Fish (sometimes FISH) was the Allied codename for any of several German teleprinterstream ciphers used during World War II[1][2][3]. While a large number of links were monitored, at least three different encryption systems were distinguished:
Tunny — the Lorenz SZ 40 and SZ 42 from Lorenz Electric. Tunny traffic was read successfully at Bletchley Park, using the famous Colossus computers. Paul Gannon's book Colossus: Bletchley Park's Greatest Secret[4] gives a detailed description of the interception of German military wireless traffic using teleprinter code (often referred to as non-morse traffic to distinguish it from the Enigma traffic) by Knockholt Intercept Station, the recording of those signals, the identification of the type of codes in use, the breaking of the codes using advanced statistical and cryptographic techniques, the development of mechanical, electro-mechanical and electronic machines (including the development of Colossus computers) to aid the decryption and an appreciation of the value of the intelligence gained.
