B-Dienst

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.

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.