In 1945, close to the end of the war in Europe, Smyth joined the covert Operation Alsos. The 50-year-old chemist flew to Europe to help determine the state of the German nuclear weapons program and capture equipment and personnel. At an abandoned factory in Celle he discovered a centrifuge used for uranium enrichment, inspiring a frantic effort to find Paul Harteck. Smyth also hunted Paul Herold, Eberhardt Elbel, and a Professor Osenberg. Smyth was awarded the Medal of Freedom for his work with Alsos.