Every day, Wehrmacht commanders in the field sent reports back to base. Their dispatches included details as mundane as the weather - and as crucial as troop movements, battle plans and supply shortages. Items like these were for the ears of Germany's top brass only. Little did the operators realise as they punched out the reports on their portable transmitters that the Allies were eavesdropping each and every time. They were also monitoring U-boats and Luftwaffe aircraft. Early in the war, Britain cracked the secret codes which the Germans used to communicate. It was a coup which they put to excellent use as the conflict progressed. For their part, the Germans maintained an unflinching faith in the ciphers they had so painstakingly developed and stayed blissfully unaware of the enormous security breach until years after the end of the war. Of course, Britain's code-crackers did not win the war on their own. The information they gathered was used in conjunction with other intelligence from agents and diplomats as well as the forces in the field, sea and air. But their breakthrough saved lives and helped Churchill and the other Allied leaders plan a strategy that could only lead to victory. Only in 1972 was the secret of Ultra unveiled to an astonished world. Bletchley Park was the wartime headquarters of the Government Code and Cypher School. Germany made use of a machine that had been specially developed to send encoded messages. The first model appeared in 1919 in Holland where it was designed. Soon after, a German modified the original and named it the Enigma. At the time it was a commercially available machine that was on open sale in Britain. While tension mounted in Europe throughout the Thirties, Enigma was brought into use by the German army, navy and finally the air force in addition to the security services and the railways. Modern warfare had rendered the telephone unreliable. As German units surged forward in their “Blitzkrieg”, they went beyond the most outlying telephone cables and risked being out of touch with their command. Also, telephone lines were subject to bomb blasts or enemy sabotage. Radio was the favoured method of communication but messages could not be broadcast in everyday language. A coding machine was necessary and Enigma was it. Now the Enigma was a far cry from the basic model unveiled at the end of the Great War. The Germans prided themselves on a series of advances which would keep their secrets safe. An Enigma machine, powered by an electric battery, had similar dimensions to a typewriter and also had a keyboard. But for each letter entered on the regular keyboard, another would appear on a second, rear keyboard that would duly become the coded message. The transposition was done by three or more wheels behind the keys whose role was to scramble each word automatically. Each wheel had a multitude of settings and the code was varied from day to day. It was a two-man operation: as one man turned the report into code, the second took a note of the new set of letters appearing in code on the rear keyboard and transmitted it, either by Morse code or by wireless. A machine which transmitted simultaneously and would require just one operator never came into use. In theory, only the receiver of the message had the correct formula to turn the gobbledegook back into good sense. He knew the setting of the sender's machine, the correct order of the wheels and could vary his to the corresponding setting. In its basic form alone, Enigma would have caused enough headaches for the decoders. However, there were further refinements added by the Germans as war approached. The codes were altered every day - or sometimes every eight hours - to protect its security. So one message successfully read could be followed by scores more in another, unintelligible code. Further security devices were added, too, including the coupling of letters through pairs of plugs. The mathematical difficulties of resolving the code were mind-boggling. For their success, the British owed a debt of gratitude to Poland and its security services. The Poles had been reading German military messages for years before the advent of Enigma. By 1929 they had acquired a German Enigma machine and within four years they had made huge strides in understanding its workings and output. The Poles in turn had the French to thank for their achievements. When documents detailing the workings of the Enigma fell into French hands via a German traitor, they were duly passed on to the Poles who put them to good use. Although the French never cracked the German codes, the Poles were regularly translating messages generated by the Third Reich. These made alarming reading. Hitler's expansionist intentions were clear for all to see. To help in the task of deciphering, the Poles had invented a machine they called a “bomba” which automatically crunched codes until it hit on the right one. This was later modified and developed by the British and operated around the country by the women of the WRENS who waited patiently for results. It could take them a few moments, a few hours or even days. Then again, sometimes they failed completely to make any sort of translation. In 1938, the Poles lost their advantage when the Germans introduced yet another complex Enigma safety system. By the time the invasion of Poland loomed in 1939, they were hopelessly at sea with the new codes. Wisely the Poles saw a brick wall ahead of them and decided to salvage what they could of their labours. In July 1939 they met with counterparts from Britain and France and shared their knowledge of Enigma. The Poles went so far as to present each of their allies with an Enigma machine. Although Poland was subsequently conquered, refugee decryptologists worked with the French until France too was overrun by Germany. A handful of Polish code crackers were snared by the Germans in France. Despite harsh conditions of captivity, they never once imparted the vital information about the Allied knowledge of the Enigma which would have prompted Germany to change its method of coding. Now it was the responsibility of Britain alone to capitalise on the knowledge so arduously gained by their Polish and latterly by their French allies. The Codes and Ciphers School was based at Bletchley Park, a rambling mansion In Buckinghamshire that dated back some 50 years. Gathered here were fluent German speakers, outstanding mathematicians, radio experts, military tacticians and chess players. Some came through the services; others were plucked from universities and colleges. Their shared aim was to listen in to the German secrets and relay the information as speedily as possible to Allied commanders to give them the upper hand in battle. Secondly, it was their avowed duty to keep their activities cloaked in secrecy. A whisper about the project could have alerted the Germans and silenced Enigma forever. It is a tribute to all those involved that the valuable work carried out at Bletchley Park remained a closely guarded secret throughout the war. The name given to information wrung from Enigma by the Allies was Ultra. Vitally important messages were called Top Secret Ultra. Still, the task of reading the codes was a mighty one. First came the problems in transmission. Broadcasts made over radio or wireless sets were often fogged by atmospheric conditions, leaving the eavesdropper short of chunks of the message. The installation of intercept stations to improve reception was made a priority. Then there were difficulties in identifying the senders of various broadcasts and in differentiating between normal radio traffic and coded Enigma messages. Directional Finding or D/F was instrumental in pinpointing the locations. British intelligence chiefs found that verbatim transcripts were not the only useful items to be gleaned from the work being done at Bletchley Park. For example, a surprise increase in the weight of traffic and a change in its locality indicated the likelihood of a fresh offensive. To break the code itself, there was only one thing the listeners could be sure about: Enigma never mirrored a letter in its transposition. So for example if the letter 'a' appeared in the encoded message, it certainly would not appear in that position in the translation. That left just 25 options per letter. However, there were short cuts which the cryptographers looked out for. Many messages contained a weather report. By matching words likely to appear in that report, they could stumble on the key to the code if they were lucky. Sometimes messages sent in a different cipher already known at Bletchley Park were translated onto the Enigma, thus providing eavesdroppers with a welcome clue. Also, German operators became slack through over-confidence and inadvertently gave themselves away. Instead of choosing a random three letter security code, they picked the same letters day in, day out, with the result that the listeners were then able to translate them with considerable ease. Every piece of information that was translated was kept stored at Bletchley Park for assessment by intelligence chiefs. Even the most innocent of messages was probed to see if it held a deeper meaning. As the skill in cracking the Enigma Code increased, so too did the volume of associated paperwork. The first code to be broken by the listening ear at Bletchley Park was that used by the German Wehrkreise, Hitler's home command. It was labelled 'Green' and provided little by way of hard information. Then at the time of the invasion of Norway in 1940 the British cracked the Enigma code used by the Supreme Command of the German Armed Forces, called 'Yellow'. For the first time the potential of Ultra was realised with operational details being read in Britain soon after they passed between German commanders. Although the translation of Yellow was by no means complete, it gave intelligence at Bletchley Park plenty to go on and masses of encouragement. Next to be decoded were the Luftwaffe Enigma codes, branded 'Red'. Thereafter a handle on all German air force messages was maintained throughout the war. Gradually, the extent to which codes were broken and the speed at which German messages were translated substantially improved. By 1944 the advantage of the system was beyond doubt. A signal containing bombing schedules for the following day sent by German High Command at 21.40 hours on 26 October 1944 was transcribed and relayed to the relevant commanders soon after midnight. Hundreds of thousands such messages were dispatched from Bletchley Park during the war. The value of the insight they gave to Allied commanders was immeasurable. By January 1941 Ultra gave clear indications about the German build-up for the invasion of Yugoslavia and Greece. There were little the British could do to prevent the attack, nor could it find sufficient troops to fend off the Germans. While the reading of codes failed to assist the Allies in Greece and Crete, it did help prompt the evacuation of troops. In the same year the Italian codes which dealt with shipping in the Mediterranean were cracked. This meant that the Allies could target Rommel's supply ships with ease and it substantially decreased the speed with which the German commander could progress in North Africa. By the end of January 1942, Bletchley Park was decrypting the naval Enigma virtually simultaneously. Convoys were routed away from wolf packs and the anti-submarine squads were able to target their prey. Ultra is believed to have saved one and a half million tons of shipping, equivalent to 350 vessels, that year alone. U-boats were temporarily withdrawn from the Atlantic at the close of 1942. When they returned they were communicating with a new and different code which Bletchley Park could not recognise. By now Germany had realised that U-boats were the ace in their naval pack and production had been stepped up to replace those sunk by the Allies and provide more besides. Only when the new Enigma key was broken in March 1943 were the convoy routes offered adequate protection again. Ultra coupled with improved radar, high frequency direction finding and more powerful forces, enabled the Allies to take the offensive against U-boats with a vengeance. The previously secret German refuelling points were sunk and they could now be attacked even while they were on their way towards the busy shipping lanes of the North Atlantic Ocean. Both the Allied victory in North Africa and their success against the U-boats were key factors in the final outcome of the war. Had Rommel triumphed in Africa it would have cost the Allies dearly in terms of a vastly extended campaign? Britain, meanwhile, could have found itself besieged on the home front had the U-boats done their worst. At the very least 'Overlord' the invasion which finally liberated Europe, would have been delayed. The invasions of both Sicily and France were significantly assisted by the knowledge gleaned from Ultra. The decrypting of codes enabled the Allies to determine the exact whereabouts of German troops, their battle formations, and the effect that air-strikes were having and all their weaknesses and strengths. Not all Enigma codes were broken. While the Luftwaffe key remained in the hands of the Allies virtually throughout the war, both the army and navy keys were harder to penetrate and the Gestapo code was never read even though it remained unchanged between 1939 and 1945. Churchill knew that Ultra was a precious gift, not to be given away lightly. It complicated issues for him and his commanders because they were unwilling to advertise its existence. Therefore, extensive use of the information gleaned from Ultra was pretty well prohibited. Only the choicest items were utilised in order that no pattern was established in the use of such high-grade intelligence. Had the Germans suspected that their codes were being widely read, they would naturally have changed them immediately. In fact, the Germans already had the Geheimschreiber, an alternative machine to Enigma used only at the highest level, which was never cracked by the decoders at Bletchley Park. There was widespread alarm that the Germans would use this for all communications, bringing Ultra to an end once and for all. Fortunately for the Allies, they never did nor did they realise the extent to which their code system had been infiltrated. It led to accusations years after the war that Churchill had known in advance about the devastating air raid planned for Coventry in November 1940 and done nothing to stop it. Certainly, British intelligence did know that a city other than London was being targeted in a raid the Germans codenamed 'Moonlight Sonata', and they believed it to be either Birmingham or Coventry. British scientists had been working on bending navigation beams used by the Luftwaffe to guide them to their targets, and thus lead them astray. On the night of 'Moonlight Sonata', 14 November, the procedure failed. It was a clear night. This aided the German pilots, while the defensive fighter planes and barrage balloons this time claimed only one casualty between them. In a single night's work German bombers caused the deaths of 568 civilians. A further 863 were injured and the city of Coventry was gutted. Germany, of course, listened to British and Allied messages where it could. One of its major success stories was the reading of the cipher used by the US military attaché in Cairo which let them into untold secrets about British troop movements in the desert. By 1940 the Fuhrer’s observation service B-Dienst was reading about 50% of Royal Navy communications, a situation that persisted until 1943 when new codes at last began to be used. This was another major contribution to turning the tide of the U-boat war in the Allies' favour. Nevertheless, on balance Britain won the radio war. Likewise, American intelligence was ahead of the Japanese. The US broke the Japanese naval code and diplomatic cipher, known as 'Purple', before the fighting began thanks to the 'Magic' organisation. Perhaps the most telling use of the US 'listening ear' was in the Battle of Midway. Admiral Nimitz was in possession of much of the Japanese battle plan days before it began. That knowledge enabled him to place some of his fleet in the Pacific where the Japanese were least expecting to find it. The Battle of Midway has since been widely acknowledged as a turning point in the war with Japan.