Let It Rain(1927)

Let-It-Rain Riley (MacLean) is a devil-may-care Marine sergeant who falls in love with a girl (Shirley Mason) who he assumes to be rich. His rival for the girl's affection is his pal, Kelly (Wade Boteler). The guys find out that the object of their affections is but a modest switchboard operator but she proves to be invaluable when she deciphers a code and discovers that a mail train is about to be robbed.