Seizing the Enigma

The Race to Break the German U- Boat Codes 1939-1943

By David Kahn

A few years earlier, in 1931, the Czech mathematician Kurt Gobel had proved that contradictions would eventually arise in certain self-referential statements that would prevent some problems from being solved; mathematical knowledge would forever remain incomplete. Turing took this idea a step further in a paper published in 1936, when he was twenty-four. He began by envisioning a mechanism that could move to right or to left an infinitely long tape marked into squared and that could read and change or read and leave unchanged the blank or the mark – the 0 or th 1 – in each squared. He demonstrated that this machine could compute anything that could be calculated. But then he proved that even this device could not tell whether the potentially solvable problems could be solved.

This remarkable paper had two results. It demonstrated that a fundamental problem in mathematics, the so-called Entscheidungs-problem – ascertaining whether certain problems could be solved – was not soluble. And, as became evident only later, the imaged device, eventually called a “universal Turing machine,” was the idealization of general-purpose computers. Turing became, in other words, the intellectual father of the computer.

(Kahn 2009, pp. 108)

But the naval Enigma still could not be read. Seeing no chance of analyzing the machine, the British began to consider ways of capturing keys. Some vague discussions took place during the summer, but the first clear proposal came from the assistant to the director of naval intelligence, an imaginative civilian who later became world famous as the creator of superspy James Bond. In a note of September 12, 1940, to his chief, Ian Fleming wrote:

D.N.I.

I suggest we obtain the loot by the following means:

Obtain from Air Ministry an air-worthy German bomber.
Pick a tough crew of five, including a pilot, W/T [wireless telegraph] operator and word-perfect German speaker. Dress them in German Air Force uniform, add blood and bandages to suit.
Crash plane in the Channel after making S.O.S. to rescue in P/L [plain language].
Once aboard rescue boat, shoot German crew, dump overboard, bring rescue boat back to English port.

In order to increase the chances of capturing an R. or M. [Raumboot, a small minesweeper; Minensuchboot, a large minesweeper] with its richer booty, the crash might be staged in mid-Channel. The Germans would presumably employ one of this type for the longer and more hazardous journey.

(Kahn 2009, pp. 145)

Each monitor listened through earphones to the peepings brought in by the radio set on a high bench in front of him or her. Each took down all the traffic – every schedule, in the intercept operators’ term – on a single frequency. Axon, for example, copied primarily a frequency used by station DAN at Norddeich, which broadcast weather reports, and secondarily a frequency used by station LLA-bar, whose location she did not know. Some stations transmitted at regular times, others only when they had messages. When nothing was being transmitted, many of the women knitted.

But when a message began, the monitor immediately started to write it down in pencil on the topmost sheet of a pad of intercept forms. No carbon copies were made. He or she noted the time, the frequency, the signal strength, the addressee, and the sender, and wrote down the code groups in the little rectangles on the form’s grid. The monitor was careful to write down only letters of which he or she was certain, omitting the others and indicating the omissions; guesses were not allowed, since a wrong letter was worse than a blank. But the German transmissions were very precise, very uniform; they reminded Axon of the goose step. When a transmission was completed, the monitor ripped the intercept form off the pad and held it up high. Often he or she was holding up one message while taking down another. A controller would take it to the teleprinter to be sent to the codebreakers.

(Kahn 2009, pp. 268)

Stocks of food and goods had not yet recovered from having been drawn down during the previous year. Imports to Britain had in January reached their lowest level of the war. Beef and veal imports had begun their 1943 slide to 310,000 tons, about half the yearly prewar average. Rationing continued. Each individual was entitled to two ounces of tea per week and four ounces of bacon and ham. The cheese ration had been halved in February from the generous eight ounces of 1942.

The Ministry of Food sought to reduce the amount of wheat brought in, on which Britain was especially dependent: in 1939 she had produced 1,668,000 tons but had imported 8,519,000, The Ministry considered raising the rate of extraction of flour from wheat from the customary average of 70 to 75 percent to 90 or 95 percent and diluting the flour with barley and oats, even though this would produce a darker, less palatable, and less digestible bread. But the barley could be obtained only by reducing beer production and closing the pubs two days a week. The committee in charge unanimously recoiled from this. It and the brewers finally agreed, however, that oats and dried potato bits would replace 10 percent of the barley used in brewing. The plan was put into effect, and 280,000 fewer tons of wheat had to be imported. Such were the contortions the British government went through to save shipping space.

(Kahn 2009, pp. 288)

Ultra was the greatest secret of World War II after the atom bomb. With the exception of knowledge about that weapon and the probable exception of the time and place of major operations, such as the Normandy invasion, no information was held more tightly. Churchill’s anxiety about the secrecy of Ultra was constant; rules in all of the armed forces forbade any action to be taken on the basis of Enigma intercepts unless some cover, such as air reconnaissance, was provided. The security implies Ultra’s significance. Ultra furnished intelligence better than any in the whole long history of humankind. It was more precise, more trustworthy, more voluminous, more continuous, longer lasting, and available faster, at a higher level, and from more commands than any other form of intelligence – spies or scouts or aerial reconnaissance or prisoner interrogations. It thus fulfilled better than ever before intelligence’s ultimate purposes, one in the psychological component of war, one in the physical. It improved command, and it magnified strength.

It improved command by reducing much of the uncertainty surrounding the enemy. As one scholar has written, “Ultra created in senior staffs and at the political summit a state of mind which transformed the taking of decisions. To feel that you know your enemy is a vastly comforting feeling. It grows imperceptibly over time if you regularly and intimately observe his thoughts and ways and habits and actions. Knowledge of this kind makes your own planning less tentative and more assured, less harrowing and more buoyant.” This benefit of Enigma solutions was intangible but real.

(Kahn 2009, pp. 323-324)

What effect, then, did Ultra have? Can it at least be estimated how many months of war the colving of the naval Enigma saved?

Any answer must be hypothetical, and similar calculations could be made about any wartime activity. Nevertheless, it is illuminating to suggest a figure. Without the shipping saved by Ultra, forces would have been withdrawn from the Pacific to attempt to keep to timetables for the invasions of Sicily and Italy and, above all, of Normandy. Calculations of ship production and of logistic problems suggest that these invasions would have been delayed by about three months. In particular, the great assault on Normandy might have taken place, not in June 1944, but in the fall, or possibly not until the spring of 1945. During this delay, Hitler’s V-weapons would have caused far greater devastation. The additional submarines that would have come into service would have made crossing the Atlantic and supplying the Soviet Union even more costly in ships and men. The Allied offensives would have come later and perhaps less strongly. The war in Europe might have been prolonged for one year, and because of the withdrawal of forces and supplies from the Pacific to the European theater, the entire conflict might not have ended until 1947. So, taken in isolation, it may be concluded that Ultra saved the world two years of way, billions of dollars, and millions of lives.

But events do not occur in isolation. Even if the codebreakers of Hut 8 and OP-20-G had been totally ineffective, even if the war had been prolonged three months or even more because of their inability, something entirely external to them would have taken control of events: the atom bomb. If Germany had continued fighting into the summer of 1945, the first nuclear weapon would probably have exploded not over Hiroshima but over Berlin. And the war would have ended then, no matter what the codebreakers had done, or had not.

(Kahn 2009, pp. 325-326)

The same defensive concerns compelled the Allies to put better men into cryptology than the offense-minded Germans did. In Poland, the Biuro Szyfrow, looking far down the road of cryptanalytic need, hired mathematicians. In Britain, Cambridge students and graduates were the cream of the nation, and G.C.&C.S. took the cream of that cream. In the United States, the draftees who scored the highest on an IQ test were proposed for cryptologic work. But in Germany, no such recruiting seems to have taken place; the Germans, on a blitzkrieg of conquest, seemed not to feel that they needed codebreakers badly. With one or two exceptions, they brought in mathematicians for cryptanalysis only later, during the war. So their agencies, despite individually bright men, did not perform as well as did the Allied units.

The leaders of Britain and Germany personified these differing behaviors. Churchill eagerly read the intercepts and encouraged his cryptanalysts to continue laying their golden eggs. Hitler, although he accepted intercepts, never visited any of his cryptanalytic agencies, never thanked them, and never showed any special interest in their output. In part this difference stemmed from the two nations’ different immediate needs: for a long time, Churchill had little more than intelligence, while Hitler was conquering Europe. In part it was a matter of background: Churchill had for decades dealt intimately with the results of codebreaking, Hitler had never done so. And in part it reflected long-standing national policies. Britain’s maintenance of the balance of power is a reactive or defensive technique that requires intelligence to succeed. Germany utilized the strategic offensive to resolve her problems of indefensible borders and severe domestic tensions. But this does not call for intelligence, and so her leaders interest themselves in it less than Britain’s leaders did.