Terrain Denial Fires on the Modern Battlefield

Stability and counterterrorism operations in Afghanistan, Iraq, and Syria have provided the primary source of operational experience for currently serving American military leaders and legal advisors. Regardless of whether U.S. forces will (or logistically can) conduct continued airstrikes in Afghanistan from “over the horizon” after the collapse of the Afghan government, the techniques developed and employed during the nearly two decade conflict are likely to impact American military practice in the future. Military leaders and legal advisors will draw on personal and institutional combat experience when deciding how to apply the law of armed conflict (LOAC) on future battlefields.

One such technique is terrain denial fires. Over the years media reports of “terrain denial” missions in Afghanistan have breathlessly described a campaign “involving manned and unmanned aircraft and unguided and guided munitions” as “a deliberate and coordinated effort to strip away actual terrain features—narrow mountainous paths, rock-topped ridgelines, and even buildings and other man-made structures—that militants might use.” They have compared it to the so-called “carpet bombing” campaigns of prior conflicts. Does “terrain denial” actually mean the U.S. military is using munitions to re-shape topography, and if so would those actions be lawful? What are terrain denial fires, and what is the legal status of targeting … the ground?

This post seeks to define terrain denial fires and analyze the technique’s lawfulness under the LOAC. It proposes a definition of terrain denial fires based on a review of U.S. military practice and doctrine; analyzes legal issues arising under LOAC and other international law, including an operational vignette; and explores potential prudential and policy considerations that stem from terrain denial fires.

The term “terrain denial fires” does not have an official unclassified definition, nor is it explicitly discussed in U.S. military doctrine. In order to analyze the lawfulness of terrain denial fires, it is necessary to define the concept. A review of reported U.S. practice and available U.S. military doctrine informs the proposed definition, and that definition undergirds the legal analysis.

U.S. Military Practice

Open source reporting reveals that over the years terrain denial fires have been delivered by a variety of manned and unmanned aerial platforms, including F-16 and F-35 fighter jets, B-52 manned bombers, attack helicopters, and MQ-9 remotely piloted aircraft. When U.S. forces had a presence on the ground, they also used rockets and cannon artillery for terrain denial fires. Terrain denial missions employed unguided “dumb” bombs, as well as sophisticated Global Positioning System (GPS) or laser guided munitions.

Although the concept of employing fires to prevent the enemy from using key or advantageous terrain is longstanding, the term terrain denial fires seems to have originated during recent counterinsurgency and stability operations. Terrain denial fires were commonly employed to deter insurgent indirect fire attacks during the Iraq War. U.S. forces also used terrain denial fires during fighting against the Islamic State in Iraq and Syria (ISIS) as a means to “leave craters in roads that slow down or stop would-be car bombers trying to attack.” In addition to Iraq and Syria, terrain denial fires were employed extensively in Afghanistan, where artillery units report “hitting spots historically used as launching pads by insurgents who shoot rockets at” friendly forces. Troops in Afghanistan also conducted terrain denial “to prevent ISIS-[Khorasan] fighters from returning to territory they once controlled in eastern Afghanistan,” as well as “regularly firing on a mountain pass, for example, to dissuade the enemy from attempting to make use of a route.” Thus, a review of contemporary practice reveals that terrain denial fires are not meant to “literally shape the terrain” in a physical sense, but to influence the enemy’s use of that terrain.

U.S. Military Doctrine

The term “terrain denial” is non-doctrinal. It is absent from the Department of Defense (DoD) internal dictionary, and does not appear in the Army’s official operational terms nor the Air Force’s glossary. Army doctrine discusses “fires [to] deny the enemy unrestricted use of the terrain and [to] prevent enemy reserves from entering the fight,” but does not use the term terrain denial fires. Aside from brief mention of “area denial” systems such as landmines, the concept is also absent from fire support doctrine. Joint forces doctrine does define “denial measures” as “action to hinder or deny the enemy the use of territory, personnel, or facilities,” while the Army defines “deny” as a “task to hinder or prevent the enemy from using terrain, space, personnel, supplies, or facilities.” In doctrine, area denial measures are never directly linked to fires, however Army doctrine seems to nod at the use of fires for terrain denial, noting that during stability operations “[f]ires may be used more frequently to defend or deny the use of key sites than to seize them.”

The most extensive quasi-official discussion of terrain denial fires comes from a 2005 article in a U.S. military professional journal for artillerists. The article describes the employment of terrain denial fires to disrupt insurgent mortar attacks against a U.S. operating base near Mosul, Iraq. The author does not define terrain denial fires and the article contains no doctrinal quotations or citations. Rather it describes conducting terrain denial with cannon artillery, mortars, and the guns and rockets mounted to attack helicopters.

Although terrain denial fires are not a doctrinal concept they have been officially acknowledged. For example, a military spokesperson explained that “terrain denial strikes are useful in enabling freedom of maneuver for our forces, elimination of cover and concealment [for] enemy forces, [and] affecting enemy pattern of life in such a way that allows us to gain invaluable intelligence on their networks.”

The best doctrinal fit for terrain denial fires seems to be as a form of interdiction operations or shaping operation. The Army’s manual on operations defines shaping operations as any operation that “establishes conditions for the decisive operation through effects on the enemy, other actors, and the terrain.” Joint doctrine defines interdiction operations as actions “to prevent adversaries from employing surface-based weaponry and reinforcing units at a time and place of their choosing.” The purposes of interdiction include diversion, delay, and destruction of the enemy. As discussed later, the use of fires to destroy the enemy constitutes a strike, and as such falls outside the definition of terrain denial fires. Thus, terrain denial fires are a subset of, not a synonym for, interdiction fires.

A Proposed Definition

Based on reported practice and relevant doctrine, a proposed definition of terrain denial fires is: direct or indirect fires intended to hinder, delay, or prevent the enemy from using terrain, space, or facilities. This definition necessarily excludes strikes against enemy personnel or facilities that intend to damage, destroy, suppress, or defeat them, as the purposes of those strikes would not be to deny terrain. There is a vigorous, ongoing conversation (and robust legal, doctrinal, and policy framework) surrounding so-called “lethal” strikes, but there is very little public discussion of terrain denial fires. A working definition of terrain denial fires is a precondition for consideration of the law and policy issues surrounding the concept, issues explored in the remainder of this article.

International Legal Implications

An “Attack”

In both international and non-international armed conflicts, an “attack” implicates the LOAC targeting regime, including rules governing distinction between lawful targets and civilian objects, obligations to take feasible precautions during an attack, and the principle of proportionality.[1]

The exact contours of what constitutes an “attack” under the law of armed conflict are hotly debated and were explored especially well in a 2020 Lieber Institute symposium. Even under the narrow definition of an attack advanced by Colonel (Retired) Dick Jackson, terrain denial fires remain an “attack” because they are “acts of violence against the adversary.” While the adversary and his objects may not be present at the location targeted at the moment of the strike, the terrain denial fires are still “against the adversary” because the intent is to “hinder or prevent the enemy from using terrain.” Interestingly, Jackson specifically excludes “altering buildings or land to enhance tactical advantage” and “dropping excess ordnance from aircraft in an open and unpopulated area” from his definition of attack—scenarios that sound a lot like the reported “dropping [of] hundreds of dumb bombs in Afghanistan to literally shape the terrain.” However, the intent is what matters. And the intent behind terrain denial fires is to use fires—a form of force or violence—to deny the enemy the use of the terrain.

Lawful Military Objectives?

The LOAC rules governing distinction limit attacks to lawful military objectives. An object—including a piece of terrain—may become a lawful military objective if it makes an effective contribution to military action by its nature, location, purpose, or use, and if the object’s partial or total destruction or neutralization offers a definite military advantage in the circumstances ruling at the time. The DoD uses the term target to include to a “place … considered for possible engagement or action to alter or neutralize the function it performs for the adversary.” Terrain denial fires are usually an example of measures to neutralize an object, rendering it useless to the enemy without capturing or destroying it.[2]

Terrain will generally qualify as a lawful military objective due to its location or use. Even if the enemy has yet to use a piece of terrain it could be a military objective because of its location alone. For example, a trail across a mountain pass might furnish an infiltration or resupply route, thus making it a lawful military objective even though the enemy has not yet begun movement along the trail. The DoD Law of War manual explicitly states that “[t]he word ‘location’ also helps clarify that an area of land can be militarily important and therefore a military objective” independent of the land’s purpose or use, although actual use for military purposes would only strengthen the case. Little Round Top during the American Civil War battle at Gettysburg was key terrain due to the strategic advantage afforded by its location and height. The U.S. Army could have classified it as a military objective and used fires to deny it to the rebel forces, even before secessionist soldiers moved to occupy the hill.

While the United States does not accept as customary international law AP I’s presumption that “in case of doubt” objects normally dedicated to civilian purposes are not military objectives, in practice U.S. forces often adopt a civilian presumption as a matter of policy. Even absent such a presumption, much of the terrain U.S. forces might seek to deny is likely to constitute a civilian object that has lost protections, and as such transformed due to its location or use into a military objective while retaining some civilian function. An object that is both a military objective and a civilian object is referred to as dual-use.

U.S. Position on Proportionality and Dual-use Objects

Proportionality prohibits attacks in which the expected harm to civilians or damage to civilian objects would be excessive as compared to the concrete and direct military advantage expected to be gained. The U.S. position on how proportionality applies to dual-use objects is somewhat contradictory, in that dual-use is not a legal classification; objects are either military objectives or they are not military objectives.

The Commander’s Handbook on the Law of Land Warfare asserts “the principle of proportionality does not impose an obligation to reduce the risk of harm to military objectives,” a position echoed by the DoD Law of War Manual. This means that once a dual-use object is a military objective the remaining civilian “parts” of the object are stripped of their protections. Thus, proportionality as applied to that object does not prevent the object, including the civilian portions, from being attacked. Proportionality still considers expected harm to nearby civilian objects, such as surrounding buildings. Thus, the Law of War Manual warns that nonetheless “it will be appropriate to consider in applying the principle of proportionality the harm to the civilian population that is expected to result from the attack on such a military objective.”

The U.S. view of proportionality as it applies to dual-use objects that emerges from reading the Handbook and the Manual together is on the one hand exceedingly narrow, in that it asserts that because a dual-use object is a military objective there is no need to weigh damage to the civilian “parts” of that object. And, yet on the other hand, it is also very broad, in that it requires one to consider the direct, foreseeable harm to the civilian population outside of the object itself. Terrain denial fires complicate this analysis—as illustrated in the vignette later in this article—because terrain is both more and less divisible than a typical “components of a whole” dual-use object, and because terrain always has a civilian (that is, non-military) function. It is hard to conceive of terrain denial fires that are not targeting a dual-use object.

The Manual generally comes down in favor of considering all “direct harms foreseeably resulting from the attack” in assessing proportionality, excluding remote effects. This means the “broad” view (harm to civilian population at large) subsumes the “narrow” view (harm to civilian parts of the targeted object). As Michael Schmitt has pointed out while arguing for an alternative interpretation, the narrow view of the U.S. position “could lead to situations in which the real impact on civilians of an attack far outweighs the military need to attack the target, but the attack would nevertheless be lawful.” Some commentators have called for taking into account indirect or reverberating effects, but the U.S. position excludes remote or speculative harms from the analysis.

As terrain denial fires constitute an attack, there is also a requirement for feasible precautions to avoid damage to civilian objects and foreseeable direct harm to civilians.  Further, there is a requirement to provide “effective advance warning of attacks that may affect the civilian population, unless circumstances do not permit.”

Environmental Modification?

If terrain denial fires were truly “a coordinated and deliberate effort to strip away actual terrain features” as reported, such environmental modification could run afoul of the U.S. position that “parts of the natural environment may not be destroyed unless required by military necessity.” The United States has signed and ratified the UN Convention on the Prohibition of Military or Any Other Use of Environmental Modification Techniques and generally adheres to AP I’s prohibition on environmental damage that is “widespread, long-term and severe” as a policy matter while maintaining AP I’s prohibition is not customary international law. The U.S. also takes the position that no means or methods of warfare employed by the United States meet that threshold. This almost certainly means the United States would argue localized terrain denial fires are not “widespread,” or that any damage caused to terrain by conventional weapons falls short of the threshold for “severe.”

Prudential Concerns and Policy Considerations 

Although terrain denial fires may be lawful given the circumstances ruling at the time, a commander may still decide there are policy restrictions or prudential considerations that militate against employing such fires in a given situation. Especially during a stability operation or on a large-scale battlefield where civilians are omnipresent, terrain denial fires are almost certain to be counterproductive.

The author of the military journal article cited earlier admits that his “commander directed the [helicopters] to ‘rock the neighborhood and knock pictures off of the walls of the houses surrounding the [point of origin]’ without causing collateral damage.” While the intent was not to place the fires on the civilians or civilian objects, it seems the commander sought to target the effects of the fires at the civilians, both in terms of physical effects (“rocking”) and sowing fear, perhaps as a form of psychological operation. Fires do not have to hit a person to have effects on them—witness the psychological impacts of World War I drumfire. At best, this may have been a counterproductive way to influence the civilian population.[3] The liberal employment of terrain denial has inspired criticism that firing weapons into the landscape actually fosters the sort of disorder and insecurity counterinsurgents seek to dispel. Although large-scale combat operations are expected to be “more chaotic, intense, and highly destructive than those the Army has experienced in the past several decades,” protection of civilians will almost certainly (and hopefully) remain a U.S. priority.

Even if terrain denial fires impacting the population at large are conducted lawfully (and the relevant AP I prohibition, which is accepted by the United States as customary international law, cautions that “[a]cts or threats of violence the primary purpose of which is to spread terror among the civilian population,” are prohibited), prudence argues against taking actions that feed a narrative of America using terrain denial fires as a form of terror-bombing against the civilian population. Army doctrine acknowledges that “civil instability increased by the destruction of civilian property, material, and equipment could have adverse effects on the outcomes of the different elements of decisive action.”

Terrain denial fires implicate financial concerns, as well. The dual-use nature of many terrain denial targets means civilians will often pursue claims against the U.S. government for damages.  Although combat losses are not compensable under the Foreign Claims Act the United States regularly makes ex gratia payments for civilian harm. In addition, the weapons themselves incur high costs. One can deduce that U.S. forces have conducted such fires using Hellfire missiles or other precision-guided munitions, from the fact that terrain denial fires were employed by MQ-9 Reaper drones and the Reaper is not reported to carry any unguided ordnance. The cost of a typical Hellfire missile is publicly reported as between $71,000-$160,000, raising questions about whether employing precision guided munitions to target the ground constitutes prudent stewardship of taxpayer dollars.

Terrain Denial Fires Vignette

The Scenario

Imagine a U.S. commander of a multi-national force seeks to conduct terrain denial fires on an agricultural field that furnishes an infiltration lane for an attack on her operating base, but that also provides food for a local village. The enemy has used the infiltration route to stage attacks in the past, but there is no evidence enemy forces are using it now, and the field is located in close proximity to the village. The field is ideally suited to provide a covered and concealed route to attack the base, thanks to its geographic location and the thick growth of crops—the same crops that furnish the food for the villagers. The commander seeks to fire cannon artillery into the field at irregular intervals both to physically deny the enemy the opportunity to infiltrate via the field, to reduce the amount of cover available to the enemy, as well as to foster awareness among the enemy that U.S. forces can fire into the field at will, with attendant psychological effects.

The Legal Advice

The commander’s legal advisor would likely advise her the field is an object normally dedicated to civilian purposes, and that some of the multinational partners will thus operate under a presumption that it remains a civilian object. It is not a military objective based on use because the enemy is not using it now, but the field is a military objective by virtue of its location providing an effective infiltration lane to the enemy.

The commander is not obliged to minimize damage to the field itself from the terrain denial fires because the field is a military objective. That said, it is “appropriate” to weigh the expected harm to the civilians resulting from the fires targeting the crops, including effects that are direct and foreseeable, against the direct, concrete military advantage of denying the terrain and demoralizing the enemy.

The legal advice would turn on the specific facts, including whether the field furnishes the majority of the villagers’ food supplies or economic activity. It would also be appropriate for the commander to consider the direct and foreseeable effects on the villagers beyond the destruction of the crops, to include “rocking the neighborhood” with nearby munitions. If the commander’s intent is to frighten the enemy into eschewing the infiltration route, such collateral harm may be acceptable—but deliberately terrorizing the villagers would be unlawful.

Even if the proposed fires satisfy proportionality, the commander must take feasible precautions to avoid direct and foreseeable harm to the civilians. This might include providing effective advance warning to the civilian population before the attack, observing the fires to ensure no civilians are present in the area where effects are expected, delaying the timing of the attack until after the field is harvested, or adjusting the weaponeering to select illumination rounds instead of high explosives. Here again, the feasibility of the precautions will be fact specific—delaying until after the harvest may not be practical because the same crops that furnish the foodstuffs also furnish cover for the enemy, and the commander may decide illumination is insufficient to deny the terrain. The legal advisor may also highlight prudential concerns—the disruption to the village could be lawful, but ultimately counterproductive thanks to a loss of popular support or grist for enemy propaganda. 

Conclusion

The use of direct or indirect fires intended to hinder, delay, or prevent the enemy from using terrain, space, or facilities is a lawful technique, although not free from controversy or legal nuance. Practitioners and scholars should ensure they are familiar with the legal and prudential issues associated with terrain denial fires so they are prepared to “evaluate[] the potential legal consequences resulting from primary and secondary effects” of using fires to deny terrain.

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Major Matt Montazzoli is an active duty Army judge advocate, currently assigned as Operations Law Attorney (Military Personnel Exchange Program), 1st Division / Deployable Joint Force Headquarters, Australian Army at Gallipoli Barracks, Brisbane.

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Footnotes

[1] With the recent collapse of the Afghan government and continued rumblings about Iraq revoking consent for American military operations, it is possible future terrain denial fires may implicate jus ad bellum considerations as well, but this article focuses on jus in bello issues.

[2] Of note, the term “neutralize” is a term of art for both legal and fires professionals, with different meanings: neutralization in the fires context means 10% or greater destruction, while legal parlance draws a distinction between partial or total destruction and neutralization.

[3] The commander’s view that his fires may rock the neighborhood “without causing collateral damage” likely represents an overly circumspect understanding of collateral damage. The DoD definition of collateral damage includes any “effect that causes unintentional or incidental injury or damage.” While there may be room for some debate as to whether the stress or fear inflicted on the population from proximity to terrain denial fires rises to the level of “injury,” the fact that this commander is deliberately using fires to inspire terror in the civilian population (as opposed to the enemy) means the effects on the civilians are not collateral, but unlawful.