At the German attack on Norway in April 1940 Jahn Dahm was a nineteen-year-old engineering student at Bergens Tekniske Skole. He had been an eager radio amateur and a member of "Bergen Radio Relé Liga" for years, and at home he also had a workshop for building radios. On 25 June 1940, while he had an examination at the school, he was taken to the Gestapo office in Bergen, where he was confronted with equipment taken from his home and told he would be charged with espionage. On 28 June he was transported by bus from Bergen to Møllergaten 19 in Oslo with ten other arrestees.