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Dear readers: Here is another in a series of posts on the laws of war and the use of nuclear weapons. This contribution is from Dr. Justin Anderson, a Research Fellow at National Defense University’s Center for the Study of WMD. Justin previously worked at SAIC in support of the Air Force, STRATCOM, OSD General Counsel/International Affairs, and the OSD Office of Treaty Compliance. From 2009-2010 he was Editor of the DoD Law of War Manual. The views expressed in this article are those of the author and do not reflect the official policy or position of the National Defense University, the Department of Defense, or the U.S. Government.

On December 7, 2015, the UN General Assembly passed A/RES/70/50, titled “Ethical imperatives for a nuclear-weapon-free-world,” by a vote of 132-36. Co-sponsored by Austria and several other states central to the “Humanitarian Impact of Nuclear Weapons” movement, the resolution charges that any use of nuclear weapons would inherently violate the laws of war, stating: “it is inconceivable that any use of nuclear weapons, irrespective of the cause, would be compatible with the requirements of international humanitarian law.” The resolution’s claim that there is an airtight legal case against any form of nuclear employment merits close assessment by jurists, strategists, and policy wonks, particularly in states fielding nuclear forces.

The law of war consists of two parts: jus ad bellum (justice of war) and jus in bello (justice in war, i.e., in the conduct of war). A great deal of literature on nuclear weapons focuses on a leader’s decision to “push the button” (or not); without explicitly mentioning the law of war, these writings often implicitly address jus ad bellum issues. While important, this focus on the highest levels of decision-making leaves a gap with regard to how states apply key jus in bello principles – such as distinction, military necessity, humanity, and proportionality – to their development and deployment of nuclear-capable forces (and the personnel who operate them). This post will briefly describe these principles and provide a “wavetops” assessment of how they apply to the U.S. nuclear deterrent – a force that directly reflects the full implementation of arms-control treaties and an enduring commitment to the law of war.

The principle of distinction expressly divides all persons and objects between those that are legitimate targets with regard to the use of armed force and those that are not, and prohibits attacks directed against the latter. The principles of military necessity and humanity are interlinked. Military necessity permits the use of force against legitimate targets in pursuit of military objectives while humanity dictates that this use not be deliberately excessive and/or pointlessly cruel (e.g., by adding poison to weapons expressly to prolong suffering or defeat medical treatment). A closely related principle is proportionality. This is not, as it is sometimes misunderstood, a principle dictating that a response to an attack be in-kind – that is, “proportional” to the amount of force used against you. Instead it refers to an assessment of whether the force contemplated for an attack, operation, or campaign is proportional to its intended military ends. In time of war, for example, every adversary military base, depot, and vehicle is a legitimate target – but it is unlikely the total destruction of all of them is necessary to secure victory. The principle of proportionality asks the commander to calibrate the use of force to a level that successfully achieves military objectives, while not exceeding a threshold that results in wanton destruction or deeply harms the prospects for a future peace. Proportionality is context- and situation-dependent; if the military requirements are great, it does not rule out significant or even massive use of force.

State adherence to these principles requires a significant investment of political and economic capital to equip militaries with the means and methods to identify and strike legitimate targets while also limiting the risk of harm to civilians and civilian objects.

These are core principles of the law of war; how does the United States apply them to its nuclear deterrent?

The U.S. government publicly states that all nuclear employment plans “must [be] consistent with the fundamental principles of the Law of Armed Conflict.” U.S. nuclear forces adhere to the principle of distinction in terms of targeting policy (as a matter of law and policy, the United States does not target civilians or civilian objects); target identification (U.S. investments in intelligence, surveillance, and reconnaissance technology are critical to correctly identifying legitimate targets); and guidance technology (hardware and software ensures delivery systems are highly accurate; U.S. ballistic missiles, for example, have a very low circular error probability).

U.S. employment doctrine and planning also integrates the principles of military necessity, humanity, and proportionality. Should the United States or an ally, for example, face an imminent nuclear attack, the U.S. military might advise the president that preventing the attack would require a rapid strike, launched at a distance, using munitions that would completely disable or destroy – rather than merely degrade – the belligerent forces preparing the attack. These requirements might rule out available conventional options; in this scenario, a U.S. nuclear strike would be a legitimate response due to the military necessity of completely neutralizing the target in order to prevent a catastrophic, mass-casualty attack against the United States or an ally.

Importantly, however, while the law of war would justify this use of force, it would also require that it be carefully calibrated; the above scenario would not be a license to unleash Armageddon. In an Air Force Law Review article titled “Taming Shiva: Applying International Law to Nuclear Operations,” Air Force Major General (ret.) Charles Dunlap – who at the time of writing was the principal legal advisor to the commander of U.S. Strategic Command – discussed a number of ways to adjust the effects of a nuclear strike, to include: “reducing weapon yield, improving accuracy through weapon system selection, employing multiple small weapons (as opposed to a single, large device), [and] adjusting the height of burst – [through utilizing some or all of these options] collateral damage can be minimized consistent with military objectives.” Many discussions of potential nuclear weapons employment appear to assume all attacks have the same effects; the measures described by Dunlap, however, can exponentially reduce the potential risk to civilians and civilian objects associated with any theoretical strike.

The U.S. commitment to integrating the law of war across all military activities, to include nuclear operations, willfully limits potential U.S. nuclear employment to “extreme circumstances” and also conditions what form – in terms of the target, delivery system, and munitions selected – this employment might take.

This is a brief assessment of a critically important topic, but one I hope helps catalyze discussion of the law of war and its relationship to the development and deployment of nuclear delivery systems and weapons in all states fielding these forces.