Seizing the Enigma (2 page)

Others helped with the substance. Sir Harry Hinsley patiently answered torrents of questions. Dr. Jurgen Röhwer steered me right on the Battle of the Atlantic. Ralph Erskine generously shared his expertise on the naval Enigma. Dr. Cipher Deavours made complex cryptanalyses plain. Carl Ellison helped in this as well. Christine Kelly located many retired Royal Navy officers and men. My researchers Alexander Lesnoff-Caravaglia and Mary Z. Pain came up with what I needed in the Public Record Office. Ilan Berkner computed times of solution for messages. Franz Selinger provided names and addresses of crew members of the German weather ships. The late Patrick Beesly furnished information and encouragement.

Archivists and historians who greatly helped included John Taylor, Harry Rilley, Tim Mulligan, Bill Cunliffe, and Bob Wolfe
at the National Archives, Dr. Dean Allard, Bernard Cavalcante, and Kathleen Lloyd at the U.S. Navy’s Operational Archives, Dr. Hansjoseph Maierhofer and Dr. Manfred Kehrig at the Militärarchiv, and David Brown at the Naval Historical Branch of the Ministry of Defence.

Richard Cornett of
Newsday
drew fine maps, and Bob Newman of that newspaper helped with art matters. Karen Bacon and Rita Porzelt typed a hard-to-read manuscript. I thank my colleagues at
Newsday
for their help and understanding: Jim Lynn, Peg Finucane, the late Lou Renzulli, Marty Hollander, Judy Bender, Jim Klurfeld, Ilene Barth, Mark Howard, and Eileen McDermott.

My friends Edward S. Miller and Dr. Louis Kruh encouraged me. Bernie Bookbinder provided valuable emotional support. Dr. Zita Brandes’s professional aid was indispensable. Others who helped include Dr. Robert N. Grant, Dr. Alec Douglas, and Gilbert Bloch, as well as all those who answered questions in interviews or in letters. Susanne Kahn discussed problems sympathetically; our sons Oliver and Michael reminded me of what really matters. My father, Jesse Kahn, offered advice, and together we remembered my mother, Florence Kahn, who died while the book was being written.

I am grateful to all for their help. The responsibility for errors lies with me, of course, and I shall appreciate any corrections that readers send.

G
REAT
N
ECK
, N
EW
Y
ORK
October 1990

B
RITISH FORTITUDE MADE IT POSSIBLE FOR THE
A
LLIES TO WIN
World War II. Russian manpower and American productivity actually won it, but they wouldn’t have been able to do so if Britain hadn’t first stood firm against Nazi Germany. And later the island gave the United States and Britain the platform on which they could build up their forces and from which they would launch their invasion of the Continent. The British people’s courage and determination made this possible, and is one of the great epics in world history, comparable (though with a better outcome) to Thermopylae.

But Britons required food to eat and raw materials to make the instruments of war. The dominions and colonies and allies overseas could furnish these items to the island kingdom only by sea. The Axis could choke off this supply by sinking the ships bringing those items to Britain. The United Kingdom therefore needed to ensure that these ships got through the U-boat blockade. It did not have enough destroyers and corvettes to do this, so it sought to turn U-boat convoy intelligence against itself by discovering it and using it to avoid the wolfpacks.

Admiral Karl Dönitz, the commander of U-boats, coordinated his attacks on the convoys by radio messages. But radio waves have the disadvantage that they can be heard not only by the intended recipients but by anybody. To prevent eavesdroppers from gaining information from the transmissions, U-boat command encrypted them – put them into secret form. It did so with a cipher machine, named the Enigma, then among the world’s best, that the German army and air force also used.

In the 1930s, however, the Poles, fearful of German revanchism and aided by spy information and mathematics, which neither the French nor the British cryptanalysts used, reconstructed the Enigma machine. Shortly before World War II, they gave reconstructed Enigmas to the British and to the French. It didn’t help. Strength, not intelligence, mattered. Blitzkrieg defeated the Poles and the French; Britain survived on its island. But it needed to know what the Germans were intending, and one source of that intelligence could come from solving German radio messages. Britain had set up a codebreaking center in Bletchley Park, a country house near Milton Keynes in Buckinghamshire. There cryptanalysts sought to solve German messages.

At first they had little success. The Enigma cryptosystem was too good. But machines are used by humans, and if they are not used well, they can fail. That is what happened with the Enigma used by the Luftwaffe. In enciphering a message, a Luftwaffe code clerk was to choose three letters to set the Enigma’s three codewheels for encipherment. (These three letters were repeated and transmitted in a secret way to the deciphering clerk so he could read the message.) Each message was supposed to have a random setting, making each message’s encipherment different from any other and so harder for an enemy to break. But instead of choosing three letters at random, such as HWX, the Luftwaffe encipherers often chose girlfriends’ names, such as ANN, or curses, or patriotic words, or letters near those of the preceding message so the setting up would be less work. This greatly reduced the number of settings that the British codebreakers had to try to solve the intercept. As a consequence, and with other help, the British began reading Luftwaffe intercepts in the spring of 1940, helping the few win the Battle of Britain.

Later on the young mathematical genius Alan Turing invented a mechanism—called a bombe, because it expanded upon a Polish device of that name—that tested guessed German plaintexts against intercepts to find the Enigma settings. This was improved by another Cambridge mathematician, Gordon Welchman, through what was called a diagonal board. These devices enabled the British sometimes to determine the Enigma key for some messages and so translate all messages enciphered
in that key. But, as with the guessed Luftwaffe three-letter settings, running the bombes to find the right key took hours, sometimes days. And sometimes the guessed plaintexts were wrong. So determining the key, which would enable the British to read all messages enciphered in that key, happened only rarely.

And they could not crack German army or
Kriegsmarine
messages. The army code clerks were more disciplined than the Luftwaffe’s in choosing the setting letters. And the German navy didn’t permit its code clerks to choose the codewheel settings at all. Basically it listed the settings that could be used—they were random groups, such as DOK—and indicated them by letter groups that bore no relation to the setting groups. These indicators the enciphering code clerk converted to secret form according to a table in a book (this is simplified here) and radioed them to the decipherer, who unconverted them, set his Enigma wheels accordingly, and deciphered the message from gibberish to German. This system, which left almost nothing to chance and so to human blunders, was so well thought-out that the British cryptanalysts could not break into the
Kriegsmarine
messages. They could almost never guess plaintexts that would enable them to use the Turing bombe. So they could not learn what the U-boats had been ordered to do and what they were reporting back to headquarters about their successes and failures.

Yet the very existence of Britain all but required the defeat of the U-boats. Everything depended ultimately upon that. Warship escorts, air cover, and enough freighters would chiefly determine the outcome. But knowing what the German submarines were planning and where their wolfpacks would assemble would enable the Allied convoys to avoid them. Later such knowledge would enable Allied warships to sink U-boats. Codebreaking could provide that knowledge. But the Allies didn’t have it. They couldn’t crack the naval Enigma.

Then a brilliant Cambridge undergraduate, Harry Hinsley, had the idea of stealing the Enigma keying books from some isolated German weather ships in the North Sea. These two dramatic seizures were followed by the rescue, by two Royal Navy sailors, of a new edition of the Short Weather Code from a sinking U-boat in the Mediterranean.
Though they drowned, they saved the codebook. It enabled Bletchley to find cribs to weather messages and so read naval Enigma. This book tells the story of those captures, which greatly helped the Britain to win the Battle of the Atlantic and so not to lose but to win World War II.

An important correction to the popular account must be made. A film,
U-571
, purported to tell the story of the captures. It is dramatic, exciting—and false. First, it maintains that what was captured was an Enigma machine. No. Captured by the British in the war were the keying books. These made naval Enigma breakable in time for convoys to be rerouted around wolfpacks. But it is simpler for viewers to understand that a coding machine was seized than to explain the intricacies of naval Enigma keying. The second, and grosser, falsehood in the film affirmed that the capture in the film was an American exploit. This was a Hollywood invention to make the film more appealing to an American audience. The capture was, from inception to conclusion, a British triumph. The film deprives the British of their just reward. Their triumph must not be forgotten.

What does the story of the Enigma seizures mean? If Britain had not solved the naval Enigma, would it have lost the war? No. Though it is impossible to prove a counterfactual, I believe that Britain would have fought on in 1941 even without naval Enigma solutions just as it had in 1940. The war certainly would have taken longer, cost more lives, imposed greater hardships, but Hitler could never have won. The powers against him were too great. The atom bomb would have been detonated over Berlin instead of Hiroshima. The great value of the Enigma captures is that, by shortening the war, they helped to make much of this unnecessary.

They played a major role in which the British critic George Steiner said about the entire codebreaking effort: “Increasingly, it looks as if Bletchley Park is the single greatest achievement in Britain during 1939–45, perhaps during this century as a whole.” And when the Queen herself visited Bletchley Park on 15 July 2011 and paid tribute to the secret men and women who had done so much to save freedom, the significance of their work was made clear to all at royal level.

—N
EW
Y
ORK
, N
EW
Y
ORK
January 2012

F
ROM UNDER THE RUFFLED WATERS OF THE SPRINGTIME
N
ORTH
Atlantic, the captain of the German submarine U-110 peered his periscope at the oncoming convoy. He chose four ships in the second column as his targets, took aim, and, at 30-second intervals, fired three torpedoes from his bow tubes.

His intended victims were members of Convoy OB 318, lumbering west toward America to be refilled with supplies for wartime Britain. An the center of the front line of the warships that surrounded the convoy steamed Escort Group 3’s flagship, the Royal Navy destroyer
Bulldog.
She was skippered by Commander A. J. (Joe) Baker-Cresswell, a fresh-faced, boyish-looking career officer, just turned forty.

Baker-Cresswell had fixed his midday position by shooting the sun with his sextant through the thickening clouds when, to his astonishment, he saw a column of water rise near the merchantman
Esmond
, which was leading the starboard column. For a moment he was incredulous. The convoy, southwest of Iceland, was only 300 miles from the Greenland coast; no submarine had ever attacked that far west. But his surprise did not stop him from swinging at once to starboard, in the direction from which he sensed the torpedo had come.