I'm really big into reading about the history of intelligence agencies and cryptography. It seems that the NSA has released a via a FOIA a history of American SIGINT operations and agencies covering the period from the end of WWII to the 80's. It's available as a PDF download and so far is very interesting reading. If you want to check it out it's available here
National Security Agency Releases History of Cold War Intelligence Activities
The page has a synopsis scroll down to get to the pdf's
National Security Agency Releases History of Cold War Intelligence Activities
The page has a synopsis scroll down to get to the pdf's