NSA released on 23 July 2013 "The History of Traffic Analysis: World War I-Vietnam." http://www.nsa.gov/about/_files/cryptologic_heritage/publications/misc/traff... It notes the formation of T/A (Traffic Analysis) and C/A (Cryptanalysis) as the two elements of code-breaking, using the mail analogy of T/A for the envelope, C/A for the contents. As noted elsewhere T/A is now publicized as "metadata."