Signals intelligence
Most of the Signals intelligence obtained by Bletchley Park on the Balkans was initially from Luftwaffe morse code traffic encoded by Enigma; initially the general Luftwaffe Red key, then various German Army keys. They also decrypted various teleprinter links for high-level traffic: "Fish" (Vienna-Athens) then "Codfish" (Straussberg-Salonika), plus medium and low grade hand cyphers. Abwehr, Sicherheitsdienst and railway communications were intercepted and decrypted, providing evidence of resistance activities. For the German policy on Yugoslavia, communications to Tokyo from the Japanese ambassador, General Oshima Hiroshi, were also useful. With the primitive communications infrastructure and the disruption of land communications, the German forces in Yugoslavia relied heavily on radio communications, which, unknown to themselves, were insecure. A 1945 comment was that "never in the field of Signals intelligence has so much been decrypted about so little".