Not only all the film's cast and credits, but also its main title, appear only at the end of the film. Just the Universal logo precedes the start of the story proper. This is quite possibly the first American film to so display its credit material.
Universal Pictures production number 1219.
Unseen Enemy is a feature film based on Fritz Duquesne and his life as a German secret agent living in the U.S. in the 1930s. Arthur D. Howden, an acquaintance and fencing opponent of Duquesne, wrote the original script in 1939, two years before Duquense's arrest and conviction by the FBI. Duquesne was sentenced to 18 years in prison. Sources: American Film Institute, Unseen Enemy; FBI, The Duquesne Spy Ring.