Lawrence S. O’Rourke began working on the Manhattan Project at Columbia University after he was called up from the Army Reserves in 1944. O’Rourke was among the first group of SEDs who worked at Columbia, where he helped research and develop the gaseous diffusion process for the separation of uranium. After nine months, O’Rourke’s group moved from the Pupin Physics Lab to the Nash Garage Building, where they helped develop the barrier material that would be used at the K-25 plant in Oak Ridge. In 1945, O’Rourke was transferred to Oak Ridge and continued to work on research and development of a barrier material at K-25. O’Rourke also spent time at the Houdaille-Hershey Plant in Decatur, IL where he helped install and train people on how to test the barrier material that was being developed. O’Rourke describes the compartmentalization and secrecy of the Manhattan Project and also recounts some of the recreational activities available to SEDs and civilians at Oak Ridge.