Lew Kowarski was a Russian-born French physicist who worked as part of the team that discovered that neutrons were emitted in the fission of uranium-235 in the late 1930s, setting the groundwork for the use of nuclear chain reactions in the design of the atomic bomb. After the Second World War, Kowarski went on to supervise the first French nuclear reactors and became a staff member in the European Organization for Nuclear Research, or CERN, in 1953. In this interview Kowarski recounts his experience secretly transporting the French supply of heavy water to England to keep it out of Nazi hands. He also discusses his time working in the Cavendish Laboratory at Cambridge University with James Chadwick and other esteemed physicist. He also explains the Manhattan Project from a European perspective, including the increasing secrecy of the project.