Rule 71. Weapons That Are by Nature Indiscriminate

Volume II, Chapter 20, Section B.

State practice establishes this rule as a norm of customary international law applicable in both international and non-international armed conflicts. Weapons that are by nature indiscriminate are those that cannot be directed at a military objective or whose effects cannot be limited as required by international humanitarian law. The prohibition of such weapons is also supported by the general prohibition of indiscriminate attacks (see Rules 11–12).

Additional Protocol I prohibits the use of weapons which are “of a nature to strike military objectives and civilians or civilian objects without distinction”.[1] This prohibition was reaffirmed in the Statute of the International Criminal Court.[2] It has also been included in other instruments.[3]

This rule is set forth in many military manuals.[4] Violations of this rule constitute an offence under the legislation of several States.[5] This rule is also supported by official statements and reported practice.[6] This practice includes that of States not, or not at the time, party to Additional Protocol I.[7]

The prohibition of weapons which are by nature indiscriminate is also recalled in numerous resolutions adopted by the UN General Assembly, as well as in some resolutions adopted by the OAS General Assembly.[8] The rule has also been recalled by several international conferences.[9]

In their submissions to the International Court of Justice in the Nuclear Weapons case, several States not at the time party to Additional Protocol I referred to the prohibition of indiscriminate weapons.[10] In its advisory opinion, the Court affirmed that this prohibition was one of the “cardinal principles” of international humanitarian law.[11]

By virtue of the customary rule that civilians must not be made the object of attack (see Rule 1), weapons that are by nature indiscriminate are also prohibited in non-international armed conflicts. This was the reasoning behind the prohibition of certain types of mines and booby-traps in Amended Protocol II to the Convention on Certain Conventional Weapons, which is applicable in non-international armed conflicts.[12] Similarly, the Ottawa Convention, which prohibits the use of anti-personnel landmines in all armed conflicts, is based, in part, on the principle that a distinction must be made between civilians and combatants.[13]

The prohibition of weapons which are by nature indiscriminate is also set forth in several military manuals which are applicable in or have been applied in non-international armed conflicts.[14] It is also supported by a number of official statements and reported practice.[15] Practice is in conformity with the rule’s applicability in both international and non-international conflicts, as States generally do not have a different set of military weapons for international and non-international armed conflicts.

In their submissions to the International Court of Justice in the Nuclear Weapons case, many States considered that the prohibition of indiscriminate weapons was based on the principle that a distinction must be made between civilians and combatants and between civilian objects and military objectives.[16] While the Court noted that it would not consider the issue of non-international armed conflicts, it did state, however, that “States must never make civilians the object of attack and must consequently never use weapons that are incapable of distinguishing between civilian and military targets”.[17]

No official contrary practice was found with respect to either international or non-international armed conflicts. No State has indicated that it may use indiscriminate weapons in any type of armed conflict.

Several military manuals and official statements mention weapons that “have indiscriminate effects”, “strike military objectives and civilians indiscriminately” or “cannot distinguish between military objectives and civilians”, without further detail.[18] Beyond such general statements, the two criteria that are most frequently referred to are whether the weapon is capable of being targeted at a military objective and whether the effects of the weapon can be limited as required by international humanitarian law. These criteria are both laid out in Additional Protocol I: Article 51(4)(b) prohibits weapons which cannot be directed at a specific military objective and Article 51(4)(c) prohibits weapons the effects of which cannot be limited as required by the Protocol.[19] These criteria are part of the definition of indiscriminate attacks under customary international law (see Rule 12).

The criterion whereby a weapon cannot be directed at a specific military objective is referred to in several military manuals, official statements and reported practice.[20] Judge Higgins, in her dissenting opinion in the Nuclear Weapons case, stated that a weapon is indiscriminate in nature if it is incapable of being targeted at a military objective.[21] In the Martić case in 1996, the International Criminal Tribunal for the Former Yugoslavia also referred to this criterion.[22]

The criterion whereby the effects of a weapon cannot be limited as required by international humanitarian law is also referred to in several military manuals and official statements.[23] In their submissions to the International Court of Justice in the Nuclear Weapons case, several States argued that a weapon is indiscriminate if it has uncontrollable effects or if the damage would be extensive and may be expected to cause incidental civilian losses which would be excessive in relation to the military advantage anticipated.[24]

In their individual opinions in the Nuclear Weapons case, those judges of the International Court of Justice who believed that nuclear weapons are indiscriminate in nature seem to have based their analysis on the criterion of a weapon whose effects cannot be limited, as they supported their opinions by referring to the widespread destruction caused by the weapon both in time and in space.[25] These judges did not, however, attempt a specific definition.

In the preamble to a resolution adopted in 1969, the UN General Assembly stated that biological and chemical weapons “are inherently reprehensible because their effects are often uncontrollable and unpredictable”.[26] The prohibition of weapons that have “indiscriminate effects” was also recalled in a resolution adopted by the Organization of American States in 1998.[27]

Although the existence of the rule prohibiting indiscriminate weapons is not contested, there are differing views on whether the rule itself renders a weapon illegal or whether a weapon is illegal only if a specific treaty or customary rule prohibits its use. In their submissions to the International Court of Justice in the Nuclear Weapons case, the majority of States used the rule prohibiting indiscriminate weapons itself to argue their case on the lawfulness or otherwise of nuclear weapons.[28] France, however, stated that it believed the existence of a specific rule to be necessary before a particular weapon could be considered by nature indiscriminate and thus illegal.[29] In their individual opinion, the judges of the Court assessed the legality of the effects of nuclear weapons on the basis of the rule itself and independent of treaty law.[30] The discussions leading to the adoption of various UN General Assembly resolutions and the Convention on Certain Conventional Weapons are ambiguous, with some statements giving the impression that certain weapons are already prohibited by virtue of this rule and others arguing the need for a specific prohibition.[31]

The following weapons have been cited in practice as being indiscriminate in certain or all contexts: chemical,[32] biological[33] and nuclear weapons;[34] anti-personnel landmines;[35] mines;[36] poison;[37] explosives discharged from balloons;[38] V-1 and V-2 rockets;[39] cluster bombs;[40] booby-traps;[41] Scud missiles;[42] Katyusha rockets; [43] incendiary weapons;[44] and environmental modification techniques.[45] There is insufficient consensus concerning all of these examples to conclude that, under customary international law, they all violate the rule prohibiting the use of indiscriminate weapons. However, there is agreement that some of them are prohibited and they are discussed in subsequent chapters.

N.B. In order to ensure that the use of a means or method of warfare complies with international humanitarian law, Additional Protocol I requires States to adopt a national mechanism or procedure to that effect.[46] Several States, including States not party to Additional Protocol I, have implemented this requirement.[47]