The British yearbook of international law, 2019, 107 p.
The purpose of this paper is to determine whether a party to an armed conflict is bound to ensure that any incidental harm it may cause to enemy military personnel not or no longer liable to attack remains below a certain threshold. While the law of armed conflict provides that incidental harm to civilians must not be excessive in relation to the military advantage anticipated from an attack, the relevant treaty rules are silent on the position of protected enemy personnel. This could indicate that protected enemy personnel may be exposed to incidental harm without any limitations. However, this position is difficult to reconcile with the humanitarian considerations that underpin the law of armed conflict. Alternatively, this silence may hint at a gap in the treaties, though not necessarily in the customary rules governing the conduct of hostilities. If so, commanders would be left guessing what degree of collateral damage is permissible, which, in the absence of clarifying the applicable rules, may lead them to break the law inadvertently. Based on a detailed assessment of the law, state practice and the competing arguments put forward in the literature, the authors conclude that the principle of military necessity, more specifically the prohibition of causing unnecessary destruction, as complemented by the duty to ‘respect and protect’ certain classes of enemy personnel, imposes an obligation on belligerents to reduce the level of incidental harm inflicted on protected enemy personnel to what is unavoidable and to justify that harm with reference to the military benefit anticipated from an attack. We term this the ‘non-civilian proportionality rule’.