international armed conflict. However, this is less important because the United States generally treats its provisions as consistent with customary international law. Other key treaties applicable in military operations to which the United States is not a party include the Ottawa Treaty on anti-personnel mines and the Convention on Cluster Munitions. Additionally, the United States is not a party to the Rome Statute of the International Criminal Court, which deals with the enforcement by that body of LOAC violations that qualify as serious war crimes.
Despite these disparities in treaty obligations, the United States recognizes many of the provisions in these treaties as reflecting customary international law binding on all States. This mitigates many potential interoperability problems. But even in such cases, the U.S. interpretation of the rule in question may differ from those of its partners. The paradigmatic example is the U.S. interpretation of the universally accepted definition of “military objective” in Additional Protocol I, Article 52(2), as including “war-sustaining” objects, a topic examined below.
Understanding these differences requires appreciation that most LOAC rules reflect a delicate balancing of military necessity and humanitarian considerations by States. As will become apparent, the differences are often explainable in part by the significant U.S. emphasis on military necessity and operational effectiveness when deciding whether and how to accept and interpret LOAC obligations. This is not to suggest that other States disregard military necessity. It simply means they have reached different conclusions regarding the appropriate balance between military necessity and humanitarian considerations when deciding whether to become a party to a treaty or how to interpret particular rules.
A significant source of disagreement between the United States and its partners concerns the treatment of irregular forces under Article 44(3) of Additional Protocol I. The traditional conditions for combatant status are found in Article 4A of Geneva Convention III on prisoners of war. It provides that members of militia and other volunteer units, including organized resistance movements, are entitled to prisoner of war status when their unit is commanded, conducts its operations in accordance with LOAC, carries its arms openly, and has identifiable indicia that distinguish its members from the civilian population.
Article 44(3) relaxes these requirements for irregular forces, granting them combatant status (including combatant immunity) and prisoner of war status if they carry arms openly during military engagements or when visible to the enemy during deployment. In such cases, there is no obligation to wear distinguishing attire or display other indicia of their group membership if, “owing to the nature of the hostilities, an armed combatant cannot so distinguish himself.”
The United States believes that this relaxation of the traditional conditions endangers civilians by making it more difficult to distinguish combatants from civilians, a customary law obligation captured in Article 48 of Additional Protocol I. Moreover, because they are not obligated to identify themselves until deployment or engagement in certain circumstances, the Additional Protocol I approach makes it more challenging to identify and target enemy fighters.
Most States take a binary approach to the status of individuals during international armed conflicts, categorizing them as either combatants protected by the Geneva Convention III on prisoners of war or civilians protected by Geneva Convention IV. However, the United States recognizes a third category, so-called “unprivileged belligerents.” It consists of those who do not qualify as combatants by the criteria in Article 4 of Geneva Convention III but nevertheless “engage in hostilities,” either on their own or as part of an organized armed group (U.S. Department of Defense (DoD), Law of War Manual, § 4.3.4).
Most States consider these individuals entitled to the protections civilians enjoy except for protection from attack while directly participating in the hostilities, a complicated subject discussed below. However, the U.S. view is that as a matter of law, they are only entitled to the “fundamental guarantees of humane treatment described in Common Article 3 of the 1949 Geneva Conventions.” It also acknowledges that Article 75 of Additional Protocol I, which articulates minimum standards for the humane treatment of all detainees during an international armed conflict, reflects customary law. Thus, except for Common Article 3, such individuals do not benefit from other Geneva Conventions III and IV protections.
The U.S. approach to mercenaries differs significantly from that set out in Additional Protocol I, Article 47, which denies them combatant or prisoner of war status. That article defines a mercenary as someone who is recruited to fight, takes direct part in hostilities, is motivated primarily by private gain, and meets several other conditions. In this regard, note that an Additional Protocol I State may elect to accord mercenaries the treatment to which combatants are entitled as a matter of policy.
By contrast, the United States is of the view that “[u]nder the customary law of war and [Geneva Convention III], ‘mercenaries’ receive the rights, duties, and liabilities of combatant status on the same basis as other persons” (U.S. DoD, Law of War Manual, § 4.21). This view reflects, in part, the U.S. reliance on private military security companies and other private entities that perform functions on or near the battlefield, and which risk being considered mercenaries subject to Article 47. It is important to point out that the United States would only accord combatant and prisoner of war status to individuals satisfying the criteria outlined in Geneva Convention III, Article 4. Those who do not would, depending on their activities and affiliations, be treated as civilians or unprivileged belligerents. Consistent with its opposition to Article 47, that the United States has not become a party to the 1989 International Convention against the Recruitment, Use, Financing, and Training of Mercenaries is unsurprising.
Direct Participation in Hostilities
Article 51(3) of Additional Protocol I provides that civilians enjoy protection from attack (and are included in proportionality and precautions in attack assessments) “unless and for such time as they take a direct part in hostilities.” Additional Protocol II, Article 13(3), sets forth the same rule in the context of non-international armed conflicts to which that instrument applies. The United States does not oppose the direct participation rules and views itself as bound by their customary law counterparts.
To clarify the concept of direct participation, the International Committee of the Red Cross (ICRC) conducted a major expert project that resulted in its publication of the Interpretive Guidance on the Notion of Direct Participation in Hostilities in 2009. However, this guidance has proven contentious, with some States, including the United States, rejecting some of its interpretive conclusions (U.S. DoD, Law of War Manual, § 5.8.1.2; for scholarship on point, see here).
Although the disagreement over direct participation is quite granular, three points stand out. First, although most States agree that there must be a direct causal link between the actions of the civilian concerned and their adverse effect on the enemy’s military operations or capacity, there is a lack of consensus on how that interpretation applies in practice. The question is whether the connection to the enemy’s operations and capabilities is direct enough to qualify as direct (as distinct from indirect) participation.
The U.S. position is that “[t]aking a direct part in hostilities extends beyond merely engaging in combat and also includes certain acts that are an integral part of combat operations or that effectively and substantially contribute to an adversary’s ability to conduct or sustain combat operations” (U.S. DoD, Law of War Manual, § 5.8.3). For example, it would characterize an individual making improvised explosive devices in the area of operations as directly participating, whereas the ICRC and States adopting its narrow approach would not.
Second, there is an ongoing debate over the period during which the individuals concerned lose protection from attack. The Interpretive Guidance suggests that they do so only for the duration of each specific act. For the United States, this creates an operationally unacceptable “revolving door of protection.” In its view, an individual engaging in a recurring series of qualifying acts directly participates throughout that period (U.S. DoD, Law of War Manual, § 5.8.4).
Third, while there is consensus that some members of “organized armed groups” are subject to attack irrespective of whether they are engaging in acts of direct participation at the time, the ICRC takes the position that only those members who have a “continuous combat function” lose their protection in this way, a view some States have embraced (see, e.g., Denmark, Military Manual, § 3.1). Those who do not have such a function may only be attacked while directly participating in the hostilities, thus implicating the previous two issues.
By contrast, the United States treats membership in a “hostile, non-state armed group as a separate basis upon which a person is liable to attack, apart from whether he or she has taken a direct part in hostilities” (U.S. DoD, Law of War Manual, § 5.8.2.1). Thus, membership standing alone in a group that has the purpose of conducting hostilities suffices. As is apparent, the United States finds the ICRC’s approach to all three issues operationally impractical. It is also concerned that it affords members of organized armed groups greater protection under the law than its own forces enjoy.
As noted earlier, the United States accepts the definition of military objectives set forth in Article 52(2) of Additional Protocol I which states,
In so far as objects are concerned, military objectives are limited to those objects which by their nature, location, purpose or use make an effective contribution to military action and whose total or partial destruction, capture or neutralization, in the circumstances ruling at the time, offers a definite military advantage.
All States agree that this definition encompasses both “warfighting” and “war-supporting” objects. Warfighting objects are those that are military in nature, such as a tank, or that are used or will be used for military purposes, like an apartment from which the enemy is commanding and controlling forces. War-supporting objects are not used directly for military operations but nevertheless have a close nexus to military operations, like a factory producing military equipment or armaments.
The United States, however, goes further by treating so-called “war-sustaining” objects as military objectives (see Goodman). These are objects without which the enemy war effort could not be sustained. The U.S. DoD Law of War Manual observes that the category includes “economic objects associated with military operations or with war-supporting or war-sustaining industries” (§ 5.6.8). Examples that have drawn attention in the past include assets related to the sale of oil by ISIS and Taliban drug income. In the opinion of the United States, it does not make sense to take enemy targets that could affect its ability to continue the fight off the table; indeed, doing so, it believes, would sometimes forfeit opportunities to shorten the conflict and thereby avoid civilian harm.
This interpretation contrasts with the mainstream understanding of Article 52(2), which limits military objectives to objects that make a relatively immediate and direct contribution to military action. Focusing on the consensus definition of military objectives, its proponents find the relationship between war-sustaining objects and ongoing military operations too remote to contribute effectively to military action and believe targeting them will seldom yield a definite military advantage (Dinstein, p. 126-27).
Dams, Dikes, and Nuclear Electrical Generating Stations
Article 56 of Additional Protocol I prohibits attacking dams, dikes, and nuclear electrical generating stations, even if they qualify as military objectives, when the attack risks releasing “dangerous forces” (i.e., water or radiation) that may cause severe civilian losses. The same restriction applies to attacks on other military objectives within or near these installations. Under certain very limited circumstances, the prohibition may be relaxed, but even then, the attacker must take all practical precautions to avoid releasing dangerous forces.
The United States opposes this provision, suggesting that there may be a valid reason for attacking such works and installations. It has observed that there “may be a number of reasons for their attack, such as denial of electric power to military sources, use of a dangerous facility (e.g., by causing release from a dam) to damage or destroy other military objectives, or to pre-empt enemy release of the dangerous forces to hamper the movement or advance of U.S. or allied forces” (U.S. DoD, Law of War Manual, § 5.13). In its estimation, other LOAC rules, such as the principle of proportionality and the requirement for distinction, suffice to protect civilians from incidental harm resulting from the attack. But it cautions, “In light of the increased potential magnitude of incidental harm, additional precautions, such as weaponeering or timing the attack such that weather conditions would minimize dispersion of dangerous materials, may be appropriate to reduce the risk that the release of these dangerous forces may pose to the civilian population” (§ 5.13).
Interestingly, the United States has voiced no significant opposition to Article 15 of Additional Protocol II, which similarly limits attacks on these installations in non-international armed conflicts.
Reprisals
Reprisals are actions that would violate the law of armed conflict but for the fact that they are engaged in to compel the enemy to cease its own violations (see my discussion here). Under Additional Protocol I, reprisals are strictly limited. That instrument bans them against civilians (art. 51(6)); civilian objects (art. 52(1)); cultural objects and places of worship (art. 53(c)); objects indispensable to the survival of the civilian population (art. 54(4)); the natural environment (art. 55(2)); and dams, dikes, and nuclear electrical generating stations (art. 56(4)).
It must be cautioned that some Additional Protocol I States have issued reservations or declarations regarding some of these provisions. For instance, the United Kingdom’s states,
If an adverse party makes serious and deliberate attacks, in violation of Article 51 or Article 52 against the civilian population or civilians or against civilian objects, or, in violation of Articles 53, 54 and 55, on objects or items protected by those Articles, the United Kingdom will regard itself as entitled to take measures otherwise prohibited by the Articles in question to the extent that it considers such measures necessary for the sole purpose of compelling the adverse party to cease committing violations under those Articles, but only after formal warning to the adverse party requiring cessation of the violations has been disregarded and then only after a decision taken at the highest level of government.
The United States has rejected a blanket prohibition on reprisals. It maintains that the availability of reprisals could prove an effective means of deterring enemy violations and enforcing LOAC rules, thereby enhancing the protection of civilians and civilian objects and safeguarding combatants from unlawful abuse. Nevertheless, some treaties to which the United States is a party limit the scope of permissible reprisals. Most significantly, the 1949 Geneva Conventions prohibit reprisals against the wounded, sick, shipwrecked, medical personnel and chaplains, medical units and facilities, hospital ships, and prisoners of war (see discussion in U.S. DoD, Law of War Manual § 18.18.3). Other reprisal prohibitions appear in the 1954 Hague Cultural Property Convention (art. 4) and the 1996 Amended Mines Protocol II to the Convention on Conventional Weapons (art. 3(7)).
It merits emphasis that the United States considers reprisals “an extreme measure of coercion.” As such, they are subject to stringent requirements. These include careful assessment of whether the reprisal is justified, exhaustion of alternative means of securing the enemy’s compliance with LOAC, national level authorization, a proportionality requirement, and public announcement to place the enemy on notice. Moreover, it acknowledges that “practical considerations may counsel against their use” even when lawful (U.S. DoD, Law of War Manual, § 18.18).
Article 35(3) of Additional Protocol I prohibits “methods or means of warfare which are intended, or may be expected, to cause widespread, long-term and severe damage to the natural environment.” The ICRC characterizes this approach as reflective of customary law in Rule 45 of its Customary International Humanitarian Law study, a position with which, as discussed below, the United States disagrees.
Additional Protocol I, Article 55(1), reinforces this protection stating,
Care shall be taken in warfare to protect the natural environment against widespread, long-term and severe damage. This protection includes a prohibition of the use of methods or means of warfare which are intended or may be expected to cause such damage to the natural environment and thereby to prejudice the health or survival of the population.
The distinction between the two articles is subtle. Whereas the former prohibits weapons and tactics anticipated to cause the requisite environmental harm as such, the latter focuses on the impact on humans. It must be emphasized that the rules set very high prohibitory thresholds.
The United States has long recognized that unnecessary environmental damage should be avoided (see Biggerstaff & Schmitt). Yet, as noted in the DoD Law of War Manual, it “has repeatedly expressed the view that these provisions are overly broad and ambiguous and not a part of customary law.” Instead, the United States is of the view that the use of environmental weapons is “prohibited only if their use is clearly excessive in relation to the concrete and direct overall military advantage anticipated,” in other words, when the weapon’s use would violate the rule of proportionality (§ 6.10.3.1).
A further point of difference between the United States and its partners, especially some who are party to Additional Protocol I, lies in the U.S. characterization of the environment as civilian. While some States consider it to be a civilian object in its entirety except when qualifying as a military objective (a binary approach), the United States takes the position that “the fact that the natural environment is not considered as intrinsically military in nature, does not necessarily mean that every element thereof should be treated as a civilian object under the law of armed conflict.” In justification, it points out that
parts of the natural environment not constituting military objectives are routinely adversely affected by lawful attacks against military objectives. This type of environmental damage (e.g., small craters in the earth formed from the use of artillery) is generally not considered as part of the implementation of the principle of proportionality.
Perfidy involves feigning protected status to trick the enemy into according that protection (see Watts). This can involve, for instance, pretending to be wounded or sick or disguising oneself as a civilian. Doing so with the intent to kill, injure, or capture the adversary violates Article 37 of Additional Protocol I. The ICRC believes that rule reflects customary law (Customary International Humanitarian Law study, rule 65).
The prohibition on perfidy is rooted in the much earlier ban in Article 23(b) of the Regulations annexed to the 1907 Hague Convention IV: “It is especially forbidden … [t]o kill or wound treacherously individuals belonging to the hostile nation or army.” The International Military Tribunal (IMT) at Nuremberg and the IMT for the Far East recognized the Regulations as reflecting customary law.
The United States is of the view that the prohibition on perfidious conduct to capture the enemy, which does not appear in Article 23(b), is not customary in character and, therefore, binding only on Additional Protocol I parties (U.S. DoD, Law of War Manual, § 5.22.2.1). By this interpretation, U.S. forces may, for example, pretend to be civilians to capture enemy soldiers without violating international LOAC. That said, the practice is generally disfavored because it might weaken the ability to distinguish civilians from combatants, a risk that led to the U.S. opposition to the Additional Protocol’s relaxation of the rule on combatant status (see discussion above).
The United States’ approach to detention during armed conflicts differs meaningfully from many of its partners, particularly regarding individuals who do not qualify for prisoner-of-war treatment in accordance with Geneva Convention IV. This is largely due to the U.S. position on human rights law in armed conflict, according to which LOAC is the dominant body of law when its provisions overlap with human rights law, and its restrictive approach to the extraterritorial application of human rights obligations (U.S., DoD Law of War Manual, § 1.6.3.2).
Furthermore, The United States does not share the same treaty obligations as many partners, especially those in the European Convention on Human Rights. The European Court of Human Rights has found them applicable extraterritorially when the State Party exercises effective control over the area or individuals concerned, even during armed conflict (e.g., Al-Skeini v. United Kingdom). Of particular note, the Court has consistently ruled that, under Article 5 of the European Convention on Human Rights, detention during an armed conflict is subject to due process guarantees, including judicial review (e.g., Al-Jedda v. United Kingdom; Hassan v. United Kingdom).
The United States takes a narrower view, one emphasizing that detention during an armed conflict is a preventive measure intended to protect military forces and prevent detainees from returning to the battlefield. The framework for the authority to detain and the related procedures for making that decision are, by its approach, found almost exclusively in Geneva Conventions III and IV, Common Article 3 for non-international armed conflict, and the customary law governing humane treatment that has been codified in Additional Protocol I, Article 75. This characterization has been challenged in U.S. federal courts. For instance, in 2008, the Supreme Court held in Boumediene v. Bush that detainees at Guantanamo Bay enjoyed a limited right to challenge their detention. However, the U.S. judgments do not go nearly as far as those of the European Court of Human Rights.
This approach reflects a practical concern about the heavy burden that full judicial review and due process would place on armed forces engaged in armed conflict. However, it sometimes creates a challenge during coalition operations when enemy personnel are initially detained by non-U.S. partners who wish to transfer them to U.S. custody. In some cases, partners have had to refrain from transferring detainees to U.S. forces lest they violate their own obligations, which in turn requires greater reliance on national detention facilities.
The United States has yet to join several weapons treaty regimes that many partners have. It has done so out of concern that the treaties will deprive it of tools that, in certain situations, are indispensable on the battlefield. The most significant such treaties operationally are those addressing anti-personnel land mines and cluster munitions.
Like most of its partners, the United States is a party to Protocol II (as amended in 1996) to the Convention on Certain Conventional Weapons (CCW), which deals with “mines, booby traps, and other devices” (see discussion at U.S. DoD, Law of War Manual, § 6.12). The instrument bans mines that are non-detectable, designed to detonate when near mine detectors, or that cause superfluous injury, and imposes strict requirements on the use of other mines.
A number of States and nongovernmental organizations, finding these safeguards insufficient, successfully led an effort to craft a more categorical treaty. The result was the 1997 Convention on the Prohibition of the Use, Stockpiling, Production and Transfer of Anti-Personnel Mines and on their Destruction, also known as the Ottawa Treaty. By it, parties agree never to “develop, produce, otherwise acquire, stockpile, retain or transfer (APL) to anyone, directly or indirectly,” or assist others in doing so (art. 1). Some States, including Australia, Canada, the Czech Republic, Montenegro, Poland, and the United Kingdom, have issued declarations that allow their forces to provide indirect support to coalition partners that use mines.
Notably, the ICRC’s Customary International Humanitarian Law study does not suggest that there is a customary law ban on anti-personnel mines per se. Instead, it simply provides, “When landmines are used, particular care must be taken to minimize their indiscriminate effects” (rule 81). This is the position of the United States. It elected not to become a party to the Ottawa Convention, in significant part because of the utility of mines in slowing down a North Korean invasion enough to allow South Korean and UN forces to respond, especially in light of Seoul’s proximity to the demilitarized zone.
Although not bound by the instrument, the United States adopted a policy in 2014 that is broadly consistent. In it, the United States committed: “(1) not to use anti-personnel landmines outside the Korean Peninsula; (2) not to assist, encourage, or induce anyone outside the Korean Peninsula to engage in activity prohibited by the Ottawa Convention; (3) to undertake to destroy anti-personnel landmine stockpiles not required for the defense of the Republic of Korea; and (4) not to produce or otherwise acquire any anti-personnel munitions that are not compliant with the Ottawa Convention” (see also U.S. DoD, Law of War Manual, § 6.12.13). The Trump Administration reversed the policy, but the Biden Administration reimplemented it in 2022 (see my discussion here). Thus, under current policy, the operational distance between the United States and States party to the Ottawa Convention is narrow, at least for the time being.
The other weapons treaty the United States has chosen not to sign is the 2008 Convention on Cluster Munitions (CCM). It prohibits the use, production, stockpiling, and transfer of cluster munitions, which scatter smaller bomblets over a targeted area. The treaty was a response to the failure of many of the bomblets to detonate, thereby posing a persistent risk to the civilian population.
The United States is opposed to the ban because it is of the view that there are circumstances in which cluster munitions would place civilians and civilian objects at less risk than other weapons. The DoD Law of War Manual provides the example of using them “against military objectives containing dangerous forces, such as dams, in order to reduce the risk that bombardment of these objectives would release such forces and cause incidental harm to the civilian population” (§ 6.13.12). Cluster munitions are also valuable for such purposes as targeting dispersed or mobile enemy forces, attacking artillery batteries and armored units, and targeting enemy troops in the open near buildings where civilians have taken shelter. Instead of banning them, the United States has since 2018 restricted its use of cluster munitions to those “containing submunitions that, after arming, do not result in more than 1% unexploded ordnance (UXO) across the range of intended operational environments.”
Significantly, Article 21(3) of the CCM facilitates interoperability with the United States and other non-parties stating, “Notwithstanding the provisions of Article 1 of this Convention and in accordance with international law, States Parties, their military personnel or nationals, may engage in military cooperation and operations with States not party to this Convention that might engage in activities prohibited to a State Party.” That said, a State party may not “expressly request the use of cluster munitions in cases where the choice of munitions used is within its exclusive control.” In other words, they cannot escape their treaty obligation to refrain from use by simply outsourcing a strike.
Of note, in July 2024, Lithuania’s Parliament voted to withdraw from the Convention; the withdrawal will be effective six months after submitting the instrument of denunciation. Its concern is the threatening Russian behavior and the utility of such weapons in the face of an invasion by Russian forces.
Protocol III of the CCW imposes a number of prohibitions on the use of incendiary weapons. By Article 2, they may not be used against the civilian population or civilian objects, against military objectives in a concentration of civilians when air delivered, within a concentration of civilians by other than air-delivered weapons except when there is a clear separation of the military objective from the civilians and precautions have been taken to limit harm to them, or against forests or other kinds of plant cover except when used to cover conceal or camouflage combatants or other military objectives, or when those objects are themselves military objectives.
The United States became a party to this instrument in 2009. However, upon doing so, it attached a reservation that allows for U.S. use of incendiary weapons to a greater extent than some partners. In it, the United States reserved the right to employ incendiary weapons against military objectives in concentrations of civilians when it judges that such use would result in less collateral damage than other weapons. The reservation emphasizes, however, that in such cases, the requirement to take feasible precautions in attack would apply, as it does to any attack. The DoD Law of War Manual gives two examples of such situations: using incendiary weapons to attack enemy biological weapons facilities to lower the risk of a release of contagions; and using them to reduce the number of sorties or attacks required to achieve the desired effect, thereby reducing the risk of collateral damage (§ 6.14.3.2).
Additionally, the Law of War Manual points out that neither white phosphorus munitions nor tracer rounds are encompassed in Protocol III’s definition of incendiary weapons (art. 1), a fact often missed by commentators. Combined-effects munitions that “combine penetration, blast, or fragmentation effects with an additional incendiary effect” likewise do not qualify, at least so long as the incendiary effect is not designed for the specific purpose of causing burn injuries. If a weapon does not meet the definition contained in the Protocol, the United States believes it may be used to set fire or burn, subject to the LOAC rules governing attack (§ 6.14.).
The United States’ position on the 1993 Chemical Weapons Convention’s prohibition on, inter alia, the use of riot control agents as a “method of warfare” (art. I(5)) is an example of how it sometimes shares a treaty commitment but interprets its differently. Some States interpret the prohibition widely. For instance, the 2013 German Military Manual states, “The use of irritants in armed conflicts to fight the adversary is thus prohibited” (para. 470).
The United States sees the reference to “method of warfare” as narrower, thereby granting it greater leeway to employ riot control agents, such as tear gas and pepper spray. In its view, they may lawfully be employed defensively to save lives. The DoD Law of War Manual, drawing on Executive Order 11850 (1975), offers the following examples (§ 6.16.2):
– in riot control situations in areas under direct and distinct U.S. military control, including controlling rioting POWs;
– in situations in which civilians are used to mask or screen attacks and civilian casualties can be reduced or avoided;
– in rescue missions in remotely isolated areas, of downed aircrews and passengers, and escaping prisoners; and
– in rear echelon areas outside the zone of immediate combat to protect convoys from civil disturbances, terrorists, and paramilitary organizations.
The United States is also of the view that the prohibition is inapplicable during hostage rescue missions, non-combatant evacuation operations, in areas of armed conflict in which the United States is not a party to that conflict, and during UN Charter Chapter VI and VII peacekeeping operations.
Clearly, the United States is more cautious about foreclosing military options as a matter of law than many partners with whom it is likely to operate during armed conflicts. Accordingly, it sometimes weighs military necessity more heavily in the balance with humanitarian considerations than some of them. But we should not be surprised that States balance military necessity and humanitarian considerations based on their own national interests with attention to the operational environment in which their forces are likely to fight. The fact that the United States is an expeditionary force is telling in this regard, but it is certainly not the only factor explaining the differences.
Before concluding, three reminders are helpful. First, this survey is far from exhaustive. Other differences include, for instance, the required scope of weapons review (Additional Protocol I, art. 36), the use of enemy flags or other indicia (art. 39(2)), and Additional Protocol I’s extension of international armed conflict status to conflicts with national liberation movements (art. 1(4)). And there are many subtle differences in the way the United States and partners address aspects of LOAC, such as the impact of doubt during attacks (see Schmitt & Schauss). Those offered here are but the ones most likely to affect coalition operations.
Second, it must also be emphasized that there are differences among States other than the United States, not only with respect to their treaty obligations but also in how they interpret rules to which they are mutually bound. While the United States is typically in the minority camp, it is seldom there alone.
Finally, readers are cautioned that this primer is not an official document and that they should consult with officials of the State concerned for definitive positions on LOAC matters. This is particularly important because the legal positions of States can change, sometimes rather precipitously.
***
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 and Professor Emeritus and Charles H. Stockton Distinguished Scholar-in-Residence at the United States Naval War College.
Photo credit: U.S. Air Force, Senior Airman Lauren Cobin
