Germany has been a member of the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) since 1970. This treaty represents the most important multilateral agreement related to nuclear weapons. Germany is a non-nuclear-weapon state party to the NPT and thus may not possess any nuclear weapons. As Article 2 of the Treaty states:
“Each non-nuclear-weapon State Party to the Treaty undertakes not to receive the transfer from any transferor whatsoever of nuclear weapons or other nuclear explosive devices or of control over such weapons or explosive devices directly, or indirectly; not to manufacture or otherwise acquire nuclear weapons or other nuclear explosive devices; and not to seek or receive any assistance in the manufacture of nuclear weapons or other nuclear explosive devices.”
United Nations, Office for Disarmament Affairs
The Two Plus Four Agreement reaffirmed this ban on the acquisition of nuclear weapons for the reunified Germany. However, the stationing of foreign nuclear weapons on the territory of a non-nuclear-weapon state is controversial at the international level. NATO allies understand the NPT to mean that the stationing of weapons in other countries is legal, provided the possessing state controls the weapons. Nuclear weapons were already stationed in Germany before the treaty negotiations began. Before it entered into force, the NATO allies set out their interpretation of the NPT:
In their view, it does not cover arrangements for the stationing of nuclear weapons on allied territory, since these do not involve the transfer of nuclear weapons or power of disposal over them unless and until a decision to go to war is made, at which time the treaty would no longer be relevant.Bundestag document 7/994, p. 17
However, this view is not shared by all parties to the NPT. Many states regularly criticize the practice of nuclear weapon sharing. The group of non-aligned countries (120 countries outside of NATO and the former Warsaw Pact) issued the following statement during a review conference of the NPT:
“In our view, any horizontal proliferation and nuclear-weapon-sharing by States Parties constitute a violation of non-proliferation obligations under articles I and II.”Statement by the non-aligned movement, April 27, 2015
A use of nuclear weapons, in which German pilots would gain power of disposal over stationed nuclear weapons, would constitute a breach of the NPT. International treaties usually retain their validity even in the event of war (for example, the Geneva Convention, or other classic arms control treaties such as the conventions on chemical and biological weapons).
The new Treaty on the Prohibition of Nuclear Weapons, which entered into force on January 22, 2021, provides legal clarity on the stationing issue. This treaty explicitly prohibits its parties from hosting foreign nuclear weapons (Article 1.1.g). Germany is not a party to this treaty, so Berlin is not currently bound by the prohibition. Furthermore, numerous states in the global South have long been members of regional nuclear-weapon-free zones that prohibit the stationing of nuclear weapons on land. Regulations on overflight and transit through territorial waters vary from region to region.
Bilateral agreements between the United States and Germany regulate the stationing of US nuclear weapons on German soil. The contents of the agreements are secret, however. An official US report lists four different agreements: an Atomic Stockpile Agreement, an Atomic Cooperation Agreement, a Service-Level Agreement and a Third-Party Stockpile Agreement.
The fundamental legality of nuclear weapons use was discussed and reviewed by the International Court of Justice in The Hague in 1996. The judges concluded that the use of nuclear weapons would be incompatible with international humanitarian law in the vast majority of scenarios. Extreme self-defense situations represented the only use case excluded in the judgment. According to the court, international humanitarian law was not specific enough, so that the judges had to leave the question of legality or illegality open.