German code breaking in World War II

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German code breaking in World War II achieved some notable successes cracking British naval ciphers until well into the fourth year of the war,[1] but also suffered from a problem typical of the German armed forces of the time: numerous branches and institutions maintained their own cryptographic departments, working on their own without collaboration or sharing results with equivalent units. This led to duplicated effort, to a fragmentation of potential, and to lower efficiency than might have been achieved.[2] There was no central German cryptography agency comparable to Britain’s Government Code and Cypher School (GC&CS), based at Bletchley Park.[3]



In Germany, each cryptographic department was responsible for cryptanalytic operations. They included:

While most contributed little to the German war effort, the Navy's OKM did have some remarkable successes in breaking Allied codes. The 2. Abteilung der Seekriegsleitung included the Marinenachrichtendienst (M.N.D.) and its III. Abteilung, radio intelligence. The B-Dienst (Beobachtungsdienst, "surveillance service",) and the xB-Dienst ("decryption service") were able to break into several important Allied radio communication circuits.


The B-Dienst, created in the early 1930s, had broken the most widely used British naval code by 1935. When war came in 1939, B-Dienst specialists had broken enough British naval codes that the Germans knew the positions of all British warships. They had further success in the early stages of the war as the British were slow to change their codes. The B-Dienst could regularly read the British and Allied Merchants Ships (BAMS) code, which proved valuable for U-boat warfare in the early phases of the Battle of the Atlantic. In February 1942, B-Dienst broke the code used for communication with many of the Atlantic convoys.[4]

Before the US entered the War at the end of 1941, B-Dienst could also read several American codes. This changed after April 1942, when the US Navy changed their code systems, but earlier, the ability to read American message traffic contributed to the success of "Operation Paukenschlag" (Operation Drumbeat), the successful U-boat attacks off the American East Coast in early 1942.

In 1941, the US Navy refused, for security reasons, to equip the British Navy with their ECM Mark 1 encryption devices, so the British Admiralty introduced "Naval Cypher No. 3" for Allied radio communication and convoy coordination in the Atlantic. The B-Dienst concentrated on deciphering the new code, in September 1942 and from December 1942 to May 1943, 80 percent of the intercepted radio messages were read but only 10 percent were decrypted in time to take action.[5]

The British "Naval Cypher No. 5" is also known to have been broken by the B-Dienst, as were various low-grade British Naval and Air codes, including COFOX, MEDOX, FOXO, LOXO, SYKO, Air Force code and Aircraft Movement code. The US "Hagelin" field cipher machine and the French "Anglp" code were also often read.

In addition, B-Dienst also cracked Soviet and Danish code systems.

Telephone cables[edit]

Apart from the notable successes of the German navy's decryption services, there were also some results from the other institutions. For example, the Reichspost was able to descramble scrambled voice transmission of the transatlantic telephone connection between the USA and Great Britain. For this purpose, an interception and descrambling facility was built in Noordwijk, in occupied Holland. From 1940, the Mail Service's descrambling specialists intercepted and understood classified telephone conversation between President Roosevelt and the British Prime Minister Winston Churchill. The facility relocated to a purpose built bunker facility in Valkenswaard where it remained until August 1944 when the facility had to relocate to Germany, the interception potential decreased, so did the number of phone calls intercepted. This was not classic codebreaking since none was involved; instead it was the exploitation of knowledge about a sophisticated technology.[citation needed]

Axis performance[edit]

Another success was the OKW/Chi 1941 cryptanalysis of the "Black" code used by US diplomats. Due to this, a huge interception facility in Lauf (Bavaria) could decrypt communication between US diplomats and Washington DC. The specialists in Lauf concentrated on the messages relating to the North African Campaign, so they could pass information to Feldmarschall Erwin Rommel about Allied plans and operations. The Germans also received the "Black" code from the Italians; Italian spies had photographed the code tables in the US embassy in Rome in September 1941. While the Germans appreciated the gift from their ally, they did not explain that they were already able to read "Black" code messages.

In general, however, German performance in code breaking was weak due to the fragmentation of responsibility and specialized personnel.[citation needed] The Navy's B-Dienst was an exception to the rule, although its successes largely ended when the Allies began using more sophisticated encryption methods by 1943.

See also[edit]


  1. ^ Marchant, Herbert "Secrets of Station X2 The Observer, 15 October 1978
  2. ^ Rezabek, Randy (2017), TICOM: the Hunt for Hitler's Codebreakers, Independently published, ISBN 978-1521969021
  3. ^ Overcamer, Arvo. "German Code Breaking of WWII".
  4. ^ Mallmann-Showell, Jak P. (2003), German Naval Codebreakers, Annapolis, MD: Naval Institute Press, ISBN 0-7110-2888-5
  5. ^ HyperWar Foundation: Compromise of Allied Codes and Ciphers by German Naval Communication Intelligence

Further reading[edit]

  • Bonatz, Heinz (1981), Seekrieg im Äther: Die Leistungen der Marine-Funkaufklaerung 1939-1945 (Naval Warfare in the Ether: The Performance of Naval Signal Intelligence 1939-1945), Herford: Verlag E.S. Mittler & Son GmbH, ISBN 3-8132-0120-1
  • Kahn, David (1996) [1967], The Codebreakers, Scribner, pp. 435–477, ISBN 0-684-83130-9
  • Jennings, Christian (2018), The Third Reich is Listening: Inside German codebreaking 1939–45, Osprey, ISBN 978-1472829504
  • Mallmann-Showell, Jak P. (2003), German Naval Codebreakers, Annapolis, MD: Naval Institute Press, ISBN 0-7110-2888-5