Is the use of nuclear weapons legal?

Seal of The International Court of Justice, Wikimedia Commons

By Maciej Lempke, Columnist

The use of nuclear weapons provokes vital moral questions. However, it is also important to ask whether the use of these weapons could ever be legally justified. Unfortunately, in the current state of the international law, there is no framework explicitly prohibiting nuclear weapons or their use. This piece examines the possibility of nuclear weapons’ use from the legal standpoint and considers the consequences of its findings for disarmament and non-proliferation activities of the international community.

In July 1996 the International Court of Justice released an opinion on the question concerning the legality of the threat or use of nuclear weapons. The court stated that the use of nuclear weapons would be generally contrary to the rules of armed conflict and humanitarian law.[1] However, the court could not conclude definitively whether the use of nuclear weapons would be lawful in an extreme circumstance of self-defense, in which the very survival of the state would be at stake.[2] Taking into account the opinion of the ICJ and the current international law, it is worth examining the circumstances under which the use of nuclear weapons could be legally justified.

The potential use of nuclear weapons would need to satisfy the requirement of jus ad bellum and related principles of last resort and proportionality. Under Article 51 of the United Nations charter, nothing impairs states’ right of individual and collective self-defense.[3] Most importantly, Article 51 does not specify what means can be used in self-defense. As the ICJ stated in its opinion, the Charter neither expressly prohibits nor permits the use of any specific weapon, including nuclear weapons.[4] Therefore, solely under the jus ad bellum principle, the use of nuclear weapons could have a legal justification on the condition that they were used in response to a nuclear attack.

After fulfilling the jus ad bellum requirements, the use of nuclear weapons would have to satisfy the jus in bello principles of distinction, proportionality, and military necessity. These three elements of the international humanitarian law impose considerable restrictions on the use of nuclear weapons. However, the main source of the international humanitarian law – the Geneva Conventions – does not explicitly prohibit the use of nuclear weapons. Nevertheless, it establishes laws that can be violated by the use of any weapons, including nuclear weapons.

Under the rule of distinction, nuclear weapons could not harm the civilian population. Given the utterly indiscriminate character of these weapons, it would be difficult to meet that requirement. However, one could argue that a counterforce strike (targeting enemy military installations) employing low yield tactical nuclear warheads could meet the restrictions imposed by the distinction rule. In this case, from a legal standpoint, the strike would have to target a military facility distanced enough from the civilian population to prevent any unintended casualties.

The use of nuclear weapons would also have to meet the proportionality requirement. Under this rule, the application of these weapons would have to correspond with the size of the threat and the military objective. Some could argue that the use of nuclear weapons would override the means required to achieve any military objective. However, following the opinion of the ICJ, states might face situations in which their very survival would be at stake, which could allow for the use of nuclear weapons. As the court indicated, every state has a “fundamental right to survival, and thus resort to self-defense in accordance with Article 51 of the Charter, when its survival is at stake”.[5] Nevertheless, only under an extremely specific set of circumstances would the use of nuclear weapons conform with the proportionality rule.

Once the use of nuclear weapons satisfied the rule of distinction and proportionality, liable decision-makers would have to show military necessity of taking such action. The rule of military necessity relates to the legal justification for attacking legitimate military targets that may have adverse consequences for civilians or civilian buildings. In this case the use of nuclear weapons would need to have an extraordinary significance for achieving the objectives of war. One could argue that a tactical nuclear attack on an enemy underground ICBM base ready to launch more missiles, would be a justified action that could override the principle of distinction. Although military necessity of nuclear weapons use would be an extraordinary situation, the international law contains no prohibition on such justification.

Ultimately, neither the customary nor conventional international law bans the use of nuclear weapons. Nevertheless, their application would still have to meet the requirements of the legal resort and conduct of war. At the same time, there is no legal framework prohibiting states to override the law of war in extreme conditions of self-defense, when they are granted with an inherent right to ensure their survival through necessary means – which are not specified. Therefore, it is difficult to judge with 100% confidence that the use of nuclear weapons would be illegal at all times.

This conclusion has serious consequences for the current disarmament and non-proliferation initiatives. Firstly, the lack of an international legal framework explicitly prohibiting the use of nuclear weapons undermines the disarmament goals of the nuclear weapon states (NWS). Most of the NWS agree that the right of self-defense – especially when the survival of the state is threatened – also includes the use of nuclear weapons.[6] This stands in contrast to the NWS pledge to eliminate nuclear weapons. Furthermore, the lack of legal prohibition on the use of nuclear weapons negatively impacts non-proliferation initiatives, as it provides some states with a reason to pursue this capability. Consequently, the introduction of a legal ban on the use of nuclear weapons should be the first step in achieving disarmament and non-proliferation goals. Without this provision, the calls for the elimination of nuclear weapons and prevention of their spread remain empty statements.

Maciej is first year M.A student in the Security Studies Program at Georgetown University. For the past two years he has focused his research on issues related to nuclear disarmament and non-proliferation. He has worked in the Permanent Mission of the Republic of Poland to the United Nations and National Atomic Energy Agency of Poland. He received a B.A degree in International Relations and International History from Aberystwyth University.


[1] International Court of Justice, “Legality of the Threat or use of Nuclear Weapons – Advisory opinion of 8 July 1996”, p.94, available at:

[2] Ibid, p.94,

[3] Charter of the United Nations and Statute of the International Court of Justice, San Francisco 1945, art.51, pp.10-11,

[4] International Court of Justice, “Legality of the Threat or use of Nuclear Weapons”, p.96,

[5] Ibid, 98,

[6] “Dangerous world: France has less than 300 nukes and still needs them”, RT, February 20, 2015, available at: , Michael J. Matheson, “Letter dated 20 June 1995 from the Acting Legal Adviser to the Department of State, together with Written Statement of the Government of the United States”, p.2, available at: , Sir. Franklin Berman, “Letter dated 16 June 1995 from the Legal Adviser to the Foreign and Commonwealth Office of the United Kingdom of Great Britain and Northern Ireland, together with Written Comments of the United Kingdom”, pp.1-2, available at:

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