The prohibition on allowing stationing, installation, or deployment
Five states not party to the TPNW—Belgium, Germany, Italy, the Netherlands, and Türkiye—engaged in conduct in 2022 that was not compatible with the Treaty’s prohibition on allowing stationing, installation, or deployment of nuclear weapons. Between them, they continue to host a total of approximately 100 US B61 gravity nuclear bombs on their territories.
The United States is the only nuclear-armed state that still stations nuclear weapons outside its own territory. As shown in the map below, they are believed to be located at six air bases in Europe: Kleine Brogel in Belgium, Büchel in Germany, Aviano and Ghedi-Torre in Italy, Volkel in the Netherlands, and Incirlik in Türkiye.
The nuclear-sharing relationships between the United States and its NATO allies were concluded prior to the establishment of the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) in 1968; however, the legality of these arrangements remain a source of international controversy and their deterrence value is often disputed. The respective hosting arrangements are thought to be governed by classified bilateral agreements, known as ‘Service-Level Agreements’, between the United States and the respective host state. Nuclear weapons are also occasionally transported between locations for deployment, retirement, maintenance, or modification.
The B61 bombs hosted under NATO nuclear sharing arrangements in Europe are assumed to have explosive yields ranging from an equivalent of 300 tons to 50 kilotons (Kt) of TNT for the B61-4, to 170 Kt for the B61-3. These older versions of the B61 will soon be replaced with the incoming B61-12, which has the same selectable yields as the B61-4.1 Mass production of the B61-12 began in 2022.
The bombs are stored in underground vaults at national airbases in the five European host nations and remain under US custody. In a scenario of use, the United States would authorise the release of these bombs, and European pilots would be tasked with delivering the US nuclear bombs to their targets using NATO dual-capable aircraft. The bases where the nuclear weapons are stored are currently being modernised with upgraded storage vaults, new command, control, and communications systems, and improved security perimeters and arrangements.
In 2022, Pentagon documents indicated that, in addition to the existing host sites, a nuclear storage site in the United Kingdom—thought to be at Lakenheath Air Force Base—would also be receiving an upgrade. While this does not necessarily indicate that nuclear weapons will be imminently returning to Lakenheath, it could allow the base to host US nuclear weapons in the future, particularly in the event that they are removed from Türkiye due to ongoing security concerns.
Each State Party undertakes never under any circumstances to: ‘Allow any stationing, installation or deployment of any nuclear weapons or other nuclear explosive devices in its territory or at any place under its jurisdiction or control.’
- This provision outlaws a particular form of assistance or encouragement of prohibited action: allowing any stationing, installation, or deployment of any nuclear weapons or other nuclear explosive devices in a state party’s territory or at any other place under its jurisdiction or control.
- The TPNW’s prohibition against such hosting of nuclear weapons applies at all times, including during escalating tension or armed conflict. There is no corresponding prohibition in the NPT.
- The concept of jurisdiction refers primarily to a state’s sovereign territory, while control extends to areas that the state party occupies or otherwise controls extraterritorially. This is irrespective of the legality of this control under international law.
- Deployment is the broadest of the three types of prohibited conduct. A violation would not require any prolonged duration, agreement, or infrastructure. Thus, although transit of nuclear weapons is not explicitly prohibited by the TPNW, if movement into the sovereign territory of a state party is not swiftly followed by exit, this might amount to assistance and encouragement to possess nuclear weapons as well as a violation of 1(1)(g).