The early years of Britain’s nuclear programme

The US–UK Mutual Defence Agreement and the Polaris Sale Agreement can be considered the heart of the nuclear cooperation between London and Washington. The Agreements are central to maintaining the Anglo-American relationship as “special”.

On 3 October 1952, the United Kingdom achieved the status of nuclear power after detonating an atomic bomb in the Monte Bello Islands in Australia. The success of the British operation – codenamed Operation Hurricane – displayed that the UK was willing to go alone to master the technology after the United States’ actions in the aftermath of the Second World War that resulted in the end of the Anglo-American cooperation in the field.

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The UK is one of the precursors of nuclear research. By 1941, Britain could be regarded as the primary source of information in the exchanges between researchers in Britain and the United States through the Tube Alloys project and MAUD Committee; the former was the British nuclear research and development programme, and the latter was the committee responsible to determine the feasibility of atomic bombs. However, by 1943 the American Government had significant investments in research and development, which were roughly 20 times more than the investments of its British counterpart. Thus, British officials in London, including Sir John Anderson, the minister responsible for Tube Alloys, advised Prime Minister Winston Churchill to aim for a “merge” of the British efforts with the American programme. The British Government achieved this objective at the Quebec Conference in August 1943. It is worth mentioning that since its early days, the British research had scientists from Canada who would also participate in the American efforts for a nuclear bomb, the Manhattan Project.

In September 1944, Churchill and Roosevelt signed the Hyde Park Agreement, also known as Hyde Park Aide-Mémoire. The Agreement represented the commitment of both parties that the Anglo-American nuclear cooperation would continue after the defeat of Japan. Both leaders agreed that the partnership could only be “terminated by joint agreement”, effectively granting the UK access to nuclear weapons when they could be made. Additionally, the Hyde Park Agreement established one of the first plans to employ a nuclear device: “when a ‘bomb’ is finally available, it might perhaps, after mature consideration, be used against the Japanese, who should be warned that this bombardment will be repeated until they surrender”.

The McMahon Act

Despite its relevance, the Hyde Park Agreement of 1944 remained obscure within the American Government’s ranks, mainly and almost exclusively known by President Roosevelt, who died in April 1945. Therefore, the Agreement was not binding for Roosevelt’s successor. When the British approached the Truman Administration and cited the Hyde Park Agreement, the physical loss of the American version further complicated matters. Even after the British Government had sent a photocopy to Washington, officials in charge of nuclear research questioned the authenticity of the document, in particular Leslie Groves, former director of the Manhattan Project. Although nuclear cooperation continued until the end of 1946, it declined steadily.

In August 1946, President Harry Truman signed the Atomic Energy Act of 1946, commonly known as the “McMahon Act”, after the name of Senator Brien McMahon, an avid supporter of this law. Senator McMahon also chaired Senate hearings that led to the passing of the Act. The McMahon Act went into effect on 1 January 1947, terminating all nuclear cooperation with other countries unilaterally. Britain and Canada were cut off from their contribution to the Manhattan Project. At the same time, the Act effectively confirmed that the Quebec Agreement of 1943 – that first stated that the UK and US should pool their resources together to build a nuclear weapon – was an Executive commitment restricted to the Roosevelt Administration. The American Administration would only find their version of the Hyde Park Agreement years later. Senator McMahon apologised to Churchill in the early 1950s, stating that if the Agreement had been known back in 1946, the McMahon Act would have never happened. However, reviving nuclear cooperation to the levels seen in the early 1940s would take more than recognising that the British Government was right about the Hyde Park Agreement.

After the McMahon Act, British officials understood that pursuing the technology would demand an independent initiative. Although Britain could not recover many of its documents and research in the United States, the British programme proceeded at a relative steady pace. On 8 January 1947, through the General Committee 163 (Gen 163 Committee) – which met only once before disbanding – the British Government approved the policy to proceed with the independent development of nuclear weapons. In May 1948, HM Government first announced in the House of Commons that the country was pursuing its own nuclear capabilities.

Hydrogen

Slightly more than five years later since the decision made during the Gen 163 Committee, the High Explosive Research (HER) achieved its primary objective through Operation Hurricane: a successful nuclear weapon test. Costing roughly 11 per cent of the Ministry of Supply budget between 1946 and 1952, the High Explosive Research’s total expenditure represented slightly more than one-sixth of the Ministry of Defence budget for 1948. Thus, beyond its technical and strategic success, Britain’s nuclear programme presented itself as a display of economic efficiency. In short, even though it had a high cost for a nation still recovering from the effects of the Second World War, the HER remains an example of balanced expenditure and enormous strategic benefits for the global standing of Britain. In the aftermath of Operation Hurricane, British civil and nuclear engineer Sir William Leonard Owen declared that “the McMahon Act was probably one of the best things that happened … as it made us work and think for ourselves along independent lines”.

Nevertheless, one month after the British nuclear test, the United States tested a thermonuclear weapon known as a “hydrogen” or “fusion” bomb. The thermonuclear bombs rendered the previous “generation” relatively obsolete. The expectations in London about increased nuclear cooperation with Washington were harshly shut down, leaving only a “modus vivendi” of exchange concerning non-critical information between the two counties, which was the only communication that survived the 1946 Act.

Once again, the UK faced another relevant decision about its nuclear programme. The British Government had to decide whether to approve the initiation of another independent initiative to achieve the “second generation” of nuclear weapons or to relinquish some of its nuclear ambitions while maintaining the less advanced but still effective fission bombs. Increasing the urgency of a final decision, in August 1953, the Soviet Union declared that it had successfully tested its first thermonuclear weapon, leaving the UK behind. Permeating the debate within the British Government, many officials adopted an approach that stated that the country could not afford a programme for these new weapons. Concerns encompassed technical and material limitations for independent research, particularly the economic resources that could be demanded from a thermonuclear programme.

No confirmation or denial

Almost two years after its first nuclear weapon test, the Cabinet decided to approve large-scale research for a British thermonuclear bomb. Official research started in July 1954, and by early-1957 Britain had three bomb projects ready for testing. The first one was the Orange Herald, a “boosted fission weapon” instead of an actual thermonuclear/hydrogen device. The second project was named Green Bamboo and classified as an “interim” or “hybrid” design. Britain considered this specific design a stepping-stone on the route to a fusion bomb, which the Green Granite project aimed to achieve.

Green Granite’s prototype, known as Short Granite, was detonated in the first of the Operation Grapple tests. On 15 May 1957, a British Vickers Valiant aircraft – flying from a height of 14 km – dropped the prototype off the shore of Malden Island in the Pacific Ocean. Internally considered a failure due to a yield far below its designed capability, the Grapple 1 test was seen as a successful thermonuclear test worldwide. At the same time, HM Government did not confirm or deny reports that it had become the third thermonuclear power. However, for British scientists involved in Operation Grapple, it was clear that they had not mastered the technology yet. While a design that behaved according to its specifications was developed, Britain performed a second test with the Orange Herald “boosted fission weapon” on 31 May 1957, omitting the fission characteristics of the device. A Grapple 3 test occurred in June of the same year.

Within months, British efforts resulted in a new design, called Round A, quickly scheduled for testing before conversations with the United States and the Soviet Union could result in any form of a test ban. The test proceeded under the name Grapple X and on 8 November 1957, a Valiant aircraft dropped Round A off the southern tip of Christmas Island. The success of Grapple X confirmed that Britain had achieved the mastery of thermonuclear weapons. The setbacks first found on 15 May had been overcome by 8 November 1957. In the following weeks, the British Government would proceed with the Grapple Y and Z tests. Seeking to improve its nuclear capabilities, between 1952 and 1991, Britain performed 45 detonations.

Britain a new level of strategic consideration for the Kremlin

The British achievements of 1952 and 1957 sent a clear signal that the country was willing to remain amongst the hall of the Great Powers, bearing the technical and material capabilities required to master the destructive power of nuclear and thermonuclear weapons. Additionally, Britain ended the American and Soviet “duopoly” over these technologies. Despite the relatively small stockpile of atomic weapons at its disposal, the independent deterrent remained an enduring principle for the British Government. The destructive potential of the nuclear arsenal built by the newest nuclear power could not be easily dismissed by the Americans and, in particular, the Soviets. Even though the Soviet Union, and later Russia, possessed far superior numbers of warheads and missiles compared to the UK, the British entered a new level of strategic considerations for the Kremlin. No longer does the United States’ willingness to intervene appear as the sole nuclear concern of the Soviets and after 1991 the Russians. It is worth noting that since 1952, the American position concerning sharing nuclear technology with the UK was changing but the central aspects of nuclear cooperation remained restricted by Washington.

Britain aimed to achieve an independent nuclear delivery system within the context of a growing arsenal. Moreover, the 1956 Suez Crisis tarnished the “special relationship” between the United States and Britain. Therefore, an independent system could have two main consequences for British foreign policy. Firstly, the country would be seen as a credible nuclear power – and threat – by the Soviet Union, for no longer Britain relied on the United States for its nuclear umbrella and nuclear targeting. Secondly, this system could give Britain a revived influence on the United States.

Following these developments in the UK, on 4 October 1957, the Soviet Union launched Sputnik 1, the world’s first artificial satellite, showing that the Soviets could be technologically ahead of the United States in some areas. The Harold Macmillan Government (1957-1963) took this opportunity and suggested that the UK and the US should strengthen the Special Relationship, including reopening high levels of nuclear cooperation. In addition, within the ranks of the Eisenhower Administration (1953-1961), the widespread position of American officials was that the United States could resume nuclear cooperation since the British had mastered the thermonuclear technology independently from the United States. Later, it became clear to the American researchers that the UK not only understood how to build a thermonuclear bomb, but it had done so with a different design from the one employed by the US.

The age of Polaris

In June 1958, the American Congress amended the McMahon Act enabling the re-opening of high-level exchanges of nuclear technology between the UK and the United States. In the following month, the two countries signed the US–UK Mutual Defence Agreement, a landmark in the Anglo-American bilateral relationship, effectively re-establishing the credibility of the Special Relationship after the Suez Crisis and the McMahon Act.

The US–UK Mutual Defence Agreement of 1958 allowed both countries to exchange “classified information” on their design of atomic weapons and fabrication capabilities. Additionally, through the Agreement United States would sell one nuclear submarine propulsion plant to the UK along with the uranium and a decade of technical support if necessary. Concerning the nuclear propulsion for submarines, the British had been involved in exchanges with the US Navy since an agreement dating from July 1956 (supported by a Presidential Directive from February 1957) allowed Royal Navy officers to be assigned to study the American nuclear submarine programme. The sale of the complete nuclear propulsion plant ended the need for British inquiries seen by some American officers as a source of delays for the deployment of the Polaris submarine-launched ballistic missile (SLBM). Lastly, amongst other matters, the 1958 Agreement enabled the sharing of intelligence on enemy nuclear capabilities and the development of nuclear delivery systems between the two Parties.

The first meeting of British and American government representatives under the auspices of the new arrangements occurred in late August 1958. Both delegations disclosed details of their nuclear weapon designs. The United States provided nine while the UK provided seven of its designs. Impressed by some British designs, the American delegation looked forward to seeing the final results of an in-progress series of new British nuclear weapon designs. The then Prime Minister, Harold Macmillan, noted that after analysing the British nuclear projects, the Americans finally realised that the US–UK Mutual Defence Agreement would not be only a “give” of information.

Meanwhile, the representatives of the UK were also impressed by one of the American devices, the “W28” or “B28” nuclear warhead. The modified version of the W28 entered British service as the “Red Snow”, considered lighter and more economical than the British Green Grass warhead. The 1958 Agreement would be amended in the following years, expanding the scope of interchange between the two countries’ nuclear programmes.

British ambitions

In December 1962, this previous nuclear arrangement paved the way for the UK and the United States to sign the Nassau Agreement to solve the Skybolt Crisis. This “crisis” occurred after the American cancellation of the air-launched Skybolt missile programme in the previous months, which the British Government had been planning to acquire since 1960. Therefore, the UK wanted an alternative missile for purchase. After lengthy negotiations, Harold Macmillan successfully pressed the John F. Kennedy Administration for the sale of the Polaris missile. London and Washington solved the acquisition details in the following year through the Polaris Sale Agreement. Britain would fit British ET.317 warheads to the Polaris missiles, a delivery system more advanced than the air-launched Skybolt.

In 2001, two of the greatest specialists in the history of the British nuclear weapons programme, historians Lorna Arnold and Katherine Pyne, wrote succinctly about the benefits of the “Special Nuclear Relationship”: “The balance of advantage in the exchanges was necessarily in Britain’s favour but they were not entirely one-sided. In some areas, notably electronics and high explosives, the British were equal or perhaps even superior, and in many areas they had valuable ideas to contribute, as the American scientists […] appreciated”. Beyond summarising nuclear cooperation, the authors also sum up the whole Special Relationship as a “balance of exchanges” that notably the British had much more to offer than its American counterparts first expected.

Concerning the UK’s path to achieving the status of nuclear power, severe setbacks marked the early years of the British nuclear programme. The events that unfolded in the year after the death of President Roosevelt, which culminated in the exclusion of British and Canadian scientists from the nuclear programme they had been contributing to since 1943, represented a significant challenge to post-war British ambitions. Nevertheless, the UK displayed the willingness and technical capabilities to resume its independent nuclear programme.

Capability cornerstone

The successful British nuclear test of 1952 and thermonuclear test of 1957 displayed that the country could reach its strategic objectives without direct support from the United States. By 1958, the designs of the British thermonuclear weapons rivalled – even surpassing in some cases – the American projects. In the following decades, the United Kingdom would employ missile systems from the United States (Polaris and Trident II) with British-made warheads. Thus, the core of the UK’s nuclear programme remains British while employing the missile delivery systems bought from the US. The British Prime Minister retains the sole authority over using the independent nuclear deterrent.

In conclusion, the US–UK Mutual Defence Agreement and its amendments remain the cornerstones of the current atomic capabilities deployed by the UK. It will stay this way with the Dreadnought-class of ballistic missile submarines, for the British Government opted to keep the Trident II D-5 missiles from the United States. In addition, one of the most relevant lessons of the early years of the British pursuit of nuclear and thermonuclear weapons is that the country remained capable of independently achieving its desired strategic objectives.