Nearly 1,000 nuclear weapon components were imported from the US to the UK between 2020 and 2023, we can reveal in a new briefing published today. The briefing examines the US-UK Mutual Defence Agreement (MDA), the treaty which governs the nuclear dimension of the US-UK ‘special relationship’. The MDA was first signed in 1958 and is due to be renewed before the end of 2024.
The MDA allows for the two states to exchange components of nuclear weapons, submarine reactor technology, nuclear materials (such as uranium and plutonium), and information about nuclear technologies. The briefing reveals that 955 non-nuclear parts of nuclear weapons were transferred from the US to the UK under the treaty in the years 2020-2023.
In response to a Freedom of Information Request by NIS the Ministry of Defence (MOD) stated that 128 non-nuclear parts of nuclear weapon systems had been transferred from the US to the UK under the MDA in 2020. In 2021 271 parts were transferred, with 302 transferred in 2022 and 254 in 2023. Only 108 components were transferred from the UK to the US during the four years. From around 2016 until 2023 the UK was carrying out the Mk4A upgrade to its nuclear warhead. This included changing the arming, fusing and firing system, neutron initiators and the gas transfer system, with these components all being imported from the US.
During barter exchanges in the 1960s and 1970s the UK sent 5.4 tonnes of plutonium to the US in exchange for 6.7kg of tritium and 7.5 tonnes of highly enriched uranium. In addition, a total of 0.47 tonne of plutonium was sent from the UK to the US and received back again prior to March 1999. However, the timing and initial direction of these plutonium ‘loans’ is not known. The MOD has refused to release any information on the recent transfer of nuclear materials under the treaty.
The briefing also reveals the subject areas for cooperative working between the two states. Much of this cooperative working takes places through ‘Joint Working Groups’, known as JOWOGs. At least 48 different JOWOGs have been active since 1958, and current areas of joint working include explosives research, nuclear weapons engineering and physics, technology to deal with accidents, and defeating missile defence systems. The MOD refused to disclose the names of a further six JOWOGs. It is likely that some of these unnamed JOWOGs are working on the US W93 and UK Astrea warhead programmes. A graphic showing the activity of JOWOGs since 1958 is included in the briefing, as well as an annotated text of the MDA.