Hays Parks and U.S. Views on Targeting Law


| Oct 11, 2021

Hays Parks Air War
Three decades after its publication, Colonel W. Hays Parks’s article Air War and the Law of War remains a key resource for attorneys who advise on targeting operations. The article is noteworthy for its deep exploration of the history of the law of war as well as its criticism of new attempts to regulate the conduct of hostilities. Indeed, half of the article focuses on the 1977 Additional Protocol I to the 1949 Geneva Conventions (AP I), which is often cited for rules governing aerial bombardment. This post showcases Parks’s enduring influence on U.S. legal policy and interpretations; it also illustrates his lifelong emphasis on the timeless importance of balancing military interests and incentives under the law of war.

Military Necessity and Distinction

To begin, it must be appreciated that Parks maintained a fundamentally realistic approach to the law of war, grounded in military actualities and State practice. He emphasized that impracticable regulations of war inevitably undermined the entire law of war. He gave pride of place to military necessity in all his work and favored Professor Francis Lieber’s sharp statement of the principle:

Art. 14: Military necessity, as understood by modern civilized nations, consists in the necessity of those measures which are indispensable for securing the ends of the war, and which are lawful according to the modern law and usages of war.

Art. 15: Military necessity admits of all direct destruction of life or limb of armed enemies, and of other persons whose destruction is incidentally unavoidable in the armed contests of the war….

Parks admitted, however, that military necessity was not the exclusive principle applicable to combat operations. Parks also explored the meaning and operation of the principle of discrimination or distinction, which he summarized as “noncombatant immunity” subject to the necessities of warfare. Describing distinction, Parks returned to Lieber’s work noting, “[T]he unarmed citizen is to be spared in person, property, and honor as much as the exigencies of war will admit” (p. 8). To Parks, “[t]he purpose of the law of war is to protect innocent persons from intentional or incidental injury to the extent they can be avoided” (p. 225).

Parks argued that regulatory restrictions on warfare, without accounting for the military value and balanced application among belligerents, will always prove unsuccessful. He repeatedly emphasized the mutual obligations of attackers and defenders. He attributed the relative success of the 1949 Geneva Conventions to their “pragmatic and balanced” approach to assigning responsibilities to belligerents (p. 59). He concluded the Conventions’ prohibitions on reprisals against protected persons who found themselves in enemy hands were acceptable and effective because they did not restrict the actual conduct of hostilities. Similarly, he attributed the relative success of the 1925 Geneva Protocol prohibitions on poison gas (the 1993 Convention on Chemical Weapons had not been adopted when Parks wrote Air War) to that instrument’s account of belligerents’ interest in assuring some degree of reciprocity.

Proportionality and Targeting Rules

However, the best way to appreciate Parks’s approach to the law of aerial warfare is to consider his debates over proportionality and targeting rules.

Georgetown Law Professor Marty Lederman, currently Deputy Assistant Attorney General in the Department of Justice Office of Legal Counsel, disagrees with Parks’s jus in bello contention that civilians assume the risk of death by locating themselves near lawful targets. To Lederman, customary international law incorporates the AP I, Article 57 requirement that “those who plan or decide upon an attack must ‘[r]efrain from deciding to launch any attack which may be expected 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.’” Parks, by Lederman’s view, “was unwilling to ‘count’ persons who [are] in the vicinity of a lawful target in any proportionality calculus.” Lederman insists:

[T]he only defensible account of the current customary law—is that although the presence of such civilians and other protected parties in or near a lawful military target does not rule out the use of force against that target per se, the commander in charge … must consider the anticipated harm to those civilians in the required proportionality analysis. It is, after all, the very purpose of the proportionality rule to protect civilians who are in the vicinity of lawful targets.

In should be noted, Parks did not fully reject the proportionality rule. In 1986, while serving as Special Assistant on Law of War Matters to the Judge Advocate General of the Army, he recorded a view that the jus in bello rule of proportionality reflected customary international law applicable to all States.

Parks dissented, however, from views that overburdened attacking forces with responsibility for preventing civilian harm during attacks. Parks asserted, “In customary international law the primary responsibility for preventing collateral civilian casualties rests with the defender and the individual civilian, with little or no responsibility imposed upon an attacker” (p. 153). Parks acknowledged a role for attackers to prevent civilian casualties. But he insisted that defenders retain primary responsibility. He wrote:

If the new rules of Protocol I are to have any credibility, the predominant responsibility must remain with the defender, who has control over the civilian population. A serious stumbling point for Protocol I is that the new rules were seen by some of its drafters, and have been seen by some proponents of the new rules … as a way of preventing attacks entirely. Such a view is unrealistic. Any law of war rule that offers the potential for a military advantage for the defender over the attacker, or vice-versa, is a rule doomed to failure. It not only would increase the risk to the innocent civilian, but in all likelihood would jeopardize the credibility of the law of war itself (p. 154, emphasis in original).

Parks explained that commanders must take feasible precautions to minimize civilian harm when attacking military objectives deliberately surrounded by or intermixed with civilian populations—the “human shields” problem. Parks maintained, however, that civilian deaths, “should be regarded as a grave breach by the leadership of the government that illegally placed human shields around these military objectives.”[1]

In a particularly prescient passage, Parks also expressed concern over civilian employees supporting forces on military installations. He asked whether these civilians truly assumed risks or instead served to prevent attacks. If the latter were correct, he judged that defenders would be encouraged to use civilians in lieu of military forces to ward off attacks. Considering objects, in Parks’s opinion, no jus in bello proportionality considerations attached specifically to objects used by both enemy forces and civilians. He concluded that use of an object for military advantage fully converted it to a military objective, negating its civilian facets.

Today, as a practical matter, U.S. and allied air forces conduct proportionality analyses prior to striking targets. Minimizing civilian casualties is an especially important goal in counterinsurgency and counter-terror operations. Still, US campaigns against enemies that embed themselves in civilian infrastructure, disguise themselves as civilians, or surround themselves with civilians have vindicated Parks’s warning that future conflicts would challenge the efficacy of rules that overburden attackers and do not sufficiently emphasize the responsibilities of defenders.

Targeting Civilian Morale

Contrary to uninformed accounts of Parks’s work, his views were not exclusively permissive with respect to targeting operations. Major General (retired) Charles Dunlap, currently a Professor at Duke University School of Law, has disagreed with Parks’s restrictive view on the lawfulness of attacking civilian morale. Dunlap advocates expanding what can be attacked to “those objects that will influence civilian morale in such a way that achieves a definite military advantage.”[2] Dunlap’s emphasis, drawn from Clausewitz, is that “[t]he object of war remains destroying the enemy’s will to resist—not merely a nation’s military capability, but a nation’s will,” and that civilian morale is simply a component of national will.[3]

Parks conceded that history supported striking war-supporting and war-sustaining objectives. He argued, however, that strikes directed at civilian morale had proved inefficient and had proved largely unsuccessful. For instance, he concluded that enemy memorials and monuments are virtually impossible to justify as militarily advantageous and have dubiously speculative effects on civilian morale. He argued that civilian objects cannot be lawfully attacked simply by redefining them as military objectives. Civilian support for war could only be lawfully and, in Parks’s view, practically affected by attacks on military objectives. Parks’s view reflects his steadfast focus on military necessity and on the instrumental purpose of the law of war to securing achievable protections.


The influence of Parks’s writings on aerial warfare and his law of war legacy cannot be overstated. His historical case studies and his emphasis on practical military necessity remain relevant even today. His views and influence are still evident in nearly every current U.S. legal interpretation of the law of war and most especially targeting law. While U.S. practitioners should turn first to the Department of Defense Law of War Manual for current guidance, they must read Parks to understand the background and motives of those directives. His work reminds us all that the law of war requires a careful balance of practical considerations involving intense and dedicated study of military realities and incentives.


Col Ted Richard is the Staff Judge Advocate at the 86th Airlift Wing Legal Office, Ramstein Air Base, Germany.



[1] W. Hays Parks, The Protection of Civilians from Air Warfare, 27 Isr. Y.B. Hum. Rts. 65, 109 (1997).

[2] Charles Dunlap, Targeting Hearts and Minds: National Will and Other Legitimate Military Objectives of Modern War, in International Law Facing New Challenges 120 (2007).

[3] Charles Dunlap, Targeting Hearts and Minds: National Will and Other Legitimate Military Objectives of Modern War, in International Law Facing New Challenges 119-20 (2007) (emphasis in original). See also Carl von Clausewitz, On War, Book 1, Chap. 1 § 2 (J.J. Graham trans., 1832), available at https://www.clausewitz.com/readings/OnWar1873/BK1ch01.html.