page_title: High Explosive Research
section_title: Decision
hierarchical_section_title: High Explosive Research / Resumption of independent UK efforts / Decision
caption_attribution_description: English: Sir William Penney
context_page_description: High Explosive Research was the British project to develop atomic bombs independently after the Second World War. This decision was taken by a cabinet sub-committee on 8 January 1947, in response to apprehension of an American return to isolationism, fears that Britain might lose its great power status, and the actions by the United States to withdraw unilaterally from sharing of nuclear technology under the 1943 Quebec Agreement. The decision was publicly announced in the House of Commons on 12 May 1948.
  HER was a civil project, not a military one. Staff were drawn from and recruited into the Civil Service, and were paid Civil Service salaries. It was headed by Lord Portal, as Controller of Production, Atomic Energy, in the Ministry of Supply. An Atomic Energy Research Establishment was located at a former airfield, Harwell, in Berkshire, under the direction of John Cockcroft. The first nuclear reactor in the UK, a small research reactor known as GLEEP, went critical at Harwell on 15 August 1947. British staff at the Montreal Laboratory designed a larger reactor, known as BEPO, which went critical on 5 July 1948.
context_section_description: An early debate among the scientists was whether the fissile material for an atomic bomb should be uranium-235 or plutonium. Tube Alloys had performed much of the pioneering research on gaseous diffusion for uranium enrichment, and Oliphant's team in Berkeley were well-acquainted with the electromagnetic process. The staff that had remained in Britain strongly favoured uranium-235; but the scientists that had worked in the United States argued for plutonium on the basis of its greater efficiency as an explosive, despite the fact that they had neither the expertise in the design of nuclear reactors to produce it, nor the requisite knowledge of plutonium chemistry or metallurgy to extract it. However, the Montreal Laboratory had designed and was building pilot reactors, and had carried out some work on separating plutonium from uranium. The Manhattan Project had pursued both avenues, and the scientists who had worked at Los Alamos were aware of work there with composite cores that used both; but there were concerns that Britain might not have the money, resources or skilled manpower for this. In the end, it came down to economics; a reactor could be built more cheaply than a separation plant that produced an equivalent quantity of enriched uranium, and made more efficient use of uranium fuel. A reactor and separation plant capable of producing enough plutonium for fifteen bombs per year was costed at around £20 million. The facility was approved by the Gen 75 committee on 18 December 1945 "with the highest urgency and importance".
  
  A few months later, Portal, who had not been appointed when this decision was taken, began to have doubts. Word reached him of problems with the Hanford Site reactors, which had been all but completely shut down due to Wigner's disease. On a visit to the United States in May 1946, Groves advised Portal not to build a reactor. By this time, there was interest from the scientists in making better use of uranium fuel by re-enrichment of spent fuel rods. A gaseous diffusion plant was costed at somewhere between £30 and £40 million. The Gen 75 Committee considered the proposal in October 1946. Perrin, who was present, later recalled that:
  The meeting was about to decide against it on grounds of cost, when [Ernest] Bevin arrived late and said "We've got to have this thing. I don't mind it for myself, but I don't want any other Foreign Secretary of this country to be talked at or to by the Secretary of State of the United States as I have just been in my discussion with Mr Byrnes. We've got to have this thing over here, whatever it costs ... We've got to have the bloody Union Jack flying on top of it." 
  Penney had joined the Los Alamos Laboratory in 1944, and had served on the Target Committee that had selected cities to be attacked. He had been in the observation plane Big Stink during the bombing of Nagasaki, and had done damage assessment on the ground following Japan's surrender. He had returned to England in November 1945 intending to resume his academic career, but was approached by C. P. Snow, one of the Civil Service Commissioners, and asked to become Chief Superintendent Armament Research (CSAR, pronounced "Caesar"), in charge of the Ministry of Supply's Armaments Research Department (ARD) at Fort Halstead in Kent. His appointment as CSAR was announced on 1 January 1946, but Groves asked him to assist in the American Operation Crossroads nuclear tests at Bikini Atoll. Penney left for the United States in March 1946, and did not return to Britain until October 1946. Portal then asked him to draw up a scheme for an Atomic Weapons Section within the Armaments Research Department which would design, develop and construct atomic bombs. In his 1 November 1946 report to Portal, which he had to type himself for security reasons, Penney provided a proposed organisation chart, detailed his staffing requirements, and listed his accommodation requirements, which he felt could be met at Fort Halstead, the Royal Arsenal at Woolwich, and Shoeburyness.
  
  In July 1946, the Chiefs of Staff Committee considered t
caption: William Penney, Chief Superintendent Armament Research
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