 The script was based on an unpublished book by I. A. R. Wylie . RKO Pictures bought the book in outline form in April 1941 , but encountered casting difficulties and sold the rights to MGM in December 1941 for $ 50 @,@ 000 . A day or two after they had obtained the rights , MGM Vice @-@ President Eddie Mannix realized the source material was political in nature and tried to abandon the project . However , following the attack on Pearl Harbor , Mannix relented and the production went forward . Once the film went into production at MGM , the book was published by Random House in April 1942 . 
