David O. Selznick originally wanted to title this movie "I'll See You Again" and use the 1929 Noël Coward song of the same title as its theme music. However, he thought Coward wanted too much money for the use of the song and its title. Instead, Selznick acquired the rights to the 1938 song "I'll Be Seeing You," with music by Sammy Fain and lyrics by Irving Kahal. The emotionally powerful song was especially beloved during WWII when it became a sentimental anthem for British and American soldiers serving overseas.
Being cast in this film prevented Joseph Cotten from taking the lead in "Spellbound", for which he was Hitchcock's first choice.
Joseph Cotten and Shirley Temple had starred in another David O. Selznick wartime film released earlier the same year, "Since You Went Away".
The quote from Lincoln under his photograph in the YMCA room is from his Cooper Union Address: "Let us have faith that right makes might, and in that faith, let us, to the end, dare to do our duty as we understand it" (February 27, 1860).