In any armed conflict, the right of parties to the conflict to choose the methods or means of warfare is not unlimited, but rather is strictly regulated by International Humanitarian Law (IHL) as codified in the Geneva Conventions and its Additional Protocols. Of particular relevance are the concepts of proportionality, military necessity, and limits on the destruction of civilian property.
Prohibition on the Indiscriminate and Disproportional Use of Force
Under Protocol I, Article 51(4), indiscriminate attacks are prohibited. Israel is not a party to Protocol I, but the provisions prohibiting indiscriminate warfare are considered to be norms of customary international law, binding on all parties in a conflict, regardless of whether it is an international or internal armed conflict.4 Indiscriminate attacks are "those which are not directed against a military objective," "those which employ a method or means of combat which cannot be directed at a specific military objective," or "those which employ a method or means of combat the effects of which cannot be limited as required by the Protocol," "and consequently, in each such case, are of a nature to strike military objectives and civilians or civilian objects without distinction."5
Among the types of attacks specifically prohibited as indiscriminate is "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."6 Also prohibited are "attacks against the civilian population or civilians by way of reprisal."7
The term "means" of combat refers generally to the weapons used; "method" refers to the way in which such weapons are used. Casualties that are a consequence of accidents, as in situations in which civilians live adjacent to military installations, may be considered incidental to an attack on a military objective-so called "collateral damage"-but care must still have been taken to try and identify the presence of civilians. Article 57 of Protocol I sets out the precautions required, among them to "do everything feasible to verify that the objectives to be attacked are neither civilians or civilian objects," to "take all feasible precautions in the choice of means and methods of attack with a view to avoiding, and in any case minimizing, incidental loss of civilian life, injury to civilians and damage to civilian objects," and to refrain from deciding to launch any attack-or to cancel or suspend any attack already in progress-"which may be expected to cause" such deaths, injuries or damage "which would be excessive in relation to the concrete and direct military advantage anticipated."8 In its authoritative Commentary on the protocols, the International Committee of the Red Cross (ICRC) states what is meant by "feasible" in Article 57: "What is required ... is to take the necessary identification measures in good time to spare the population as far as possible."9
The principle of proportionality places a duty on combatants to choose means of attack that avoid or minimize damage to civilians. In particular, the attacker should refrain from launching an attack if the expected civilian casualties would outweigh the importance of the military objective.10 Protocol I, Article 57 ("Precautions in attack") requires those who plan and/or execute an attack to cancel or desist from the attack in such circumstances.
The ICRC Commentary on Article 57 of Protocol I sets out a series of factors that must be taken into account in applying the principle of proportionality to the incidental effects that attacks may have on civilian persons and objects:
The danger incurred by the civilian population and civilian objects depends on various factors: their location (possibly within or in the vicinity of a military objective), the terrain (landslides, floods etc.), accuracy of the weapons used (greater or lesser dispersion, depending on the trajectory, the range, the ammunition used etc.), technical skills of the combatants (random dropping of bombs when unable to hit the intended target).11
As expressed in the ICRC Commentary, "the golden rule to be followed" when making determinations about the proportionality of an attack is "the duty to spare civilians and civilian objects in the conduct of military operations."12
Military necessity is an urgent need, admitting of no delay, for the taking by a commander, of measures which are indispensable for forcing as quickly as possible the complete surrender of the enemy by means of regulated violence, and which are not prohibited by the laws and customs of war.
The Commentary to Protocol I subsequently refers to this definition by saying that it is "based on four foundations: urgency, measures which are limited to the indispensable, the control (in space and time) of the force used, and the means which should not infringe on an unconditional prohibition."14
While military necessity does grant military planners a certain degree of freedom of judgment about the appropriate tactics for carrying out a military operation, "it can never justify a degree of violence which exceeds the level which is strictly necessary to ensure the success of a particular operation in a particular case."15 Hence, the degree of autonomy granted to military planners by the concept of military necessity is subservient to the rule of proportionality and other "laws and customs of war."
Limits on the Destruction of Civilian Property
Destruction of civilian property can be a grave breach of the Fourth Geneva Convention, and thus a war crime, if it amounts to "extensive destruction and appropriation... not justified by military necessity and carried out unlawfully and wantonly."18 To amount to a grave breach, the destruction and appropriation "must be extensive: an isolated case is not enough."
4 See Dieter Fleck (ed.), The Handbook of Humanitarian Law in Armed Conflict (Oxford: Oxford University Press, 1995), p. 120 ("The general prohibition against indiscriminate warfare applies independently of Arts. 48 and 51 [of Protocol I]. The relevant provisions of the Additional Protocols merely codify pre-existing customary law, because the principle of distinction belongs to the oldest fundamental maxims of established customary rules of humanitarian law. It is also virtually impossible to distinguish between international and noninternational armed conflicts in this respect....").
9 ICRC, Commentary to the Protocol Additional to the Geneva Conventions of 12 August 1949, and relating to the Protection of Victims of International Armed Conflicts (Protocol I), 8 June 1977, pp. 681-82