In the heated debate about drones, relatively little attention has been given to their use by the US military to carry out attacks in battlefield zones such as Afghanistan, Iraq, and Libya. In that context it is generally accepted that drone strikes against enemy forces are not illegal per se. Rather, drones may be deployed in the battlespace as long as their actual use comports with the law of armed conflict (LOAC). But, can we speak not merely of a right to use drones, but also of an actual legal obligation to use them?

Consider a scenario in which a military commander engages in the planning of an operation against the enemy in a densely populated urban area. Unfortunately, such an operation may result in collateral damage—loss of civilian life, injury to civilians, or damage to civilian objects. Yet, despite such harms, the attack may still be carried out lawfully under LOAC since the legal regime merely aims at minimizing civilian casualties, not eliminating them altogether. But, if the commander is to attempt to minimize such casualties, mustn’t she employ the most precise of weapons in her arsenal? Shouldn’t she deploy the most discriminating means of warfare at her disposal, allowing her to distinguish combatants from civilians, attacking the former while sparing the latter? And if, in fact, drones offer the twin promises of greater precision and reduced lethality, ought not the commander to deploy them rather than call for alternative methods of air support or bombardment or introduce “boots on the ground”? Does international law impose a legal duty on states that possess the relevant advanced technology to use that technology in battlespace? If so, what are the contours of such a legal duty, and what is its temporal and substantive scope? And if such a duty does not exist, should it? Put in more general terms, while there is no obligation, of course, to use any weapons at all, if weapons are to be used, must a party to an armed conflict use the more accurate of two weapons it has available, all other things being equal? In short, does a legal obligation exist in some circumstances to use more accurate weapons (MAWs)? 

Let’s take a step back and understand why belligerents would seek more accurate weapons as opposed to more lethal ones. The story of advancements in weapons technology has been about enabling the exercise of ever-greater lethal force from increasing distances. It is a human instinct to fight from a distance: Increased physical and mechanical separation from the enemy reduces a soldier’s fear of being killed and, perhaps even more significantly, his reluctance to kill others. However, an inverse relationship exists between distance and accuracy. Projectiles have not proven the most efficient way to kill the enemy. No matter how trained their operator, once released, projectiles — arrows, canon balls, bullets, missiles, and bombs — are subject to factors that are beyond the operator’s control. In order to compensate for the inherent inefficiency of projectile-based weapons, their lethality has continuously been increased. Both the quantity and the quality of projectile weapons had to be augmented. If a single weapon could not guarantee a sufficient probability of hitting the target, deploying a large number of weapons (and a large number of soldiers operating them) against the same target would improve the odds. Making each projectile more lethal would similarly improve the chances that, even if the target were not hit with precision, it would be destroyed. On the other hand, technological improvements to weapons systems accuracy meant that distance was no longer necessarily gained at the expense of accuracy and that smaller, less-lethal munitions could be used, both resulting in a potential reduction in collateral damage. Consider, for example, precision-guided munitions. In the fall of 1944, a bomb released at a medium altitude by a fighter-bomber in a 40-degree dive had a circular error probable (CEP) — the radius of a circle within which half the bombs or missiles fired would be expected to hit — of at least one thousand feet (305 meters). In Operation Desert Storm and Operation Allied Force, precision weapons had a CEP of approximately three meters. Greater accuracy also means that smaller munitions can be used to obtain the required military objectives and that fewer bombs (and fewer aerial sorties or artillery salvos) are required to ensure that the target is hit. Greater accuracy and smaller armaments, in turn, entail a potential reduction in collateral damage.

In a recent article, I explored the specific context of drones. If drones, I argued, actually reduce collateral damage, compared to alternative means and methods of warfare, should they not be the first choice on the menu of military commanders? Since drones offer greater accuracy against the intended military targets, reduced lethality among both friendly forces and innocent civilians, and the potential for more robust accountability, we need to examine whether a duty to use them exists or ought to exist.

A legal requirement to use MAWs could be pegged to the twin LOAC principles of proportionality and avoidance. Jus in bello proportionality prohibits military attacks anticipated to result in “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.” The principle of avoidance imposes an affirmative duty on military planners to “take all feasible precautions” in the choice of means and methods of attack “with a view to avoiding, and in any event to minimizing, incidental loss of civilian life, injury to civilians and damage to civilian objects.” It is not enough to not intend to kill civilians while attacking legitimate targets. Rather, a deliberate effort has to be made not to harm them. Military commanders must exercise due care when selecting their targets and matching the weapons and tactics to use against those targets. Thus, even when the proportionality calculus indicates that the likely collateral damage is not going to be excessive when compared with the anticipated military objective sought by the attack, LOAC imposes a duty on soldiers to take precautions — all feasible precautions, that is — in order to minimize that otherwise proportionate harm to civilians. Both of these principles may allow for considerations of capabilities and resources to enter the equation. A party to an armed conflict that possesses weapons, munitions, and modes of delivery capable of greater accuracy in targeting than those possessed by its adversary may thus be subject to a higher level of responsibility both with respect to the enemy’s soldiers and, more significantly, to innocent civilians.

However, the imposition of a legal obligation on states to use MAWs as their go-to weapons in war is not without its challenges. First, precision and accuracy may not be required as a legal matter in all scenarios, for example, when the targets are enemy forces spread over a large area where no civilians are to be found.

A second challenge pertains to resource management and availability. While some MAWs are cheaper than the alternatives — drones, for example, come with a significantly lower initial price tag than fighter jets, their cost per flight hours are lower than those for fighter jets, and drone pilots require significantly less training than do fighter pilots — others may be significantly more expensive. May the state, in such circumstances, engage in economy of force calculations in determining which weapons system to deploy? Similarly, would an imposition of a legal obligation to use MAWs entail a MAWs-first obligation, that is, would a party to a conflict need to use all of its more accurate weapons first — emptying its arsenal before ever resorting to the less accurate weapons?

Finally, would not an imposition of a duty to use MAWs create incentives for states to divert resources from research, development, production, and procurement of such weapons systems to alternative means of warfare, precisely so as not to be subject to the legal obligation to use them or to use them before using any other weapons?

There are additional, secondary, aspects to the availability challenge. What should we make of a country that does have the financial and technological capacities to develop, manufacture, and acquire MAWs, but elects not to do so? When such a state does not have a particular, more precise, weapon is that state obligated to spend resources to acquire or develop it? Is there a concomitant obligation not to use the weapons it does have unless and until it develops the more precise capacity? Does it matter if the country chooses not to develop MAWs technology because it professes objection to the use of such weapons; because it wishes to keep its military expenditures low; because it does not anticipate being involved in armed conflicts; or because it wishes to direct its resources in other directions, be they civilian or military? On the other hand, if we find that an obligation to use MAWs does exist, how far upstream does the obligation extend? If an “obligation to use” exists, does it logically extend to a duty to develop, manufacture, or procure such weapons? And what, precisely, are “such” weapons? How do we define the “more” component of the “more accurate weapon”?

A third, conceptual, challenge to a legal obligation to use MAWs pertains to the very nature of the law of armed conflict. Premised on notions of sovereign equality, the principle of parity or moral equality of combatants, and the rejection of reciprocity as a condition for compliance — LOAC has always been applied equally to all belligerent states, as well as to all individuals based on their status as combatants or civilians. Attempts to deviate from this universality and generality in the application of LOAC and impose different normative obligations on different states based on each nation’s capabilities go against the grain of traditional LOAC.

Finally, even if we accept the existence of an obligation to use MAWs, either now or in the future, we must still define the substantive scope of such an obligation. Unfortunately, the precise criteria for the imposition of such an affirmative duty may prove extremely difficult to define in advance. That this is the case is the result of a basic conundrum. Although the principles of LOAC impose both negative and positive duties on the parties to an armed conflict, as far as the rules that pertain to weapons are concerned, the obligations are, for the most part, structured as negative obligations. The overarching principle that pertains to weapons systems is the prohibition of superfluous injury or unnecessary suffering. It is true that Additional Protocol I imposes a positive obligation on each High Contracting Party — as part of any “study, development, acquisition or adoption of a new weapon” — to determine whether the employment of a new weapon will be prohibited under international law, but this obligation is ancillary to the basic prohibition on weapons that cause unnecessary suffering. However, the obligation we have been exploring may comprise affirmative duties, for example, to develop, acquire, or adopt a weapon rather than to refrain from doing so.

The difficulties noted above suggest that rather than attempting to delineate and define, in advance, the contours of the obligation to use MAWs, a better method would be to approach the issue on a case-by-case basis, building experience as we go along and as practice is accumulated.