 In 1939, he joined the German Navy, working in the High Command as a staff judge and advisor for international law.Berthold's apartment at Tristanstraße in Berlin, where his brother Claus also lived for some time, was a meeting place for the 20 July conspirators, including their cousin Peter Yorck von Wartenburg.As Claus had access to the inner circle around Hitler, he was assigned to plant a bomb at the "Führer"s briefing hut at the military high command in Rastenburg, East Prussia, on 20 July 1944.