The production license required that any evidence that the Wawona Hotel within Yosemite National Park was ever used to impersonate an Allied Military Hospital in postwar Bavaria had to be totally removed within 24 hours after the movie's exodus. Compliance with this condition was the only way Producer William Perlberg could get into the National Park area for his picture.
The writing credits not only include Roald Dahl's short story, "Beware of the Dog", as the source of the plot but also an original film story by Luis H. Vance and Carl K. Hittleman. It has been suggested that MGM bought the Vance-Hittleman plot whilst unaware of the Dahl story, also unknown to the writers and director George Seaton. However, after the script was coincidentally offered to Dahl's wife, Patricia Neal, she spotted the resemblance straight away and brought it to her husband's attention. (She turned down the female lead, which went to Eva Marie Saint.) MGM was required to pay a large sum for the film rights of Dahl's very brief story to avoid a lawsuit.
This movie features both Sig Ruman who played German internment camp guard Sergeant Schultz in Stalag 17 (1953) and John Banner who played one by the same name in Gli eroi di Hogan (1965). Coincidentally, Ruman's only scene is with Banner.
Roald Dahl may seem a surprising source for such a serious adult drama since the late author is best known for his wealth of popular children's stories. Among his work are books such as Charlie and the Chocolate Factory, The Witches and James and the Giant Peach, all of which were also made into successful movies. No stranger to the details of World War II, the British-born Dahl had been a pilot in the Royal Air Force when fighting broke out. After he was injured on duty, he was transferred to Washington D.C. in 1942 where he worked as an air attaché and began his career as a writer recounting his horrifying experiences during the war. His original story "Beware of the Dog" is included in his very first short-story collection, "Over to You", which is entirely concerned with stories of war.
Local towns and villages, populated with actors posing as natives, are a part of advanced military training in many countries, including the U.S.
James Doohan: The soon-to-be "Montgomery Scott" of Star Trek (1966) is uncredited as a British orderly in the opening scenes. Doohan served in Canadian forces during the Normandy Invasion (which the film is about) where he lost part of a finger. Future Imperfect (1990) and Stratagem (2004) were inspired by this film.