Practical training at the Zeiss company, university study at Gt̲tingen, Berlin, and the Potsdam Observatory, doctorate in 1939; nuclear physics crash course at Leipzig under Robert Dp̲el. Hartwig's interest in astrophysics and nuclear physics. With the outbreak of war, joins the Army nuclear physics research group under Kurt Diebner. The first uranium machine (G-I) experiment at the Army Weapons Testing Lab in Berlin-Gottow. Radiation protection. Tension between the research groups under the direction of Diebner and Werner Heisenberg. Question of internal uranium machine design, cubes or layers? The second uranium machine (G-II), a lattice of metal uranium cubes immersed in heavy water, a great success. The last years of the war, evacuation and survival. Occupation by the Allied armies, life in the Russian-controlled eastern zone of Germany. Hartwig's move to the new Federal German Republic, teaching first at a private engineering school, later state technical university (Fachhochschule). The 1950s atomic euphoria.