Related Rule
United States of America
Practice Relating to Rule 74. Chemical Weapons
The US Field Manual (1956) provides:
Although the language of the 1925 Geneva Protocol appears to ban unqualifiedly the use in war of the chemical weapons within the scope of its prohibition, reservations submitted by most of the Parties to the Protocol, including the United States, have, in effect, rendered the Protocol a prohibition only of the first use in war of materials within its scope. Therefore, the United States, like many other Parties, has reserved the right to use chemical weapons against a state if that state or any of its allies fails to respect the prohibitions of this Protocol. 
United States, Field Manual 27-10, The Law of Land Warfare, US Department of the Army, 18 July 1956, as modified by Change No. 1, 15 July 1976, § 38(d).
The US Air Force Pamphlet (1976) states:
The first use of lethal chemical weapons is now regarded as unlawful in armed conflicts. During World War II President Roosevelt, in response to reports that the enemy was seriously contemplating the use of gas warfare, stated: “Use of such weapons has been outlawed by the general opinion of civilized mankind … We shall under no circumstances resort to the use of such weapons unless they are first used by our enemies.” This United States position has been reaffirmed on many occasions by the United States as well as confirmed by resolutions in various international forums. 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 6-4(c), quoting Statement by the President, Use of Poison Gas, 12 June 1943, State Department Bulletin, Vol. 8, 1947, No. 207, p. 507.
The US Air Force Commander’s Handbook (1980) states:
The United States, however, has reserved the right to use chemical weapons against “an enemy State if such State or any of its allies fails to respect the prohibition of the Protocol.” The USSR and the People’s Republic of China have reserved similar rights. 
United States, Air Force Pamphlet 110-34, Commander’s Handbook on the Law of Armed Conflict, Judge Advocate General, US Department of the Air Force, 25 July 1980, § 6-3(a).
The US Operational Law Handbook (1993) states: “The US has renounced first use of chemical weapons.” 
United States, Operational Law Handbook, JA 422, Center for Law and Military Operations and International Law Division, The Judge Advocate General’s School, United States Army, Charlottesville, Virginia 22903-1781, 1993, p. Q-182, § (i).
The US Naval Handbook (1995) states:
The United States considers the prohibition against first use of lethal and incapacitating chemical weapons to be part of customary international law and, therefore, binding on all nations whether or not they are parties to the 1925 Gas Protocol … Consistent with its first-use reservation to the 1925 Gas Protocol, the United States maintained a lethal and incapacitating chemical weapons capability for deterrence and possible retaliatory purposes only. National Command Authorities (NCA) approval was required for retaliatory use of lethal or incapacitating chemical weapons by U.S. forces. Retaliatory use of lethal or incapacitating chemical agents was to be terminated as soon as the enemy use of such agents that prompted the retaliation had ceased and any tactical advantage gained by the enemy through unlawful first use had been redressed. Upon coming into force of the 1993 Chemical Weapons Convention, any use of chemical weapons by a party to that convention, whether or not in retaliation against unlawful first use by another nation, will be prohibited.
[The 1993 Chemical Weapons Convention] will, upon entry into force, prohibit the development, production, stockpiling and use of chemical weapons, and mandate the destruction of chemical weapons and chemical weapons production facilities for all nations that are party to it. 
United States, The Commander’s Handbook on the Law of Naval Operations, NWP 1-14M/MCWP 5-2.1/COMDTPUB P5800.7, issued by the Department of the Navy, Office of the Chief of Naval Operations and Headquarters, US Marine Corps, and Department of Transportation, US Coast Guard, October 1995 (formerly NWP 9 (Rev. A)/FMFM 1-10, October 1989), §§ 10.3.1.1 and 10.3.1.2.
The US Naval Handbook (2007) states:
10.3 Chemical Weapons
International law prohibits the use of chemical weapons in armed conflict.
10.3.1 Treaty Obligations
Prior to 1993, the 1925 Geneva Gas Protocol for the Prohibition of the use in War of Asphyxiating, Poisonous or Other Gases, and of Bacteriological Methods of Warfare (“the 1925 Gas Protocol”) was the principle international agreement in force relating to the regulation of chemical weapons in armed conflict. The far more comprehensive 1993 Convention on the Prohibition of Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction (the “1993 Chemical Weapons Convention”) prohibits the development, production, stockpiling and use of chemical weapons, and mandates the destruction of chemical weapons and chemical weapons production facilities for all nations that are party to it. … The Chemical Weapons Convention does not, however, modify existing international law with respect to herbicidal agents. The United States is a party to both treaties. 
United States, The Commander’s Handbook on the Law of Naval Operations, NWP 1-14M/MCWP 5-12.1/COMDTPUB P5800.7, issued by the Department of the Navy, Office of the Chief of Naval Operations and Headquarters, US Marine Corps, and Department of Homeland Security, US Coast Guard, July 2007, § 10.3.1.
The US Manual for Military Commissions (2010), Part IV, Crimes and Elements, includes in the list of crimes triable by military commissions:
EMPLOYING POISON OR SIMILAR WEAPONS.
a. Text. “Any person subject to this chapter who intentionally, as a method of warfare, employs a substance or weapon that releases a substance that causes death or serious and lasting damage to health in the ordinary course of events, through its asphyxiating, bacteriological, or toxic properties, shall be punished, if death results to one or more of the victims, by death or such other punishment as a military commission under this chapter may direct, and, if death does not result to any of the victims, by such punishment, other than death, as a military commission under this chapter may direct.”
b. Elements.
(1) The accused intentionally employed a substance or a weapon that releases a substance as a result of its employment;
(2) The substance was such that causes death or serious damage to health in the ordinary course of events through its asphyxiating, poisonous, bacteriological properties;
(3) The accused employed the substance or weapon with the intent of utilizing such asphyxiating, poisonous, bacteriological properties as a method of warfare;
(4) The accused knew or should have known of the nature of the substance or weapon employed; and
(5) The conduct took place in the context of and was associated with hostilities.
c. Comment.
(1) The “death or serious damage to health” required of the offense must be a direct result of the substance’s effect or effects on the human body (e.g., asphyxiation caused by the depletion of atmospheric oxygen secondary to a chemical or other reaction would not give rise to this offense).
(2) The clause “serious damage to health” does not include temporary incapacitation or sensory irritation.
(3) The use of the “substance or weapon” at issue must be proscribed under the law of armed conflict. It may include chemical or biological agents.
(4) The specific intent element for this offense precludes liability for mere knowledge of potential collateral consequences (e.g., mere knowledge of a secondary asphyxiating or toxic effect would be insufficient to complete the offense).
d. Maximum punishment. Death, if the death of any person occurs as a result of the employment of the substance or weapon. Otherwise, confinement for life. 
United States, Manual for Military Commissions, published in implementation of Chapter 47A of Title 10, United States Code, as amended by the Military Commissions Act of 2009, 10 U.S.C, §§ 948a, et seq., 27 April 2010, § 5(8), pp. IV-7 and IV-8.
The US Chemical Weapons Act (1998) provides:
It shall be unlawful for any person knowingly
(1) to develop, produce, otherwise acquire, transfer directly or indirectly, receive, stockpile, retain, own, possess, or use, or threaten to use, any chemical weapon; or
(2) to assist or induce, in any way, any person to violate paragraph (1), or to attempt or conspire to violate paragraph (1). 
United States, Chemical Weapons Act, 1998, § 229.
The US Military Commissions Act (2009) amends Chapter 47A of Title 10 of the United States Code as follows:
§ 950t. Crimes triable by military commission
“The following offenses shall be triable by military commission under this chapter at any time without limitation:
“ …
“(8) EMPLOYING POISON OR SIMILAR WEAPONS.—Any person subject to this chapter who intentionally, as a method of warfare, employs a substance or weapon that releases a substance that causes death or serious and lasting damage to health in the ordinary course of events, through its asphyxiating, bacteriological, or toxic properties, shall be punished, if death results to one or more of the victims, by death or such other punishment as a military commission under this chapter may direct, and, if death does not result to any of the victims, by such punishment, other than death, as a military commission under this chapter may direct. 
United States, Military Commissions Act, 2009, § 950t(8).
In 1966, during a debate in the First Committee of the UN General Assembly, the United States, in reply to allegations made by Hungary that the United States were using chemical weapons in Viet Nam, stated: “Allegations that the United States was using poison gas in Viet-Nam were completely unfounded.”  
United States, Statement before the First Committee of the UN General Assembly, UN Doc. A/C.1/ SR.1451, 11 November 1966, § 41.
In 1966, during a debate in the First Committee of the UN General Assembly, the United States stated that it supported the 1925 Geneva Gas Protocol, even though it had not ratified it. 
United States, Statement before the First Committee of the UN General Assembly, UN Doc. A/C.1/ SR.1452, 14 November 1966, p. 158.
In 1970, during a debate in the Third Committee of the UN General Assembly, the United States was criticized by different States for using chemical weapons in Viet Nam in violation of the 1925 Geneva Gas Protocol. It rejected the allegations and proclaimed “its intention to abide strictly by [the 1925 Geneva Gas Protocol] terms” even though it was not a party. 
United States, Statement before the Third Committee of the UN General Assembly, UN Doc. A/C.3/ SR.1789, 12 November 1970, p. 289.
At the CDDH, the United States voted against the Philippine amendment (see supra) because:
Grave breaches were meant to be the most serious type of crime; Parties had an obligation to punish or extradite those guilty of them. Such crimes should therefore be clearly specified, so that a soldier would know if he was about to commit an illegal act for which he could be punished. The amendment, however, was vague and imprecise … The amendment would also make it unlawful to use certain gases in retaliation, whereas under Protocol I only first use of such gases was unlawful. It would also punish those who used the weapons, namely, the soldiers, rather than those who made the decision as to their use, namely, Governments. 
United States, Statement at the CDDH, Official Records, Vol. VI, CDDH/SR.44, 30 May 1977, pp. 280–281, § 7.
In 1980, in a memorandum of law on the “Reported Use of Chemical Agents in Afghanistan, Laos, and Kampuchea”, a legal adviser of the US Department of State stated:
The prohibition of the first use in war of chemical weapons has, by reason of the practice and affirmations of states, become a part of the rules of customary international law which are binding on all states; and neither the limitations of the [1925 Geneva Gas] Protocol text nor reservations to it can detract from these obligations. Therefore, all states should be regarded as being bound to refrain from such first use, whether or not they or their opponents are parties to the Protocol.
In theory, an attempt might also be made to justify the use of chemical weapons in Afghanistan as a lawful reprisal against violations of the general laws of war by Afghan insurgents (such as the summary execution of Soviet prisoners). However, such an argument would face several serious problems. First, the prohibition in the [1925 Geneva Gas] Protocol and in customary international law apparently itself precludes use of chemical weapons in reprisal except in response to enemy use of weapons prohibited by the [1925 Geneva Gas] Protocol. 
United States, Department of State, Memorandum of law by a Legal Adviser on the “Reported Use of Chemical Agents in Afghanistan, Laos, and Kampuchea”, 9 April 1980, reprinted in Marian Nash Leich, Digest of United States Practice in International Law, 1980, Department of State Publication 9610, Washington, D.C., 1986, pp. 1027 and 1041, footnote 38.
The Department of State noted: “The Afghan conflict seems clearly to be an external invasion and occupation to which the rules of international armed conflict, including the rules against first use of chemical weapons, apply.” It added:
The [1925 Geneva Gas] Protocol itself does not apply to the Afghan conflict, because Afghanistan has never adhered to the Protocol … However, … the prohibition on the first use of chemical weapons in war has become a part of customary international law binding on all states, whether or not parties to the Protocol.
With respect to the conflict in Laos, the memorandum stated: “The customary law prohibition [has] generally been described as rules applying in international armed conflicts … There are at this time no strong precedents establishing that the prohibition on chemical weapons would be regarded as applying to a conflict of this character.” 
United States, Department of State, Memorandum of law by a Legal Adviser on the “Reported Use of Chemical Agents in Afghanistan, Laos, and Kampuchea”, 9 April 1980, reprinted in Marian Nash Leich, Digest of United States Practice in International Law, 1980, Department of State Publication 9610, Washington, D.C., 1986, pp. 1033 and 1036.
In 1986, during a debate in the UN Security Council, the United States stated: “The use of chemical weapons is a serious violation of international law.” 
United States, Statement before the UN Security Council, UN Doc. S/PV.2666, 24 February 1986, p. 27.
In 1987, during a debate in the UN Security Council, the United States stated that chemical weapons were not capable of distinguishing between combatants and civilians. 
United States, Statement before the UN Security Council, UN Doc. S/PV.2750, 20 July 1987, p. 18.
In an executive order issued in 1990, the US President stated: “The proliferation of chemical … weapons constitutes an unusual and extraordinary threat to the national security and foreign policy of the United States.” The order also provided for the possibility of imposing sanctions against foreign persons and governments found to have “knowingly and materially” contributed to efforts to “use, develop, produce, stockpile or otherwise acquire chemical … weapons”. 
United States, Executive Order 12735, Chemical and Biological Weapons Proliferation, 16 November 1990, preamble and Section 4(b)(1), Federal Register, Vol. 55, 1990, p. 48587.
In 1991, in a diplomatic note to Iraq concerning operations in the Gulf War, the United States stated that it “expects the Government of Iraq to respect its obligations under the Geneva [Gas] Protocol of 1925 not to use chemical … weapons”. 
United States, Department of State, Diplomatic Note to Iraq, Washington, 19 January 1991, annexed to Letter dated 21 January 1991 to the President of the UN Security Council, UN Doc. S/22122, 21 January 1991, Annex I, p. 2.
In 1991, during a debate in the UN Security Council, the United States supported the resolution on the elimination of Iraq’s chemical weapons in order to keep the region secure. 
United States, Statement before the UN Security Council, UN Doc. S/PV.2981, 3 April 1991, pp. 86–87.
In 1991, during a debate in the First Committee of the UN General Assembly, the United States stated that a ban on chemical weapons was a top priority in its foreign policy. 
United States, Statement before the First Committee of the UN General Assembly, UN Doc. A/C.1/ 46/PV.4, 15 October 1991, p. 34.
In 1993, during a debate in the First Committee of the UN General Assembly, the United States stated that it had worked for the elimination of chemical weapons. 
United States, Statement before the First Committee of the UN General Assembly, UN Doc. A/C.1/ 48/SR.5, 19 October 1993, p. 10.
At the First Conference of States Parties to the Chemical Weapons Convention in 1997, the United States stated: “The United States recognises the importance of our full participation in the chemical weapons convention at entry into force.” It added: “The United States stands committed to stopping the spread of weapons of mass destruction and to ensuring that the Chemical Weapons Convention is implemented effectively.” It further reconfirmed its good intentions by once more emphasizing its commitment to global chemical disarmament. 
United States, Statement at the First Conference of States Parties to the Chemical Weapons Convention, The Hague, 6–23 May 1997.
In 1998, in a legal review of Oleoresin Capsicum (OC) pepper spray, the Deputy Assistant Judge Advocate General of the US Department of the Navy stated:
Like the Biological Weapons Convention, the [1993 Chemical Weapons Convention] is an arms control treaty and is not limited to application during international armed conflict (i.e., it applies at all times and under all circumstances unless the treaty indicates otherwise) …
… The chemical, of course, must be potentially toxic, i.e., have harmful chemical action on life processes. Furthermore, the toxicity must affect humans or animals. 
United States, Department of the Navy, Deputy Assistant Judge Advocate General, International and Operational Law Division, Legal Review of Oleoresin Capsicum (OC) Pepper Spray, 19 May 1998, § 6(c), pp. 11–12.
In 1998, CNN alleged that the United States used chemical weapons (sarin) to kill defectors in the Vietnam War. The US State Department responded that it had not used sarin in the operation, and that “the US policy since World War II has prohibited the use of lethal chemical agents, including sarin, unless first used by the enemy”. 
United States, Department of Defense, Review of allegations concerning “Operation Tailwind”, 21 July 1998.
Later, the CNN President apologised for the report and stated: “There is insufficient evidence that sarin or any other deadly gas was used.” 
United States, American Forces Press Service, “DoD Welcomes CNN Retraction, Apology for Sarin Report”, July 1998.
In April 2006, the US permanent representative to the Organisation for the Prohibition of Chemical Weapons issued a statement requesting a US extension of the final chemical weapons destruction deadline to 29 April 2012. In that statement, he reiterated US dedication to the success of the Chemical Weapons Convention (CWC):
The United States is dedicated to the success of the Chemical Weapons Convention. We played a leading role in negotiating it. In fact, the basis for the CWC text finally opened for signature in Paris was a draft presented to the Conference on Disarmament by former president George H. W. Bush. We played a leading role in the Preparatory Commission. And we have played an active, constructive role since the treaty entered into force. We began destroying our chemical weapons stockpile years even before the Convention entered into force. And we have provided funding and assistance to other States Parties seeking to destroy chemical weapons stockpiles. Our commitment to the Chemical Weapons Convention is deep, and it is long-standing.
The United States possesses the second largest chemical weapons stockpile in the world. Safely and effectively destroying more than 27 thousand metric tons of assorted chemical weapons is an enormous challenge – one we have made strenuous efforts to meet. We expect to spend over $32 billion before we are finished. We have made every effort to ensure that our chemical weapons are destroyed safely, without harm to people or the environment; verifiably, under the eyes of OPCW inspectors; and as rapidly as feasible. 
United States, US permanent representative to the Organisation for the Prohibition of Chemical Weapons, Ambassador Eric Javits, Statement Concerning Request to Extend the United States’ Destruction Deadline Under the Chemical Weapons Convention, The Hague, The Netherlands, 20 April 2006.