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World War II
A Narrative History

Anthony Cave Brown
Bodyguard of Lies, Vol. 1 (1975)

The Turing Machine, or "Bomb"
Britain had successfully intercepted and decrypted German military, diplomatic and commercial telegrams for many years. But Hitler knew the importance of secrecy, and in 1934 the German government began to change its ciphers to a new system. MI-6 had long been involved in a worldwide inquiry to establish the nature of that new system. Now, four years later, it seemed that [Stewart] Menzies had the information MI-6 had been searching for.
That search had begun when Major Francis Foley, the MI-6 resident at Berlin (known to the service as "1200"), learned that the German army was experimenting with a cipher machine called Enigma. He reported this information to Admiral Sir Hugh Sinclair, the chief of MI-6, and Sinclair gave Menzies the task of finding out what was known about the machine. Menzie's men discovered that Enigma was the invention of a Dutchman, Hugo Koch of Delft, who had patented a Geheimschrijfmachine -- a "secret writing machine" -- at The Hague in October 1919. Koch had established a company to develop and market his invention, but he had not been able to build a machine and had assigned the patents to a German, Artur Scherbius, an engineer and inventor living in Berlin. Scherbius did build a machine from Koch's plans and he called it "Enigma," after the Enigma Variations of Sir Edward Elgar, in which Elgar described his friends in musical cipher. Scherbius's model, a primitive form of rotor cipher machine, was exhibited publicly for the first time at the 1923 Congress of the International Postal Union ... According to a brochure circulated in English, the machine was originally conceived to protect the secrets of business, not the secrets of war ....
But Scherbius's venture did not prosper and he sold the Enigma patents to another company. By that time Hitler had come to power, rearmament and reorganization of the Wehrmacht was under way, and his generals were scouring the laboratories and workshops for some new cipher machine with which to protect their secrets. The evaluation of Enigma was the responsibility of Colonel Erich Fellgiebel, who was to become chief signals officer of the German army and of the German high command. Significantly, Fellgiebel would also become one of the most active conspirators of the Schwarze Kapelle.
Enigma disappeared from the commercial world as Fellgiebel experimented with the machine. It was found to be inexpensive, sturdy, portable, simple to operate, easy to service, and it produced ciphers in great abundance. Above all, it was pronounced secure from even the most advanced cryptanalytical attack. It was relatively unimportant whether or not the machine was captured by an enemy; it was quite useless to him without knowledge of the keying procedures. Enigma was deemed suitable in every way to the needs of the Wehrmacht.
MI-6 knew this much of the machine, but little else until Major Harold Lehr Gibson, the MI-6 resident at Prague, reported that the Polish secret intelligence service, which worked with MI-6 against the Russians and the Germans, was also interested in Enigma. Department BS4, the cryptographic section of the Polish General Staff, had legally acquired the commercial version of Enigma; and Polish cryptanalysts ... had managed to resolve some of the mathematical problems involved in deciphering its transmissions .... But the Polish penetration of Enigma was ... not mechanical; and they had experimented only with the commercial model, which, it could be assumed, the Germans had modified and refined for the Wehrmacht's use.
It was the French who first managed to penetrate the military version, not through the trial-and-error of mathematical analysis, but through treason .... [I]n the summer of 1937 a German presented himself at the French Embassy at Berne and offered to work in the service of France against the Third Reich. He was, he declared, an officer of the Forschungsamt, the Reich's main cryptographic bureau, and his motives, he said, were ideological. His offer was reported to Colonel Louis Rivet at 2 bis [the French cryptanalytical bureau], and at first the French were inclined to believe that the German, who was codenamed "Source D," might be an agent provocateur sent to compromise their diplomatic status and privileges in Switzerland. But Rivet ... declared that this might be "a chance that will never come again," and he despatched a Captain Navarre of 2 bis to Berne. After prolonged interrogation of Source D, Navarre reported that he was "a traitor acting out of avarice," but he had revealed that "German technicians have developed a coding and decoding apparatus of a completely new type." It was Enigma.
.... When [Source D] later met Navarre in a small cafe in Brussels, he produced "a secret instruction manual on the use of the machine," as well as a cipher text and its plain text counterpart. The original of the manual was returned to the German the next day, along with part of the "generous payment" that had been promised ....
Navarre then returned to Paris, and [2 bis], with the data supplied by Source D, was able to produce ... a replica of Enigma. Moreover, if French claims were correct, Source D began to send 2 bis notice of the monthly keying changes employed by the Wehrmacht to thwart cryptographic attack. In short, the French had the capacity to read the Germans' most secret ciphers -- an intelligence coup of majestic importance. But they could do so only as long as Source D continued to supply the keying changes.
The British intelligence attack against Enigma took a somewhat different course. In June of 1938, Menzies had received a message that would prove to be the most important in the intelligence history of the Second World War. It came, again, from Gibson at Prague, who reported that he had just returned from Warsaw where, through the Polish intelligence service, he had encountered a Polish Jew who had offered to sell MI-6 his knowledge of Enigma. The Pole, Richard Lewinski (not his real name), had worked as a mathematician and engineer at the factory in Berlin where Enigma was produced. But he had been expelled from Germany because of his religion.... At the interview with Gibson, Lewinski announced his price: 10,000, a British passport, and a resident's permit for France for himself and his wife .... Lewinski claimed he knew enough about Enigma to build a replica, and to draw diagrams of the heart of the machine -- the complicated wiring system in each of its rotors.
....Menzies decided to send two ... experts to Warsaw to interview Lewinski in person .... One ... was Alfred Dilwyn Knox, a tall, spare man who was England's leading cryptanalyst. [The other] was Alan Mathison Turing, a young and burly man with an air of abstraction and a reputation as an outstanding mathematical logician. Briefing the men on their mission, Menzies said their task was to go to Warsaw, interview Lewinski and report upon his knowledge. If they were satisfied that it was genuine, they were to arrange with Gibson to take the Pole and his wife to Paris and place him in the charge of Commander Wilfred Dunderdale, the MI-6 resident there, known to the service as "2400." Then, under their supervision, Lewinski was to re-create the Enigma machine.
.... [T]he two men who journeyed to Warsaw to discover how much Richard Lewinski knew about Enigma ... met him first at the Madame Curie Museum, and their conversation continued as they walked along the bank of the Vistula to Lewinski's rooms in the ghetto. Lewinski was a dark man in his early forties, thin and bent; Commander Dunderdale later said that he reminded him of a "raven plucking an abacus." Knox and Turing already knew much about Enigma; their interest lay in how the Germans had modified it, how they managed the keying procedures and which German departments used it. It was clear that Lewinski's knowledge of these questions was considerable. Knox and Turing recommended to Menzies that his bargain be accepted. The necessary arrangements were made, and Lewinski and his wife were taken by Major Gibson and two other men to Paris, traveling on British diplomatic laissez-passez through Gdynia and Stockholm to avoid Germany. In Paris they came under the charge of Dunderdale, who, through his connections with the French intelligence service, obtained residential papers for them without revealing what Lewinski was doing in France.
Under Dunderdale, Enigma took shape. Lewinski worked in an apartment on the Left Bank, and the machine he created was a joy of imitative engineering. It was about 24 inches square and 18 inches high, and was enclosed in a wooden box. It was connected to two electric typewriters, and to transform a plain-language signal into a cipher text, all the operator had to do was consult the book of keys, select the key for the time of day, the day of the month, and the month of the quarter, plug in accordingly, and type the signal out on the left-hand typewriter. Electrical impulses entered the complex wiring of each of the rotors of the machine, the message was enciphered and then transmitted to the right-hand typewriter. When the enciphered text reached its destination, an operator set the keys of a similar apparatus according to an advisory contained in the message, typed the enciphered signal out on the left-hand machine, and the right-hand machine duly delivered the plain text.
Until the arrival of the machine cipher system, enciphering was done slowly and carefully by human hand. Now Enigma, as Knox and Turing discovered, could produce an almost infinite number of different cipher alphabets merely by changing the keying procedure. It was, or so it seemed, the ultimate secret writing machine. Hitler evidently trusted Enigma completely .... Enigma had been adopted for use throughout the three armed services of the Wehrmacht; it was being, or already had been, introduced from the highest down to the regimental level of command. It was used to encipher Hitler's communications and those of Field Marshal Wilhelm Keitel, the Chief of Staff of the Oberkommando der Wehrmacht (OKW), the Supreme Command of the German armed services .... Field Marshal Hermann Goering used it as C-in-C of the Luftwaffe, and Admiral Erich Raeder as C-in-C of the Kriegsmarine. And so did their staffs, U-boats and even small ships liable to capture were equipped with the machine, for the possession of an Enigma by an enemy was not sufficient to enable him to read encoded traffic. Only knowledge of the keying system and procedures would permit that. As a result, Hitler had allowed Enigma to be sold to Japan, which used it as her main cipher machine for naval and diplomatic traffic; to Italy,  whose Commando Supremo used it; and to Rumania and Bulgaria. Most important to Menzies, Admiral Wilhelm Canaris of the Abwehr also used Enigma for his main-line communications ... and Canaris would be Menzie's principal opponent if Britain and Germany went to war.
.... But the British realized that, unlike the Poles, they could not rely solely upon painstaking and time-consuming mathematical decryptions of Enigma transmissions; the real value of such intelligence depended upon the speed with which it could be deciphered and distributed.  Nor, unlike the French, could they rely upon the services of a traitor to provide the keying schedules. It had to be presumed that the Germans would guard these schedules with the greatest of care, and if they fell into enemy hands, it would be a simple matter to change them. Therefore the only way to penetrate the secrets of Enigma was to make another machine that could imitate or interpret the performance of each of the thousands of Enigmas that would come to exist in the Wehrmacht. The machine would also have to extrapolate the constant changes of keying procedure that every major German command ordered every day and every night, year in and year out; and it would have to be capable of making an almost infinite number of mathematical calculations at speeds far beyond human ability. Such a machine existed only in theory -- the theories embodied in Turing's Universal Machine. But could Turing and the other cryptanalytical experts build one in fact? Was it beyond the technology of the times?
....The Foreign Office obtained an appropriation for the machine, specifications were soon ready, and they were with the engineers during the last quarter of 1938. The contract went to the British Tabulating Machine Company at Letchworth, not far from Bletchley, and BTM assigned the task of building "The Bomb" -- as the Turing engine came to be called -- to its chief engineer, Harold Keen, and a team of twelve men. In complete secrecy ... the machine took shape .... It was a copper-colored cabinet some 8 feet tall and perhaps 8 feet wide at its base, shaped like an old-fashioned keyhole. And inside the cabinet was a piece of engineering which defied description. As Keen said, it was not a computer .... "Neither was it a complex tabulating machine, which was sometimes used in cryptanalysis. What it did was to match the electrical circuits of Enigma. Its secret was in the internal wiring of (Enigma's) rotors, which 'The Bomb' sought to imitate."
The machine was installed at Hut 3, a large Nissen hut under the trees in Bletchley's parkland, and the time soon came to begin operational trials by feeding Enigma intercepts to "The Bomb." These intercepts were simply obtained from the string of tall-pyloned wireless interception posts which the British government had established around the world. The posts recorded all enemy, hostile and suspect wireless traffic and radioed it to Bletchley Park, where Enigma transmissions were identified, put on tape and fed into "The Bomb." If "The Bomb" could find the keys in which the transmissions had been ciphered the cryptanalysts at Bletchley could then "unbutton" the messages.
The experiments at Bletchley were conducted with the utmost secrecy, but even if they proved to be successful, there was a danger ahead. With the cryptographers of three nations attempting to read Enigma traffic, how long would it be before the Germans discovered that their most secret cipher machine had been compromised? And if they did, they would almost certainly replace it with a new system, or modify Enigma in a way that would negate further penetration.
....{"The Bomb's" initial performance was uncertain, and its sound was strange; it made a noise like a battery of knitting needles as it worked to produce the German keys. But with adjustments, its performance improved and it began to penetrate Enigma at about the same time the Germans prepared to attack Poland .... "The Bomb's" initial production seemed to have been a matter of chance rather than calculation. Nevertheless, it had proved that it was not the dream of some mad inventor. It worked. When the Germans invaded Poland on September 3, 1939 ... Britain was ill-prepared for the conflict, but "The Bomb" was operational; and it was a machine that promised to provide the most valuable intelligence material of the war -- Ultra.
Bodyguard of Lies is available from AMAZON
 Bletchley Park

Victorian manor situated 80 km (50 miles) northwest of London. Known as Station X, from 1939 it was the site of the British Government Code and Cypher School (Government Communications HQ from 1942). This had been formed in 1919, from the cryptanalytical sections of the Admiralty )Room 40 O.B.) and the War Office, "to advise as to the security of codes and cyphers used by all Government departments and to assist in their provision," but it was also secretly ordered to "study the methods of cypher communications used by foreign powers." This meant that its staff worked to break those ciphers and it was, in fact, not a school at all but a highly secret organization which came under the aegis of the head of MI6.
In 1939 the staff, headed by Alistair Denniston, numbered about 150, but it grew so rapidly that wooden huts were erected to accommodate the overflow. By late 1942 the numbers had risen to about 3,500, and to more than 10,000 by 1945. Some were civilians; others came from the armed services of several nations, including France, Poland, and the USA. They worked on the decryption of German and Japanese hand codes and ciphers [and] on the Enigma and Purple machine ciphers, which produced Ultra and Magic intelligence .... Initially, "bombes" -- devices which simulated the workings of an Enigma -- helped decrypt signals, but by June 1944 the first electronic digital computer, Colossus II, was being used. Staff in Hut 6 deciphered the German Army and Luftwaffe Enigma signals ... ; those in Hut 3 translated and interpreted them, and dispatched the resulting intelligence to Special Liaison Units and other recipients; and those in Huts 4 and 8 dealt with naval Enigma signals, which were passed to the Naval Intelligence Division.
Bletchley had three cryptanalytical outposts overseas: the Combined Bureau, Middle East; the Wireless Experimental Centre at Delhi; and the Far East Combined Bureau, all of which had their own outposts.
The Germans never knew the purpose of Bletchley Park ....
Oxford Companion to World War II, Dear and Foot, eds. (1995)
 Menzies, Maj. Gen. Sir Stewart
(1890-1968) Director of MI-6, the British Secret Intelligence Service, from 1939 to 1953. Menzies (pronounced MING--iss) was responsible for much of Britain's intelligence activities during the war, including operations at Bletchley Park.
Menzies served as an officer in the Army's Life Guards from 1910 to 1939 and saw action in France during World War I. As a colonel he was deputy to Adm. Sir Hugh Sinclair (head of MI-6 from 1923 until his death in 1939), and then succeeded to head MI-6. His position was particularly difficult during the war in that he worked for Prime Minister Churchill, who had an insatiable appetite for intelligence and secret projects.
A strong proponent of code-breaking, under Menzie's personal sponsorship Bletchley Park developed the Bombe machine that began deciphering the German Enigma machine cipher in 1940. He was promoted to major general in 1945. He remained head of MI-6 until 1953, when he retired in the aftermath of the defection of British intelligence officials Donald McLean and Guy Burgess to the Soviet Union.
World War II: America at War, 1941-1945, Polmar and Allen (1991)