The use of any weapon not expressly mentioned under this Section of the Manual is subject to the general rules and principles of customary and treaty law of international armed conflict (in particular the principle of distinction and the prohibition of unnecessary suffering), as well as to any other treaty law applicable for Contracting Parties.

[Commentary]

(a) Air-Delivered Land Mines
1. There is no customary international law prohibition on the use of land mines.
2. For Contracting Parties to the 1997 Ottawa Convention, the use of all anti-personnel land mines — including those that are air-delivered — is prohibited.^[166] However, the 1997 Ottawa Convention does not cover command-detonated weapons or anti-tank/vehicle mines.
3. The 1996 Amended Protocol II to the CCW — while prohibiting certain types of booby traps^[167] — does not ban the use of anti-personnel mines, but restricts their use (and the use of anti-vehicle mines) for Contracting Parties to this instrument. In particular, air-delivered mines dropped from an aircraft or otherwise qualify as “remotely delivered mines”^[168] to which (Art. 6 of the 1996 Amended Protocol II to the CWC)^[169] special restrictions regarding self-destruction and self-deactivation apply.

(b) Air-Delivered Naval Mines
1. The use of air-delivered free-floating (unanchored) naval mines is prohibited unless they are directed against a military objective and become harmless within a reasonable time after being dropped. Art. 1 (1) of the 1907 Hague Convention (VIII)^[170] imposes a one-hour time limit, an approach adopted in the Commentary on the SRM/ACS.^[171] The laying of either armed mines or the arming of pre-laid mines must be notified, typically through the NOTMAR (“Notice to Mariners”) system, as soon as exigencies permit, unless they are designed only to detonate against vessels that qualify as military objectives.

(c) Beyond Visual Range Weapons Systems
1. The term “beyond visual range” refers to situations in which the target cannot be visually identified, for instance because it is too distant (“over the horizon”) or where it cannot be seen due to night, weather conditions, terrain, etc.
2. Beyond visual range weapons systems are not treated separately, either in treaty law or in customary international law. Their use is subject to all standard rules applicable to attacks in international armed conflict.^[172]
3. Missiles and other projectiles fired from beyond visual range are lawful when their employment permits distinguishing military objectives and combatants from civilians and civilian objects. Such may be accomplished through sensors on the weapon itself, or through external guidance, for instance from the aircraft.

(d) Blast Weapons
1. Blast weapons create a pressure wave triggered by an explosion in order to damage objects and/or injure enemy combatants. In other words, the destructive force of a blast weapon is the overpressure it causes. For instance, a bomb relying on blast may be used to cause a building to collapse. Blast weapons must be distinguished from fragmentation weapons, such as a hand grenade, causing material destruction or combatant injury through the fragments of the weapon itself, or through items (e.g., nails) contained within the weapon. Blast is an inherent aspect of high explosive munitions, whether they are weapons dependent solely on blast or a combination of blast and fragmentation. For fragmenting munitions, see the Commentary on Rule 7 (h).
2. Damage to or destruction of military objectives and combatant death or injury through blast has been a feature of air-delivered weapons since the beginning of air warfare. No treaty of the law of international armed conflict prohibits blast weapons. Based upon State practice, blast weapons are not regarded as “calculated, or of a nature, to cause unnecessary suffering or superfluous injury to combatants” (see Rule 5 (b)).
3. Some blast weapons may appear to be incendiary weapons because the explosion that causes the blast can cause a fire. However, blast weapons have no greater fire-starting capability than other high-explosive munitions. Nor do blast weapons have a fire-sustaining capability. In view of the definition of incendiary weapon in Protocol III to the CCW,^[173] blast weapons are not incendiary weapons. For incendiary weapons, see the Commentary on Rule (7) (i).

(e) Cluster Munitions
1. Cluster munitions consist of a canister or delivery body containing multiple, conventional explosive fragmenting submunitions intended to apply force uniformly over an area. Depending on their nature, submunitions can be effective against enemy heavy armour, vehicles with light armour, parked aircraft, similar “soft” material targets, and enemy combatants.
2. The Final Report to the Prosecutor of the ICTY by the Committee Established to Review the NATO Bombing Campaign against the Federal Republic of Yugoslavia reviewed the use of cluster munitions dur-ing the 1999 Operation Allied Force Campaign.^[174] It recommended against prosecution based on the use of cluster munitions because the law of international armed conflict did not specifically address such weapons, although the report did caution (paragraph 27) that “cluster bombs must be used in compliance with the general principles applicable to the use of all weapons”. In the years that followed, international concern grew with respect to cluster munitions. In particular, considering that cluster munitions disperse large numbers of explosive submunitions or bomblets over wide areas, they are liable to cause hazard to civilians (especially when they are used in densely populated areas). In addition, submunitions become a long-term hazard to civilians when they fail to detonate. Technological advances in recent years have dramatically decreased the failure rates of newly produced cluster munitions used by some modern armed forces. Nevertheless, concern also exists about the widespread distribution of the submunitions (bomblets) of cluster munitions.
3. In part, the problem was addressed with the adoption of the 2003 Protocol V to the CCW, which focuses on clearance of all forms of explosive remnants of war from the battlefield (not necessarily cluster munitions). Contracting Parties to the 2003 Protocol V to the CCW agree to mark, clear, remove, or destroy explosive remnants of war in territories under their control as soon as feasible after the cessation of active hostilities. Where a user of explosive remnants of war does not control the territory on which the explosive remnants are located, it must, where feasible, provide technical, financial, material or human resources assistance to effect clearance.^[175] Although not reflecting customary international law, the explosive remnants of war treaty obligations are not objected to by any State.
4. However, many States felt that the 2003 Protocol V to the CCW would not be sufficient to address, in a comprehensive way, the humanitarian problems caused during and after the use of cluster munitions, in particular because of some of their inherent characteristics. This led to the adoption, in 2008, of the Dublin Convention on Cluster Munitions. Art. 1 (1) of the Convention bans, inter alia, the use of many cluster munitions.^[176] This Convention, which obviously applies only to Contracting Parties, does not address (as per the definition of “cluster munition” contained in Art. 2 (2)), munitions containing submunitions of 20 kilograms or more, containing fewer than 10 submunitions, weighing more than four kilograms, that have self-deactivating and self-destructive features, and containing submunitions designed to detect and engage a single target. At the time of writing, there are thirty States that are Contracting Parties to the Convention and one hundred and four States are signatories. However, the Convention is openly opposed by a number of States.

(f) Delayed-Action Munitions
• Delayed-action munitions are high-explosive munitions generally employed in conjunction with standard, instant-detonation munitions. A key purpose of air-delivered delayed-action munitions is to impede damage control of targeted airfields or similar military objectives. While their employment against military objectives is not as such prohibited, their effects in areas where civilians may be present must be weighed in light of Section D, in particular the principle of proportionality (see Rule 14).

(g) Depleted Uranium Munitions
• Air-delivered penetrating munitions are common. Penetrating munitions are high velocity projectiles con-taining a heavy penetrator, generally depleted uranium or tungsten, designed to pierce armoured targets. Depleted uranium (DU) is used in some air-delivered penetrating munitions because its density and toughness create a particularly effective penetrating combination to defeat enemy armour at greater range. DU has been the subject of multiple national and international organization health studies. None of these studies has found that DU munitions could be considered an unlawful weapon.

(h) Fragmenting Munitions
1. Fragmenting munitions are anti-personnel and/or anti-materiel munitions that (as suggested by their name) project a large number of projectiles on detonation. They have been a major casualty producer on the battlefield, either through fragmenting artillery shells, “grape shot”, hand grenades, or more modern forms of pre-fragmented ground and air-delivered munitions. The purpose of multiple-fragmenting munitions is to increase the probability of wounding enemy combatants within range of its fragments. Air-delivered fragmenting munitions include single bombs in a variety of weights and canister bombs containing smaller bomblets, the latter commonly referred to as cluster munitions (on cluster munitions, see Commentary on Rule 7 (e)).
2. The fragmenting munitions referred to here ought not to be confused with the weapons dealt with under Rule 6 (f) (“weapons the primary effect of which is to injure by fragments which in the human body escape detection by x-ray), because the fragment munitions referred to here contain fragments that can be detected by x-ray.

(i) Incendiary Weapons
1. An incendiary weapon is any weapon which is primarily designed to set fire to objects or to cause burn injury to persons through the action of flame, heat, or combination thereof, produced by a chemical reaction of a substance on the target. Incendiary weapons can take the form of bombs, rockets, shells, and other containers of incendiary substances.^[177]
2. Although the 1868 St. Petersburg Declaration prohibited the use of exploding or inflammable projectiles with a weight under 400 grammes on the basis that their employment would uselessly aggravate “the sufferings of disabled men, or render their death inevitable”,^[178] State practice demonstrates that tracer ammunition is not prohibited. This practice was confirmed in Art. 18 of the HRAW which provided that the “use of tracer, incendiary or explosive projectiles by or against aircraft is not prohibited”.^[179] State practice validates the provision of Art. 18 of the HRAW. Aircraft often employ a mix of tracers and standard ammunition against combatants for range-finding purposes during darkness. The simultaneous use of such ammunition against a variety of targets, including vehicles and personnel, is not unlawful because it is not exclusively designed for anti-personnel use.
3. Air-delivered incendiary weapons include anti-personnel flame weapons that may start fire, such as napalm, or anti-materiel fire-sustaining weapons using thermite or thermate. The 1980 Protocol III to the CCW restricts use, but does not prohibit incendiary weapons per se. With respect to air-delivered incendiary weapons, the 1980 Protocol III to the CCW prohibits “in all circumstances” (Art. 2 (2)), for Contracting Parties, the employment of air-delivered incendiary weapons against military objectives located within a concentration of civilians.^[180] All States, including non-Contracting Parties to the 1980 Protocol III to the CCW, are governed, in particular, by the Rules prohibiting indiscriminate attacks or attacks violating the principle of proportionality and the obligation to take feasible precautions in attack (see, respectively, Rule 13 and Rule 14 as well as Section G).
4. Art. 2 of the 1980 Protocol III to the CCW (“Protection of civilians and civilian objects”) restricts use, but does not prohibit the employment of incendiary weapons against combatants.^[181]
5. Unless intentionally used for incendiary purposes, munitions which may have incidental incendiary effects, such as illuminants, tracers, smoke or signalling systems (such as white phosphorous) are not considered incendiary weapons.^[182] For example, use of the non-pyrophoric compound barium nitrate in a tracer round is to enable a gunner to direct his rounds onto his target. Similarly, munitions can be used which contain fragments of white phosphorous. Such use is usually intended for marking a target or masking friendly force movement. These weapons do not qualify as incendiary weapons if they are used for such purposes. However, because they may incidentally start fires, caution is called for if used in densely populated areas.
6. Smoke is an inherent by-product of battlefield munition use, but is also deployed as a ground and air-delivered munition for screening movement of friendly forces. It is expressly (Art. 1 (b) (i)) excluded from the definition of incendiary weapon in the 1980 Protocol III to the CCW. Smoke is a chemical weapon only if it meets the definition of a chemical weapon in the CWC. Military smoke weapons historically have not.
7. Incendiary weapons are not chemical weapons as defined in the CWC,^[183] nor are they blast weapons (see Rule 7 (d)).

(j) Non-Lethal Weapons
1. Non-lethal weapons (often labelled less-lethal) are intended to incapacitate or repel personnel or disable equipment without causing death or serious injury. The distinction between non-lethal and lethal weapons is that the former are intentionally designed with non-lethal effects in mind. Nevertheless, in practice, non-lethal weapons may occasionally cause grave injuries or fatalities, whereas lethal weapons may cause only minor wounding. Therefore, some commentators object to the designation of a category of weapons as “non-lethal”.
2. No treaty addresses non-lethal weapons, whether air-delivered or not, as a generic category. Still, if the designation of weapons as “non-lethal” is accepted, it must be remembered that all weapons — however labelled — are governed by the law of international armed conflict. Some weapons which could be considered “non-lethal,” such as blinding laser weapons (see Rule 6 (c)), have been prohibited for Contracting Parties through treaty law. The use of all weapons, however labelled, is governed by the law of international armed conflict.

(k) Nuclear Weapons
1. Ever since Hiroshima and Nagasaki, the use of nuclear weapons has been the subject of heated debates.
2. The ICJ, in its 1996 Nuclear Weapons Advisory Opinion, held that “[i]n the view of the vast majority of States as well as writers, there can be no doubt as to the applicability of humanitarian law to nuclear weapons.”^[184] The ICJ stressed in this context the importance of the cardinal principles of distinction and unnecessary suffering,^[185] as well as the principle of proportionality and the rules governing the protection of the environment (see Rule 14 as well as Section D and Section M).^[186]
3. The ICJ further pronounced, by an eleven to three majority, that “[t]here is in neither customary nor conventional international law any comprehensive and universal prohibition of the threat or use of nuclear weapons as such.”^[187] This decision of the ICJ was arrived at after reviewing a long list of treaties, ranging from reviewing the prohibition of poison, poisoned weapons, poisonous gases, bacteriological weapons, chemical weapons, to those relating to protection of the environment and those establishing nuclear weapon free zones.
4. The ICJ added (by seven votes to seven, with the President’s casting vote): “It follows from the above-mentioned requirements that the threat or use of nuclear weapons would generally be contrary to the rules of international law applicable in armed conflict, and in particular the principles and rules of humanitarian law; However, in view of the current state of international law, and of the elements of fact at its disposal, the Court cannot conclude definitively whether the threat or use of nuclear weapons would be lawful or unlawful in an extreme circumstance of self-defence, in which the very survival of a State would be at stake.”^[188] The last sentence of this part of the Advisory Opinion has been harshly criticized in the legal literature on the ground that it confuses the jus in bello with the jus ad bellum.
5. As a matter of policy, authority to employ nuclear weapons is generally retained at the highest level of government.

(l) Small-Calibre Projectiles
1. In the late 1970s, proposals were made for a CCW protocol to regulate certain types of military small-calibre projectiles. However, such proposals received little or no support in the CCW review conferences.
2. Small calibre weapons historically have seen widespread use by air forces, although much less so in post-WWII conflicts. Small-caliber weapons retain relevance in modern air warfare for certain aircraft and missions, such as rotary-wing gunships.

166. Art. 1 (1) of the 1997 Ottawa Convention: “Each State Party undertakes never under any circumstances: (a) To use anti-personnel mines; (b) To develop, produce, otherwise acquire, stockpile, retain or transfer to anyone, directly or indirectly, anti-personnel mines; (c) To assist, encourage or induce, in any way, anyone to engage in any activity prohibited to a State Party under this Convention.”

     The concept “anti-personnel mine” is defined in Art. 2 (1) of the 1997 Ottawa Convention.

167. Art. 7 (1) and Art. 7 (2) of the 1996 Amended Protocol II to the CCW (“Prohibitions on the use of booby-traps and other devices”): “(1) Without prejudice to the rules of international law applicable in armed conflict relating to treachery and perfidy, it is prohibited in all circumstances to use booby-traps and other devices which are in any way attached to or associated with: (a) internationally recognized protective emblems, signs or signals; (b) sick, wounded or dead persons; (c) burial or cremation sites or graves; (d) medical facilities, medical equipment, medical supplies or medical transportation; (e) children’s toys or other portable objects or products specially designed for the feeding, health, hygiene, clothing or education of children; (f) food or drink; (g) kitchen utensils or appliances except in military establishments, military locations or military supply depots; (h) objects clearly of a religious nature; (i) historic monuments, works of art or places of worship which constitute the cultural or spiritual heritage of peoples; or (j) animals or their carcasses. (2) It is prohibited to use booby-traps or other devices in the form of apparently harmless portable objects which are specifically designed and constructed to contain explosive material.”
168. Art. 2 (2) of the 1996 Amended Protocol II to the CCW defines “remotely-delivered mines” as mines “not directly emplaced but delivered by artillery, missile, rocket, mortar, or similar means, or dropped from an aircraft. Mines delivered from a land-based system from less than 500 metres are not considered to be “remotely delivered”, provided that they are used in accordance with Article 5 and other relevant Articles of this Protocol.”
169. Art. 6 of the 1996 Amended Protocol II to the CCW (“Restrictions on the use of remotely-delivered mines”): “(1) It is prohibited to use remotely-delivered mines unless they are recorded in accordance with sub-paragraph I (b) of the Technical Annex. (2) It is prohibited to use remotely-delivered anti-personnel mines which are not in compliance with the provisions on self-destruction and self-deactivation in the Technical Annex. (3) It is prohibited to use remotely-delivered mines other than anti-personnel mines, unless, to the extent feasible, they are equipped with an effective self-destruction or self-neutralization mechanism and have a back-up self-deactivation feature, which is designed so that the mine will no longer function as a mine when the mine no longer serves the military purpose for which it was placed in position. (4) Effective advance warning shall be given of any delivery or dropping of remotely-delivered mines which may affect the civilian population, unless circumstances do not permit.”
170. Art. 1 (1) of the 1907 Hague Convention (VIII): “It is forbidden: (1) To lay unanchored automatic contact mines, except when they are so constructed as to become harmless one hour at most after the person who laid them ceases to control them.”
171. Para. 82 of the SRM/ACS: “It is forbidden to use free-floating mines unless: (a) they are directed against a military objective; and (b) they become harmless within an hour after loss of control over them.”
172. Para. 78 of the SRM/ACS: “Missiles and projectiles, including those with over-the-horizon capabilities, shall be used in conformity with the principles of target discrimination as set out in paragraphs 38–46.”

     NWP, Para. 9.10 (“Over-the-horizon weapons systems”): “Missiles and projectiles with OTH or beyond-visual-range capabilities are lawful provided they are equipped with sensors or are employed in conjunction with external sources of targeting data that are sufficient to ensure effective target discrimination.”

173. For the definition of “incendiary weapons” in Art. 1 (1) of the 1980 Protocol III to the CCW, see fn. 177.
174. Final Report to the Prosecutor by the Committee Established to Review the NATO Bombing Campaign Against the Federal Republic of Yugoslavia, available via www.icty.org/x/file/About/OTP/otp_report_nato_bombing_en.pdf
175. Art. 3 of the 2003 Protocol V to the CCW (“Clearance, Removal or Destruction of Explosive Remnants of War”): “(1) Each High Contracting Party and party to an armed conflict shall bear the responsibilities set out in this Article with respect to all explosive remnants of war in territory under its control. In cases where a user of explosive ordnance which has become explosive remnants of war, does not exercise control of the territory, the user shall, after the cessation of active hostilities, provide where feasible, inter alia technical, financial, material or human resources assistance, bilaterally or through a mutually agreed third party, including inter alia through the United Nations system or other relevant organisations, to facilitate the marking and clearance, removal or destruction of such explosive remnants of war. (2) After the cessation of active hostilities and as soon as feasible, each High Contracting Party and party to an armed conflict shall mark and clear, remove or destroy explosive remnants of war in affected territories under its control. Areas affected by explosive remnants of war which are assessed pursuant to paragraph 3 of this Article as posing a serious humanitarian risk shall be accorded priority status for clearance, removal or destruction. (3) After the cessation of active hostilities and as soon as feasible, each High Contracting Party and party to an armed conflict shall take the following measures in affected territories under its control, to reduce the risks posed by explosive remnants of war: (a) survey and assess the threat posed by explosive remnants of war; (b) assess and prioritise needs and practicability in terms of marking and clearance, removal or destruction; (c) mark and clear, remove or destroy explosive remnants of war; (d) take steps to mobilise resources to carry out these activities. …”
176. Art. 1 (1) of the 2008 Dublin Convention on Cluster Munitions: “Each State Party undertakes never under any circumstances to: (a) Use cluster munitions; (b) Develop, produce, otherwise acquire, stockpile, retain or transfer to anyone, directly or indirectly, cluster munitions; (c) Assist, encourage or induce anyone to engage in any activity prohibited to a State Party under this Convention.”
177. Art. 1 (1) of the 1980 Protocol III to the CCW defines “incendiary weapons” as “any weapon or munition which is primarily designed to set fire to objects or to cause burn injury to persons through the action of flame, heat, or a combination thereof, produced by a chemical reaction of a substance delivered on the target. (a) Incendiary weapons can take the form of, for example, flame throwers, fougasses, shells, rockets, grenades, mines, bombs and other containers of incendiary substances. (b) Incendiary weapons do not include: (i) Munitions which may have incidental incendiary effects, such as illumuninants, tracers, smoke or signalling systems; (ii) Munitions designed to combine penetration, blast or fragmentation effects with an additional incendiary effect, such as armour-piercing projectiles, fragmentation shells, explosive bombs and similar combined-effects munitions in which the incendiary effect is not specifically designed to cause burn injury to persons, but to be used against military objectives, such as armoured vehicles, aircraft and installations or facilities.”
178. Fourth operative paragraph of the 1868 St. Petersburg Declaration, see fn. 134.
179. Art. 18 of the HRAW, see fn. 160.
180. Art. 2 (2) of the 1980 Protocol III to the CCW: “It is prohibited in all circumstances to make any military objective located within a concentration of civilians the object of attack by air-delivered incendiary weapons.”

     The expression “concentration of civilians” is defined in Art. 1 (2) of the 1980 Protocol III to the CCW as “any concentration of civilians, be it permanent or temporary, such as in inhabited parts of cities, or inhabited towns or villages, or as in camps or columns of refugees or evacuees, or groups of nomads.”

181. However, the ICRC takes the position that “The anti-personnel use of incendiary weapons is prohibited, unless it is not feasible to use a less harmful weapon to render a person hors de combat.” (see Rule 85 of the ICRC Customary IHL Study, at page 289)
182. Art. 1 (b) of the CCW: “Incendiary weapons do not include: (i) Munitions which may have incidental incendiary effects, such as illuminants, tracers, smoke or signalling systems; (ii) Munitions designed to combine penetration, blast or fragmentation effects with an additional incendiary effect, such as armour-piercing projectiles, fragmentation shells, explosive bombs and similar combined-effects munitions in which the incendiary effect is not specifically designed to cause burn injury to persons, but to be used against military objectives, such as armoured vehicles, aircraft and installations or facilities.” The latter are often referred to as combined effects munitions.
183. Art. II (1) of the CWC, see fn. 146.
184. ICJ, Nuclear Weapons Advisory Opinion, para. 85.
185. ICJ, Nuclear Weapons Advisory Opinion, para. 78.
186. ICJ, Nuclear Weapons Advisory Opinion, para. 30.
187. ICJ, Nuclear Weapons Advisory Opinion, para. 105 (2) B.

     At the time of signature of AP/I, the United Kingdom declared that it had signed AP/I on the basis of the understanding that “the rules introduced by the Protocol apply exclusively to conventional weapons without prejudice to any other rules of international law applicable to other types of weapons. In particular, the rules so introduced do not have any effect on and do not regulate or prohibit the use of nuclear weapons.” Similarly, the USA (which, while having signed AP/I, has not ratified it), at signature of AP/I, stated that its signature is subject to the understanding that “the rules established by this protocol were not intended to have any effect on and do not regulate or prohibit the use of nuclear weapons.”

188. ICJ, Nuclear Weapons Advisory Opinion, para. 105 (2) E.