The B-Dienst (German:Beobachtungsdienst, English:observation service), also called xB-Dienst, X-B-Dienst and χB-Dienst  was a Department of the Naval Intelligence Service (German:Marinenachrichtendienst) (MND III) of the OKM, that dealt with the interception and recording, decoding and analysis of the enemy, in particular British radio communications before and during World War II. B-Dienst dealt with the cryptanalysis and de-ciphering of enemy and neutral states message traffic and security control of Kriegsmarine key processes and machinery.
- "The ultimate goal of all evaluation was recognizing the opponents goal by pro-active identification of data." 
B-Dienst was instrumental in molding Wehrmacht forces operations during the battle of Battle of Norway and France in the spring of 1940, primarily due to the cryptanalysis successes it has achieved against earlier and less secure British Naval Cyphers.
B-Dienst broke British Naval Cypher No. 3 in December 1941, which was used for all Allied North Atlantic convoy messages, providing intelligence for the Battle of the Atlantic, until the British Admiralty introduced Naval Cypher No. 5 on 10 June 1943.
The B-Dienst unit began as the German Radio Monitoring Service, or educational and news analysis service (German: Funkhorchdienst/Horchdienst) by the end of World War One, in 1918. as part of the navy of the German Empire.
As a counterpart to the B service, in the British side, was the Y-service or 'Y Service. The Y was onomatopoeic for the initial syllable of the word wireless, similar to the B initial for German service.
Kapitänleutnant Heinz Bonatz, (Born: 18 August 1897) in Witzenhausen  was Chief of German Naval Radio Intelligence, head of Group III of 4 SKL of OKM (German: Marinenachrichtendienst, English: Marine Communications), which was responsible for cryptanalysis of enemy signals. An energetic man, he joined B-Dienst in 
The most important individual at B-Dienst was former radio man  and energetic cryptologist Oberregierungsrat (English:Senior Civil Service Councillor) Wilhelm Tranow, head of the English language crypt analysts. The American military historian of cryptography David Kahn stated:
- If one man in German intelligence ever held the keys to victory in World War II, it was Wilhelm Tranow.
Wilhelm Tranow was in charge of section IIIF of group III of 4 SKL of OKM, which was the English desk and was responsible for the interception of enemy radio communications, the evaluation of those enemy crypts, and the deciphering of enemy crypts specifically in relation. The organization of the German radio security processes was also another important responsibility.
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- Friedrich L. Bauer (2000-01-01). Entzifferte Geheimnisse, Methoden und Maximen der Kryptographie 3rd. edition. Berlin: Springer. p. 449. ISBN 3-540-67931-6.
- Heinz Bonatz (1981-01-01). Seekrieg im Äther. Die Leistungen der Marine-Funkaufklärung 1939-194. Herford: Springer. p. 56. ISBN 3-8132-0120-1.
- Heinz Bonatz, 1981 p.56
- B-Dienst-vs-bletchley-park-invasion-of.html "B-Dienst vs Bletchley Park - The invasion of Norway and the Battle of the Atlantic". Christos Military and Intelligence Corner. Retrieved 2015-05-16.
- Christopher PHD, Sterling H., ed. (2007-11-16). Military Communications: From Ancient Times to the 21st Century. ABC-CLIO.
- "Leaders Of The Reich". www.leaders-reich.co.uk. Leaders Of The Reich. Retrieved 2015-06-21.
- "German Naval Communications Intelligence". www.ibiblio.org. http://www.ibiblio.org/hyperwar. Retrieved 2015-06-21. External link in
- "B-Dienst (Navy)". www.ticomarchive.com. TICOM Archive. Retrieved 2015-06-15.
- David Kahn.... (2001-01-01). The Journal of Intelligence History Vol 1, No. 1. Hamburg, London: Lit Verlag & (Transaction publishers). p. 12.
- David Kahn (2012-01-01). Seizing the Enigma - The Race to Break the German U-Boat codes 1939-1943. Annapolis: Naval Institute Press. p. 246. ISBN 978-1-59114-807-4.
- Heinz Bonatz: Seekrieg im Äther. Die Leistungen der Marine-Funkaufklärung 1939-1945. Mittler: Herford 1981. ISBN 3-8132-0120-1
- Merchant Navy wireless signal codes
- Jak P. Mallmann-Showell (2003). German Naval Codebreakers. Annapolis, MD: Naval Institute Press. ISBN 0-7110-2888-5.
- Winterbotham, F.W. (2000) . The ULTRA Secret. Orion Books Ltd. pp. 84–85. ISBN 0-7528-3751-6.
- David Kahn (1996) . The Codebreakers. Scribner. pp. 435–477. ISBN 0-684-83130-9.
- Merchant Navy codes A good summary