The principal purpose of the rule on proportionality in international humanitarian law is to require a certain type of balancing exercise in the execution of any targeting operation. While in principal a military objective may always be attacked, the rule recognises the reality of situations where the attack on the military objective yields only a limited military advantage, while the expected civilian losses, or damage to civilian objects, appear excessive compared to that advantage. In such situations, the principle of proportionality operates to prohibit the attack as disproportionate. Thus, even if a target is a lawful military objective, the issue of proportionality arises and may either affect the means and methods of warfare, or even effectively prohibit the execution of an attack. According to the First Additional Protocol, violating the rule of proportionality renders the attack indiscriminate.152 This rule is not expressed in
151 See ICRC, ‘Basic Rules of the Geneva Conventions and Their Additional Protocols’ (1988), available at http://www.icrc.org/eng/assets/files/other/icrc_002_0365.pdf, (accessed 14th July 2015). 152 See AP I, supra n.104, Article 51(5)(b) and Article 57(2)(a)(iii).
either Common Article 3 or the Second Additional Protocol, but it is deemed to be a rule of customary international law, applicable to both international and non-
international armed conflicts.
According to Rule 14 of the ICRC’s study of customary international humanitarian law:
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.153
The key issue, therefore, is in defining what exactly constitutes “excessive”. In the commentary to Article 51(5) of the First Additional Protocol, from where the text expressing the rule on proportionality originates, it is stated:
Of course, the disproportion between losses and damages caused and the military advantages anticipated raises a delicate problem: in some situations there will be no room for doubt, while in other situations there may be reason for hesitation. In such situations the interests of the civilian population should prevail.154
Thus, the principle of proportionality acts as a check on the broader principle of military necessity. The expected collateral damage from an attack must not be
excessive in relation to the anticipated military advantage.155
The first step, then, in any assessment of proportionality is a pre-execution consideration of the expected collateral damage, rather than a post-execution evaluation of the outcomes of a military operation.156
Civilian casualties are always regrettable, however if the expected level of casualties is not excessive relative to the anticipated military advantage of an attack, those
153 See Jean-Marie Henckaerts and Louise Doswald-Beck, Customary International Humanitarian
Law, supra n.113, at Rule 14.
154 See Yves Sandoz, Christophe Swinarski and Bruno Zimmermann (eds), Commentary on the
Additional Protocols, ICRC, Geneva (1987), at paras.1979-1980.
155 See AP I, supra n.104, Article 51(5)(b), Article 57(2)(a)(iii), and Article 57(2)(b).
156 See AP I, ibid, Article 51(5)(b). See also Joseph Holland, ‘Military Objective and Collateral Damage: Their Relationship and Dynamic’, 7 Y.B of Int’l Hum. Law 35 (2004), at 50.
casualties would not be disproportionate under this analysis, and the attack would not be unlawful for lack of proportionality. The principle of proportionality is not a counsel for perfection and does not demand a nil rate of civilian casualties. The objective of the rule is to mitigate, rather than eliminate, the effects of warfare, as it is recognised that the latter would be an impossible objective during any armed conflict. The immunity enjoyed by civilians is not an absolute, provided of course that they are not targeted indiscriminately.157
The second step in any proportionality assessment relates to evaluating the expected military advantage of an attack. While this assessment must be completed for each and every intended attack, debate has arisen over the scope of the anticipated
advantage a state may use to justify an attack. Some scholars, in particular Duffy and Neuman, argue that the specific attack must be weighed against the specific military objective that an individual attack will achieve.158 An alternative analysis would be to assess the anticipated advantage as a whole, considering the overarching military objective of the entire military campaign. For example, the US could justify the killing of the eleven civilians surrounding Baitullah Mehsud as collateral damage weighed against either the specific objective of eliminating Mehsud or the
overarching objective of defeating the Taliban. The analysis proffered by Duffy and Neuman places a greater restriction on the targeting state, as only the military
advantage of a specific target can be used to justify collateral damage, while the latter analysis permits the targeting state greater latitude by allowing it to weigh the
collateral damage of a specific attack to the military benefit in the context of the objectives of the entire campaign.
The final step in any proportionality assessment is to weight the prospectively determined collateral damage against the military advantage, so as to ensure that the damage will not be excessive to the anticipated gain. The term ‘excessive’ is vague, and unfortunately there exists little by way of state practice or opinio juris to readily determine its exact meaning and scope. Proportionality is assessed on a case-by-case
157 See ibid.
158 See Helen Duffy, The ‘War on Terror’ and the Framework of International Law, (Cambridge University Press, 2005), at 231-235. See also Noam Neuman, ‘Applying the Rule of Proportionality: Force Protection and Cumulative Assessment in International Law and Morality’, 7 Y.B of Int’l Hum. Law 79 (2004), at 96-98.
basis, requiring that, for each intended attack, the targeting state must weigh the value of the target, the location of the attack, the timing of the attack, the number of
anticipated civilian casualties, and the amount of damage anticipated to civilian objects.
Returning to the drone strike that killed Baitullah Mehsud, the key issue in any prospective proportionality assessment would have been whether the anticipated collateral damage, including people in the house, other civilians nearby, and the house itself, was excessive relative to the value of targeting and eliminating Mehsud.
Obviously, given Mehsud’s position as a Taliban leader, the US could have justified a greater number of civilian casualties resulting from the strike.