Rule 73. Biological Weapons
Rule 73. The use of biological weapons is prohibited.
Summary
State practice establishes this rule as a norm of customary international law applicable in both international and non-international armed conflicts. This rule applies to biological weapons that are meant to affect humans. Whether it is intended to apply to herbicides is discussed under Rule 76.
International and non-international armed conflicts
The prohibition of the use of biological weapons in international armed conflicts is based on the Geneva Gas Protocol and the Biological Weapons Convention.[1]  When they became party to the Geneva Gas Protocol, 37 States entered a reservation to the effect that they retained the right to retaliate if an adverse party (and in some cases that party’s ally) violated the terms of the Protocol. Because 17 of these “no first use” reservations have been withdrawn,[2]  only 20 such reservations remain.[3]  However, 18 of the remaining 20 States that have kept their reservations are party to the Biological Weapons Convention, which prohibits any possession of biological weapons, thereby making it unlawful for them to retaliate using such weapons.[4]  Thus, at present, Angola and Israel are the only States that have maintained their “no first use” reservation to the Geneva Gas Protocol and are not party to the Biological Weapons Convention.
It can be concluded from the drive to eliminate biological weapons over the last three decades that States believe that these weapons should not exist and therefore must not be used in any circumstances, including in non-international armed conflicts.
Virtually all allegations of possession by States have been denied. When Russia admitted in 1992 that it continued to have a biological weapons programme, it stated that it would definitely halt the programme. Since then, it has vigorously denied allegations that it continued to manufacture biological weapons.[5]  Reports of Iraq’s biological weapons programmes attracted the condemnation of the international community.[6]  Statements and other practice of States, both parties and non-parties to the Biological Weapons Convention, indicate that the prohibition on using biological weapons in any circumstances is not purely treaty-based.[7] 
There is widespread State practice in the form of military manuals and legislation to the effect that the use of biological weapons is prohibited irrespective of whether the State concerned is a party to the Biological Weapons Convention or whether it has made a “no first use” reservation to the Geneva Gas Protocol.[8]  The US Naval Handbook states that the prohibition of biological weapons is part of customary law and binds all States, whether or not they are party to the Geneva Gas Protocol or the Biological Weapons Convention.[9]  Three States not party to the Biological Weapons Convention have criminalized the production, acquisition, sale or use of biological weapons.[10]  There is also national case-law to the effect that biological weapons are prohibited, including in non-international armed conflicts.[11] 
The prohibition of the use of biological weapons is also supported by a number of official statements. For example, in January 1991, the United Kingdom and the United States informed Iraq that they expected it not to use biological weapons, although at that time Iraq had a “no first use” reservation to the Geneva Gas Protocol and was not yet party to the Biological Weapons Convention.[12]  In 2001, the United States accused Syria of violating the terms of the Biological Weapons Convention, although Syria was not a party to the Convention.[13]  In its submission to the International Court of Justice in the Nuclear Weapons case, Australia stated that the use of biological weapons would be contrary to “fundamental general principles of humanity”.[14] 
Several UN General Assembly resolutions called for States to adhere to the Geneva Gas Protocol and/or the Biological Weapons Convention and for strict observance by all States of the principles and objectives contained therein.[15] 
In 1990 and 1991, the ICRC reminded all parties to the Gulf War that the use of biological weapons was prohibited under international humanitarian law.[16]  In 1994, it recalled the prohibition in the context of the conflict in Angola, although Angola had a “no first use” reservation to the Geneva Gas Protocol and was not party to the Biological Weapons Convention.[17]  In neither instance was the ICRC’s assertion contested.
Practice is in conformity with the rule’s applicability in both international and non-international armed conflicts, as States generally do not have a different set of military weapons for international and non-international armed conflicts. All allegations of use of biological weapons by States have been denied and in most cases disproved.[18] 

[1] Geneva Gas Protocol (cited in Vol. II, Ch. 23, § 1); Biological Weapons Convention, preamble (ibid., § 4) and Article 1 (ibid., § 5).
[2] Australia, Belgium, Bulgaria, Canada, Chile, Estonia, France, Ireland, Republic of Korea, Netherlands, New Zealand, Romania, Russian Federation, Slovakia, South Africa, Spain and United Kingdom (ibid., § 1).
[3] Algeria, Angola, Bahrain, Bangladesh, China, Fiji, India, Iraq, Israel, Jordan, Democratic People’s Republic of Korea, Kuwait, Libyan Arab Jamahiriya, Nigeria, Pakistan, Papua New Guinea, Portugal, Solomon Islands, Viet Nam and Yugoslavia (ibid., § 1).
[4] Biological Weapons Convention, Article 1 (ibid., § 5).
[5] See the practice of the Russian Federation (and formerly the USSR) (ibid., §§ 210–213).
[6] See, e.g., the statements of Cuba (ibid., § 106), Ecuador (ibid., § 115), France (ibid., § 121), USSR (ibid., § 209), United Kingdom (ibid., §§ 219–220 and 222), United States (ibid., § 233) and Yemen (ibid., § 237); UN Secretary-General, Reports on the work of the Special Commission established pursuant to Security Council resolution 687 (1991) (ibid., § 257); UNSCOM, Final report of the Panel on disarmament and current and future ongoing monitoring and verification issues (ibid., § 258).
[7] See, e.g., the statements, practice and reported practice (ibid., §§ 76–241).
[8] See, e.g., the military manuals of Australia (ibid., §§ 12–13), Belgium (ibid., § 14), Bosnia and Herzegovina (ibid., § 15), Cameroon (ibid., § 16), Canada (ibid., § 17), Colombia (ibid., § 18), Ecuador (ibid., § 19), France (ibid., §§ 20–22), Germany (ibid., §§ 23–25), Italy (ibid., § 26), Kenya (ibid., § 27), Netherlands (ibid., §§ 28–29), New Zealand (ibid., § 30), Nigeria (ibid., § 31), Russian Federation (ibid., § 32), South Africa (ibid., § 33), Spain (ibid., § 34), Switzerland (ibid., §§ 35–36), United Kingdom (ibid., §§ 37–38), United States (ibid., §§ 39–43) and Yugoslavia (ibid., § 44) and the legislation of Armenia (ibid., § 45), Belarus (ibid., § 47), Brazil (ibid., § 48), China (ibid., § 49), Colombia (ibid., § 50), Croatia (ibid., § 51), Estonia (ibid., § 52), Georgia (ibid., § 54), Germany (ibid., § 55), Hungary (ibid., § 57), Italy (ibid., § 58), Republic of Moldova (ibid., § 61), Poland (ibid., § 64), Switzerland (ibid., § 66), Tajikistan (ibid., § 68), Ukraine (ibid., § 69) and Yugoslavia (ibid., § 73).
[9] United States, Naval Handbook (ibid., § 43); see also France, LOAC Teaching Note (ibid., § 22).
[10] See the legislation of Kazakhstan (“production, acquisition or sale”) (ibid., § 60), Republic of Moldova (draft legislation adopted in 2003) (“use”) (ibid., § 61) and Tajikistan (“production, acquisition” or “sale” and “use”) (ibid., § 68).
[11] Japan, District Court of Tokyo, Shimoda case (ibid., § 75); Colombia, Constitutional Court, Constitutional Case No. C-225/95 (ibid., § 74).
[12] United Kingdom, Letter to the President of the UN Security Council (ibid., § 220); United States, Department of State, Diplomatic Note to Iraq (ibid., § 233).
[13] United States, Statement at the Fifth Review Conference of States Parties to the Biological Weapons Convention (ibid., § 236).
[14] Australia, Oral pleadings before the ICJ in the Nuclear Weapons case (ibid., § 79).
[15] See, e.g., UN General Assembly, Res. 3256 (XXIX) (ibid., §§ 245–247) and Res. 32/77 and 33/59 A (ibid., §§ 245–246 and 253), all of which were adopted without a vote.
[16] ICRC, Memorandum on the Applicability of International Humanitarian Law (ibid., § 272) and Press Release No. 1658 (ibid., § 273).
[17] ICRC, Memorandum on Respect for International Humanitarian Law in Angola (ibid., § 274).
[18] See, e.g., the practice of the Russian Federation (and formerly USSR) (ibid., §§ 212, 231 and 277) and United States (ibid., § 108).