Orson Welles recorded the commentary written by Ernest Hemingway and receives on-screen credit, but Hemingway decided to use his own voice instead. It is not clear which version of the film uses Hemingway's voice; the most common print does use the more cultured voice of Welles, which seemed jarring to members of the Contemporary Historians production company--formed by Herman Shumlin, Lillian Hellman and Dorothy Parker, which produced the movie. Both versions are available.
The production company, Contemporary Historians, was formed by a group of American writers and intellectuals, including Ernest Hemingway, Lillian Hellman, Archibald Macleish, John Dos Passos and Dorothy Parker.
His narration for this film represents the very first professional film work of Orson Welles, then a theatre and radio celebrity in his early twenties. Prior to this project, other than home movies, Welles had been involved with minor film projects only twice: a recorded 1933 rehearsal of a stage production of Shakespeare's Twelfth Night for his alma mater, The Todd School for Boys, and a very short, amateur, avant-garde parody film The Hearts of Age (1934), which was never intended for commercial release.
Both John Dos Passos and Ernest Hemingway spent time on location with director Joris Ivens' frontline crew, in addition to which Hemingway wrote and rendered the commentary.