Britain appears in the account as a scientific and political partner in the wartime effort to develop an atomic weapon. London was a place where Niels Bohr was briefed on the British program; British physicists later joined the work at Los Alamos. Through these connections, Britain linked the European history of nuclear research to the industrial-scale American project and to growing concern about what would follow the bomb’s invention.

A British program and a route to America

After escaping occupied Denmark, Bohr reached London, where James Chadwick began briefing him on the British-American bomb project. Bohr had understood since 1939 that nuclear fission made an atomic weapon conceivable, but had considered the industrial effort required to separate uranium-235 prohibitive. Learning that the United States was devoting its resources to precisely that task made the project’s scale newly apparent to him.

Bohr’s twenty-one-year-old son, Aage Bohr, joined him in London. Over seven weeks, father and son were briefed on Tube Alloys, the British code name for the bomb project. Niels Bohr agreed to serve as a British consultant, and Britain then agreed to send him to the United States. General Leslie Groves was reluctant to admit him to the secret work, but Bohr’s standing in physics helped secure permission for him to visit Los Alamos.

British scientists at Los Alamos

Britain’s contribution also took the form of scientific personnel. In February 1944, a team of British scientists led by Rudolf Peierls arrived at Los Alamos. Peierls had worked on all aspects of Tube Alloys and, with Otto Frisch, had written the 1940 paper that helped persuade the British and American governments that a nuclear weapon was feasible. Prime Minister Winston Churchill had sent Peierls to the United States in 1942 and again in September 1943 to help expedite the work.

Peierls had met J. Robert Oppenheimer in 1929, when both were studying under Wolfgang Pauli. On an earlier visit to the United States, he had been impressed by Oppenheimer’s command of the project and by his attention to the weapon’s physical implications. His first visit to Los Alamos lasted only two and a half days, but he and Oppenheimer agreed that the British team could make a substantial contribution to the study of implosion hydrodynamics. A month later, Peierls returned to Los Alamos for the duration of the war.

A connection extending beyond the laboratory

Britain’s role was not limited to transferring expertise. Bohr used his access to British and American officials to press the political implications of the bomb. He argued that its development was becoming inevitable, but that the postwar consequences still demanded attention. In particular, he feared a nuclear arms race between the West and the Soviet Union and urged that the Soviet Union be told that the project existed and was not directed against it.

The account thus connects Britain both to the practical collaboration that advanced the weapon and to an early debate over international trust and postwar danger. British participation helped bring people and knowledge into the American project; Bohr’s time in London and his subsequent journey to the United States also carried the argument about the bomb beyond the laboratory, toward the unresolved question of how states might live with its existence.