Seizing the Enigma (36 page)

They dated the letter October 21, 1941—the anniversary of the Battle of Trafalgar, when Nelson’s defeat of the French fleet saved England from a Napoleonic invasion—a date that would not be lost
on Churchill. To prevent the letter’s being blocked in the bureaucratic hierarchy, they decided to deliver it personally to Churchill.

The job fell to Milner-Barry. On the twenty-first, he took the train to London. Scarcely believing what he was doing, he told a cab driver to take him to No. 10 Downing Street, the prime minister’s residence and office. There he rang the bell, stated his business, was ushered inside, and was told to wait. Soon there appeared the shortish, dapper figure of Churchill’s principal private secretary. Milner-Barry explained that he had come from a secret establishment and had an important letter to deliver to the prime minister in person. But the secretary knew nothing of G.C.&C.S. or of
ULTRA
, and Milner-Barry could not tell him, and the secretary quite naturally said that no one could see the prime minister without an appointment. Milner-Barry insisted, however, that the matters were of great importance but that he could not discuss them with anyone not authorized to know about them. He had no Foreign Office pass to prove his identity and nothing to show that he was on secret business. But he referred to Churchill’s visit to Bletchley knowledgeably, showing that he had been present on that occasion, which the secretary knew about. This resolved the impasse, and the secretary promised to place the letter, unopened, before Churchill personally.

The very next day, Churchill wrote to the secretary of the Committee of Imperial Defence: “
ACTION THIS DAY
. Make sure they have all they want on extreme priority and report to me that this has been done.” In less than a month, Menzies reported to Churchill that Bletchley’s needs were rapidly being met. And though he criticized Welchman for having violated the chain of command, he appointed an independent investigator to look into the B.P. administration.

For the cryptanalysts’ letter had revealed administrative stress. B.P.’s sevenfold expansion, from some 200 at the start of the war to 1,500 in early 1942, had rendered the creative anarchy of a small cryptanalytic bureau almost counterproductive. Services—housing, transport, and food—were faltering. B.P. also needed a stronger
hand to fight the intelligence directorates on priorities and personnel. Several power struggles had already been resolved by outside authorities, but a new and more serious one—whether the army and air force or G.C.&C.S. should control production of the solutions and their evaluation—came to a head soon after the letter went to Churchill. (The Admiralty had resolved this problem by setting up a close liaison between the O.I.C. and Naval Section.)

Many Bletchleyites blamed the chaos on G.C.&C.S.’s operating head. Alastair Denniston’s noncombative personality made it difficult for him to demand the resources needed to overcome these problems. He was perhaps a defender but not an aggressor. If his subordinates said they needed twenty bombes, he would say, “Well, one, maybe two.” Nigel de Grey, an assistant director of G.C.&C.S., as well as Frank Birch and others, agreed that Denniston simply could not cope. His era—one of a few eccentrics, of protecting his little domain from Whitehall’s bureaucratic rules, even of the country-house spirit of the early days—had passed. He was not the man for the job.

Menzies’s independent investigator reached the same conclusion, and in February 1942 a reorganization booted Denniston sideways. His title had always been deputy director; now another deputy directorship was created. An unhappy Denniston, removed from Bletchley entirely, became deputy director (C), handling commercial and diplomatic solutions from an office building in Berkeley Street, London. His deputy, Travis, a table thumper, a tough customer, a man whose ruddy face looked like “a carving in Spam,” who had come up through the codemaking side, where he had worked since World War I, became deputy director (S), for the armed services, at Bletchley. Travis was a man who, when his cryptanalysts asked for twenty bombes, said he would get them—and did so. Bletchley now had a manager who could bring it into the modern era of cryptanalytic mass production.

*     *     *

Another change occurred that same year, but it was more gradual. The energetic chess champion, Hugh Alexander, took over more and more from Turing as head of Hut 8. He had the taste and the skills for administration—the attention to detail and the ability to deal well with people—that Turing lacked. Once, wishing to get rid of a particular woman as head of a shift, he reorganized the three shifts into a complicated arrangement of five, adding two women to head the new ones; after a while, claiming that the new system was not working, he reformed them back into the original three—dropping the woman he did not want. Turing never had that subtlety, and though he felt the loss of the headship, he recognized Alexander’s superiority in it. Later in 1942, while Turing was in the United States, a form came to Hut 8 asking for the name of the head of the unit. “Well, I suppose I am,” said Alexander, and thereafter he remained in smooth control of solving the naval Enigma.

The capture of the Short Weather Cipher from the
München
let B.P. steal kisses from weather messages. Hut 10 did the necessary preliminary work. Its head was George C. McVittie, a tall, thin mathematician-turned-weatherman. Professorial, unkempt, with a fine head of hair and a high voice, always jolly, never upset, good to his subordinates, and with a mind that absorbed everything quickly, McVittie and his section of less than a dozen people attacked German meteorological ciphers to get information about the weather in and around Europe that would be helpful to British air and sea operations.

Among the systems they worked on was the
Kriegsmarine
’s weather cipher (not the same as the Short Weather Cipher). Messages in it were transmitted from various observation posts, including ships at sea, to a central point, sent from there to the great maritime radio station DAN in Norddeich, Germany, and broadcast on 150 kilocycles from the long, many-windowed building for the use of naval units all around Europe. The cipher was based on the International Meteorological Code. It represented such parameters as wind direction,
precipitation, barometric pressure, and temperature by figures in a particular order. The German cipher grouped these figures in threes and replaced each triad with a three-digit codegroup. These equivalencies were listed in tables, of which the Germans used five at a time, each one for a different class of message (ground observation or ship report, for example); they changed these five tables five times a day. Hut 10 first cracked this cipher in February 1941. This solution, combined with the capture of the Short Weather Cipher, allowed Hut 8 to solve Enigma messages. It worked the two ciphers like a crossruff in bridge.

The German navy’s high command had ordered U-boats to make weather reports. The submarines, like the weather ships, converted their observations into letters, using the Short Weather Cipher, and enciphered these letters with the Enigma. They radioed this cryptogram to Germany. Whichever radio station received it acknowledged receipt, stripped off the Enigma encipherment, and then forwarded it to a central meteorological station. Using the Short Weather Cipher, this center turned the letters back into meteorological data. Then, when it thought the information valuable, it enciphered these data in a German weather code and broadcast them to German ships at sea and posts ashore.

The British intercepted these broadcasts. Hut 10, having cracked the German weather codes, could reduce them to their meteorological plaintext version. It therefore had the same meteorological data that the U-boats were transmitting.

Now, using the Short Weather Cipher obtained from the
München
, Hut 10 could do what the U-boats had done: convert these data into letters, the plaintexts of the U-boats’ Enigma weather messages. These served Hut 8 as cribs to the Enigma encipherments. A chief problem was identifying the U-boat message that eventuated in the broadcast, but Hut 10 was able to do that often enough. One of the cryptanalysts, the dark-haired, mustachioed Philip E. Archer, dealt so frequently in these matters with Hut 8 that the naval cryptanalysts called the meteorological kisses—in the Bletchley word-play tradition—“Archery.”

When Bletchley solved intercepts about U-boats and passed them to the O.I.C., each sub was marked with a pin on the chart of the Atlantic in the Submarine Tracking Room. As successive intercepts came in, revealing new positions, the watchkeepers moved the pins. Sometimes the U-boats formed into wolfpacks; sometimes they stretched into long straggly patrol lines; sometimes they coalesced into loose gatherings heading toward one general area. The watch-keepers always viewed the sub pins in relation to the pins representing the convoys, of which usually eight or nine were crossing the Atlantic in each direction at any given time.

The United States was providing cargoes and convoy escorts to Britain, and every day the Admiralty transmitted to the Navy Department in Washington its estimate of German submarine positions in the North Atlantic. The data came from sightings, engagements, and torpedoings, from direction-finding, and—though this was not made explicit—from solutions of the U-boats’ own estimates of their positions. On the basis of this information, the Admiralty also sent the Navy Department proposed routes for forthcoming convoys. One such route, sent on October 8, 1941, was for convoy HX 155, scheduled to sail a week later from Halifax, Nova Scotia.

HX 155’s route was specified by a series of latitude and longitude points, each identified by a letter, through which the convoy should pass. The time for the convoy to be at the mid-ocean meeting point, or MOMP, where American escorts transferred control to British (and vice versa, for westbound convoys) was given in Z, or Greenwich Mean Time, the point itself being designated by the letter P. The Admiralty’s message read: “HX 155 route recommended (1) D 47–00 north 51–00 west, E 54–00 38–00, F 58–50 30–00, (2) 1000Z/25th October, (3) P 58–50 22–40, (4) Q 58–50 20–00, R 59–50 07–00.” A few hours after receiving the recommended route, the U.S. Navy told the Admiralty it concurred.

On October 12, five American destroyers were designated as Task Unit 4.1.7 and were ordered to “escort convoy HX 155 scheduled
depart Halifax October 16. Escort meet convoy on or to westward of 55 meridian west and proceed via such route as may be prescribed by Opnav [Operations Division, Navy Department].” The navy ordered the convoy to proceed at 8.8 knots. On Thursday, October 16, the fifty-four ships of HX 155 steamed out of the entrance of Halifax harbor and assumed a sailing order of eleven columns of four, five, or six ships each. The
City of Bath
was carrying copper and general cargo to Loch Ewe, Scotland. The
Margarita Chandris
, heading for the same port, had grain in her hold. The
British Chemist
was taking fuel oil to the Clyde, Glasgow’s river. Almost half the convoy was carrying some kind of oil—gasoline, aviation spirits, or other fuel.

At 12:55
A.M.
on Saturday, the five destroyers of Task Unit 4.1.7 left Argentia, Newfoundland, where, two months before, President Franklin D. Roosevelt and Prime Minister Churchill had met and signed the Atlantic Charter, in which they proclaimed their high moral purposes in opposing fascism. At 9:30 that morning, the lead destroyer spotted the convoy off her port bow. Under high clouds, pushed by a gentle breeze and pitching to a swell from the west, the escort joined the merchantmen, and both headed due east into the Atlantic.

Around midnight, they turned a little northward. After about four hours, they swung still more toward the north until they were steaming northeast. They continued on this course through Sunday, passing through the first specified location, Point D.

In Britain, Submarine Tracking Room chief Rodger Winn and his subordinates continued to read the teletypes of solutions from Naval Section, some of which gave submarine locations. The direction-finding stations sent in bearings on which they had heard transmissions. Direction-finding head Peter Kemp plotted the bearings on his own chart and informed the duty officer at the main plot of the results. (Kemp’s experience often enabled him to give the approximate location of a transmitter just by seeing the bearings sent in.) Winn pulled all of this together. From it emerged a U-boat estimate.

On the Thursday the convoy sailed, the report sent to the Americans estimated seven submarines in an area of the east central North Atlantic bounded by 53° and 57° north and 22° and 28° west. Four subs were thought to form a sparse line from Cape Farewell, at the southern tip of Greenland, southeast almost 300 miles. The next day, the seven U-boats had become “eight or nine” and their area had expanded north and west. The information was solid: eight ships from the unlucky convoy SC 48 from Sydney, Nova Scotia, had been torpedoed in that area. That convoy had been carefully rerouted past a U-boat concentration that Winn and his team had detected—but then had been spotted accidentally by a U-boat arriving to join a patrol line; among the ships attacked was the escorting American destroyer
Kearney.

This news perhaps increased jitteriness among the escorts, for at 3:10
A.M.
the next day, Sunday, the U.S.S.
Bainbridge
went to general quarters when it was reported that flashes, a searchlight, and possibly gunfire had been seen and heard broad on the port bow. But whatever these were, they proved to be a false alarm, and the destroyer secured from general quarters ten minutes later. The convoy continued northeast. The submarine report that day merely stated that U-boats were “probably” in the same area as before, and the report of the next day showed Winn’s predictive abilities when it stated that “Admiralty presumes U-boats recently southeast of Greenland and those pursuing SC 48 about to take up new dispositions. Trend to westward thought likely.”

Perhaps as a consequence of this report, the Admiralty recommended that HX 155 change its route to pass through two new points, H, at 50° 00′ north 46° 30′ west, and J, at 57° 30′ north 40° 00′ west. This would shift the convoy’s march 165 miles to the west of the abandoned Point E, keeping it that much farther from the U-boat concentration. But HX 155 did not make this diversion until noon on Monday, October 20. Of course, the move sent the convoy closer to the U-boats that Winn had aligned southeast of Cape Farewell. But since there were only four of them, and their distance apart averaged
75 miles, far greater than the maximum visibility of 13 miles from the top of a conning tower, the danger seemed much smaller than that from the mass of U-boats that the Submarine Tracking Room was trying to avoid.