Heavy water
Although a scientific curiosity from the start, considerable interest in heavy water was aroused in 1939 when Hans von Halban and Lew Kowarski suggested that heavy water could be used as a neutron moderator in a nuclear reactor using natural uranium. They carried out experiments on uranium using ordinary water, but had found that the hydrogen atoms absorbed neutrons, thus preventing the desired chain reaction. Heavy water though, was an ideal moderator. The Office of Scientific Research and Development (OSRD) put Hugh S. Taylor, a British physicist at Princeton University in charge of heavy water research. Taylor and Urey began looking at means for producing heavy water on an industrial scale. For his plutonium project, Arthur H. Compton requested of it. The heavy water project was codenamed the "P-9 Project" in October 1942.