German code breaking in World War II German code breaking in World War II achieved some notable successes , 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 . There was no central German cryptography agency comparable to the legendary British Bletchley Park facility . Instead , 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 , the B - Dienst specialists had broken enough British naval codes that the Germans knew the positions of all British warships . They had further successes in the early stages of the war ; 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 , the B - Dienst broke the code used for communication with many of the Atlantic convoys . Before the U . S . entered the War at the end of 1941 , the B - Dienst could also read several American codes . This changed after April 1942 , when the US Navy changed code systems ; before that , however , the ability to read American message traffic contributed to the success of " Operation Paukenschlag " , the successful U - boat attacks off the American East Coast in early 1942 . In 1941 , the U . S . Navy refused , for security reasons , to equip the British Navy with their ECM Mark 1 encryption devices , so the British Admiralty introduced the " Naval Cypher No . 3 " for Allied radio communication and convoy coordination in the Atlantic . The B - Dienst concentrated on deciphering the new code , and finally were successful in September 1942 . From December 1942 to May 1943 , 80 percent of the intercepted radio messages were read . However , only 10 percent of them were decrypted in time to take effective action . 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 , the B - Dienst also cracked Soviet and Danish code systems . Apart from the notable successes of the 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 , occupied Holland . From 1940 , the Mail Service ' s descrambling specialists intercepted and understood classified telephone conversation between President Roosevelt and Prime Minister Winston Churchill . After the facility had to relocate to Germany in 1944 , the interception potential decreased , and so did the number of phone calls intercepted . This was not classic codebreaking since none were involved ; it was instead the exploitation of knowledge about a sophisticated technology . Another success was the OKW / Chi 1941 cryptanalysis of the " Black " code used by U . S . diplomats . Due to this , a huge interception facility in Lauf ( Bavaria ) could decrypt communication between U . S . diplomats and Washington DC . The specialists in Lauf concentrated on the messages relating to the Middle East Theatre of World War II , so they could pass information to " Feldmarschall " Erwin Rommel about Allied plans and operations . It is a noteworthy footnote that the Germans also received the " Black " code from the Italians ; Italian spies had photographed the code tables in the U . S . 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 . The Navy ' s B - Dienst is an exception to the rule , though its successes largely ended when the Allies began using more sophisticated encryption methods by 1943 .