Recently I was skimming through the NSA's "classified history of COMSEC" (posted at governmentattic.com)
. This "history" is a transcription of lectures by David G. Boak, who liked to explain NSA-related topics from a historical perspective. He clearly inspired a generation of NSA's employees. The last "real" page of the document contains a humorous story and a crypto puzzle (link to pdf)
The NSA had an incinerator in their old Arlington Hall facility that was designed to reduce top secret crypto materials and such to ash. Someone discovered that it wasn't in fact working. Contract disposal trucks had been disposing of this not-quite-sanitized rubish, and officers tracked down a huge pile in a field in Ft. Meyer.
How did they dispose of it? The answer is encrypted in the story's text!