Following the Liberation of Paris in August 1944, Halban returned on a visit to London and Paris, where he saw Joliot-Curie for the first time since leaving France. Although he maintained that he did not divulge any nuclear secrets to his previous boss (Joliot-Curie), General Groves, the head of the Manhattan Project, had Halban removed from his job in Montreal, and replaced by John Cockcroft. Furthermore, Halban was not allowed to leave North America for a year, nor to work.