Editing Battle of the Atlantic (section)

===Germans break Admiralty codes===

In 1941, American intelligence informed Rear Admiral [[John Henry Godfrey]] that the UK naval codes could be broken.  In March 1942, the Germans broke Naval Cipher 3, used for Anglo-American communication. Eighty per cent of the Admiralty messages from March 1942 to June 1943 were read by the Germans.  The sinking of Allied merchant ships increased dramatically.

[[Günter Hessler]], Admiral Dönitz's son-in-law and first staff officer at U-boat Command, said:
"We had reached a stage when it took one or two days to decrypt the British radio messages. On occasions only a few hours were required. We could sometimes deduce when and how they would take advantage of the gaps in our U-boat dispositions. Our function was to close those gaps just before the convoys were due."{{sfn|Williams|2003|p=244}} The code breakers of Bletchley Park assigned only two people to evaluate whether the Germans broke the code. After five months, they finally determined that the codes were broken. In August 1942, the UK Admiralty was informed.  The Admiralty did not change the codes until June 1943.

Captain Raymond Dreyer, deputy staff signals officer at Western Approaches, the British HQ for the Battle of the Atlantic in Liverpool, said, "Some of their most successful U-boat pack attacks on our convoys were based on information obtained by breaking our ciphers."<ref>{{cite news |last= Joseph |first= Claudia |year= 2002 |url=https://www.independent.co.uk/news/uk/home-news/revealed-the-careless-mistake-by-bletchleys-enigma-code-crackers-that-cost-allied-lives-5360971.html |title=Revealed: the careless mistake by Bletchley's Enigma code-crackers that cost Allied lives; |newspaper=The Independent |access-date=2019-04-09}}</ref>