Britain’s Nuclear Deterrent Development – Part Six

Part of the Britain's Nuclear Deterrent Development series

Two weeks before the first nuclear weapon was used for warfare, dropped on the Japanese city of Hiroshima, the results of the UK general election were announced. On 26 July 1945, Labour had won power and Clement Attlee was appointed Prime Minister. Attlee had been Deputy Prime Minister of a coalition government led by Winston Churchill since May 1940, and had attended the later stages of the Potsdam Conference where he negotiated with President Truman and Joseph Stalin.

After being Prime Minister for only a matter of weeks, and only a day after the second nuclear bomb was dropped on Japan, Attlee convened the Gen 75 Committee. The committee was created to establish the government’s nuclear policy. The Prime Minister dubbed the committee the “Atom Bomb Committee”. The committee and their discussions were shrouded in secrecy and not even discussed at full cabinet meetings.

GEN 75/1 28 August 1945

Attlee had quickly appreciated that the atomic bomb changed the landscape of war. The best deterrent against any aggressor with this new weapon would be that the retaliation would be made with the same hugely destructive weapon. This was the concept of a nuclear deterrent and “mutually assured destruction”. He wrote his thoughts in a secret memo just three weeks after Hiroshima:

…the modern conception of war to which in my lifetime we have become accustomed is now completely out of date. We recognised or some of us did before this war that bombing could only be answered by counter bombing. We were right. Berlin and Magdeburg were the only answer to London and Coventry. Both derive from Guernica. The answer to an atomic bomb on London is an atomic bomb on another great city.

Clement Attlee

Guernica, 1937 by Pablo Picasso

Guernica is a town of cultural importance in the Basque region of Spain. From 1936 to 1939 there was a civil war in Spain. The Nationalists and the Republican government were fighting for control of the country. The Nationalist forces received backing from Fascist Italy, Nazi Germany and others, and the Republican side received support from the Soviet Union, Mexico and others. In April 1937, Guernica was bombed by Nazi Germany’s Luftwaffe and the Italian Aviazione Legionaria.

For almost four hours bombs rained down on Guernica in an experiment for the Nazi blitzkrieg tactics and bombing of civilians, seen in later years during WWII. Blitzkrieg means “lightning war” and is a term used to describe a method of offensive warfare designed to strike a swift, focussed blow at an enemy. The event at Guernica is considered to be the beginning of the Luftwaffe tactic of terror bombing, where specific civilian targets were selected to demoralize the enemy.

Attlee also sent his views to President Truman.

Memorandum from Prime Minister Clement Attlee to President Harry S. Truman © Truman Library

In November 1944, the previous year, James Chadwick, John Cockcroft, Mark Oliphant, Rudolph Peierls, Harrie Massey and Herbert Skinner had met in Washington, DC. They drew up a proposal for a British atomic energy research establishment. In April 1945, the Tube Alloys Committee endorsed their recommendation which had been calculated to cost £1.5 million. With knowledge of the recently formed Gen75 committee, Sir John Anderson, who was responsible for the Tube Alloys project in the early days and was now the Chairman of the Advisory Committee on Atomic Energy (ACAE) submitted the memorandum advocating the proposal. The Gen75 Committee endorsed the creation of the Atomic Energy Research Establishment (AERE) in September 1945. Britain had provided considerable efforts to achieve the atomic bomb with the US. Now they had started on the path to become a Nuclear Weapon State and, importantly, have an independent nuclear deterrent.

On 22 September 1945, in the Fuller Lodge at Los Alamos, the British Mission hosted a party to celebrate the collaboration between Britain and America on the Manhattan Project.

The British Mission party © Los Alamos Science Winter/Spring 1983

The celebration had a very British flavour, including formal invitations, a “footman” to announce the arrival of the guests, an entree of steak-and-kidney pie, a dessert of trifle, and the best port for ceremonial toasts to the King, the President, and the Grand Alliance.

By December 1945, members of the British Mission began returning home. Rudolph Peierls left in January 1946. At the request of Norris Bradbury, who had replaced Oppenheimer as laboratory director, Klaus Fuchs remained until 15 June 1946. Eight British scientists, three from Los Alamos and five from the United Kingdom, participated in Operation Crossroads, the nuclear tests at Bikini Atoll in the Pacific in June 1946.

On 9 November 1945, Attlee and the Prime Minister of Canada – Mackenzie King met with President Truman on board the presidential yacht, USS Sequoia. Attlee had previously sent a message to President Truman wanting to discuss the control of atomic arms. He referred to both of them as “heads of the Governments which have control of this great force”. The discussion was about future cooperation in nuclear weapons and nuclear power.

President Harry Truman and Rt. Hons. Clement Attlee and Mackenzie King boarding USS Sequoia for discussions about the atomic bomb

The previous heads of state for UK and America, Churchill and Roosevelt, had signed a post-war collaboration agreement on nuclear weapons in September 1944 which extended the Quebec Agreement. After Roosevelt’s death in April 1945, the Hyde Park Aide-Mémoire wasn’t binding on subsequent US administrations.

At the USS Sequoia meeting, Attlee, Truman and King agreed to revise the Quebec Agreement, replacing it with a looser cooperation between the three governments. The Combined Policy Committee remained, but the Quebec Agreement’s requirement for “mutual consent” before using nuclear weapons was replaced with one for “prior consultation”. The meeting also decided that there would be a “full and effective cooperation in the field of atomic energy”. The final version, which was signed by Attlee and Truman on 16 November, changed this point to being only “in the field of basic scientific research”. This new Memorandum of Intention replaced the Quebec Agreement.

The British government had trusted that America would share nuclear technology, which it considered a joint discovery, but the next meeting of the Combined Policy Committee on 15 April 1946 produced no agreement on collaboration. This resulted in an exchange of cables between Truman and Attlee. The “special relationship” was becoming a lot less special. The issue was not just technical co-operation, but also the allocation of uranium ore. During the war this wasn’t a concern as Britain had not needed any. At the time all the production of the Congo mines and all the ore seized from Germany had gone to the United States, but now it was also required by the British atomic project.

Memo by a Subcommittee of the CPC to the Committee May 1946 – Source: US Office of The Historian

An agreement was eventually reached with the help of Groves and Chadwick’s very good relationship.

As plans for the Atomic Energy Research Establishment progressed, John Cockcroft was tasked with finding a site to build the research facility that was to include a nuclear reactor. At the time Cockcroft was Director of the Montreal Laboratory for the Manhattan Project, working in similar facilities in Canada. It was decided that an RAF airfield would be chosen, due to the size of the hangars being suitable to house a reactor. Cockcroft chose RAF Harwell.

The blue plaque now on the main gate describing the Harwell Laboratory as a National Chemical Landmark

The RAF station was closed at the end of 1945 and the site transferred to the Ministry of Supply on 1 January 1946, becoming the Atomic Energy Research Establishment.

Cockcroft also recruited the team for the new facility. Klaus Fuchs from the Manhattan Project’s Los Alamos Laboratory was to become head of the Theoretical Physics. Robert Spence, Cockcroft’s deputy at Montreal Laboratory, became head of Chemistry. Herbert Wakefield Banks Skinner was head of General Physics. Otto Frisch was chosen as head of Nuclear Physics. And, John Dunworth was the head of Reactor Physics.

While Britain was forging its own path, America was shutting more doors on the sharing of atomic information.

In mid-1944, a proposal was made for legislation in the US to control nuclear energy. The proposal was submitted to the Secretary of War Henry L. Stimson and in May 1945 it was passed to the Interim Committee, a body created by President Truman to supervise, regulate and control nuclear energy until Congress created a permanent body for the role. The atomic bombings of Hiroshima and Nagasaki lifted the veil of secrecy surrounding the Manhattan Project. Consultation could now be had with the Attorney General, the Judge Advocate General and the Office of Scientific Research and Development and legislation was being drafted.

The May-Johnson Bill on atomic energy was introduced to the House of Representatives in October 1945 but come up against some criticism including the proposed penalties for security breaches, which were ten years in prison and huge fines.

On 20 December 1945, Senator Brien McMahon introduced an alternative bill on atomic energy, which became known as the McMahon Bill. The McMahon Bill attempted to address the controversial aspects of the May-Johnson Bill.

16 February 1946 – While the new bill was being debated news came of the defection of Igor Gouzenko in Canada, and the subsequent arrest of 22 people.


Gouzenko was a cipher clerk for the Soviet Embassy to Canada and he defected with 109 documents on the espionage activities of the Soviet Union in the West. He had exposed Soviet intelligence’s efforts to steal nuclear secrets as well as the technique of planting sleeper agents. Was this the start of the Cold War?

The members of Congress debating the McMahon bill feared that atomic secrets were being stolen by Soviet atomic spies. McMahon convened an executive session. The Federal Bureau of Investigation Director J. Edgar Hoover was called to appear along with the Secretary of State James F. Byrnes, and Major General Leslie R. Groves Jr. Groves revealed that the British physicist Alan Nunn May had passed information about the Manhattan Project to Soviet agents. Congress moved to toughen the act.

Some of the amendments included a changed to Section 10. Previously titled “Dissemination of Information”, it was changed to “Control of Information”. This new section contained the policy described as “born secret” or “classified at birth”. All information concerning the design, development and manufacture of nuclear weapons was “restricted data”. The data was considered classified unless it was specifically declassified. A “wall of secrecy” was set up by the Act.

President Harry S. Truman signs the Atomic Energy Act into law on August 1, 1946. Behind the President, left to right, are Senators Tom Connally, Eugene D. Millikin, Edwin C. Johnson, Thomas C. Hart, Brien McMahon, Warren R. Austin and Richard B. Russell Jr. Source: Department of Energy Office of History and Heritage

After some political discussions the act was passed and Truman signed the final bill into law on 1 August 1946. The Atomic Energy Act of 1946 (McMahon Act) made it clear that the UK would no longer be allowed access to the United States’ atomic research. When it went into effect at midnight on 1 January 1947, the newly created Atomic Energy Commission assumed responsibility for nuclear energy from the wartime Manhattan Project. The remaining British scientists working in the United States were denied access to papers that they had written just days before.

Back in the UK, Air Staff Operational Requirement OR.1001 was issued in August 1946. The requirement anticipated the government decision to authorise research and development work on atomic weapons, with the knowledge that the Atomic Energy Act of 1946 (McMahon Act) would shut down future collaboration.

OR.1001 scoped a weapon not to exceed 24 ft 2 inch in length, 5 ft in diameter and 10,000 lb in weight. The weapon had to be suitable for release from 20,000 ft to 50,000 ft.

Now what was needed was an aircraft to carry the weapon. In January 1947, the Ministry of Supply distributed Specification B.35/46 to UK aviation companies. The specification was to satisfy Air Staff Operational Requirement OR.229 for a medium range bomber. The aircraft was to be capable of carrying one 10,000 lb bomb-load to a target 1,500 nautical miles at height of 45,000–50,000 ft. at a speed of 575 mph. A total of six companies submitted designs to this specification, including Avro.

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