One of the first films after World War II to portray the German people--outside of the Nazi regime--in a sympathetic light.
Oskar Werner and Richard Basehart did most of their own stunt work, including jumping in and swimming the fast currents of the Rhine River on location in Germany.
Based on a true story. Towards the end of the war, Allied military intelligence services did recruit, train and utilize German POWs to return to Germany and spy for them.
December 8, 1944 was the date on which Karl Maurer (Oskar Werner) is captured in the film; it was in real life the actual date on which Werner deserted from the Wehrmacht.
The producers and director Anatole Litvak chose to film the movie on location in postwar Germany because of its authentic background--many of the country's large cities still had areas that had been bombed into rubble and not been rebuilt yet, and there was a lot of actual WW II German military equipment (tanks, rifles, uniforms, etc.) still available.