The prohibition on transfer
One state not party — the United States — engaged in conduct in 2021 which was not compatible with the TPNW’s prohibition on transfer of nuclear weapons, by virtue of its export of key components to the United Kingdom’s nuclear arsenal.
Each State Party undertakes never under any circumstances to: ‘Transfer to any recipient whatsoever nuclear weapons or other nuclear explosive devices or control over such weapons or explosive devices directly or indirectly.’
• ‘Transfer’ means to transmit either possession or ownership.
• Because transfer is prohibited ‘to any recipient whatsoever’ and irrespective of whether this occurs ‘directly or indirectly’, it is also illegal to transmit possession or ownership to any other state or to any natural or ‘legal’ person (e.g. a company or organization) of key components of any nuclear explosive device in separate instalments or via intermediaries or third parties where there is knowledge they will be used to produce a nuclear weapon or other nuclear explosive device.
• Unlawful transfer does not necessarily involve payment or other form of ‘consideration’.
• Under Article 1 of the NPT, the five nuclear-weapon states parties have committed never to transfer nuclear weapons ‘to any recipient whatsoever’. The NPT does not include a corresponding prohibition on non-nuclear-weapon states to either transfer nuclear weapons or other nuclear explosive devices or to assist in a transfer. These important lacunae are addressed by Article 1(1)(b) and (e) of the TPNW.
The United States has effectively transferred nuclear weapons to the United Kingdom, because the United Kingdom’s nuclear-weapon system in very large measure is imported from the United States: the UK leases its Trident II (D5) SLBMs from the United States’ stockpile; the design for the UK’s Holbrook nuclear warhead for its Trident missiles is based on the US W76 design; key components for the warhead are imported from US nuclear-weapons laboratories; key components of the UK’s SSBNs are imported from the United States (the Trident SLBM fire control system and missile compartments); and the submarines’ reactors were developed from a US design.
The nature of the cooperation between the United States and the United Kingdom was first set out in the 1958 Mutual Defense Agreement, a bilateral treaty between the two nations. It has been renewed several times, most recently in 2014, covering the ten years through to 2024. Whether this arrangement is compliant with the corresponding prohibition on transfer by nuclear-weapon states under the NPT is also highly questionable.
UK officials have reportedly lobbied the US Congress to expedite the development of a new warhead, the W93, on which a replacement for the Holbrooke warhead would be based. If the United States shares its warhead design with the UK, it will almost certainly be violating Article I of the NPT. This is so, because it will be indirectly transferring nuclear weapons to the United Kingdom.