Codes and Signals
Over the centuries governments and individuals have used codes and signals to transmit messages over long distances. Sometimes the code, such as Morse Code was not meant to be secret, but merely to convey messages as simply as possible. However, many codes and crypto devices have been developed to prevent the interception of a message, especially messages that might fall into the hands of an enemy.
The word "code" and "signal" have come to have different meanings over the years. Code usually refers to a cryptological effort at concealment, while signals convey messages simply, using an open format. However, both "signal" and "code" at various times have been used interchangeably.
The importance of codes is manifestly obvious. Information in the wrong hands can prove destructive. In World War I as the Russians attempted an invasion of East Germany, they sent radio messages to their various units "in the clear" (meaning they were not encoded). The German army staff was able to anticipate every move the Russians made and decisively defeated them at the Battle of Tannenberg and later at the Masurian Lakes.
One of the most famous books written entirely in code is the Voynich Manuscript. It is thought by some to have been written by John Dee or Francis Bacon. World War II cryptologists were fascinated by it and tried to break its code during their spare time, "just for the fun of it". Most scholars now believe it was a fraud, written to be sold to a 17th century European sovereign.