This adaptation of Lillian Hellman's play was written by her longtime companion, Dashiell Hammett. Hellman was unable to write the adaptation herself as she was contracted to work on the screenplay for The North Star (1943). She recommended that Hammett be given the assignment as he was very familiar with the material. (Hammett also needed the money.)
A first-time film director, Herman Shumlin had to be constantly reminded that he couldn't do repeated takes of each scene as celluloid film had to be rationed during World War II.
Jack L. Warner paid $150,000 for the rights to the play, which had enjoyed a successful run on Broadway. Warner had great faith in the material, feeling that its patriotic nature would go down well with wartime audiences.