Spies in the Ether
Bart Lee (KV6LEE) has written a very interesting paper titled Radio Spies - Episodes in the Ether Wars, which goes into the history of SIGINT, or the art of signal interception for intelligence uses. Whether or not you are interested in government secrecy, Bart Lee does an excellent job of explaining how radio communication technology help to get the decisive edge in several military conflicts.
The link is here:
http://www.trft.org/TRFTPix/spies9eR2006.pdf
