 In 1950 he returned to Germany, where he was head of the Siemens & Halske research department for communications technology in Munich until 1962.Hans Ferdinand Mayer was the author of the "Oslo Report", one of the most serious breaches of German security in World War II.He signed it as "a German scientist, who is on your side", before sending it to the British Embassy in Oslo, Norway, in early November 1939.