were in danger of being arrested. The Danish resistance helped the family escape by sea to Sweden. Bohr arrived there in October 1943, and then flew to Britain on a de Havilland Mosquito operated by British Overseas Airways Corporation. The Mosquitoes were unarmed high-speed bomber aircraft that had been converted to carry small, valuable cargoes or important passengers. By flying at high speed and high altitude, they could cross German-occupied Norway, and yet avoid German fighters. Bohr, equipped with parachute, flying suit and oxygen mask, spent the three-hour flight lying on a mattress in the aircraft's bomb bay. On arrival in London, Bohr rejoined his father, who had flown to Britain the week before. He officially became a junior researcher at the Department of Scientific and Industrial Research, but actually served as personal assistant and secretary to his father. The two worked on Tube Alloys, the British atomic bomb project. On 30 December 1943, they made the first of a number of visits to the United States, where his father was a consultant to the Manhattan Project. Due to his father's fame, they were given false names; Bohr became James Baker, and his father, Nicholas Baker. In 1945, the director of the Los Alamos Laboratory, J. Robert Oppenheimer, asked them to review the design of the modulated neutron initiator. They reported that it would work. That they had reached this conclusion put Enrico Fermi's concerns about the viability of the design to rest. The initiators performed flawlessly in the bombs used in the atomic bombings of Hiroshima and Nagasaki in August 1945. Career In August 1945, with the war ended, Bohr returned to Denmark, where he resumed his university education, graduating with a master's degree in 1946, with a thesis concerned with some aspects of atomic stopping power problems. In early 1948, Bohr became a member of the Institute for Advanced Study in Princeton, New Jersey. While paying a visit to Columbia University, he met Isidor Isaac Rabi, who sparked in him an interest in recent discoveries related to the hyperfine structure of deuterium. This led to Bohr becoming a visiting fellow at Columbia from January 1949 to August 1950. While in the United States, Bohr married Marietta Soffer on 11 March 1950. They had three children: Vilhelm, Tomas and Margrethe. By the late 1940s it was known that the properties of atomic nuclei could not be explained by then-current