The interception and analysis of enemy radio communications was the most effective means available to the Allies for obtaining knowledge of the activities of the German U-boats during the Second World War. Commander Kenneth A. Knowles, USN, the head of the US Navy’s Uboat tracking organisation, observed after the Second World War that the Allied intelligence victory over the U-boats was greatly owing to the ability to exploit, by means of radio direction finding [D/F] and decryption, the huge volume of radio communications generated by the German U-boat service’s centralised command and control system.1 All the German U-boat operations were commanded and controlled from a headquarters ashore, either in Germany or France, and were known as the Befehlshaber der Unterseeboote [BdU].2 Very rarely did a U-boat go to sea with a complete set of written operational orders. It was the BdU’s standard operating procedure to send a U-boat, by radio, orders and instructions after the German vessel was at sea.3 Not only were all the orders required for the conduct of U-boat operations during the Battle of the Atlantic dispatched by radio, but also all the information required to be able to issue these orders, in the form of reports from Uboats at sea, was sent by radio to the BdU. This system of centralised command and control produced an almost endless series of radio messages between U-boats at sea and the BdU ashore. For instance, in a seven-day period in February 1943 the British intercepted 262 radio messages from U-boats attacking Convoy SC 118.4 Overall there are in the American archives more than 49,000 intercepted radio messages received or sent by German U-boats during the Battle of the Atlantic.5 It was ultimately this cascade of German radio messages which provided the Allies with the intelligence required to defeat the German U-boats during the Battle of the Atlantic.