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At first, without an Enigma machine, there wasn't much hope of breaking the German codes and the British had almost given up trying. In particular, the rotor wiring was unknown until, on July 25, 1939, the Poles handed an Enigma replica over to the dumbfounded British during a secret meeting near Pyry and, by the time Hitler invaded Denmark and Norway, on April 9, 1940, Bletchley Park had begun to decoding some of the German signal traffic. Enigma was pioneered as early as 1923 by Dr Arthur Scherbius, a German engineer and used by businesses to transmit trade secrets - The London Patent Office granted a patent in 1927 but there was little interest until the outbreak of war when the British were given two replicas made by the Poles, the fact that the London Patent Office already held much information on the machines seemingly being unknown to the very people trying to unravel the machine's mysteries ! Its basic principle - substituting letters of the alphabet - was of schoolboy simplicity - The machine would encode or decode letters typed on its keyboard, flashing up substitute ones on a parallel "lampboard" but, the Enigma used not one alphabet but permutations of literally billions, changing with each coded letter. 
Between the two keyboards are three rotors each with 26 starting positions, these gearing with one another and giving 26 x 26 x 26 possible settings - a permutation of 17,576 alphabets - The turn of a knob could create a further 17,576 and variable wiring brought the total available to five followed by 92 noughts. The weak point of the Enigma was the radio transmission of simple six-letter instructions for the daily rotor settings, such as HSB ZAH - Marian Rejewski, a Polish mathematical genius, calculated that, although there were billions of possibile alphabets, a set of just six equations enabled a codebreaker to work out which one was being used - He was unwittingly aided by lazy operators choosing banal keys such as ABC SSS and by the idiosyncrasies of the German language - A 17-letter German word with the same letter in eighth and ninth positions and another the same in third, tenth and l6th positions was obviously Obergruppenfuhrer. 
DOWNLOAD THIS PAPER ENIGMA MACHINE AND FIND OUT HOW THE ROTORS WORK The British were not the only ones who were reading the enemy's messages. The German Beobachtungs-Dienst (B-Dienst, Observation Service), in conjunction with Entzifferungs-Dienst (E-Dienst, Cryptanalysis Service) were regularly monitoring British traffic. The Germans picked up and decoded British intentions to occupy Narvik and were able to send a decoy force which distracted the British until after their own occupation troops had landed. There were far more serious consequences however for the German raider "Atlantis" had captured three British vessels, the "City of Baghdad", "Benarty" and, on November 11, 1940, "Automedon", from which they obtained the British merchant ship codes. With this knowledge their U-boats could be directed to sink ships supplying vital supplies to England. B-Dienst had another source of information for some American maritime insurance companies shared underwriting costs with their European counterparts and regularly cabled ship manifests and routes to their offices in Switzerland. The Swiss, in turn, shared this information with their German co-insurers providing the Germans with every detail of ship sailings and cargoes ! In May, during the battle of France, the British were reading most of the Luftwaffe messages. This intelligence, dubbed "Ultra," was passed on to the the appropriate authorities, the most eminent of whom was Winston Churchill (who had a special fondness for it). Knowing what the enemy was about to do was of little use to the Allies, who lacked the means to counteract it. Advance warning from Ultra that the situation was hopeless did however allow advance planning for the Dunkirk evacuation. Ultra intelligence was carefully guarded; any tactical information was carefully "sanitized" before being passed on, generally preceded by "according to a most reliable source". The word "Ultra" was never mentioned. | 
