On 1 April 1939, Gollnow became a reserve officer in the Luftwaffe with the rank of second lieutenant. In June 1940, Gollnow was drafted to a Luftwaffe Jagdfliegerschule in Tutow where he taught aircraft identification. While there, he underwent paratrooper training. In the summer of 1941 he was promoted to first lieutenant. At Arvid Harnack's suggestion, Gollnow continued his studies at the institute. Gollnow met Harro Schulze-Boysen through Mildred Harnack. Under the guise of helping him, Schulze-Boysen became an influence on Gollnow in the hope of turning him into an informer. In October 1941, Gollnow was promoted to a position in The Foreign Branch of the Abwehr in the Oberkommando der Wehrmacht of the Armed Forces High Command. Looking to impress the Harnacks, resulted in gross carelessness as Gollnow gave away information on the Abwehr that should have remained secret. Eventually, he became an important source to both the Harnacks and Schulze-Boysen.
