Heilmann's father was Halle city architect Jakob Adolf Heilmann, and his mother was Helene Heilmann. Heilmann joined the Hitler Youth in 1937 and the Nazi Party in 1941. Heilmann was a student of Federal Foreign Office in Berlin until his conscription in the Wehrmacht. Heilmann mother had ensured he learned a number of languages and this meant he was selected to be trained as a cryptologist and translator. After training, he was posted to the Inspectorate 7/VI, where he worked in Referat 7 and later Referat 1 before being posted to work at the Agents Referat, that later became Referat 12. At the Referat Heilmann worked on the desk that deciphered English, French and Russian intercept traffic.
