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, asking 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 for political offenses by the Gestapo in 1943 and was imprisoned at Dachau and Nazi concentration camps until the war ended, the Nazis never knew of the Oslo Report.