Declassified NSA Document Reveals the Secret History of TEMPEST

(WIRED) - It was 1943, and an engineer with Bell Telephone was working on one of the U.S. government's most sensitive and important pieces of wartime machinery, a Bell Telephone model 131-B2. It was a top secret encrypted teletype terminal used by the Army and Navy to transmit wartime communications that could defy German and Japanese cryptanalysis.
Then he noticed something odd. Continued

Photo: National Cryptologic Museum, Fort Meade, Maryland