II. The Targets‎ > ‎

B-Dienst (Navy)

            Germany’s Naval SIGINT service was founded almost by accident during the First World War. German Army radiomen, finding themselves with little to do after the belligerent armies dug into static trench warfare, began searching for any signals that were detectable. They discovered that they were able to monitor Royal Navy traffic from the Dover Patrol, most of it in the clear. This information, passed to the Naval Staff in Berlin, who realized that a system of dedicated monitoring stations in Belgium and France could be used for intelligence purposes. An “Observation Service” (Beobachtungsdienst or B-Dienst) was created to exploit this opportunity. As the practice of enciphering messages became more common, the B-Dienst also developed skills in cryptanalysis. The service proved its value to the Naval Staff during the war by tracking British cruiser squadrons, convoy sailings, and assisting in the breakthrough of German raiders.


            The end of the war and the impounding and later scuttling of the fleet almost brought an end to the German Navy. Cutbacks eliminated the B-Dienst, but by the end of 1919, the admirals realized that an effective intelligence organization was as necessary in peacetime as it was in war. The service, reestablished under its former commander Kapitänleutnant (Lieutenant Commander) Martin Braune, had only six civil service employees. However, one of them was Wilhelm Tranow, former naval radioman and veteran of the wartime B-Dienst, who had originally demonstrated his talent by breaking a top-secret coded message sent to his own ship when his officers had trouble decrypting it.


            A lack of budget, frequent rotation of its naval officer commanders, and lack of support by the higher-level naval staff meant that the B-Dienst struggled to survive the lean years of the 1920s. As a cost cutting measure, in 1928 the service moved to Kiel where it was headquartered with the Inspector of Torpedoes and Mines, further limiting its influence. The tide turned in 1934, when a reorganization of the naval high command brought the B-Dienst back to Berlin as one of the three elements of the Office of Communications and Intelligence. The appointment of an energetic new chief, Kapitänleutnant Heinz Bonatz, resulted in the addition of additional men and listening posts to the service and enabled the B-Dienst to put teams aboard ships.


            During the 1930s the Navy developed two chains of costal radio stations, a North Sea chain anchored at Borkum in the west, which then ran to Nordholz, near Cuxhaven in the center and terminating at List in the west. The Baltic chain started at Falshöf near Flensburg on the Danish border, ran through the naval base at Kiel and along the Baltic coast to Pillau, in the then far eastern end of Prussia. Wilhemshaven acted as control center for these chains. Each of these stations were equipped with state of the art receivers, transmitters and direction finders, all interconnected with landline telephone and teletype lines. By the start of the war, the Kriegsmarine had a modern and efficient radio intelligence interception system, one that eventually proved critical in the coming naval war.


            Wilhelm Tranow kept busy during the 1930s. Now appointed head of the English language cryptanalysis section he led the attack on the codes and ciphers of the Royal Navy, solving their 5-digit Naval code in 1935 by comparing the encoded messages with merchant ship movements reported in Lloyd’s Weekly Shipping Report. Historian David Kahn later wrote “...(this) success, and the attacks in 1937 on four other English, five French, four Russian and three Danish cryptosystems enlarged the B-Dienst. The 30 men in its Berlin Central in 1936 became 90 by the summer of 1939.’ Monitoring foreign naval exercises and experience in the Spanish Civil War further added to the reputation of the B-Dienst.


            Mobilization at the start of the war expanded the service. For the first time academics and businessmen with language skills were recruited as reserve officers, and a six week training course was established. Within a few years, the B-Dienst had expanded to over 6,000 staff. A reorganization of the Naval Staff at the beginning of the war, followed by a further reorganization with the appointment of Dönitz as Grand Admiral, resulted in the B-Dienst becoming the third division of the fourth branch of the Maritime Warfare Command, the Seekriegsleitung (i.e. 4 SKL/III, the name referred to by TICOM).


            Heinz Bonatz rotated out of the B-Dienst to take command of the torpedo boat Kondor in 1932. He returned to command the service again in March 1943 with the rank of Kapitän zur See. He was superseded in January 1944 by Kapitän zur See Max Kupfer, who remained in command until his capture by TICOM at the end of the war. Tranow, as a civilian, became the chief cryptanalysis and remained with the service throughout the war. Among his accomplishments was reconstructing the Royal Navy Administrative Code prior to the war, the breaking within six months of the new Navy Cipher, and by May 1940 cracking the British Merchant Navy Code, which allowed the U-Boat command to track and anticipate the routing of allied convoys. However, this source dried up at the beginning of 1943 when the British switch to a new Cipher #5, superenciphered with a machine cipher.


            The heavy bombing of Berlin in November 1943, which damaged or destroyed so many of Germany’s military and government agencies, also destroyed most of the B-Dienst’s records and forced them to move to Eberswalde, a small village some 25 miles northeast of Berlin. Forced to move again by the Russian advance in the spring of 1945, they went first to Aurich, in northern Germany, then onto the naval radio station at Neumünster, quickly followed by a final move to the Signals School at Flensburg, where TICOM caught up with them on May 17th.


            In his interrogations by the allies, Admiral Dönitz credited the B-Dienst with contributing half the operational intelligence that the Kriegsmarine used in fighting the war. It was a record unmatched by any other German intelligence agency.




History of German Naval Radio Intelligence Service. NARA,  RG 457, HCC, Box 604, Folder 1571.


NSA. BATTLE OF THE ATLANTIC, Volume III: German Naval Communications Intelligence (SRH – 024).


TICOM. Capture of OKM 4 SKL/III from the Team 6 report.


TICOM I-165 Interrogation of Kapitan Zur See Otto Von Baumbach.


TICOM DF-225 Organization of the Communications Service of the German Navy, 4/SKL




Mallman Showell, Jak P. German Naval Code Breakers. Annapolis, MD.: Naval Institute Press, 2003 Review by Dale C. Rielage


Axis History Factbook. Organization of the German Naval Intelligence Department. Axis History.com


David Kahn. Hitler's Spies. Chapter 14, ‘The Codebreaker Who Helped the U-Boats.’ Cambridge, MA: Da Capo Press, 1978, 213- 222.

Faulkner, Marcus. 'The Kriegsmarine, Signals Intelligence and the Development of the B-Dienst Before the Second World War', Intelligence and National Security, (2010) 25: 4, 521 — 546.


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