Proportionality under International Humanitarian Law: The 'Reasonable Military Commander' Standard and Reverberating Effects.

Author:Henderson, Ian
Position::Special Issue: The Law of Armed Conflict


The purpose of this Article is to expand on two points that were raised and generated interesting discussion at The Second Israel Defense Forces International Conference on the Law of Armed Conflict during a panel that dealt with contemporary issues in proportionality. (1) Those two issues are:

  1. What does the "reasonable military commander" standard for assessing proportionality entail?

  2. Should "reverberating effects" (i.e., collateral effects that are only expected to materialize in the long term) be accounted for as part of the assessment of collateral damage?

    The principle of proportionality protects civilians and civilian objects against expected incidental harm from an attack that is excessive to the military advantage anticipated from the attack. Military commanders are prohibited from planning or executing such indiscriminate attacks. The principle of proportionality is accepted as a norm of customary international law applicable in both international and noninternational armed conflict. (2) The test for proportionality has been codified in Additional Protocol I. The relevant provisions of Additional Protocol I prohibit attacks that: "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." (3)

    Despite its status as a fundamental norm of IHL, (4) neither Additional Protocol I nor any other international treaty provides definitions for key terms such as "may be expected" or "military advantage." This has caused challenges for both academics and military commanders alike in explaining and applying the test for proportionality. (5)

    Unfortunately, subsequent case law has not greatly assisted in the interpretation of this test. In Prosecutor v. Kupreskic, the Trial Chamber held the principle of proportionality requires that "any incidental (and unintentional) damage to civilians must not be out of proportion to the direct military advantage gained by the military attack." (6) The Court was not required in that case to undertake a detailed analysis. In Prosecutor v. Galic, the Trial Chamber held the express prohibition of indiscriminate attacks in Additional Protocol I is reflective of the customary law applicable in all conflicts. (7) Regrettably for commentators and practitioners, the Court did not need to engage in further legal analysis before applying the test for proportionality to the facts in that case.

    Most recently in Prosecutor v. Prlic, the Trial Chamber found the destruction of the Old Bridge of Mostar caused "indisputable and substantial" damage to the civilian population by reducing the available supply routes for food and medical supplies and thereby resulting in serious deterioration of the humanitarian situation in the local area. (8) Further, the destruction of the Old Bridge was said to have "a very significant psychological impact" on the Muslim population of Mostar. (9) The Court then held this harm to the civilian population "was disproportionate to the concrete and direct military advantage expected by the destruction of the Old Bridge." (10) With great respect, the Court's conclusion was wrongly drawn.

    First, the test for proportionality requires consideration only of expected civilian deaths and injuries and damage to civilian objects. Other intangible effects on the civilian population, such as inconvenience, irritation, stress, or fear are not factored into collateral damage. (11) Accordingly, consideration of the inconvenience of being required to use alternate supply routes or the stress of observing the Old Bridge being destroyed resulted in an incorrect application of the proportionality test in Prlic.

    Second, while a deterioration of the humanitarian situation may result in civilian deaths and injuries, that was not identified in the Court's reasoning. (12)

    And finally, the Court did not appear to truly engage with evaluating the anticipated military advantage and the expected collateral damage. At paragraph 1582, the Court said "the Old Bridge was essential to the ABiH [Army of Bosnia and Herzegovina] for combat activities of its units on the front line" and "its destruction cut off practically all possibilities for the ABiH to continue its supply operations." (13) Having made only general comments about harm to the civilian population, and having made quite strong findings about the military importance of the bridge, the Court simply said:

    The Chamber therefore holds that although the destruction of the Old Bridge by the HVO may have been justified by military necessity, the damage to the civilian population was indisputable and substantial. It therefore holds by a majority, with Judge Antonetti dissenting, that the impact on the Muslim civilian population of Mostar was disproportionate to the concrete and direct military advantage expected by the destruction of the Old Bridge. (14) With respect, the anticipated collateral damage identified by the Court was not so obviously out of all proportion to the anticipated military advantage identified by the court so as to warrant such a perfunctory analysis.

    Three of the six accused appealed their conviction with respect to the destruction of the Old Bridge on, inter alia, grounds related to the Trial Chamber's findings that the destruction was disproportionate. (15) Unfortunately for current purposes, the Appeals Chamber found it did not have to address any of the proportionality arguments raised by Stojic, Praljak, and Petkovic. Rather, the Appeals Chamber upheld this aspect of the appeal on the following basis:

    The Appeals Chamber recalls that the elements of wanton destruction not justified by military necessity, as a violation of the laws or customs of war, include, inter alia, the destruction of property that occurs on a large scale and that the destruction is not justified by military necessity. Since the Trial Chamber found that the Old Bridge was a military target at the time of the attack, and, thus, its destruction offered a definite military advantage, the Appeals Chamber, Judge Poear dissenting, finds that it cannot be considered, in and of itself, as wanton destruction not justified by military necessity. (16) An explanation of the application of the proportionality test in state practice, evidenced namely in the armed forces' manuals on the law of armed conflict, is also scarce. Most of these military manuals simply recite the law but provide limited discussion on the practical application of the test. An exception appears to be the United States Department of Defense (US DoD) Law of War Manual, which provides a detailed analysis of the prohibition on attacks expected to cause excessive incidental harm. (17)

    In the absence of clarity on the application of the proportionality test, we will consider two issues which require immediate attention in light of current military operations. First, noting the test is not mechanical but requires an assessment of disparate values (i.e., expected incidental harm and anticipated military advantage), what is the standard for assessing proportionality? We will contend it is that of the "reasonable military commander."

    Second, should "reverberating effects" or "indirect effects" be accounted for as part of the assessment of collateral damage? We will contend that reverberating or indirect effects are counted as part of the collateral damage assessment but only where that harm will arise as an expected consequence of the attack. While there is no definitive temporal or geographical limitation, any incidental harm to civilians or damage to civilian objects that is too remote to have been reasonably caused by the attack or is but a mere possibility does not form part of the assessment.


    What does the "reasonable military commander" standard for assessing proportionality entail?

    This was the opening question to the panel and set the parameters for the discussion that followed. Of course, as was no doubt well known by the very experienced panel moderator, (18) a whole workshop could be dedicated to this question alone. What follows addresses why the "reasonable military commander" was adopted as the standard against which the ensuing discussion was conducted.

    The first point to note is that the codified principle of proportionality in Additional Protocol I, article 57(2)(a)(iii), does not refer to a "reasonable military commander" at all. The obligation to comply with the principle of proportionality lies with either "those who plan or decide upon an attack," (19) or those who execute an attack. (20) The reference to a "reasonable military commander" does not describe who has the obligation, but rather the standard against which a decision on proportionality is to be made or judged. Determining the standard against which proportionality decisions are to be evaluated is important because:

    [C]enturies of discussion by philosophers and jurists about the meanings of necessity and proportionality in human affairs do not seem to have produced general definitions capable of answering concrete issues. As with many abstract concepts, the answers to specific questions depend on the circumstances, appraised in the light of the humanitarian ends that justify the restraints. Determining the proper relation between means and ends in situations of great complexity and uncertainty is never easy. Decision makers are faced with their own inadequacies and lack of knowledge, together with the pressures inherent in conflict. They cannot forget the risks and costs of restraint, yet they must also be mindful of the legal imperative to avoid unnecessary and disproportionate force. (21) As the proportionality decision...

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