Means and Methods of Warfare

A means of warfare is a weapon or weapon platform. A method of warfare is the manner in which a weapon is used. In addition to the general rules on the conduct of hostilities, the use of weapons is subject to two general customary principles.¹

Inherently indiscriminate weapons

The use of an inherently indiscriminate weapons is unlawful in any armed conflict. This general principle, which seeks to protect civilians, is a corollary of the IHL prohibition on indiscriminate attacks.²An indiscriminate weapon is one that either cannot be targeted at a military objective or whose effects cannot be sufficiently limited.³

Only a very few weapons are agreed to be inherently indiscriminate. This is the case for biological weapons⁴ and certain unguided missiles.⁵

Although they may often have indiscriminate effects, anti-personnel mines are not inherently indiscriminate, as they may be used in a discriminate manner by being placed in a marked and fenced area to exclude civilians.⁶Their use is comprehensively prohibited for all States Parties under the 1997 Anti-Personnel Mine Ban Convention.

Superfluous injury and unnecessary suffering

The use in any armed conflict of means and methods of warfare of a nature to cause superfluous injury or unnecessary suffering is prohibited.⁷ This second general principle primarily protects combatants and others directly participating in hostilities. The rule prohibits the use of weapons whose characteristics are such that they would inflict injury or suffering beyond what is necessary to render a fighter hors de combat.⁸

The use of exploding or expanding bullets; projectiles filled with glass; and poison and poisoned weapons are examples of weapons that are of a nature to cause superfluous injury or unnecessary suffering.⁹Blinding laser weapons also cause superfluous injury or unnecessary suffering.¹⁰

Rules on specific weapons

In addition to the general principles on means and methods of warfare outlined above, certain IHL rules address specific weapons. By way of example, customary IHL (and the corresponding underlying treaties) prohibits the use of chemical weapons,¹¹ including the use of riot-control agents as a method of warfare.¹² The use if incendiary weapons is restricted.¹³ Disarmament treaties prohibit the use by States Parties of anti-personnel mines, cluster munitions,¹⁴ and nuclear weapons.¹⁵

Rules on Methods of Warfare

Certain methods of warfare are prohibited in any circumstances, such as an order not to accept the surrender of the enemy (“denial of quarter”), perfidy and pillage.

Prohibition on perfidy

The prohibition on perfidy is a long-standing customary rule of IHL, applicable in all armed conflicts and designed to outlaw conduct that would undermine the protections afforded by IHL to certain objects and individuals.¹⁶ The rule prohibits acting in a manner to cause an adversary to believe that a person or object is entitled to protection under the rules of IHL, with the intent to betray that confidence in order to kill, injure or capture that adversary.¹⁷ Thus, pretending to be medical personnel engaged in treating patients and then attacking the enemy would be unlawful. Conversely, ruses of war (e.g. tactics intended to mislead an adversary) are not prohibited.¹⁸

Giving or ordering no quarter

The prohibition ‘to order that there shall be no survivors, to threaten an adversary therewith or to conduct hostilities on this basis’¹⁹ is linked to the protection of the persons hors de combat, who may no longer be attacked as long as they do not engage in hostile acts or attempt to escape.²⁰ Persons hors de combat include persons in the power of the adverse party or who clearly express an intention to surrender.²¹

Treatment of property

There is an absolute prohibition of pillage.²² Described by the ICRC as ‘a specific application of the general principle of law prohibiting theft’,²³ pillage is defined in the ICC’s Elements of Crimes as an appropriation of property, without the consent of the owner, for private or personal use.²⁴

IHL rules governing belligerent occupation regulate the treatment of property in occupied territory, distinguishing between appropriation and destruction of property, and between private and public property, and movable and immovable property. IHL generally prohibits the confiscation of private property; contributions in kind and requisition of essential supplies may exceptionally occur to satisfy the needs of the occupying forces in cases of imperative military necessity. This is only possible if the requirements of the civilian population have been taken into account and subject to the payment of fair value.²⁵ When it comes to public property, movable objects (except for the property of municipalities and of institutions dedicated to religion, charity and education, the arts and sciences) may be confiscated (without compensation) and used for military operations.²⁶ On the other hand, immovable public property must be administered by the Occupying Power according to the rules of usufruct, safeguarding its underlying value.²⁷ IHL only allows the destruction of the public and private property in occupied territory when this is rendered absolutely necessary by military operations.²⁸

Outside occupied territory and in situations of NIAC, seizing and destroying the property of an adversary is possible when ‘imperatively demanded by the necessities of war’.²⁹

1
S. Casey-Maslen, ‘Weapons’, in B. Saul and D. Akande (eds), The Oxford Guide to International Humanitarian Law, Oxford University Press (Oxford, 2020), p 265
2
ICRC, Customary IHL Rule 71: ‘Weapons That Are by Nature Indiscriminate’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule71
3
Art 51(4)(b)–(c); commentary to ICRC, Customary IHL Rule 71: ‘Weapons That Are by Nature Indiscriminate’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule71
4
See, eg, UN General Assembly Resolution 2603 A (XXIV), 16 December 1969, second preambular para; commentary to ICRC, Customary IHL Rule 71: ‘Weapons That Are by Nature Indiscriminate’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule71
5
See ICRC, Commentary on the Additional Protocols of 8 June 1977 to the Geneva Conventions of 12 August 1949, para 1958
6
A. Bellal and S. Casey-Maslen, The Additional Protocols to the Geneva Conventions in Context, Oxford University Press (Oxford, 2022), para 12.43
7
Art 23(e), 1899 and 1907 Hague Regulations; Art 35(2) AP I; ICRC, Customary IHL Rule 70: ‘Weapons of a Nature to Cause Superfluous Injury or Unnecessary Suffering’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule70
8
The International Court of Justice (ICJ) has defined unnecessary suffering as ‘a harm greater than that unavoidable to achieve legitimate military objectives’: ICJ, The Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, 8 July 1996, para 78
9
ICRC, Commentary on the Additional Protocols of 8 June 1977 to the Geneva Conventions of 12 August 1949, para 1419
10
ICRC, Customary IHL Rule 86: ‘Blinding Laser Weapons’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule86; 1995 Protocol IV on Blinding Laser Weapons to the 1980 Convention on Certain Conventional Weapons
11
ICRC, Customary IHL Rule 74: ‘Chemical Weapons’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule74; 1993 Chemical Weapons Convention
12
ICRC, Customary IHL Rule 75: ‘Riot Control Agents’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule75; Art I(5), 1993 Chemical Weapons Convention
13
ICRC, Customary IHL Rules 84–85; A. Bellal and S. Casey-Maslen, The Additional Protocols to the Geneva Conventions in Context, Oxford University Press (Oxford, 2022), para 12.19; United Nations Office for Disarmament Affairs(UNODA), The Regulation of Incendiary Weapons under International Humanitarian Law, Geneva, 2024, paras 4.2 and 6.2
14
Art 1, 2008 Convention on Cluster Munitions
15
Art 1, 2017 Treaty on the Prohibition of Nuclear Weapons
16
ICRC, Customary IHL Rule 65: ‘Perfidy’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule65
17
Art 37(1) AP I; ICRC, Customary IHL Rule 65: ‘Perfidy’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule65
18
Art 37(2) AP I; ICRC, Customary IHL Rule 57: ‘Ruses of War’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule57
19
Art 40 AP I ICRC, Customary IHL Rule 46: ‘Orders or Threats that No Quarter Will Be Given’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule46. See also Art 4(1) AP II
20
Art 41(1) AP I; ICRC, Customary IHL Rule 47 : ‘Attacks against Persons Hors de Combat’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule47.
21
Art 41(2) AP I; ICRC, Customary IHL Rule 47 : ‘Attacks against Persons Hors de Combat’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule47.
22
Arts 28 and 47, 1899 and 1907 Hague Regulations; Art 33(2) GC IV; Art 4(2)(g) AP II; ICRC, Customary IHL Rule 52: ‘Pillage’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule52
23
ICRC, Commentary to Customary IHL Rule 52
24
ICC, Elements of Crimes, ‘War crime of pillaging – ICC Statute, Arts 8(2)(b)(xvi) and 8(2)(e)(v), pp 17 and 25
25
Arts 46 and 52, 1899 and 1907 Hague Regulations; Art 55(2) GC IV; ICRC, Customary IHL Rule 51: ‘Public and Private Property in Occupied Territory’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule51
26
Arts 53 and 56, 1899 and 1907 Hague Regulations; ICRC, Customary IHL Rule 40: ‘Respect for Cultural Property’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule40; ICRC, Customary IHL Rule 51: ‘Public and Private Property in Occupied Territory’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule51 The same applies to war booty, ie military equipment captured or found on the battlefield: see ICRC, Customary IHL Rule 49: ‘War Booty’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule49
27
Art 55, 1899 and 1907 Hague Regulations; ICRC, Customary IHL Rule 51: ‘Public and Private Property in Occupied Territory’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule51
28
Art 53, GC IV; ICRC, Customary IHL Rule 51: ‘Public and Private Property in Occupied Territory’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule51.
29
Art 23(g), 1899 and 1907 Hague Regulations; ICRC, Customary IHL Rule 50: ‘Destruction and Seizure of Property of an Adversary’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule50; ICRC, Updated Commentary on GC IV, 2025, para 3456