Blackett's War (30 page)

The other problem was the navy’s indicator encryption system, which was the true nightmare. Breaking one army or air force message each day with the bombe was all that was needed to read all the rest of the day’s traffic on the same network. The basic setup of the machine changed only once a day, following a printed list. The individual setting used for each message was then varied by choosing a different starting position of the Enigma’s three rotors. The rotors each had 26 different positions, labeled A through Z with the letters of the alphabet, so there were 26 × 26 × 26 different possible start positions, 17,576 in all. The starting position for any given message was specified by a three-letter indicator, such as GHW or QYZ, and the simple system the army and air force used for encrypting these indicators at the start of each message allowed the Bletchley code breakers to read them off as easily as their intended recipient, once they had recovered the basic setting of the day using the bombes. The navy’s external code tables and more complex system for enciphering the message indicators, however, meant that breaking one message got the code breakers no further than that one message. A bombe run took hours to crack a single message; tackling every message individually was impossible.

With the code tables from
U-110
in hand the whole problem split wide open. A flood of cribs for future work was provided along with a regular trove of decoded orders to U-boats and sighting reports sent from the submarines. With traffic in hand for May and June, Turing was able to develop a way to reconstruct future months’ code tables even without having any more lifted copies. Just to make sure, the Admiralty cautiously agreed to one more “pinch,” and on June 25 another German weather trawler, the
Lauenburg
, was captured in the Norwegian Sea about 900 miles north of Scapa Flow with the July list of daily settings aboard. (When the captain of the British destroyer
Tartar
explained to his crew that he wanted them to fire on the trawler but not hit her, the chief gunnery mate replied, “Christ, that should be easy.”)
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The code breakers soon discovered that some hand cipher systems used by the German navy, mainly to communicate with small ships in the Baltic, frequently carried weather reports and mine warnings that were repeated verbatim in Enigma messages sent to larger ships and U-boats. This became another fertile source of cribs for breaking future traffic; on several occasions the British were able to speed the process by laying mines with the deliberate purpose of generating a German message. By July and August 1941 information from naval Enigma signals more than once was available in time to divert a convoy around a waiting wolf pack. Sinkings by U-boats in August dropped dramatically to 80,000 tons.

CHURCHILL’S ENTHUSIASM
for scientific invention was arguably exceeded only by his enthusiasm for cloak-and-dagger intrigue; that, too, caused its share of disasters throughout the war. Still, it meant that the prime minister needed no selling on the importance of the Enigma decrypts. In an initial burst of utterly unrealistic excitement, he demanded to have a copy of
every
decoded Enigma message delivered to him daily, in a special dispatch box. Later he settled for receiving a selection of the most important messages, but still insisted on seeing the actual texts, not summaries. He constantly bombarded the chiefs of staff and theater commanders with cables and memoranda calling their attention to what he considered significant bits of the decoded messages.

Churchill also took an early opportunity to show his support for the code breakers. On September 6, 1941, the prime minister paid a surprise visit to Bletchley Park. Standing on a tree stump by the lake on the grounds
of the park, he addressed the assembled staff. “You all look very … innocent,” he jokingly began.
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The work was becoming much more technical as well as much more of an assembly line than anything that GC&CS’s old-school donnish linguists had ever known, and the breakthrough on the naval Enigma now brought the clash of cultures to a head. Bletchley’s director, Alastair Denniston, was still struggling to run things the old way; he was conscientious but simply overwhelmed by the logistical problems of recruiting, hiring, and housing hundreds of new staff. He reacted touchily to complaints from the naval Enigma group throughout the summer of 1941 that they were desperately short of manpower to maintain the bombes, carry out IBM punch card operations that were an essential part of the job, test the bombe results on the replica Enigmas, and even get their results typed up.

Simply, Bletchley was unprepared for success. Having achieved the near-miraculous in cracking the naval Enigma problem, they were now unable to exploit it to the fullest. In August the head of GC&CS’s naval section, Frank Birch, wrote to Denniston pointing out that the shortage of typists alone was causing their output to queue up for days. Administrators were wasting an inordinate amount of time on recruiting, but it was proving almost impossible to get young women in particular to work at Bletchley given the low salaries, lack of recreational facilities, inadequate meals, and poor housing, notably the primitive plumbing that was standard in private billets in the area—“no baths at all and the W.C. at the bottom of the garden.”
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All this did was to elicit a testy dismissal from Denniston of Birch’s “somewhat destructive memorandum,” as he termed it. “What does Birch suggest,” Denniston continued, “that we should move to Harrogate or some such place.… There are worse places in the country where there is not even a cinema. There is certainly one good cinema in Bletchley.”
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Meanwhile Dilly Knox was furiously resisting any attempts at mass-producing the process of reading enemy messages, fighting a rearguard action from his embattled ivory tower to preserve what he thought was his sole right to keep control of his discoveries, rather than collaborating as part of a team. “As a scholar, for of all Bletchley I am by birth breeding education profession + general recognition almost the foremost scholar,” he crazily wrote Denniston, “to concede your monstrous theory of collecting material for others is impossible … had the inventor no right to the development and production of his discourses, we should still be in the Dark Ages.… There are occasions when disobedience is a primary duty.”
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Something had to be shaken up. In October several of the key Bletchley mathematicians working on the Enigma decided on an audacious move. For reasons that he said he could not remember, Stuart Milner-Barry, an international chess master who had been recruited to Bletchley in early 1940 and was now deputy head of Hut 6, which was responsible for army and air force Enigma, was chosen by the others to carry a message to the prime minister himself. It was Trafalgar Day, October 21, 1941, the 136th anniversary of Nelson’s victory in 1805 over the French fleet. “What I do recall,” Milner-Barry said, “is arriving at Euston Station, hailing a taxi, and with a sense of total incredulity (can this really be happening?) inviting the driver to take me to 10 Downing Street.”
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The taxi driver did not bat an eye, and arriving at the prime minister’s residence Milner-Barry boldly marched in and announced he had come from a secret war station and needed to see the prime minister immediately on a matter of national importance. He was, unsurprisingly, told that was impossible. Milner-Barry countered that he could not possibly leave the letter he was carrying with anyone but the prime minister himself, given its sensitive nature. Finally, Churchill’s principal private secretary, Brigadier George Harvie-Watt, appeared; Milner-Barry was able to establish that he wasn’t a raving lunatic by referring to the prime minister’s recent visit to Bletchley, which Harvie-Watt knew of; and the secretary promised to see that the letter would be handed directly to the prime minister.

The code breakers emphasized in their letter that crucial work was “being held up, and in some cases not being done at all” due to the manpower shortages; the recovery of the naval Enigma keys was being delayed at least twelve hours each day; promises made back in July that the work of testing the bombe solutions would be turned over to a contingent of Wrens—members of the Women’s Royal Naval Service—had come to nothing. The next day the code breakers’ letter landed on the desk of General H. L. Ismay, the prime minister’s chief military aide, with one of Churchill’s famous red
ACTION THIS DAY
labels affixed. Beneath the label Churchill had scrawled a succinct instruction: “Make sure they have all they want on extreme priority and report to me that this has been done.”

Within a few months Denniston was out; orders for more bombes were issued; the Ministry of Labour was ordered to meet with the head of the British Secret Service and arrange whatever manpower Bletchley needed; the army, navy, and air force were told to make additional servicemen and servicewomen available. Bletchley’s staff would reach about 1,500 by the end
of the year, and from the naval Enigma group in Hut 8 a steady stream of decrypts flowed to the Admiralty’s Operational Intelligence Centre, where U-boat positions were updated with pins on a huge wall chart.

The combined effect of Bletchley’s breakthrough in reading U-boat messages and the growing efficiency of British antisubmarine patrols as they began to implement the recommendations of Blackett’s team delivered a sharp check to Dönitz’s offensive in the second half of 1941: the “Happy Time” was over. Monthly sinkings by U-boats, which had been averaging 250,000 tons in the first half of the year, dwindled to half that figure as convoys were safely rerouted around the lurking wolf packs, while the number of U-boats sunk doubled.

Puzzling over his abrupt change of fortune, in particular the failure of his boats to intercept one expected convoy after another, Dönitz confided his frustrations and suspicions in his war diary entry of November 16, 1941. “Coincidence does not fall on the same side every time,” he wrote. Yet nothing really seemed to explain it. It was possible the British had a new method of radio direction finding that was precisely locating the U-boats’ positions at sea; there were rumors about new kinds of radar; there was always the possibility of spies or treason. All seemed unlikely. The one thing the admiral was certain of was that it was impossible for anyone to have broken the Enigma cipher, given the sheer number of mathematical permutations and the safeguards used to encrypt the setting changes. “This possibility is continuously checked by the Naval War Staff,” Dönitz noted, “and regarded as out of the question.”
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FOLLOWING GERMANY’S ATTACK
on Russia on June 22, 1941, Hitler had again sought to buy time in the Atlantic. At a conference with Admiral Raeder the day before, he told his naval commander-in-chief that he desired “absolutely to avoid any possibility of incidents with the U.S.A. until the development of Operation Barbarossa”—the invasion of the Soviet Union—“becomes clearer.” A month later he reiterated that he wanted “to avoid having the U.S.A. declare war while the Eastern Campaign is still in progress.”
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But incidents were taking place regardless of any restraint Hitler was inclined to show as the U.S. Navy asserted a steadily mounting presence in the Atlantic. Following his election to an unprecedented third term as president, Roosevelt had taken another huge step toward war. In March 1941 he secured congressional passage of the Lend-Lease Act, which allowed the
United States to provide whatever arms Britain needed on credit. Even more important, the act lifted the old neutrality laws’ prohibition on transporting armaments on U.S. merchant ships. American cargo vessels now were plying the dangerous waters of the Atlantic carrying tanks, planes, trucks, fuel, and steel to keep the British war machine running.

In July, U.S. Marines landed in Iceland to take over bases that the British had manned since Hitler’s invasion of Denmark, which owned the island. Admiral Harold Stark, the chief of naval operations, drafted the proposed order and sent it to the White House for approval. He wrote in a covering note to Harry Hopkins: “I realize that this is practically an act of war.”
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U.S. Navy warships began convoying merchant ships to Reykjavik; though nominally independent of the interlocking Canadian and British convoy system, the American convoys were open to any neutral vessels that wished to join them. To bolster the force available for escort duty, the U.S. Navy shifted from the Pacific three battleships, an aircraft carrier, four light cruisers, and two destroyer squadrons. American warships were instructed not to attack U-boats they sighted but they could pass on the information to the British—and could defend themselves if attacked.

On September 4, 1941,
U-652
was doggedly pursued by the U.S. destroyer
Greer
for three hours. A British Hudson bomber from Coastal Command dropped three depth charges on the U-boat, which responded by firing two torpedoes at the
Greer
, which responded in turn with a depth charge attack of her own. No damage was done on either side, but it gave FDR an opportunity to commit America further. Playing down the
Greer
’s initial pursuit of the U-boat, he denounced the German action in a fireside chat a week later as “piracy legally and morally” and offered a stark warning: “When you see a rattlesnake poised to strike, you do not wait until he has struck before you crush him.” Two days later he officially ordered the U.S. Navy to begin escorting Canadian convoys from Halifax as far as the Iceland meridian—a plan already secretly worked out by the British and American naval staffs—and to shoot on sight any German U-boats encountered along the way. The move immediately freed up forty British destroyers and corvettes. Far more important, it was another giant step toward intervention in the war by the United States.
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British government exasperation over the failure of America to formally enter the war was mounting, but Churchill told the War Cabinet that American opinion under Roosevelt’s leadership had moved far faster than anyone
could have expected and it was important to understand “the peculiarities of the American Constitution,” which reserved to Congress the power to declare war: it was unwise for a president of the United States to get too far ahead of public feeling. London and Washington were still heaving a collective sigh of relief over the bare one-vote margin by which the U.S. House of Representatives in August passed an eighteen-month extension to the one-year army draft approved the year before. The next month the isolationist bloc in the Senate almost succeeded in scuttling an amendment to the Neutrality Act that the president sent up following his speech, to permit the arming of American merchant ships and the convoying of shipping all the way to British ports. Privately, though, Churchill shared the frustrations. “The American Constitution was designed by the Founding Fathers to keep the United States free of European entanglements,” he told one of his private secretaries that fall, “and by God it has stood the test of time.”
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