The enigma of HMS Bulldog

On the 9th of May 1941 Sub Lt David Balme of HMS Bulldog got on board the sinking U-Boat U110, and got out again with a priceless set of code books for the German Navy's Enigma machine. Most Enigma traffic could be decrypted thanks to the work of British code breakers working at Bletchley Park continuing the work of Polish code breakers. While the rest of the german military were a bit sloppy in their use of their encryption machines, a fact that Bletchley Park exploited ruthlessly. However the navy had much better cypher discipline, a code book to get keys from, and an Enigma machine with four encrypting rotors all of which combined to keep their messages secret. Bletchley Park knew all of this, and they knew that getting into the radio traffic to and from the German Navy's prowling U-Boats was vital if they shipping lanes were to stay open. If they didn't then Britain could loose the Battle of the Atlantic and be staved into submission. They knew how to break the Enigma. They knew how to figure out the settings on the extra rotor wheel. They even knew the from that the entries in the code book would take, but without the actual book there was no way that they could break the code. King George VI famously said that capturing the code book was the most important event in the war at sea, and Bletchley Park have just opened an exhibition on it including eye witness accounts from both sides.