The Germans were also capable for ca. two years to read the convoys“primary code the Naval Cypher Number Three until summer 1943. ( From Secret in Bulding 26 )
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Interesting sites on the subject:
HyperWar: Battle of in the Atlantic: Allied Communication Intelligence [Chapter 6]
Cat and Mouse
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Compromise of Naval Cipher #3 demonstrated, May 1943. Naval Cipher #5 introduced 10 June 1943.
While the weakness of combined Naval Cipher #3 was appreciated in some circles it was not until May 1943 that its compromise was so thoroughly demonstrated that action could be taken. In the middle of May 1943 the Germans offered the necessary proof of combined cipher compromise in the form of three Offizier messages to groups Rhein, Elbe, and Drossel during the course of their patrol and action against convoys HX 237 and SC 129. Convinced that cipher compromise was involved, the Atlantic Section gained access to Commander 10th Fleet Convoy and Routing files. The compromised Allied dispatches were identified and the evidence was submitted to COMINCH. The conclusions were accepted.
An exchange of signals followed between COMINCH and Admiralty involving proposals for additional security precautions, but the marked increase in similar compromise messages in German traffic toward the end of May led to the introduction of Naval Cipher #5 on 10 June.
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Other German Cryptanalytic Successes.
In addition to Naval Cipher #3 and #5, the following systems are known to have been read by the German naval Communication intelligence organization:
Various British Naval and Air codes (low grade): including COFOX, MEDOX, FOXO, LOXO, SYKO, Air Force code and Aircraft Movement code.
U.S. Hagelin: A Hagelin reencryption of 26 September 1943 was read by the Germans. The compromise was noted by the British from their reading of German Mediterranean traffic.
Anglo-French.
Merchant signals: Supplied with the books from merchant shipping abandoned or sunk, the enemy had no difficulty with Mersigs.
Russian: aircraft reporting system, weather system, and low grade naval traffic.