Von Ardenne, who had worked on isotope separation for the "Reichspostministerium" (Reich Postal Ministry), was also sent to the Soviet Union to work on their atomic bomb project, along with Gustav Hertz, Nobel laureate and director of Research Laboratory II at Siemens, Peter Adolf Thiessen, director of the "Kaiser-Wilhelm Institut für physikalische Chemie und Elektrochemie" (KWIPC, Kaiser Wilhelm Institute for Chemistry and Electrochemisty, today the Fritz Haber Institute of the Max-Planck Society), and Max Volmer, director of the Physical Chemistry Institute at the Berlin "Technische Hochschule" (Technical University of Berlin), who all had made a pact that whoever first made contact with the Soviets would speak for the rest. Before the end of World War II, Thiessen, a member of the Nazi Party, had Communist contacts. On 27 April 1945, Thiessen arrived at von Ardenne's institute in an armored vehicle with a major of the Soviet Army, who was also a leading Soviet chemist, and they issued Ardenne a protective letter ("Schutzbrief").