Due to the declaration of war by China against the German Reich, he returned as a refugee in 1918, passing through Manchuria, Siberia and Russia to Germany.

On 3 June 1926, the day of Rudolf Oeser's death he was selected by the board of directors to become the German railway's general manager.

In April 1938, when a Berlin train stopped in Passau, Dorpmüller was ceremonially welcomed and escorted to the Danube, where he continued his trip to Linz and Vienna on board the Austrian Wotan.

According to Albert Speer, Dorpmüller confessed that "The Reichsbahn has so few cars and locomotives available for the German area that it can no longer assume responsibility for meeting the most urgent transportation needs."

Speer then convinced Hitler to name Albert Ganzenmüller as State Secretary in place of Dorpmüller's long-time deputy, Wilhelm Kleinmann.

In accordance with an October 1949 letter from Lübeck's denazification main committee to Maria Dorpmueller, Julius's sister, he was said to have obtained "relief" under category V classification.

In a letter from them in response in January 1995, they said that the former BD Hamburg had maintained the grave until the end of 1991, a decision by the former executive committee of the German Federal Railroads meant there was no more provision for maintenance thereafter.