Architectural historian of medieval architecture at the Herziana, Rome. Hahn was the son of Otto Hahn (1879-1968), a Nobel-prize-winning Chemist, and Edith Junghans (Hahn) (1887-1968), an artist. He attended the humanistic Arndt-Gymnasium entering Friedrich-Wilhelms-Universität Berlin in 1940 studying theater, German studies and philosophy. In 1942 he enlisted in the German army, commissioned as a lieutenant and fought on the eastern front as a Panzer (tank) leader. Heavily decorated, he was badly wounded in 1944 at Pietrow, requiring an arm amputation.