Rosbaud served in the Austrian army during World War I from 1915 to 1918. After the war ended his unit was taken as prisoner of war by British forces; this experience ended up giving him a liking of the British. He studied chemistry at Darmstadt Technische Hochschule beginning in 1920. He continued his studies at Kaiser Wilhelm Institut in Berlin and took his doctoral thesis at Berlin-Charlottenburg Technische Hochschule. He then started working at the scientific periodical Metallwirtschaft, but quit after Adolf Hitler came to power, as the owner was a Nazi.
Through his work at Springer Verlag, Rosbaud knew most of the scientific community in Germany, and posing as a Nazi he could supply the allied forces with vital intelligence without any suspecting him of being a spy.
One of his first scoops as an agent was to publish Otto Hahn's work on fission in the German physics magazine Naturwissenschaften in January 1939. Rosbaud seemed to be well aware of the possible use of this in a nuclear bomb. His immediate publishing thus helped alarm the international physics community and can be connected to the letter Albert Einstein wrote to warn president Roosevelt of a German nuclear bomb.
Among the reports he supplied to the British was that Germany produced rockets (V2) and that the German project for a nuclear bomb was not successful. Rosbaud has also been connected to the "Oslo report", a detailed list of new German weapons systems, but this seems to be the work of Hans Ferdinand Maier, technical director at Siemens.
Many of his reports were smuggled out of Germany by couriers working for the Norwegian intelligence organisation XU. Norwegians that were studying at technical schools in Germany, such as Sverre Bergh, linked up with Rosbaud and transported the intelligence to occupied Norway, and from there it was sent to neutral Sweden. One daring route involved a flight from Berlin to Oslo, with airport mechanics at each end helping to hide microfilms on the plane.
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