page_title: B-Dienst
section_title: U-Boat operations
hierarchical_section_title: B-Dienst / Operations / U-Boat operations
context_page_description: The B-Dienst, also called xB-Dienst, X-B-Dienst and χB-Dienst, was a Department of the German Naval Intelligence Service 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 worked on cryptanalysis and deciphering 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 opponent's goal by pro-active identification of data."
  B-Dienst was instrumental in moulding Wehrmacht operations during the Battles of Norway and France in spring 1940, primarily due to the cryptanalysis successes it had achieved against early and less secure British Naval cyphers.
  B-Dienst broke British Naval Combined Cypher No. 3 in October 1941, which was used to encrypt all communications between naval personnel, for Allied North Atlantic convoys. This enabled B-Dienst to provide valuable signals intelligence for the German Navy in the Battle of the Atlantic. The intelligence flow largely ended when the British Admiralty introduced Naval Cypher No. 5 on 10 June 1943.
context_section_description: Sending a message to a U-boat usually began with Rear Admiral Dönitz (Commander of the Submarines, German: Befehlshaber der U-Boote, abbr. BdU) who maintained tight control on U-boat operations. The Officer of the watch would take the message, timestamp it, and hand it to the duty radio technician watch officer for encryption. Fifteen to twenty radiomen worked per shift enciphering and deciphering messages. As only officers could set the rotor positions, which remained in force for two days, the watch officer set every Enigma with a new inner key, bar one, just before midnight every second day. One Enigma cipher machine remained on the previous key setting to decipher late messages. After the officer completing setting the rotors, the radio technician configured the Plugboard and turned the rotors to the key. When the Enigma was configured, the message was enciphered and then immediately deciphered on another Enigma to ensure that it could be read. If readable, it was sent to the appropriate location. To do that, the radio technician determined the location of the target, usually a U-boat, and the specific circuit to transmit it on (Cryptochannel, Telecommunication circuit). Naval Command had several geographical nets, the Kriegsmarine version of the German Naval Grid System (German: Marinequadratkarte), which were called, Amerika A, for the northern Atlantic area, Amerika B for the southern Atlantic area, Afrika 1 and 2, Ireland and others. Two other nets were also used for submarines attacking convoys, one code-named Diana, the other Hubertus. Each net had three frequencies, configured at the time of day to ensure best reception. Hubertus had six different frequencies used at different times. Occasionally a Wolfpack would get its own frequency.
  Once the correct configuration was chosen, the message was transmitted in Morse code along a wire to a radio transmitter (radio tower) at Lorient. The messages were also re-transmitted by the much more powerful transmitter tower in Sainte Assise in France (Sainte Assise Radio Towers). The Sainte Assise tower would repeat the message at two, six, twelve and twenty four hours, and if critically important two days later. On any particular day, the unit would transmit twenty to thirty messages, with each message taking fifteen to thirty minutes.
  On the U-boat, a radio technician was always on watch. Radio messages were received when a submarine was surfaced, at periscope depth and even down to forty feet. The radio technician always wrote the message down, even if it was not for that sub, with message serial numbers informing the technician if he had missed any. The U-boat captain also monitored the serial numbers on a regular basis to ensure no messages were missing and to ensure the radio technician was not negligent. The technician then ran a complicated process that yielded the key, set the rotors on the Enigma and reversed the message encipherment to yield the message, which was passed to the captain, with the captain taking appropriate actions in accordance with messages orders or reading to keep informed of current events.
caption: Enigma radioman aboard U-124 March 1941
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