Alfred Hitchcock prepared the sequence involving Ida Lupino, and was to have directed it; scheduling prevented him, and it was directed by René Clair, who used Hitchcock's script.
All cast and crew worked without pay as an aid to war propaganda.
This film has more credited writers than any other.
Adm. Eustace Trimble (played by C. Aubrey Smith) quotes from William Wordsworth's poem "We Must Be Free or Die": "We must be free or die, who speak the tongue / That Shakespeare spoke . . . " (lines 11-12).