Oslo report

The Oslo Report was one of the most spectacular leaks in the history of military intelligence. Written by German mathematician and physicist Hans Ferdinand Mayer on 1 and 2 November 1939 during a business trip to Oslo, Norway, it described several German weapons systems, current and future.

Mayer mailed the report anonymously in the form of two letters to the British Embassy in Oslo, where they were passed on to MI6 in London for further analysis, and proved to be an invaluable resource to the British in developing counter-measures, especially to navigational and targeting radars, and contributed to the British winning the Battle of Britain.

Hans Ferdinand Mayer received his doctorate in physics from the University of Heidelberg in 1920. After spending two years as a research associate there in his doctoral supervisor's (Philipp Lenard) laboratory, he joined Siemens AG in 1922. He became interested in telecommunications and joined Siemens' communication research laboratory, becoming its director in 1936. Because of this position, he had contacts all over Europe and the United States and had access to a wide range of information about electronics development in Germany, especially in the military sector. After Hitler invaded Poland on 1 September 1939, Mayer decided to divulge to the British as much as he could about military secrets to defeat the Nazi regime. He arranged a business trip to Scandinavia in late October 1939. He arrived at his first scheduled stop, Oslo, Norway, on 30 October 1939 and checked into the Hotel Bristol.

Mayer borrowed a typewriter from the hotel, and typed the seven-page Oslo Report in the form of two letters over two days. He mailed the first on 1 November which asked the British military attaché to arrange for the BBC World Service to alter the introduction to its German-language programme if he wished to receive the Report. This was done, and he sent the Report along with a vacuum tube from a prototype proximity fuze. He also wrote a letter to his long-time British friend Henry Cobden Turner, asking him to communicate with him via their Danish colleague Niels Holmblad. This indirect communication path was required since Britain and Germany were at war, but Denmark was at that time neutral. Mayer continued his travels to Denmark to visit Holmblad, asking if he could relay information between himself and Turner. Holmblad readily agreed, but once Hitler invaded Denmark on 9 April 1940, this communication route was no longer feasible. Mayer then returned to Germany. Although Mayer was arrested by the Gestapo in 1943 and was imprisoned in Nazi concentration camps until the war ended, the Nazis never knew of the Oslo Report.

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