Source: https://ihl-databases.icrc.org/customary-ihl/eng/docs/v2_cou_us_rule72
Timestamp: 2019-04-24 09:03:15+00:00

Document:
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, § 37(a).
making use of poisoned … arms or ammunition … [and] poisoning of wells or streams.
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, § 504(a) and (i).
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 6-2.
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 6-3b(2).
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 6-4f.
United States, Your Conduct in Combat under the Law of War, Publication No. FM 27-2, Headquarters Department of the Army, Washington, November 1984, p. 10.
The US Operational Law Handbook (1993) states that “using … poison weapons” is “expressly prohibited by the law of war” and is “not excusable on the basis of military necessity”.
EMPLOYING POISON OR SIMILAR WEAPONS.
(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 the Military Commissions Act of 2006, 10 U.S.C. §§ 948a, et seq., 18 January 2007, Part IV, § 6(8), pp. IV-6 and IV-7.
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.
Under the US War Crimes Act (1996), violations of Article 23(a) of the 1907 Hague Regulations are war crimes.
“(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, 2006, Public Law 109-366, Chapter 47A of Title 10 of the United States Code, 17 October 2006, p. 120 Stat. 2626, § 950v(b)(8).
United States, Military Commissions Act, 2009, § 950t(8).
The United States did not ratify the 1925 Geneva Protocol until 1975. Accordingly, the Protocol cannot be said to have constituted “a treaty of the United States,” … during the period relevant to this appeal. Even at the time of ratification, the United States and other states reserved the right to respond in kind to a belligerent’s first use of poisonous weapons and further limited the treaty obligation to apply only against other treaty parties. … Given the nature and scope of the reservations to ratification, however, it would be an impermissible stretch to find that the 1925 Geneva Protocol had acquired the status of binding customary international law during the Vietnam conflict.
… In 1969, the United States 7 objected to a proposed United Nations resolution that would have “ma[d]e a clear affirmation that the prohibition contained in the Geneva Protocol applied to the use in war of all chemical, bacteriological and biological agents (including tear gas and other harassing agents) which presently existed or which might be developed in the future.” The following year, after the United States ceased its use of Agent Orange upon a study revealing its deleterious effects on humans, the Secretary of State wrote a letter to President Nixon recommending that the President transmit to the Senate for advice and consent the ratification of the 1925 Geneva Protocol. In his letter, the Secretary stated that “[i]t is the United States’ understanding of the Protocol that it does not prohibit the use in war of riot-control agents and chemical herbicides.” When President Ford ratified the Geneva Protocol in 1975, he clarified that “[a]lthough it is our position that the [P]rotocol does not cover riot control agents and chemical herbicides, I have decided that the United States shall renounce their use in war as a matter of national policy.” Moreover, in ratifying the 1925 Geneva Protocol in 1975, the Senate made clear its understanding that the United States’ prior use of herbicides in Vietnam had not violated that treaty and that the government intended the Protocol to be only prospective in effect.
United States, US Court of Appeals for the Second Circuit, Agent Orange case, Judgment, 22 February 2008, pp. 23–24, 27–28 and 30.
United States, Department of the Army, Memorandum for US Army Research, Development and Engineering Center, M829A2 Cartridge, 120MM, APFSDS-T (Depleted Uranium Tank Round), Law of War Review, 27 December 1994, § 6(b).
United States, Department of the Air Force, Legal Review of 30MM Ammunition, 14 March 1975, § II(1).
In its written statement submitted to the ICJ in the Nuclear Weapons case in 1995, the United States accepted the prohibition of poison as such. However, it considered the prohibition to be applicable only to “weapons that carry poison into the body of the victim” or “that are designed to kill or injure by the inhalation or other absorption into the body of poisonous gases or analogous substances”.
United States, Written statement submitted to the ICJ, Nuclear Weapons case, 20 June 1995, p. 24.

References: § 37
 § 504
 § 6
 § 6
 § 6
 § 6
 § 5
 § 950
 § 950
 § 6