Existing International Humanitarian Law
Although there is no treaty that specifically regulates cluster munitions, Additional Protocol I of 1977 to the Geneva Conventions offers internationally accepted legal standards for evaluating the problems posed by these weapons.4 The articles discussed below are considered customary law, that is, legal norms deriving from common state practice that bind all nations regardless of specific legal commitments. The CCW Protocol V on Explosive Remnants of War, agreed to in November 2003, is also relevant to cluster munitions.5
Protocol I, along with the Fourth Geneva Convention, lays out the law that protects civilians during war.6 The basic principle of this branch of IHL is that of distinction between civilians and combatants. Article 48 of Protocol I states, the Parties to the conflict shall at all times distinguish between the civilian population and combatants and between civilian objects and military objectives and accordingly shall direct their operations only against military objectives.7
Attacks that strike military objects and civilians or civilian objects without distinction are considered indiscriminate and are prohibited.8 While Protocol I recognizes that some civilian deaths are inevitable, it says states cannot legally target civilians or engage in indiscriminate attacks. Article 51(4) and Article 51(5) define the concept of indiscriminate attacks in several ways.9 Cluster munitions raise concerns under most of the definitions. These weapons are prone to being indiscriminate, particularly when certain methods of attack or older or less sophisticated models are used.
The legal analysis of cluster munitions can be organized according to their immediate impact and after-effects. Damage done during strikes raises concerns under Protocol Is proportionality test, which balances military advantage and civilian impact.10 According to Article 51(5)(b), an attack is disproportionate, and thus indiscriminate, if it 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.11 Certain kinds of cluster munition attacks tend to tip the scale toward being disproportionate. Strikes in or near populated areas are particularly problematic because when combatants and civilians commingle, civilian casualties are difficult to avoid. Based on research in Iraq, Afghanistan, and Yugoslavia, Human Rights Watch believes that when non-precision guided submunitions are used in any type of populated area, there should be a strong, if rebuttable, presumption under the proportionality test that an attack is indiscriminate. In other words, a cluster munition strike on a populated area should be considered indiscriminate under the law, unless the military, which should bear the burden of proof, could show the military advantage of a particular strike outweighed the civilian harm.
Cluster munition strikes also have the potential to be indiscriminate because the weapons cannot be precisely targeted. Article 51(4)(b) prohibits attacks which employ a method or means of combat which cannot be directed at a specific military objective.12 Article 51(5)(a), drafted in response to the carpet bombings of World War II, similarly prohibits bombings that treat separated and distinct military objectives as one.13 Cluster munitions are area weapons, useful in part for attacking dispersed or moving targets. They cannot, however, be directed at specific soldiers or tanks, a limitation that is particularly troublesome in populated areas. Cluster bombing a populated area in order to kill individual soldiers is not unlike carpet bombing a city in order to destroy separate military bases. In both cases the attack is indiscriminate.
The after-effects of cluster munitions also raise concerns under IHL. Experts disagree about the scope of the proportionality test. If it is interpreted as encompassing more than immediate loss, as Human Rights Watch believes it should be, the large number of explosive duds, which become de facto landmines, may make cluster munition use disproportionate. Unexploded submunitions cause greater loss of civilian life, injury to civilians, and damage to civilian objects14 than most types of unexploded ordnance. Taking into account both strike and post-strike casualties greatly increases the likelihood that the loss would be excessive in relation to the military advantage, especially if an attack occurred in a populated area or an area to which people might return.
Because of their dud rate, cluster munitions also exemplify weapons that can be indiscriminate in effect. Article 51(4)(c) of Protocol I says that indiscriminate attacks include those which employ a method or means of combat the effects of which cannot be limited as required by this Protocol.14 Even if a cluster munition strike is not indiscriminate, its effects may be. The effects become more dangerous if the submunitions litter an area frequented by civilians or the dud rate is high due to poor design, use in inappropriate environments, or other factors. Cluster submunition duds cannot distinguish between combatants and non-combatants and will likely injure or kill whoever disturbs them. Under either the proportionality test or the effects provision, the high dud rate of cluster munitions combined with the large number of submunitions they release challenges the principle of distinction.
Regardless of whether cluster munitions are indiscriminate, states are legally bound to minimize civilian harm from strikes and duds. Article 57(2)(a)(ii) of Protocol I imposes a duty on states to take all feasible precautions in the choice of means and methods of attack with a view to avoiding, and in any event to minimizing, incidental loss of civilian life, injury to civilians and damage to civilian objects.15 All feasible precautions implies that the weapons should be used sparingly, if at all, when it is foreseeable that they will cause more than incidental harm to civilians. The availability of alternative weapons with more precise targeting and limited after-effects should also be considered.16
CCW Protocol V on Explosive Remnants of War governs post-conflict remedial measures to minimize the effects of ERW, including submunition duds.17 It requires parties to clear ERW in their territory and facilitate clearance of explosive ordnance they used in territory not under their control. It also sets up duties to record and share information, protect humanitarian missions, and take all feasible precautions to protect civilians from ERW. The protocol does not mandate any preventive measures, but States Parties are encouraged to take generic preventive measures aimed at minimizing the occurrence of explosive remnants of war, some of which are outlined in a technical annex.18 Although it does not mention cluster munitions specifically, the obligations and voluntary recommendations apply to unexploded submunitions.
 Protocol Additional to the Geneva Convention of 12 August 1949, and Relating to the Protection of Victims of International Armed Conflicts (Protocol I) of 8 June 1977 [hereinafter Protocol I].
 Convention on Prohibitions or Restrictions on the Use of Certain Conventional Weapons Which May Be Deemed To Be Excessively Injurious or To Have Indiscriminate Effects, Protocol V on Explosive Remnants of War [hereinafter CCW Protocol V], available in Procedural Report of the Group of Governmental Experts of the State Parties to the CCW, CCW/GGE/VI/2, December 11, 2003, Annex II, Protocol on Explosive Remnants of War, pp. 10-21.
 Protocol I; Geneva Convention Relative to the Protection of Civilian Persons in Time of War of August 12, 1949. These treaties apply primarily to international conflicts. Geneva Conventions, Common Art. 2; Protocol I, Art. 1(3).
 Protocol I, Art. 48.
 Ibid., Art. 51(4).
 The five kinds of indiscriminate attacks enumerated in Protocol I are those that: are 1) not directed or 2) cannot be directed at a specific military objective, 3) have effects that violate the Protocol, 4) treat separate urban military objectives as one (carpet bombing), and 5) are disproportionate. Ibid., Art. 51(4, 5).
 In this context, disproportionate attacks are a subset of indiscriminate attacks. The attacks which form the subject of this paragraph [Art. 51(5)] fall under the general prohibition of indiscriminate attacks laid down at the beginning of paragraph 4. Claude Pilloud et al., Commentary on the Additional Protocols of 8 June 1977 to the Geneva Conventions of 12 August 1949 (Geneva: International Committee of the Red Cross, 1987), p. 623. See also ibid., p. 683.
 Protocol I, Art. 51(5)(b).
 Ibid., Art. 51(4)(b).
 Ibid., Art. 51(5)(a).
 Ibid., Art. 51(4)(c) (emphasis added).
 Protocol I, Art. 57(2)(a)(ii).
 The law of war also prohibits the use of inhumane weapons, which are those that cause superfluous injury or unnecessary suffering. See, e.g., ibid., Art. 35(2). This prohibition is designed to protect combatants, not civilians, from inhumane weapons, such as mustard gas or dum dum bullets. A few opponents have argued that cluster bombs cause superfluous injury and unnecessary suffering and should be banned as inhumane, but most critics focus on their humanitarian problems. For more information on this debate, see Major Thomas J. Herthel, On the Chopping Block: Cluster Munitions and the Law of War, Air Force Law Review 51 (2001): 256-59; Thomas Michael McDonnell, Cluster Bombs over Kosovo: A Violation of International Law? Arizona Law Review 44 (2002): 66-74.
 CCW Protocol V.
 CCW Protocol V, Art. 9, Technical Annex.