1958 US-UK Mutual Defence Agreement
The 1958 US–UK Mutual Defence Agreement is a bilateral treaty
A treaty is an express agreement under international law entered into by actors in international law, namely sovereign states and international organizations. A treaty may also be known as an agreement, protocol, covenant, convention or exchange of letters, among other terms...

 between the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 and the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 on nuclear weapons cooperation.

It was signed after the UK successfully tested its first hydrogen bomb during Operation Grapple
Operation Grapple
Operation Grapple, and operations Grapple X, Grapple Y and Grapple Z, were the names of British nuclear tests of the hydrogen bomb. They were held 1956—1958 at Malden Island and Christmas Island in the central Pacific Ocean. Nine nuclear detonations took place during the trials, resulting in...

. While the U.S. has nuclear cooperation
Nuclear sharing
Nuclear sharing is a concept in NATO's policy of nuclear deterrence, which involves member countries without nuclear weapons of their own in the planning for the use of nuclear weapons by NATO, and in particular provides for the armed forces of these countries to be involved in delivering these...

 agreements with other countries, including France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

 and some NATO countries, this agreement is by far the most comprehensive.

The treaty is renewed every ten years, most recently extending the treaty to 2014.

Details of the agreement

The agreement enables the U.S. and the UK to exchange classified information
Classified information
Classified information is sensitive information to which access is restricted by law or regulation to particular groups of persons. A formal security clearance is required to handle classified documents or access classified data. The clearance process requires a satisfactory background investigation...

 with the objective of improving each party's "atomic weapon design, development, and fabrication capability".

This includes development of defence plans; training personnel in the use and defence against nuclear weapons; evaluation of enemy capabilities; development of nuclear delivery systems; and research, development and design of military reactors. The agreement also provides for the transfer of special nuclear material (e.g. plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...

, highly enriched uranium, tritium
Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...

), components, and equipment between the two countries, and the transfer of "non-nuclear parts of atomic weapons" to the UK.

The agreement also covered the export of one complete U.S. submarine nuclear propulsion
Nuclear marine propulsion
Nuclear marine propulsion is propulsion of a ship by a nuclear reactor. Naval nuclear propulsion is propulsion that specifically refers to naval warships...

 plant and its enriched uranium
Enriched uranium
Enriched uranium is a kind of uranium in which the percent composition of uranium-235 has been increased through the process of isotope separation. Natural uranium is 99.284% 238U isotope, with 235U only constituting about 0.711% of its weight...

 fuel which was installed in the UK's first nuclear powered submarine, HMS Dreadnought
HMS Dreadnought (S101)
The seventh HMS Dreadnought was the United Kingdom's first nuclear-powered submarine, built by Vickers Armstrongs at Barrow-in-Furness. Launched by Queen Elizabeth II on Trafalgar Day 1960 and commissioned into service with the Royal Navy in April 1963, she continued in service until 1980...


The UK was able to carry out underground nuclear tests at the U.S. Nevada Test Site
Nevada Test Site
The Nevada National Security Site , previously the Nevada Test Site , is a United States Department of Energy reservation located in southeastern Nye County, Nevada, about northwest of the city of Las Vegas...

, the first taking place on 1 March 1962, following this agreement.

There are also confidential intelligence matters covered by the agreement. The UK government has not published these sections "because of the necessity for great confidentiality and because ... it might well assist proliferation".

This agreement replaced the earlier "Agreement for Cooperation Regarding Atomic Information for Mutual Defense Purposes" of 1955. A separate Polaris Sales Agreement
Polaris Sales Agreement
The Polaris Sales Agreement was an agreement between the United States and the United Kingdom which formally arranged for the Polaris missile system to be provided to the UK to maintain its independent nuclear deterrent. The arrangement had been set up in principle as a result of the Nassau Agreement...

 was signed on 6 April 1963.

Assistance to UK nuclear weapons development

An early benefit of the agreement was to allow the UK to "Anglicise" the U.S. W28 nuclear warhead as the Red Snow
Red Snow
Red Snow was a British thermonuclear weapon. Its physics package was apparently similar, if not identical, to that of the United States W28 nuclear warhead used in the B28 nuclear bomb and AGM-28 Hound Dog missile, with an explosive yield of approximately 1.1 megaton.The Red Snow warhead was...

 thermonuclear weapon for the Blue Steel missile
Blue Steel missile
The Avro Blue Steel was a British air-launched, rocket-propelled nuclear stand-off missile, built to arm the V bomber force. It was the primary British nuclear deterrent weapon until the Royal Navy started operating Polaris missile armed nuclear submarines....

 by 1961. In 1974 a CIA proliferation assessment noted that "In many cases [Britain's sensitive technology in nuclear and missile fields] is based on technology received from the U.S. and could not legitimately be passed on without U.S. permission."

The U.S. President
President of the United States
The President of the United States of America is the head of state and head of government of the United States. The president leads the executive branch of the federal government and is the commander-in-chief of the United States Armed Forces....

 authorised the transfer of "nuclear weapon parts" to the UK between at least the years 1975 to 1996.

The UK National Audit Office
National Audit Office (United Kingdom)
The National Audit Office is an independent Parliamentary body in the United Kingdom which is responsible for auditing central government departments, government agencies and non-departmental public bodies...

 noted that most of the UK Trident
UK Trident programme
The UK Trident programme is the United Kingdom's Trident missile-based nuclear weapons programme. Under the programme, the Royal Navy operates 58 nuclear-armed Trident II D-5 submarine-launched ballistic missiles and around 200 nuclear warheads on 4 Vanguard-class ballistic missile submarines from...

 warhead development and production expenditure was incurred in the U.S. who would supply "certain warhead-related components". Some of the fissile materials for the UK Trident warhead were purchased from the U.S. There is evidence that the warhead design of the British Trident system is similar to, or even based on, the U.S. W76
The W76 is a United States thermonuclear warhead. It was manufactured from 1978-1987, and is still in service .The W-76 is carried inside a Mk-4 re-entry vehicle. U.S...

 warhead fitted in some U.S. Navy Trident missiles
Trident missile
The Trident missile is a submarine-launched ballistic missile equipped with multiple independently-targetable reentry vehicles . The Fleet Ballistic Missile is armed with nuclear warheads and is launched from nuclear-powered ballistic missile submarines . Trident missiles are carried by fourteen...

, with design and blast model data supplied to the UK.

Special nuclear materials barter

Under the agreement 5.37 tonnes (11,838.8 lb) of UK-produced plutonium was sent to the U.S. in return for 6.7 kilograms (14.8 lb) of tritium and 7.5 tonnes (16,534.7 lb) of highly enriched uranium over the period 1960-79. A further 470 kilograms (1,036.2 lb) of plutonium was swapped between the U.S. and the UK for reasons that remain classified. Some of the UK produced plutonium was used in 1962 by the U.S. for the only known nuclear weapon test of reactor-grade plutonium .

The plutonium sent to the U.S. included some produced in UK civil Magnox
Magnox is a now obsolete type of nuclear power reactor which was designed and is still in use in the United Kingdom, and was exported to other countries, both as a power plant, and, when operated accordingly, as a producer of plutonium for nuclear weapons...

 reactors, and the U.S. gave assurances that this civil plutonium was not used in the U.S. nuclear weapons program. It was used in civil programmes which included californium
Californium is a radioactive metallic chemical element with the symbol Cf and atomic number 98. The element was first made in the laboratory in 1950 by bombarding curium with alpha particles at the University of California, Berkeley. It is the ninth member of the actinide series and was the...

 production and reactor research. However, the UK did obtain military nuclear material in return, so via this barter UK civil power stations probably provided weapons material.

See also

  • Atomic Weapons Establishment
    Atomic Weapons Establishment
    The Atomic Weapons Establishment is responsible for the design, manufacture and support of warheads for the United Kingdom's nuclear deterrent. AWE plc is responsible for the day-to-day operations of AWE...

  • Nassau agreement
    Nassau agreement
    The Nassau Agreement, concluded on 22 December 1962, was a treaty negotiated between President John F. Kennedy for the United States and Prime Minister Harold Macmillan for the United Kingdom...

  • Quebec Agreement
    Quebec Agreement
    The Quebec Agreement is an Anglo-Canadian-American document outlining the terms of nuclear nonproliferation between the United Kingdom and the United States, and signed by Winston Churchill and Franklin Delano Roosevelt on August 19, 1943, two years before the end of World War II, in Quebec City,...

  • Project E
    Project E
    Project E was a joint project between the United States and the United Kingdom during the cold war to provide nuclear weapons to the British Royal Air Force prior to Britain's own nuclear weapons becoming available...

  • Nuclear weapons and the United Kingdom
    Nuclear weapons and the United Kingdom
    The United Kingdom was the third country to test an independently developed nuclear weapon, in October 1952. It is one of the five "Nuclear Weapons States" under the Nuclear Non-Proliferation Treaty, which the UK ratified in 1968...

  • Nuclear weapons and the United States
    Nuclear weapons and the United States
    The United States was the first country to develop nuclear weapons, and is the only country to have used them in warfare, with the separate bombings of Hiroshima and Nagasaki in World War II. Before and during the Cold War it conducted over a thousand nuclear tests and developed many long-range...

  • Special relationship
    Special relationship
    The Special Relationship is a phrase used to describe the exceptionally close political, diplomatic, cultural, economic, military and historical relations between the United Kingdom and the United States, following its use in a 1946 speech by British statesman Winston Churchill...

External links

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