Fish (sometimes FISH) was the UK's GC&CS

Bletchley Park Bletchley Park is an English country house and estate in Bletchley, Milton Keynes (Buckinghamshire) that became the principal centre of Allied code-breaking during the Second World War. The mansion was constructed during the years following ...

codename for any of several German

teleprinter A teleprinter (teletypewriter, teletype or TTY) is an electromechanical device that can be used to send and receive typed messages through various communications channels, in both point-to-point (telecommunications), point-to-point and point- ...

stream cipher stream cipher is a symmetric key cipher where plaintext digits are combined with a pseudorandom cipher digit stream ( keystream). In a stream cipher, each plaintext digit is encrypted one at a time with the corresponding digit of the keystream ...

s used during

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...

. Enciphered teleprinter traffic was used between German High Command and Army Group commanders in the field, so its intelligence value (

Ultra adopted by British military intelligence in June 1941 for wartime signals intelligence obtained by breaking high-level encrypted enemy radio and teleprinter communications at the Government Code and Cypher School (GC&CS) at Bletchley Park ...

) was of the highest strategic value to the Allies. This traffic normally passed over landlines, but as German forces extended their geographic reach beyond western Europe, they had to resort to wireless transmission. Bletchley Park decrypts of messages enciphered with the Enigma machines revealed that the Germans called one of their wireless teleprinter transmission systems ''"Sägefisch"'' (sawfish) which led British

cryptographer Cryptography, or cryptology (from grc, , translit=kryptós "hidden, secret"; and ''graphein'', "to write", or '' -logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adv ...

s to refer to encrypted German radiotelegraphic traffic as Fish. The code Tunny (tunafish) was the name given to the first non-Morse link, and it was subsequently used for the Lorenz SZ machines and the traffic enciphered by them.

History

In June 1941, the British "Y" wireless intercept stations, as well as receiving Enigma -enciphered

Morse code Morse code is a method used in telecommunication to encode text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code is named after Samuel Morse, one ...

traffic, started to receive non-Morse traffic which was initially called NoMo. NoMo1 was a German army link between Berlin and Athens, and NoMo2 a temporary air force link between Berlin and Königsberg. The parallel Enigma-enciphered link to NoMo2, which was being read by

Government Code and Cypher School Government Communications Headquarters, commonly known as GCHQ, is an intelligence and security organisation responsible for providing signals intelligence (SIGINT) and information assurance (IA) to the government and armed forces of the Unit ...

, revealed that the Germans called the wireless teleprinter transmission systems ''"Sägefisch"'' (sawfish). This led the British to use the code ''Fish'' dubbing the machine and its traffic ''Tunny''. The enciphering/deciphering equipment was called a ''Geheimschreiber'' (secret writer) which, like Enigma, used a

symmetrical Symmetry (from grc, συμμετρία "agreement in dimensions, due proportion, arrangement") in everyday language refers to a sense of harmonious and beautiful proportion and balance. In mathematics, "symmetry" has a more precise definit ...

substitution alphabet. The teleprinter code used was the International Telegraph Alphabet No. 2 (ITA2)—Murray's modification of the 5-bit Baudot code. When the Germans invaded Russia, during World War II, the Germans began to use a new type of enciphered transmission between central headquarters and headquarters in the field. The transmissions were known as Fish at Bletchley Park. (See

Lorenz cipher The Lorenz SZ40, SZ42a and SZ42b were German rotor stream cipher machines used by the German Army during World War II. They were developed by C. Lorenz AG in Berlin. The model name ''SZ'' was derived from ''Schlüssel-Zusatz'', meaning ''cip ...

Cryptanalysis of the Lorenz cipher Cryptanalysis of the Lorenz cipher was the process that enabled the British to read high-level German army messages during World War II. The British Government Code and Cypher School (GC&CS) at Bletchley Park decrypted many communications betwe ...

.) The German army used Fish for communications between the highest authorities in Berlin and the high-ranking officials of the German Army in the field. The Fish traffic which the personnel at Bletchley Park intercepted, contained discussions, orders, situation reports and many more details about the intentions of the German Army. However, these transmissions were so challenging to decrypt that even with the assistance of the high speed Colossus computer, the messages could not be read until several days later. “Vital intelligence was obtained about Hitler’s intentions in the run up to D-Day 1944.”

Traffic code names

Tunny

The NoMo1 link was initially named Tunny (for tunafish), a name which went on to be used both for the Lorenz SZ40/42 machines and for the Bletchley Park analogues of them. The NoMo1 link was subsequently renamed Codfish. A large number of Tunny links were monitored by the Y-station at

Knockholt Knockholt is a village and civil parish in the Sevenoaks District of Kent, England. It is located north west of Sevenoaks & south of Orpington, adjacent to the Kent border with Greater London. The village is mostly a ribbon development, surr ...

and given names of fish. Most of these were between the '' Oberkommando der Wehrmacht'' (German High Command, OKW) in Berlin and German army commands throughout occupied Europe.

at Bletchley Park, assisted initially by a machine called

Heath Robinson William Heath Robinson (31 May 1872 – 13 September 1944) was an English cartoonist, illustrator and artist, best known for drawings of whimsically elaborate machines to achieve simple objectives. In the UK, the term "Heath Robinson contr ...

and later by the

Colossus computer Colossus was a set of computers developed by British codebreakers in the years 1943–1945 to help in the cryptanalysis of the Lorenz cipher. Colossus used thermionic valves (vacuum tubes) to perform Boolean and counting operations. Colossus ...

s yielded a great deal of valuable high-level intelligence. Tunny decrypts provided high-grade intelligence in an unprecedented quality. Walter Jacobs, a US Army codebreaker who worked at Bletchley Park, wrote in an official report on the operation to break Tunny that in March 1945 alone 'upward of five million letters of current transmission, containing intelligence of the highest order, were deciphered'.

Sturgeon

This was the name given to traffic encoded with the Siemens and Halske T52 ''Geheimschreiber''. In May 1940, after the German invasion of Norway, the Swedish

mathematician A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians are concerned with numbers, data, quantity, mathematical structure, structure, space, Mathematica ...

and

Arne Beurling Arne Carl-August Beurling (3 February 1905 – 20 November 1986) was a Swedish mathematician and professor of mathematics at Uppsala University (1937–1954) and later at the Institute for Advanced Study in Princeton, New Jersey. Beurling worked ...

used traffic intercepted from telegraph lines that passed through Sweden to break this cipher. Although Bletchley Park eventually diagnosed and broke Sturgeon, the relatively low value of the intelligence gained, compared to the effort involved, meant that they did not read much of its traffic.

Thrasher

This was the name used for traffic enciphered on a ''Geheimschreiber'' that was probably the Siemens T43

one-time tape In cryptography, the one-time pad (OTP) is an encryption technique that cannot be cracked, but requires the use of a single-use pre-shared key that is not smaller than the message being sent. In this technique, a plaintext is paired with a ra ...

machine. This was used only on a few circuits, in the later stages of the war and was diagnosed at Bletchley Park, but considered to be unbreakable.

List of senior staff involved at Bletchley Park

Including both executives and cryptographers on FISH (Tunny) in the

Testery The Testery was a section at Bletchley Park, the British codebreaking station during World War II. It was set up in July 1942 as the "FISH Subsection" under Major Ralph Tester, hence its alternative name. Four founder members were Tester himself a ...

. :

Ralph Tester Ralph Paterson Tester (2 June 1902 – May 1998) was an administrator at Bletchley Park, the British codebreaking station during World War II. He founded and supervised a section named the '' Testery'' for breaking Tunny (a Fish cipher). Back ...

— linguist and head of the ''Testery'' *

Peter Benenson Peter Benenson (born Peter James Henry Solomon; 31 July 1921 – 25 February 2005) was a British barrister, human rights activist and the founder of the human rights group Amnesty International (AI). He refused all honours for most of his li ...

— codebreaker * John Christie — codebreaker * Tom Colvill — general manager * Peter Edgerley — codebreaker * Peter Ericsson — shift-leader, linguist and senior codebreaker * Peter Hilton — codebreaker and mathematician *

Roy Jenkins Roy Harris Jenkins, Baron Jenkins of Hillhead, (11 November 1920 – 5 January 2003) was a British politician who served as President of the European Commission from 1977 to 1981. At various times a Member of Parliament (United Kingdom), ...

— codebreaker and later cabinet minister * Victor Masters — shift-leader *

Max Newman Maxwell Herman Alexander Newman, FRS, (7 February 1897 – 22 February 1984), generally known as Max Newman, was a British mathematician and codebreaker. His work in World War II led to the construction of Colossus, the world's first operatio ...

— mathematician and codebreaker who later set up the

Newmanry The Newmanry was a section at Bletchley Park, the British codebreaking station during World War II. Its job was to develop and employ statistical and machine methods in cryptanalysis of the Lorenz cipher. It worked very closely with the Testery wh ...

* Denis Oswald — linguist and senior codebreaker * Jerry Roberts — shift-leader, linguist and senior codebreaker * John Thompson — codebreaker * John Tiltman — codebreaker and intelligence officer *

Alan Turing Alan Mathison Turing (; 23 June 1912 – 7 June 1954) was an English mathematician, computer scientist, logician, cryptanalyst, philosopher, and theoretical biologist. Turing was highly influential in the development of theoretical c ...

- mathematician, mainly on ''Enigma'' traffic * W.T. Tutte — codebreaker and mathematician

Notes

References

* in * * (reprinted in Cryptology: Yesterday, Today and Tomorrow, Artech House, Norwood, 1987) * * * (Reprinted in: Cryptology: Yesterday, Today and Tomorrow, Artech House, Norwood, 1987) * (reprinted in Selections from Cryptologia: History, People, and Technology, Artech House, Norwood, 1998) * * * {{DEFAULTSORT:Fish (Cryptography) Encryption devices World War II military equipment of Germany Cryptographic hardware History of cryptography Signals intelligence of World War II Bletchley Park Military communications of Germany