His claiming to have long had a desire to emigrate to the US in an interview for Operation Paperclip while also applying for a professorship in Germany is one of several indicators historians point to, labeling him as an adaptive opportunist.

He started studying physics in Leipzig, Heidelberg and Berlin 1932. In 1933, the year of its formation, he joined the German Air Sports Association, an organization set up by the Nazi Party that allowed him to learn flying as a fighter pilot.[2] In 1934, he interrupted his studies to volunteer in the German Airforce, Luftwaffe, partaking in several deployments. At the end of this part of his military service he was promoted to ltd. of the reserve.[3] He continued his studies obtaining his doctorate, Haber voluntarily participated in World War II for the German Luftwaffe as a reconnaissance aviator in the 2. Staffel der (Nah-)Aufklärungsgruppe 41, which was active in the Invasion of Poland and later the eastern Front. He served there until he was shot down and wounded 1942, shortly after being promoted to captain.[4][5] He was awarded the Iron Cross 2nd Class (1939) and 1st Class (1940) during his service.[2] He returned to the Kaiser-Wilhelm-Institut für Physik, where he headed a small Potsdam-based division constructing a diffraction spectrograph.[6]