In early 1945, 50-year-old physical chemist Charles Phelps Smyth, having completed his assigned duties with the Manhattan Project, was cleared for overseas duty with the Alsos Mission. The hunt for Germany’s military secrets was on and Alsos’ goal was to investigate the state of German nuclear science and to capture material and personnel.
When the Alsos team failed to find information in Paris, they turned their focus directly on Germany. On March 22, American troops began crossing the Rhine River in force, and by the next day reached Aachen. April 17 found Smyth in Celle, in southern Germany near Stuttgart, visiting a factory that made parachute silk. Smyth took a small piece of camouflage as a souvenir and also came across a tantalizing clue: at the factory he discovered a centrifuge used to concentrate fissile uranium-235 from uranium-238.
Science History Institute/Gregory Tobias
The centrifuge set off a continental chase. After a supply of alkali metals was found the next day, a naval intelligence officer put Smyth on the trail of Paul Herold and Eberhardt Elbel, who were rumored to be in possession of heavy water (water containing a high proportion of deuterium), which is used to slow down neutrons released in fission, allowing a chain reaction.
When this lead was followed to Osterode, south of Hannover, 21 large cylinders were recovered, but none contained true deuterium oxide. A trip further east, to Stassfurt, yielded a large supply of yellowcake (uranium salt) and the name of another scientist, Paul Harteck, whose centrifuge Smyth had found earlier at Celle. But Harteck was in Hamburg, and, although the war was rapidly drawing to a close, that area was still enemy territory.
On May 5 the Alsos Mission finally reached Harteck. For the next seven months Harteck would be detained with other scientists, including Werner Heisenberg, at Farm Hall near Cambridge, England. There the Allies secretly recorded the reactions of the captured German scientists to the atomic bombing of Hiroshima. Their surprise at hearing the news of Hiroshima confirmed that German science and technology had never come close to creating an atomic bomb.