of my mind", but he continued because he thought the only way to prevent Nazi Germany from using a nuclear bomb was if Britain had one to act as a deterrent. He worked with Chadwick on Tube Alloys, the British atomic bomb project. In February 1944, Rotblat joined the Los Alamos Laboratory as part of Chadwick's British Mission to the Manhattan Project. Although he was upset by the morality of the project, he believed the allies needed to be able to threaten retaliation in case Germany developed the bomb. The usual condition for people to work on the Manhattan Project was that they had to become US citizens or British subjects. Rotblat declined, and the condition was waived. At Los Alamos, he was befriended by Stan Ulam, a fellow Polish-Jewish scientist, with whom he was able to converse in Polish. Rotblat worked in Egon Bretscher's group, investigating whether high-energy gamma rays produced by nuclear fission would interfere with the nuclear chain reaction process, and then with Robert R. Wilson's cyclotron group. Rotblat continued to have strong reservations about the use of science to develop such a devastating weapon. In 1985, he related that, at a private dinner at the Chadwicks' house at Los Alamos in March 1944, he was shocked to hear the director of the Manhattan Project, Major General Leslie R. Groves, Jr., say words to the effect that the real purpose in making the bomb was to subdue the Soviets. Barton Bernstein said the remark may have been made to test Rotblat's loyalty. By the end of 1944, it was also apparent that Germany had abandoned the development of its own bomb in 1942. Rotblat then asked to leave the project on grounds of conscience and returned to Liverpool. Chadwick learned that the chief of security held a security dossier in which Rotblat was accused of intending to return to England so that he could be flown over Poland and parachute into Soviet territory to pass on the secrets of the atomic bomb. He was also accused of visiting someone in Santa Fe and leaving them a blank cheque to finance the formation of a communist cell. Rotblat was able to show that much of the information within the dossier had been fabricated. In addition, FBI records show that in 1950, Rotblat's friend in Santa Fe was tracked down in California, and she flatly denied the story; the