1. Edged Weapons

Edged Weapons are any offensive or cutting blades or other weapons made of metal or steel, such as knives, swords, machetes, daggers, or bayonets. Their use is restricted by the general rules of IHL, which prohibit attacking non-combatants, killing or wounding treacherously, and causing superfluous injury or unnecessary suffering (art. 23 of the Hague Convention IV; API, arts. 35–37).

2. Firearms

This is a very broad category of weapons, including all weapons that shoot cartridges or explosive projectiles, such as shotguns, cannons, bombs, missiles, cluster munitions, and so on. Only some of these weapons are prohibited:

•Explosive projectiles that weigh less than four hundred grams (fourteen ounces), as established by the 1868 St. Petersburg Declaration Renouncing the Use, in Time of War, of Certain Explosive Projectiles;

•Bullets that expand or flatten easily in the human body, as set forth in the 1899 Hague Peace Declarations;

•Any weapon for which the main effect is to injure by fragments that are not detectable by X-rays once inside the human body, as established by Protocol I to the 1980 Convention on Conventional Weapons (Protocol on Non-detectable Fragments); and

•Cluster munitions, as established by the Convention on Cluster Munitions adopted in Dublin in 30 May 2008 and entered into force in August 2010, which prohibits all use, stockpiling, production, and transfer of cluster munitions. As of July 2024, 124 States have joined the Convention: 112 have ratified and 12 are Signatories. In order to monitor the application of the Convention, States Parties meet regularly to make decisions regarding the application or implementation of the Convention, including the operation and status of the Convention. The First Assembly of State Parties was held in Vientiane, in Laos, from 9 to 12 September 2010. The second Assembly was held in Beirut, Lebanon, from 12 to 16 September 2011. The First Review Conference of the Convention, required to take place five years after the entry into force of the Convention under article 12, took place from 7 to 11 September 2015 in Dubrovnik (Croatia). The purpose of this Review Conference was, among other things, to review the operation and status of the Convention. The Second Review Conference was held in Geneva on 25-27 November 2020 and in a virtual format on 20-21 September 2021.

On 30 April 2010, the Central African Convention for the Control of Small Arms and Light Weapons, their Ammunition, Parts, and Components that can be used for their Manufacture, Repair, and Assembly, known as the “small arms treaty” or the Kinshasa Convention, was signed in Kinshasa, Democratic Republic of the Congo, at the 35 Ministerial Meeting of the United Nations Standing Advisory Committee on Security Questions in Central Africa. The eleven signatories are Angola, Burundi, Cameroon, the Central African Republic, Chad, the Democratic Republic of the Congo, Equatorial Guinea, Gabon, the Republic of Congo, Rwanda, Sao Tomé and Principe. The Convention entered into force on 8 March 2017. As of July 2024, it has been ratified by eight countries: Angola, Cameroon, the Central African Republic, Chad, the Democratic Republic of Congo, Equatorial Guinea, Gabon, Sao Tomé and Principe. The purpose of this Convention is to prevent, combat, and eradicate the illicit trade and trafficking in small arms and light weapons (SALW), in order to combat armed violence and ease the human trafficking caused in Africa by the illicit trade of SALW (art. 1(1) and (3)).

The obligations resting upon States Parties are, among other things, to prohibit any transfer of SALW to non-State armed groups (art. 4); to designate a national body that shall be responsible for handling issues relating to the issuance of transfer authorizations both to public institutions and to qualified private actors (art. 5); to draw up an end-user certificate that shall be issued for all import shipment (art. 6); to prohibit and penalize the possession, carrying, use, and trade of SALW by civilians within their respective territories (art. 7); and to conduct semi-annual inspections to evaluate and inventory stockpiles of SALW in the possession of armed and other authorized security groups and to collect, seize, register, and destroy any SALW that are surplus, obsolete, or illicit (art. 15). In order to monitor the application of the Convention, State Parties are required to support the establishment by the responsible for follow-up and appraisal of the implementation of activities (art. 32).

CIHL also prohibits the use of certain types of firearms in international and non-international armed conflicts. Rule 77 of the customary IHL study states that “the use of bullets which expand or flatten easily in the human body is prohibited”; Rule 78 provides that “the anti-personnel use of bullets which explode within the human body is prohibited”; Rule 79 states that “the use of weapons the primary effect of which is to injure by fragments which are not detectable by X-rays in the human body is prohibited”; while Rule 80 states that “the use of booby-traps which are in any way attached to or associated with objects or persons entitled to special protection under international humanitarian law or with objects that are likely to attract civilians is prohibited.”

3. Incendiary Weapons

These weapons come under the category of firearms. Their aim is to set fire to objects or to cause burn injuries to humans. As with all weapons, it is illegal to use them against individuals and objects protected by IHL (e.g., civilians and civilian goods, including forests).

It is also illegal to use incendiary weapons against combatants and military objectives that are located “within a concentration of civilians,” as per Protocol III to the 1980 Convention on Conventional Weapons (Protocol on Incendiary Weapons).

Rule 84 of the customary IHL study provides that “if incendiary weapons are used, particular care must be taken to avoid, and in any event to minimize, incidental loss of civilian life, injury to civilians and damage to civilian objects,” and Rule 85 states 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.” Those two rules are applicable in both international and non-international armed conflicts.

4. Weapons of Mass Destruction

This denomination includes three categories of weapons: biological, chemical, and nuclear.

Since weapons of mass destruction (WMD) are indiscriminate, by nature, their use is hard to reconcile with the spirit of IHL, which is based on the military ability to distinguish between civilian objects and military objectives and between civilians and members of armed forces.

5. Mines

For details on mines, refer to the entry on ➔ Mines

CIHL also limits the use of landmines. Rule 81 of the customary IHL study provides that “when landmines are used, particular care must be taken to minimize their indiscriminate effects,” while Rule 83 states that “at the end of active hostilities, a party to the conflict which has used landmines must remove or otherwise render them harmless to civilians or facilitate their removal.” Rules 81 and 83 are applicable in both international and non-international armed conflicts. Rule 82 provides that “a party to the conflict using landmines must record their placement, as far as possible” and is customarily applicable in international armed conflict and, arguably, in non-international ones.

6. Autonomous Weapon System, Drones and Unmanned Combat Aerial Vehicle (UCAVS)

The ICRC defines autonomous weapons as “any weapon system with autonomy in its critical functions. That is, a weapon system that can select and attack (i.e. apply force to) targets without human intervention.” Autonomous weapon systems may apply at different moment/ stage of the targeting process with some form of remaining human command control applied to the identification of the target, its confirmation, its acquisition, and its attack. However, it departs from IHL framework related to duty of commander and methods of war since it creates situation where the specific target, its location, and the timing of the subsequent attack(s) is not known to the user.

A weapon can be programmed so that it autonomously triggers an attack in response to its environment, based on a generalized target profile. In some other type of technologies one machine will undertake a certain course of action based on the information it received from another machine. As well, artificial intelligence, can be used to help assess military objectives and, consequently, to influence targeting choices of military commander. One example is the SKYNET program that used big data analytics for pattern recognition in intelligence data. Using machine-learning algorithms, this US program was searching for the multitude of communication data generated by the millions of cellular phone users in Pakistan in order to track messages between al-Qaeda members and localize some high officials for targeting purpose that would after be carried out using drones.

Whether information generated through metadata is being used in assisting a commander for targeting a military objective or an algorithm-dependent weapon is directly capable of undertaking attacks due to deep learning techniques, human judgement is slowly being put aside and replaced with algorithmically derived choices. There is currently a prevailing concern and profound worry on its usage and the unacceptability of entrusting life-and-death decisions the artificial intelligence of a machine.

There is today a controversy regarding the legal status under IHL of unmanned aerial vehicles and drones. The debate has initially focused on drone warfare applied to remote and selected targeted killing in counterterrorism operation such as in Yemen, Afghanistan, or Palestinian territory. It has later reached the level of full engagement of autonomous weapons on the battlefield. Example of the use of drones during full fledge armed conflict has been demonstrated in Libya in 2020, in the 2021 war between Armenia and Azerbaijan in Nagorno Karabagh, and in 2022 during the war in Ukraine. Although there is no treaty or customary rule prohibiting the use of autonomous attack technology, such practice raises two main questions, first regarding the autonomy of software in an attack decision, and second questioning the possibility of articulating this autonomous decision with the duty of distinction and precaution binding on all targeting rules (API, arts. 36 and 51). The qualitative legal requirement to assess the risk for civilians and the balance between this risk and the expected military advantage cannot be left to autonomous technology, and requires some form of direct human involvement, even if remote. Another important element lies in the extraterritorial dimension of such attacks, which generally take place far from the national territory of the country involved and are aggravated by the confidentiality of the agencies often operating such weapons, outside of official military command.

The targeted killing of the Chechenia president Djokhar Doudaiev by Russia in 1996 was among the first reported instance of using automated weapon system. However main public debates have occurred in relation to the use of drones by United States of America. In an especially well-known case, Yemeni-American imam Anwar al-Awlaki was killed by a drone strike in 2011. The killing, done without due process of law and carried out in Yemen, a country with which the United States was not at war, was authorized by then-President Barack Obama. Two weeks later, Obama authorized a second drone strike, which resulted in the death of al-Awlaki’s sixteen-year-old son, Abdulrahman, also a U.S. citizen. Although Obama issued the executive order 13732 in 2016 titled “United States Policy on Pre- and Post-Strike Measures to Address Civilian Casualties in U.S. Operations Involving the Use of Force”, requiring U.S. intelligence officials to publish the number of civilian casualties of drone strikes outside of war zones. Unfortunately, this executive order was not passed into law and as a result it was easy for President Trump to rollback this policy in March of 2019, calling the rule “superfluous” and distracting. A single formal check still remains on the secrecy surrounding drone killings with the 2018 National Defence Authorization Act (NDAA) that requires the Pentagon to submit annual reports on each 1st of May on confirmed or suspected civilian casualties caused by U.S. military operations. The reporting requirements were strengthened in the 2019 NDAA by congress to eliminate some of the weakness exposed in the 2018 report. For example, the treatment of all strikes as if they were occurring in the battlefield while some were carried outside of combat zones. Nonetheless, the targeted killing program has been folded into the status quo of U.S. foreign policy as demonstrated by the assassination, on 3 January 2020, of the Iranian military commander Mr. Qassem Suleimani in Iraq by a U.S. drone airstrike.

Sometime around March 2020, this longstanding trope of science fiction—autonomous attack drones eliminating human beings on the futuristic battlefield—crossed over into science fact. That’s when, during the Second Libyan Civil War, the interim Libyan government attacked forces from the rival Haftar Affiliated Forces (HAF) with Turkish-made Kargu-2 (“Hawk 2”) drones, marking the first reported time autonomous hunter killer drones targeted human beings in a conflict, according to a United Nations report.

Unmanned combat aerial vehicles, loitering munitions, and the Kargu-2 “hunted down and remotely engaged” HAF logistics convoys and retreating fighters, the UN report found. The autonomous drones were programmed to attack targets “without requiring data connectivity between the operator and munition,” meaning they located and attacked HAF forces independent of any kind of pilot or control scheme.

7. Cyber Weapons

Cyber weapons are emerging as a new category of arms in conflict and warfare. The first major publicly reported cyber-attack that resulted in material destruction was the so-called “Stuxnet worm” attack in 2006, in which the United States took over a number of nuclear centrifuges at an Iranian nuclear enrichment facility at Natanz. The Stuxnet worm caused a number of centrifuges to spin too quickly or too slowly, unbalancing the centrifuges and causing them to explode. Massive cyber operations were also reported against a State’s critical infrastructures in Estonia in 2007 as well as in Georgia during the war with Russian Federation in 2008. Since then, they are becoming routine.

Because of the novelty of the field, there is no universally accepted definition of a “cyber weapon.” The Tallinn Manual on the International Law Applicable to Cyber Warfare (“Tallinn Manual”) is the most authoritative document on the subject. It is a non-binding, academic study compiled by 19 cyber conflict experts, with input from civil society organizations like the ICRC. The writing of the Tallin Manual answered an invitation of the Tallinn based NATO Cooperative Cyber Defence Centre of Excellence gathering 38 countries. The Manual primarily focuses on how international law, including IHL, applies to cyber warfare. The Tallinn Manual 2.0, published in 2017, defines cyber weapons in the Commentary to Rule 103 as “cyber means of warfare [including any cyber device, material, instrument, mechanism, equipment or software] that are used, designed, or intended to be used to cause injury to, or death of, persons or damage to, or destruction of, objects, that is, that result in the consequences required for qualification of a cyber operation as an attack.” Throughout its 97 rules, it addresses the most severe cyber operations, those that violate the prohibition of the use of force and entitle States to exercise their right of self-defence, or those occurring during armed conflict.

The past few years have seen an increasing number of important cyber-attacks being reported publicly. Some of them were directed against - or affected - electricity and water networks, health services, banks, major logistic companies, industries, governmental bodies and administrations, and a former nuclear power plant. Some of them takes place in countries involved in armed conflicts and other in country at peace. It is necessary to distinguish cyber operations related to criminal activities and groups that must be handled under cyber security law and procedure from cyber-attacks falling within the scope the use of force against State security and the law of armed conflict. Between private criminality and use of force against State there is another range of cyber operations aimed influencing foreign public opinion and interfering in foreign election process. The attribution of a cyber-attack to a given foreign government is technically complex because they are carried out under cover of non-State bodies that may be located outside their national territory. While they may not cause direct casualties, they cost billion and they highlighted the vulnerability of essential civilian infrastructures to cyber-attacks their huge impact on the life of population, including their personal and public data.

The most important agreement regarding cyber-crime among states up to date is the Council of Europe 2001 Budapest convention on Cybercrime, with 75 States parties as of July 2024. States parties to the Convention committed to adopt legislative measure to establish as criminal offences acts ranging from illegal data interception and interference to computer-related forgery, child pornography, copyright issues, etc. It also establishes a framework for international cooperation between State parties. While many member States promote the ratification of the Budapest Convention, Russia strongly opposes this convention and, together with China and allies, argues for negotiating a new universal convention at the UN. A controversial resolution to that effect passed in November 2019 at the UN General Assembly with the aims to establish a group to examine cybercrime and set up a convention to prevent it (A/RES/74/247, 27 December 2019) However, many States opposed it stating that in its current form, this treaty is intended to create international law that would make it easier for countries to cooperate to repress political dissent instead of being directed against hackers, etc.

There has been some debate about whether IHL rules regulating weapons apply to cyber weapons. There is a consensus that IHL applies to any use of force whatever the nature of the weapon. Therefore, IHL applies as well to cyber weapon.

The Tallinn Manual emphasizes that IHL rules apply to weapons that are “indiscriminate by nature.” Cyber weapons, in turn, are indiscriminate when they cannot be “(a) directed at a specific military objective, or (b) limited in the effects as required by the law of armed conflict.” It also stresses that civilian data and civilian cyber infrastructure are not lawful target of cyber weapons. The ICRC has commented that, although cyber weapons themselves are often very precise, they spread quite easily, in part because the same cyberspace is shared by both military and civilian actors. Second and third-order effects must therefore be taken into account when making a legal determination of the status of a cyber weapon.

With regard to hackers (persons who gain unauthorized access to computers, often to manipulate them for a particular purpose), the ICRC has said that most hackers are engaged in operations unrelated to armed conflict, and therefore remain civilians protected by IHL. However, hackers who take direct part in hostilities and use their skills in support of one side or another in an armed conflict would lose their legal protection against direct attack.