I have been reading a book that contains letters written by General Robert E. Lee to his wife and children. I would like to know how these letters would have delivered during the Civil War. The main reason for the question is due to the sensitive information that is being written. General Lee might mention planned troop movements and if that letter were to fall into the wrong hands it would have grave consequences. And for that matter ... how did the Generals communicate with each other in the field? Was there some kind of code being used?