Figure 1.--The Battle of the Atlantic was clarly the most important campaign of World War II. All the other campaigns depended on success in the Atlantic. Given this reality and the knowledge that even complicated code systens like Enigma could be broken, one would excpect that Royal Navy (RN) would have had the most secure codes of the War and to change them regularly. For whatever reason, probably bcause commanders gave less imprtance to merchant shipping that naval codes, the Germans broke the convoy codes wide open. Merchant sailors paid a steep price for the RN's miscalculation.

The British had several different codes of interest to the various German code breaking units. Their major successes came with British maritime codes and greatly aided the U-boat effort to cut the vital sea lanes on which the British war effort depended. The Reichswehr code unit was especially interested in the British Government’s telegraph code. This code was used to advise the British Admiralty about the location and movement of non-British naval shipping. After the Spanish Civil War, Generalissimo Francisco Franco permitted Germany which had supported the Nationalists during the War, to set up wireless surveillance posts in Spain. Their primary purpose was to intercept Royal Navy communications in the Atlantic and Mediterranean. Germany’s Naval B-Dienst (Beobachtungsdienst - Surveillance Service) was primarily interested in the British Royal Navy. B-Dienst was by 1941 using German city names as designations for the different British naval codes. “Köln” was one cover name; “München-Blau” and “München-Braun” were two other names. A four-digit American-British naval communications system was codenamed “Frankfurt”. Germany was, however, never able to break secure British diplomatic communications. The German code breaking effort had little impact on the War with the exception of breaking into naval codes which was a major asset to the U-boats.

Government Telegraph Code

The Reichswehr code unit was especially interested in the British Government’s telegraph code. This code was used to advise the British Admiralty about the location and movement of non-British naval shipping.

Naval Codes

The 2. Abteilung der Seekriegsleitung included the Marinenachrichtendienst (M.N.D.) and its III. Abteilung, radio intelligence units. B-Dienst (Beobachtungsdienst, surveillance service,) and the xB-Dienst (decryption service) was primarily interested in the British Royal Navy and worked to break into British and other Allied secure radio communications. B-Dienst was created (early 1930s) and suceeded in breaking into Royal Navy codes (1935). German efforts to read Royal Navy transmissions were impaired by the inability of largely land locked Germany to intercept Royal Navy signals in the Atlantic. The Spanish Civil War (1936-39) changed this. After the Spanish Civil War, Generalissimo Francisco Franco permitted Germany which had supported the Nationalists during the War, to set up wireless surveillance posts in Spain. Their primary purpose was to intercept Royal Navy communications in the Atlantic and Mediterranean. At the outbreak of the War (September 1939), B-Dienst specialists had broken sufficent Royal Naval codes that the OKM was aware of the location of all fleet units. B-Dienst continue to crack Royal Navy codes in the first years of the War. B-Dienst used German city names as designations for the different British naval codes. “Köln” was one cover name; “München-Blau” and “München-Braun” were two other names. A four-digit American-British naval communications system was codenamed “Frankfurt”. The Royal Navy committed a cardinal mistake in that they did not regularly change their codes on a timely basis. B-Dienst regularly read the transmissions of ships using the British and Allied Merchants Ships (BAMS) code. Allied nations included occupied countries (Norway, the Netherland, Belgium, and Greece). The ability to read this traffic was of greater importance than Royal Navy ships. The Germans did not have surface ships of taking in the Home Fleet. The U-boats could, however, attack merchant shipping if it could be located. The Atlantic is a big ocean. The U-boats no matter how cleverly position would have expended a great deal if their effort finding ships. Merchant shipping intercepts were an invaluable assett during the early phases of the Battle of the Atlantic when the U-boat fleet was still quite small. B-Dienst broke into the code used for many Atlantic convoys (Februry 1942). The U.S. Navy had refused, for security reasons to equip Royal Navy units with the new ECM Mk.1 encryption devices (194). The Royal Navy thus decided to use Naval Cypher No.3 for Allied radio communication and Atlantic convoy operations. B-Dienst focused its resources on the new code. They broke into it (September 1942). The Kreigsmarine thus had access to the convoy transmissiions (December 1942-May 1943). This was a critical phase in the Battle of the Atlantic. One source suggests that the Germans were reading something like 80 percent of the intercepted messages. Time was, however, a critical factor. While B-Dienst had cracked into the code, the process they were using took time. Only about 10 percent of the messages were decoded in time for the U-boats to act on them. Even more importantly they never learned that the British were reading German naval transmissions. At the same time that the Allied transmissions went dark, Allied anti-submarine warfare (ASW) began to wreak havoc on the German wolf packs. B-Dienst also broke British Naval Cypher No.5 as well as several low-grade British Naval codes.

Army Codes

Air Force Codes

B-Dienst broke several low grade Air codes. This included COFOX, MEDOX, FOXO, LOXO, SYKO, Air Force code and Aircraft Movement codes.

Trans-Atlantic Telephone Connection

President Roosevelt and Primeminister Churchill had a secure telephone system set up. The Reichspost suceeded in descramblingh the voice transmission of the transatlantic connection. The Germans established an intercept facility at Noordwijk in the occupied Netherlands (1940). The Reichspost's descrambling unit was thus able to intercept and understand the conversatios throughout the War until the Noordwijk facility had to be evacuated (September 1944). The relocation of the unit meant that far fewer conversations were intercepted and thus unscrabled. This was not codebreaking, but descrabling. We do not know of any information gleaned from the conversations that proved of actionanle benefit to the Germans.

Diplomatic Codes

Germany was never able to break secure British diplomatic communications.

Created: 1:03 AM 3/12/2011
Last updated: 8:06 PM 5/19/2019