All Hell Let Loose_ The World at War 1939-1945 - Max Hastings [232]
The volume of Ultra intelligence was now increasing dramatically, with critical influence in every theatre. In earlier years, decrypts were priceless, especially to the naval war, but their flow was erratic. From mid-1942 onwards, with a few important breaks, the Allies became privy to much of their enemies’ signal traffic; the penetration of German and Japanese ciphers made a massive contribution to victory. Beyond the achievements of British and American decrypters, it was a secondary miracle that the Axis powers never seriously suspected that their most secret communications were being accessed by the enemy. Not all important traffic was read all the time: Axis telephone landlines, always the link of choice where available, remained secure. The quality of Allied analysis and exploitation varied in accordance with the prejudices of field commanders and their intelligence chiefs. For instance, Ultra would later reveal the December 1944 German armoured build-up in the Ardennes, but staffs failed to draw appropriate conclusions about an impending offensive. Knowing the enemy’s hand did not of itself diminish the strength of his cards, and provided no guarantee of success in clashes between armies and fleets. But Ultra revealed to the Allies more about what the other side was doing and planning than had been vouchsafed to any previous combatants in history.
The Ultra achievement owed much to three Polish mathematicians, led by Marian Rejewski, who conducted critical early work on the German Enigma between 1932 and 1939, after acquiring a commercial example of the ciphering machine. The French assisted, providing the Poles with a list of 1931 Wehrmacht keys, acquired from a German source. Though Rejewski served with the Polish Army in Britain between 1943 and 1945, he was never told of the rich fruits of his pioneering achievements. In 1939 the Poles presented both the British and the French with reconstructed Enigma machines. The following year, these enabled the British Code and Cypher School at Bletchley Park to begin to break some German and Italian messages. At intervals thereafter, captures at sea of further Enigmas and monthly settings lists reinforced Bletchley’s armoury of knowledge.
Ultra was a collective Allied designation for a large variety of Axis keys, more than two hundred by 1945, some of which proved slow to surrender their secrets. Luftwaffe signals were broken first, towards the end of May 1940, followed by army and navy traffic. In 1941, a substantial volume of Wehrmacht messages were being read and their contents passed to Allied field commanders with an average delay of six hours. This proved too slow usefully to influence tactical decisions in ground fighting. It became progressively understood that Ultra could be used most effectively to guide strategy, as it was during the summer 1942 Alamein battles.
Allied handling of Ultra intelligence became superbly sophisticated, with information passed to commanders by locally deployed Special Liaison Units whose role was not merely to protect secrecy, but also to ensure that no initiative or pre-emption of German action revealed Allied foreknowledge. If a prospective naval target was located at sea through cryptanalysis, whenever possible reconnaissance aircraft overflew the enemy before an attack, to mask Ultra’s role. From 1942 onwards, Bletchley Park became an industrial centre, with 6,000 staff working in a hutted township, processing a flood of messages in shifts around the clock. The heart of its operation was Colossus, the electronic ‘bombe’ which dramatically speeded exploration of multiple mathematical possibilities. The codebreaking teams were dominated by some hundreds of brilliant