An early participant of the German program, the Uranprojkt, in 1939, Döpel was taken in the Soviet custody and was held in Russia after the World War II.

As opposed to his fellow German scientists, Döpel was held in Russia for a longer time and was not allowed to return to his homeland until 1957, only to teach physics at the Technical University in Ilmenau, Germany.

He continued his work on the canal rays, which were the basis of his doctoral thesis, at the private laboratory of Rudolf Freihern von Hirsch zu Planegg, just west of Munich, along with the Physics Nobel Laureate Johannes Stark.

Just seven days later, a group, organized by Dames, met at the Ministry of Education to discuss the potential of a sustained nuclear chain reaction.

Their Working Community for Nuclear Physics was known informally as the first Uranverein (Uranium Club) and included the physicists Walther Bothe, Wilhelm Hanle, his friend[7] Robert Döpel, Hans Geiger, Wolfgang Gentner, Gerhard Hoffmann, and Joos.

The second Uranverein began after the Army Ordnance Office squeezed out the Imperial Research Council of the Ministry of Education and started the formal German program on develoing the nuclear weapons.

[8][9][10] A second meeting soon thereafter included Klaus Clusius, Carl Friedrich von Weizsäcker, Werner Heisenberg and Robert Döpel, his counterpart as an experimental physicist at the University of Leipzig.

In a letter written in December 1943, Döpel recounted that allied air raids had destroyed 75% of Leipzig, including his institute.

The Russian air raids during that year had also burned down Döpel's institute apartment and Heisenberg's house in Leipzig.

Sixteen months later, on April 6, 1945–just 32 days before the surrender of Germany– Klara was killed in an air raid, while she was working in the physics building.

The main search team, headed by Colonel General Zavenyagin, arrived in Berlin on 3 May, the day after Russia announced the fall of Berlin to their military forces; it included Colonel General V. A. Makhnjov, and nuclear physicists Yulij Borisovich Khariton, Isaak Konstantinovich Kikoin, and Lev Andreevich Artsimovich.