Related Rule
United States of America
Practice Relating to Rule 43. Application of General Principles on the Conduct of Hostilities to the Natural Environment
The US Naval Handbook (1995) provides: “The commander has an affirmative obligation to avoid unnecessary damage to the environment.” 
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), § 8.1.3.
The US Naval Handbook (2007) states:
Destruction of the natural environment not necessitated by mission accomplishment and carried out wantonly is prohibited. Therefore, a commander should consider the environmental damage that will result from an attack on a legitimate military objective as one of the factors during targeting analysis. 
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, § 8.4.
The Agent Orange case in 2005 involved a class action suit filed on behalf of various Vietnamese nationals and an organization, The Vietnamese Association for Victims of Agent Orange/Dioxin, against Dow Chemical and other US chemical manufacturers, for harms allegedly done to them and their land through the United States’ use of Agent Orange and other herbicides during the Vietnam War from 1965 to 1971 and by the South Vietnamese government’s subsequent use of such herbicides until 1975. In dismissing the claims, the Court found that, while recognizing the evolution of international law since 1975, the use of herbicides did not violate, at the time they were used, either customary or conventional international law binding on the United States. On the question of whether any source of international law in effect during the period 1961–1975 limited environmental damage during the conduct of hostilities, the Court stated:
Treaties limiting environmental damage in warfare were not in effect during the period of 1961–1975. The United States did not violate any such provision, defendants could not be held liable under them and plaintiffs could not state a claim under them. The United States signed Protocol Additional to the Geneva Conventions of 12 August 1949, and Relating to the Protection of Victims of International Armed Conflict (Protocol I), June 8, 1977, 1125 U.N.T.S. 3 (entered into force Dec. 7, 1978), on December 12, 1977, but never ratified it … While it might be interpreted to apply to future use of herbicides in the way they were used in Vietnam, it had no application prior to 1975. 
United States, Eastern States District Court (EDNY), Agent Orange case, Judgment, 28 March 2005, p. 207.
In 1991, during a debate in the Sixth Committee of the UN General Assembly on the protection of the environment in armed conflict, the United States stated:
The deliberate release of oil into the Gulf and the burning of Kuwaiti oil wells had constituted a serious violation of the prohibition of the destruction of property unless required by military necessity contained in [the 1949 Geneva Convention IV and the 1907 Hague Regulations]. Those acts had also been a violation of the prohibitions under customary international law against any military operation which was not directed against a legitimate military target or which could be expected to cause incidental death, injury or damage to civilians that was clearly excessive in relation to the direct military advantage of the operation. In the situation under consideration, the oil well destruction had taken place at a time when it had been clear to Iraq that the war had ended … Those violations of international law had definite legal consequences, as [the 1949 Geneva Convention IV] acknowledged in stipulating that the destruction of property not justified by military necessity was a grave breach and that persons committing such breaches incurred criminal liability … Iraq’s actions did not demonstrate that existing international law was inadequate, but, rather, that the problem involved compliance with existing law, and no new rule or conventions were needed. 
United States, Statement before the Sixth Committee of the UN General Assembly, UN Doc. A/C.6/ 46/SR.18, 22 October 1991, §§ 37–40.
In 1992, during the debate in the Sixth Committee of the UN General Assembly on protection of the environment in time of armed conflict, the United States stated: “In time of war some collateral damage to the environment … is inevitable.” 
United States, Statement before the Sixth Committee of the UN General Assembly, UN Doc. A/C.6/ 47/SR.9, 6 October 1992, § 55.
In 1992, in its final report to Congress on the conduct of hostilities in the Gulf War, the US Department of Defence considered that the destruction of oil well heads and the release of crude oil into the Gulf by Iraq violated Article 23(g) of the 1907 Hague Regulations and Article 147 of the 1949 Geneva Convention IV. It further stated:
As the first Kuwaiti oil wells were ignited by Iraqi forces, there was public speculation the fires and smoke were intended to impair Coalition forces’ ability to conduct both air and ground operations, primarily by obscuring visual and electro-optical sensing devices. Review of Iraqi actions makes it clear the oil well destruction had no military purpose, but was simply punitive destruction at its worst. For example, oil well fires to create obscurants could have been accomplished simply through the opening of valves; instead, Iraqi forces set explosive charges on many wells to ensure the greatest possible destruction and maximum difficulty in stopping each fire. Likewise, the Ar-Rumaylah oil field spreads across the Iraq-Kuwait border. Had the purpose of the fires been to create an obscurant, oil wells in that field on each side of the border undoubtedly would have been set ablaze; Iraqi destruction was limited to oil wells on the Kuwaiti side only. As with the release of oil into the Persian Gulf, this aspect of Iraq’s wanton destruction of Kuwaiti property had little effect on Coalition offensive combat operations. In fact, the oil well fires had a greater adverse effect on Iraqi military forces. 
United States, Department of Defence, Final Report to Congress on the Conduct of the Persian Gulf War, 10 April 1992, Appendix O, The Role of the Law of War, ILM, Vol. 31, pp. 636–637.
Prior to the adoption of UN General Assembly Resolution 47/37 in 1992 on the protection of the environment in times of armed conflict, Jordan and the United States submitted a memorandum to the Sixth Committee of the UN General Assembly entitled “International Law Providing Protection to the Environment in Times of Armed Conflict”. In it, they stated that “the customary rule that prohibits attacks which reasonably may be expected at the time to cause incidental loss of civilian life, injury to civilians, damage to civilian objects, or a combination thereof, which would be excessive in relation to the concrete and direct military advantage anticipated, are prohibited” provides protection for the environment in times of armed conflict. 
Jordan and United States, International Law Providing Protection to the Environment in Times of Armed Conflict, annexed to Letter dated 28 September 1992 to the Chairman of the Sixth Committee of the UN General Assembly, UN Doc. A/C.6/47/3, 28 September 1992, § 1(h).
In 1993, in a report to Congress on international policies and procedures regarding the protection of natural and cultural resources during times of war, the US Department of Defense stated:
The United States considers the obligations to protect natural, civilian, and cultural property to customary international law … Natural resources are protected from intentional attack so long as they are not utilized for military purposes … The United States recognizes that protection of natural resources, as well as protection of the environment, is important even in times of armed conflict. Natural resources are finite, and reasonable measures must be taken to protect against their unnecessary destruction … What is prohibited is unnecessary destruction, that is destruction of natural resources that has no or limited military value. 
United States, Department of Defense, Report to Congress on International Policies and Procedures Regarding the Protection of Natural and Cultural Resources During Times of War, 19 January 1993, pp. 202–204.
According to the Report on US Practice, it is the opinio juris of the United States that “collateral environmental damage caused by otherwise lawful military operations should be assessed for its proportionality to the expected military value of such operations”. 
Report on US Practice, 1997, Chapter 4.5.
In 2005, the US Department of Justice submitted a Statement of Interest of the United States to the US District Court for the Eastern District of New York prior to that Court’s consideration of Agent Orange Product Liability Litigation (The Vietnam Association for Victims of Agent Orange/Dioxin, et al. v. Dow Chemical Company, et al.). In that statement, the Department of Justice's reiterated the US position that no rule of international law barred the use of chemical herbicides in war generally nor barred the destruction of crops intended for use by enemy forces. With regard to the military necessity for attacks against the natural environment, it stated:
The decision to use chemical herbicides was made by President Kennedy upon a recommendation by Secretary of State Rusk that “successful plant-killing operations in Viet-Nam, carefully coordinated with and incidental to larger operations, can be of substantial assistance in the control and defeat of the Viet Cong.” Rusk Memorandum. There can be little doubt that, as the then-Acting Assistant Secretary of Defense testified before Congress, the “use of… herbicides [in Vietnam] . .. had one purpose – to [s]ave the lives of Americans and those of our allies.” 1974 House Hearings at 154 (Statement of Amos Jordan, Acting Assistant Secretary for International Security Affairs, Department of Defense). Thus, as the Second Circuit has recognized, “at issue is a decision of the veterans’ highest military superiors that was designed to help, the veterans in fighting the armed conflict in which they were engaged.” FTCA/Feres Opinion. 818 F.2d at 200. 
United States, Department of Justice, Statement of Interest of the United States submitted to the US District Court for the Eastern District of New York, In re: Agent Orange Product Liability Litigation (The Vietnam Association for Victims of Agent Orange/Dioxin, et al. v. Dow Chemical Company, et al), 12 January 2005,§ II, p. 17.
The United States Use of Chemical Herbicides in Vietnam Did Not Violate Any Other Specifically Defined Norm
To the extent that plaintiffs’ claims are based not on the alleged per se illegality of the use of chemical herbicides in war, but rather on the specific manner in which the United States used such herbicides in Vietnam – i.e., to the extent that plaintiffs are alleging that the United States used a legal weapon in an illegal maimer – their claims must also fail, because no specifically defined norm barred the United States’ actions. In this regard, plaintiffs allege that the United States’ use of chemical herbicides violated the laws of war by, inter alia, causing “the wanton destruction of cities, towns, villages, or the natural environment, or devastation not justified by military necessity.” Am.Compl., ¶ 261. Presumably, plaintiffs are relying on the prohibitions in the 1907 Hague Convention against the destruction of enemy property “unless such destruction or seizure be imperatively demanded by the necessities of war.” 1907 Hague Convention, art. 23(g). The United States recognizes that the principles of necessity and proportionality – i.e., the requirements that no other means exist to achieve the desired military advantage and that civilian damage not be disproportional to military advantage – have attained the status of customary international law.
Pursuant to Sosa Sosa v. Alvarez-Machain, US Supreme Court, 2004] however, that is only the beginning of the inquiry. For there remains the question of whether the principles, as accepted by the international community, are defined with sufficient “specificity” comparable to the 18th Century paradigms noted in Sosa so as to allow for a cause of action under federal common law. In Sosa. the Court found that the claim of arbitrary detention had not achieved the status of a well-defined international law principle such that it could be enforced under the ATS [Alien Tort Statute]. The Supreme Court explained that any consensus concerning this norm was “at a high level of generality.” Sosa, 124 S. Ct. at 2768 n.27. The same is true here. There are simply no established international law standards of the specificity required by Sosa for establishing a federal common law cause of action for unnecessary or disproportionate use of military force.
Indeed, the very nature of the principles defy specificity, for they require the balancing of competing considerations and are inherently imprecise. That is, the rules do not proscribe any particular conduct that is readily identifiable. Rather, they require consideration by combatant commanders of a variety of factors – unique to the context of any particular military action – that affect decisions on what means may be available to achieve the military objective and whether the harms that particular military actions might cause would be disproportionate to the advantages attained. In light of the balancing nature of the principles, the very same act that might be deemed both necessary and proportionate in one circumstance, might be deemed unnecessary or disproportionate in another. It is one thing, therefore, to recognize that these principles generally exist in customary international law. It is “harder,” if not impossible, to “say which policies cross [the] line with the certainty afforded by Blackstone’s three common law offenses” 124 S. Ct. at 2769.
A recent report by a Committee established to review the NATO bombing campaign in Yugoslavia provides a good illustration of the imprecise nature of the rule of proportionality:
The main problem with the principle of proportionality is not whether or not it exists but what it means and how it is to be applied. It is relatively simple to state that there must be an acceptable relation between the legitimate destructive effect and undesirable collateral effects. For example, bombing a refugee camp is obviously prohibited if its only military significance is that people in the camp are knitting socks for soldiers. Conversely, an air strike on an ammunition dump should not be prohibited merely because a farmer is plowing a field in the area. Unfortunately, most applications of the principle of proportionality are not quite so clear cut. It is much easier to formulate the principle of proportionality in general terms than it is to apply it to a particular set of circumstances because the comparison is often between unlike quantities and values. One cannot easily assess the value of innocent human lives as opposed to capturing a particular military objective.
Final Report to the Prosecutor by the Committee Established to Review the NATO Bombing Campaign Against the Federal Republic of Yugoslavia ¶ 48 …
Because any consensus regarding the necessity and proportionality principles necessarily exists solely “at a high level of generality,” id at 2768 n.27, and because the principles are not “defined with … specificity,” id at 2761, and clearly have “less definite content” than the 18th Century offenses discussed in Sosa. id. at 2765, the Court should not recognize a federal common law cause of action for alleged violations of the necessity and proportionality principles. See also Flores. 343 F.3d at 160–61. 
United States, Department of Justice, Statement of Interest of the United States submitted to the US District Court for the Eastern District of New York, In re: Agent Orange Product Liability Litigation (The Vietnam Association for Victims of Agent Orange/Dioxin, et al. v. Dow Chemical Company, et al), 12 January 2005,§ II, pp. 33–36.