The movie viewed by the crew, "Young Dr. Jekyll Meets Frankenstein", never existed. It was fabricated by matching some newly made shots into existing footage from The Walking Dead (1936) a Warner Brothers release starring Boris Karloff and Edmund Gwenn. Karloff and Gwenn are credited on the screen, as is another actor, Morgan Paull, who appears in some of the new shots. Paull's on-screen credit reads "And Introducing Morgan Paull as Young Dr. Jekyll".
Jack Lemmon did not reprise his Oscar-winning breakthrough role from Mister Roberts (1955), however his future friend and frequent cast mate Walter Matthau does appear in this film. This was two years before their first film together, The Fortune Cookie (1966).
Several members of the cast and crew were actual military veterans. Most of whom served in World War II: Writer-director-producer Joshua Logan, editor William Reynolds and actor Peter Marshall were in the Army, while composer George Duning and author Thomas Heggen served in the Navy; Heggen based the novel "Mister Roberts" on his experiences as a communications officer aboard the Navy cargo ship, the USS Virgo. Actor Gerald S. O'Loughlin served in the Marine Corps while Walter Matthau and Burl Ives served in the U.S. Army Air Forces; Ives also served in the regular Army. Composer Les Brown performed in USO tours with Bob Hope for American troops around the world. Actor Warren Hull traveled about the country and in Canada entertaining troops at military bases. Actors Edmund Gwenn and Wade Boteler served in the First World War; Gwenn was an officer in the British Army, while Boteler served in the U.S. Army. Boris Karloff was rejected for military service in World War I due to health and back issues. Actors Al Freeman Jr., Larry Hagman and George Lindsey served in the Air Force during the Korean War. Other cast members served in the armed forces during peacetime: Jack Nicholson was a firefighter in the California Air National Guard. Tommy Sands also served in the Air Force while Dick Gautier, Ronnie Rondell Jr. and Buck Taylor served in the Navy.