What is the Mutual Defense Agreement between the United Kingdom and the United States?
The 1958 bilateral Mutual Defense Agreement on nuclear weapons cooperation between the United Kingdom and the United States is by far the most comprehensive agreement that either country has in this area. It enables them to exchange classified information to enhance each party's "atomic weapon design, development and fabrication capability". It also provides for the exchange of special nuclear material (e.g. plutonium, highly enriched uranium), components and equipment between the two countries, as well as the transfer of "non-nuclear parts of atomic weapons" to the UK.