To a scene of a train speeding along tracks and under a signal gantry the narrator says "Arriving in Germany Dr. Kassel finds a totally different Fatherland from the one he left 10 years earlier" However the engine, no 464, the carriages and signals are obviously British.
According to the film the spies are allegedly working for "German Naval Intelligence." In reality no such agency ever existed. The Abwehr was the joint intelligence service that coordinated foreign espionage for the entire German military. Before and during most of WWII the Abwehr was headed by Adm. Wilhelm Canaris. Also, Canaris and Heinrich Himmler, the head of the SS, detested one another and would never have cooperated as shown in the film (the producers may not have known this in 1939.)