Tube Alloys

Tube Alloys was the research and development programme authorised by the United Kingdom, with participation from Canada, to develop nuclear weapons during the Second World War. Starting before the Manhattan Project in the United States, the British efforts were kept classified, and as such had to be referred to by code even within the highest circles of government.

The possibility of nuclear weapons was acknowledged early in the war. At the University of Birmingham, Rudolf Peierls and Otto Robert Frisch co-wrote a memorandum explaining that a small mass of pure uranium-235 could be used to produce a chain reaction in a bomb with the power of thousands of tons of TNT. This led to the formation of the MAUD Committee, which called for an all-out effort to develop nuclear weapons. Wallace Akers, who oversaw the project, chose the deliberately misleading code name "Tube Alloys". His Tube Alloys Directorate was part of the Department of Scientific and Industrial Research.

The Tube Alloys programme in Britain and Canada was the first nuclear weapons project. Due to the high costs for Britain while fighting a war within bombing range of its enemies, Tube Alloys was ultimately subsumed into the Manhattan Project by the Quebec Agreement with the United States. Under the agreement, the two nations would share nuclear weapons technology, and refrain from using it against each other, or against other countries without mutual consent. However, the United States did not provide complete details of the results of the Manhattan Project to the United Kingdom. The Soviet Union gained valuable information through its atomic spies, who had infiltrated both the British and American projects.

The United States terminated co-operation after the war ended, under the Atomic Energy Act of 1946. That prompted the United Kingdom to relaunch its own project, High Explosive Research. Production facilities were established and British scientists continued their work under the auspices of an independent British programme. In 1952, Britain performed a nuclear test under the codename "Operation Hurricane" and became the third nuclear-weapon state. In 1958, in the wake of the Sputnik crisis, and the British demonstration of a two-stage thermonuclear bomb, the United Kingdom and the United States signed the US–UK Mutual Defence Agreement, which resulted in a resumption of Britain's nuclear Special Relationship with the United States.

The neutron was discovered by James Chadwick at the Cavendish Laboratory at the University of Cambridge in February 1932. In April 1932, his Cavendish colleagues John Cockcroft and Ernest Walton split lithium atoms with accelerated protons. Enrico Fermi and his team in Rome conducted experiments involving the bombardment of elements by slow neutrons, which produced heavier elements and isotopes. Then, in December 1938, Otto Hahn and Fritz Strassmann at Hahn's laboratory in Berlin-Dahlem bombarded uranium with slowed neutrons, and discovered that barium had been produced, and therefore that the uranium atomic nucleus had been split. Hahn wrote to his colleague Lise Meitner, who, with her nephew Otto Robert Frisch, developed a theoretical justification which they published in Nature in 1939. The phenomenon was a new type of nuclear disintegration, and was more powerful than any seen before. Frisch and Meitner calculated that the energy released by each disintegration was approximately 200,000,000 electron volts. By analogy with the division of biological cells, they named the process "fission".

That was followed up by a group of scientists at the Collège de France in Paris: Frédéric Joliot-Curie, Hans von Halban, Lew Kowarski, and Francis Perrin. In February 1939, the Paris Group showed that when fission occurs in uranium, two or three extra neutrons are given off. That important observation suggested a self-sustaining nuclear chain reaction might be possible. The term "atomic bomb" was already familiar to the British public through the writings of H. G. Wells, in his 1913 novel The World Set Free. It was immediately apparent to many scientists that, in theory at least, an extremely powerful explosive could be created, although most still considered an atomic bomb was an impossibility. Perrin defined a critical mass of uranium to be the smallest amount that could sustain a chain reaction. The neutrons used to cause fission in uranium are considered slow neutrons, but when neutrons are released during a fission reaction they are released as fast neutrons which have much more speed and energy. Thus, in order to create a sustained chain reaction, there existed a need for a neutron moderator to contain and slow the fast neutrons until they reached a usable energy level. The Collège de France found that both water and graphite could be used as acceptable moderators.

Early in 1940, the Paris Group decided on theoretical grounds that heavy water would be an ideal moderator. They asked the French Minister of Armaments to obtain as much heavy water as possible from the only source, the large Norsk Hydro hydroelectric station at Vemork in Norway. The French discovered that Germany had already offered to purchase the entire stock of Norwegian heavy water, indicating that Germany might also be researching an atomic bomb. The French told the Norwegian government of the possible military significance of heavy water. Norway gave the entire stock of 187 litres (41 imp gal; 49 US gal) to a Deuxième Bureau agent, who secretly brought it to France just before Germany invaded Norway in April 1940. On 19 June 1940, following the German invasion of France, it was shipped to England by the Earl of Suffolk and Major Ardale Vautier Golding aboard the steamer Broompark. The heavy water, valued at £22,000, was initially kept at HM Prison Wormwood Scrubs, and was later secretly stored in the library at Windsor Castle. The Paris Group moved to Cambridge, with the exception of Joliot-Curie, who remained in France and became active in the French Resistance.

In Britain, a number of scientists considered whether an atomic bomb was practical. At the University of Liverpool, Chadwick and the Polish refugee scientist Joseph Rotblat tackled the problem, but their calculations were inconclusive. At Cambridge, Nobel Prize in Physics laureates George Paget Thomson and William Lawrence Bragg wanted the government to take urgent action to acquire uranium ore. The main source of this was the Belgian Congo, and they were worried that it could fall into German hands. Unsure as to how to go about this, they spoke to Sir William Spens, the master of Corpus Christi College, Cambridge. In April 1939, he approached Sir Kenneth Pickthorn, the local Member of Parliament, who took their concerns to the Secretary of the Committee of Imperial Defence, Major General Hastings Ismay. Ismay in turn asked Sir Henry Tizard for an opinion. Like many scientists, Tizard was sceptical of the likelihood of an atomic bomb being developed, reckoning the odds of success at 100,000 to 1.