Figure 1.--.

Both the British and Germans worked n each others naval codes. The German naval code was one of the highest priorities of British code breakers at Blechly Park. The naval enigma machines proved more difficult to crack than the Wehrmacht and Luftwaffe enigmas. The Kriegsmarine was more security conscious. Codes were changed every month and security procedures wre very closely foilowed. Finally the Royal Navy succeeded in taking the German weaher boat Munchen off Norway and with it code books (May 7, 1941). The next dy the Navy took the U-110 and with it a priceless enigma machine (May 8, 1941). The Germans were unaware of this and surprised with the U-boats begn to have trouble locating convoys. The Germans had been sinking an average of 58 merchant vessels monthly, but this fill to 17 in July 1941. The Germans 6 months later changed their enigma machines to include a third encryption wheel (November 1941). This change meant that the Blechley Park Ultra team could no longer read neaval nessages. Until the team again unraveled the emigma code, the Royal Navy was in the dark for much of 1942. It took Ultra code breakers 9 months to begin to read the Germn naval code agaun (July 1942). Eventually it was the Ultra decripts that helped the Allies locate the wolfpacks. This allowed naval authorities to route the convoys and to deploy hunter-killer groups. Ultra also helped located the milch-cow U-boats that kelped the wolf-packs supplied. The Germans also worked on British naval codes. The British introduced Naval Cipher 3 (October 1941). The Germans managed to break the code in 3 months. At the height of the Battle of the Atlantic this provided Dönitz's U-boat fleet invaluable information.

British Code Breaking

Both the British and Germans worked on each others naval codes. The German naval code was one of the highest priorities of British code breakers at Blechly Park. The naval enigma machines proved more difficult to crack than the Wehrmacht and Luftwaffe enigmas. The Kriegsmarine was much more security conscious because Admiral Dönitz insusted on it. Codes were changed every month and security procedures were very closely followed. Finally the Royal Navy in May 1941 provided Bletchley Park a series of vital finds. First, the Royal Navy took the German weaher boat Munchen off Norway and with it code books (May 7, 1941). , the British learned that the weather ship Munchen was headed to an Atlantic station. The British found the ship using directional locators. A boarding party recovered the Short Weather Cipher Book (a map of the Atlantic Ocean with a rectangular grid and the numerical grid codes). While this was not part of cracking Enigma, it was critical in understanduing Enigma decrypts. The boarding party also recivered rotor settings (keys) for June 1941 which of course was helpful in cracking Enigma. [Sebag-Montefiore] Second, on the next day HMS Bulldog forced the U-110 to the surface and managed to recover a priceless enigma machine and codebooks (May 8, 1941). And imprtantly the Royal Navy managed to conduct both actions without Kriegsmarine Headquaters ldearning of their success. The Germans simply assumed that the vessels had been lost. The British with new insights into German radio traffic was able to route convoys away from the Wolfpacks. his was a major accomplishment as the Royal Navy was still not in the position to fight it out with the Wolf oacks. Dönitz and his staff were surprised with the U-boats began to have greater trouble locating convoys. The Germans had been sinking an average of 58 merchant vessels monthly, but this fill to 17 in July 1941. The Germans 6 months later changed their enigma machines to include a third encryption wheel (November 1941). This change meant that the Blechley Park Ultra team was in the dark again and could no longer read neaval messages. Until the team again unraveled the emigma code, the Royal Navy was in the dark for much of 1942. It took Ultra code breakers 9 months to begin to read the German naval code agaun (July 1942). Eventually it was the Ultra decripts that helped the Allies locate the wolfpacks. This allowed naval authorities not only to route the convoys, but with expanding naval power and improved weaponry to deploy hunter-killer groups to engage the Wolf packs. Ultra also helped located the milch-cow U-boats that helped keep the wolf-packs supplied. Not only could they locate them, but they could help time attacks when a U-boat was being supplied so as to find two U-boats in a vulnerable position on the surface. Word of this did gt back to Dönitz. Such perfetly timr attacks could not be ascribed to chance. Cracking Enigma was an obvious possibility. Dönitz appears to have comclude that spies were operating at headquarters. Atually it was Dönitz himself that aided Bletchley Park. He insisted in directing U-boat operatijs in detail. Ghis meant that the codebreakers had plaenty of messages to work with also to located the U-boats.

German Code Breaking

The Germans also worked on British naval codes. The British introduced Naval Cipher 3 (October 1941). The Germans managed to break the code in 3 months (January 1942?). At the height of the Battle of the Atlantic this provided Doenitz's U-boat fleet invaluable information. Bletchely Park learned of the German success and informed the Royal Navy Operations Center (May 1942?). Incredibly the Royal Navy does not change its code for another 10 months (March 1943?). It is unclear why the Royal Navy failed to change the code for such a long period. Some argue that it was incompetence. Beaurecratic inertia may have ben a factor and the complications and cost of implementing new codes. A factor may have been that the Royal Navy was not told of the source of the finding that their codes had been compromised because Ultra was such a cloesly guarded secret.

Sources

Sebag-Montefiore, Hugh. Enigma (2000).

Created: 6:49 PM 5/2/2005
Last updated: 4:46 AM 1/7/2014