Seizing the Enigma: The Race to Break the German U-Boat Codes, 1933-1945

by Kahn, David

  As a boss he was less successful, some thought. Birch was a Prussian in his directing style, which didn’t work very well at Bletchley. He never encouraged: if the cryptanalysts got stuck, he’d come in at once and demand, “What’s wrong?” A poor judge of people, he played favorites. Knowing that he would probably be unable to get a knighthood because of wartime secrecy, he sought his reward in power: he liked results that he could display to the admirals. Once he admonished his cryptanalysts, “Don’t tell Hut 3 [the army and air force cryptanalysts] about this.” But although he was not the best leader of the 200 people eventually in his section, and although an element of ruthlessness and prejudice limited the number of his friends, he could be kind. After one of Knox’s young women assistants had been married three days, Birch took her into the operations room. Just as her husband’s convoy was being pointed out to her on the plot of the Atlantic, a U-boat symbol was put down next to it. Birch put his arm around her. “We’ll send the whole navy,” he said.

  Many of the positions immediately beneath these senior levels, such as the heads of huts or the heads of shifts, were occupied by new recruits. Some came, as Turing did, through the King’s College connection. Conel Hugh O’Donel Alexander, called Hugh, was a mathematician with a powerful intellect and extraordinary vitality. A former British boys’ chess champion, he had gained first-class honors in mathematics at King’s but not the star for exceptional distinction that he wanted. He attributed this to having played too much chess, which was probably an accurate assessment: he won the university championship his first year and every year after that but one. Nor did he succeed in becoming a fellow of King’s. Instead he taught mathematics at Winchester, one of England’s great public schools. Then, at the urging of his wife, a cosmopolitan, not to say Bohemian, Australian who had lived in Paris, he took a job in an elegant London’s men’s clothing store where the owner, a chess fanatic, maintained the London Chess Center. It was a ridiculous move, friends thought. As a member of the British chess team, Alexander was in Buenos Aires for a competition when war broke out. With mental visions of London in flames, he returned home. Early in 1940, he joined the team at Bletchley and was assigned to work in Hut 8, the naval cryptanalysts, under Turing.

  Here he became a remarkable asset. His intellect was powerful—one of his coworkers later said that “Alexander was one of the most intelligent people I’ve known, and I’ve known a lot of intelligent people”—and his vitality extraordinary. A lively, talkative, enthusiastic person, he incorporated several contradictions. Though he worked in the solitary pursuit of mathematics, he dealt with people extremely well. He proved an excellent organizer and administrator though he was personally untidy: his desk was a mess, he dressed sloppily, his hair was all over. And though not good at most ball games, he played table tennis in an ungainly but effective way, rarely letting a ball get past him. He soon became Turing’s chief assistant.

  One of Alexander’s great friends was Stuart Milner-Barry, the Times’s chess correspondent, who had preceded him as British boys’ chess champion, had played chess with him at Cambridge, and had been a member of the team that went to Buenos Aires. When Milner-Barry arrived later at Bletchley, he was very glad to see his old friend. But it was through Welchman, not Alexander, that Milner-Barry got to B.P. He and Welchman were exact contemporaries at Trinity College, Cambridge, had later lived in Cambridge at the same time, and had played tennis together often. Soon after the war started, Welchman thought that Milner-Barry, a chess player, would do well as a cryptanalyst. So he recruited him. And shortly after Milner-Barry joined G.C.&C.S., he began recruiting others, driving his little blue Austin 7 to pick them up.

  In other cases, chance and mystery played roles in obtaining people. Because Leonard Forster had gotten along better with his German master than his French at his public school, he specialized in the Teutonic tongue, took his degree in it at Cambridge, spent four years working and studying in German-speaking lands, and finally returned to Britain to instruct at Cambridge. One day in March 1939 he was summoned to a briefing in Broadway Buildings; he never found out how he came to be invited. He took the introductory course in cryptology that G.C.&C.S. gave and went to London a few times in the spring and summer to help solve a simple two-letter German code. When war came, he went straight to Bletchley, vanishing into an organization that was one of the great unseen fighters of the war.

  But neither the recruiting of Britain’s best brains, nor the remarkable breakthroughs of Turing and Welchman, nor the occasional solution of the Luftwaffe Enigma led to the cracking of the naval Enigma. Then, as sometimes happens in war, help came from an unexpected source.

  8

  THE ROTORS

  IN THE FALL OF 1939, SOON AFTER WORLD WAR II HAD BEGUN, Lieutenant Heinz Rottmann, a slender, energetic, twenty-five-year-old naval careerist, was summoned to the U-boat fleet. The summons came from the man who had captained the cruiser Emden during Rottmann’s officer training cruise a few years earlier and who now commanded the entire U-boat fleet, Captain Karl Dönitz. He gave Rottmann his choice of the U-33 or the U-34. Rottmann chose the U-33, a three-year-old Type VIIA submarine because he knew her skipper, Hans von Dresky, from the Emden and because he liked her number.

  Before Rottmann joined, the U-33 had sailed on an operational cruise—she had actually gone to sea in anticipation of hostilities and was in her patrol area when Dönitz instructed his U-boat captains to “commence hostilities against England at once.” She had sunk three ships and, at her berth in Wilhelmshaven, had been given the highest mark of esteem to which the members of a U-boat crew could aspire: a visit from the Führer himself. Rottmann participated in the U-33’s second cruise, in which she laid mines and sank some trawlers. Then the 700-ton, 212-foot-long submarine was returned to her builder, Germania Werft in Kiel, for an overhaul that included the replacement of a bad diesel.

  Finally, in early February 1940, she was ready to sail again. At about 2 A.M. on the fourth, she was lying at a wharf in Wilhelmshaven’s solidly frozen harbor, with sailors and longshoremen loading provisions and munitions, when she rapidly and unexpectedly listed 15 degrees to port and dipped by the bow. Water and ice poured through a torpedo hatch into the bow area. One of the seamen ran to the control area and blew all ballast tanks, thus preventing greater problems. At about that time the engineer, Lieutenant Commander Friedrich Schilling, came on board. He concluded that the damage was minor and controllable and, in the morning, when he reported the incident to the submarine’s commander, Dresky ordered the vessel to depart on schedule.

  At 8 A.M., Dönitz came to the dock to see the U-33 off. To the newspaper reader, to the average German watching the newsreels in the cinema, even to some members of the Kriegsmarine, a submarine was just the letter U followed by a number; the subs under these impersonal designations seemed indistinguishable. But to Dönitz, each number summoned up the face of the U-boat’s commander, as well as her officers and crew. Each ship was an individual, with her own characteristics, temperament, and qualities. Dönitz saw, rightly, that in addition to making operational decisions such as where to concentrate his boats for the greatest effect, his chief job was to inspire “his” crews, to make them want to do their best for him in their dangerous tasks. So he went down to the harbors to send them off and to greet them on their return. And the crew of the U-33 did not forget that he had come on that wintry morning to wish them a successful cruise.

  Of those forty-two men, only four were new. Most were regular seamen; many had been together since the submarine’s 1936 launching, and they had been forged into a team by sharing the thrills and the fears of combat. Time had expunged any lingering claustrophobia: they were used to being enclosed underwater. Morale was good—despite the captain. His first two patrols were successes, but Dresky, tall, with a thin beard and a pointed nose, was not an inspiring leader. He was introspective, too serious, too quiet, and not enough of a driver or daredevil to win the full respect of his youthful, eager crew.
Moreover, he hoped on this voyage to sink one of Britain’s giant ocean liners, the Queen Mary or the Queen Elizabeth, or some capital ship of the Royal Navy, as Günther Prien had sunk the Royal Oak in Scapa Flow four months earlier; he felt that his destiny depended on how well he did. The sense of fate constrained his command. And his men smelled it.

  Their baleful feelings grew when the U-33 had difficulty getting out of the harbor. Heavy pack ice forced her back several times. Not until an icebreaker and a freighter preceded her did the U-33 succeed in passing the bar. It was an inauspicious beginning.

  Once out in the tumbling, windy North Sea, the crew discovered the cause of the earlier listing: water had come in through two holes, one the size of a thumb hole in the port torpedo tube, the other a quarter-inch accidental drill hole in a copper pipe. The leaks were stopped with a wooden wedge and with rubber until the U-33 reached Heligoland, the cliff-sided German island and naval station in the North Sea. There she lay over for several days owing to thick fog, and the holes were sealed better. But the repairs were not properly completed, and this intensified the crew’s foreboding: they could not forget the three days they had spent on the bottom repairing a diesel during the first cruise.

  Finally, at 4:30 in the wintry afternoon of Wednesday, February 7, the U-33 cast off from a tug that had towed her out to sea and began her third war patrol. She moved on the surface in the darkness at 12 to 15 knots; with the coming of daylight, she settled to the bottom, even though she was still within the vast German minefield that protected the north German ports from the Royal Navy. When night fell, she surfaced and headed northwestward, engines running strongly at 85 percent of capacity. Once, to the east of Scotland, her lookouts’ hearts stopped as they spotted several destroyers, almost certainly British. But the warships did not see the low profile of the submarine, and she continued undisturbed. She curved north around Scotland, taking the Fair Isle Passage between the Orkneys and the Shetlands. Three or four times her lookouts warned of aircraft, but again the submarine was not sighted.

  On the morning of Sunday, February 11, she headed south into the entrance of the North Channel, which divides northern Ireland from Scotland. The channel swarmed with ships, both illuminated and darkened; lighthouse beacons swept over the waters. As it grew light—around 9 A.M. in those northern latitudes at that time of year—Dresky put the U-33 on the bottom in 200 feet of water. He planned to surface at darkness and to race at top speed as close as possible to the entrance to the Firth of Clyde, one of Britain’s busiest estuaries and the home of the nation’s most important shipbuilders. There he would again settle at daylight, surface at night to sow the mines the U-33 was carrying, and then get back to the open Atlantic before dawn.

  It was cold and damp in the boat. The heating, not very strong in any case, was rarely turned on because it used up precious electricity. The sailors could see their breath when they spoke. Condensation ran down the bulkheads. But the men were well dressed. Their shoes had thick cork soles; they wore heavy underwear, and the elastic cuffs of their leather jackets and pants gripped wrists and ankles to retain body heat.

  The day passed slowly. Little could be done for fear of making too much noise. Finally, night brought the tedious Sunday to a close, and Dresky put his plan into operation. On the surface of the black waters, visibility was about half a mile. Around 2 A.M. of February 12, the U-33 Passed a huge shape, probably a heavy cruiser at anchor. The lookouts did not spot her. Below decks Schilling, the engineer, checked the machinery. Everything seemed in Ordnung: batteries at 161 volts at 30 degrees centigrade with 34 millimeters of acid. At 4 o’clock, he climbed to the conning tower. Dresky told him of the cruiser they had passed and said, almost as if it were a joke, that just now a destroyer was speeding toward them.

  It was not a destroyer but a minesweeper, H.M.S. Gleaner, which had been on night patrol at the 15-mile-wide entrance to the Firth of Clyde. Under instructions to watch along the 25-fathom contour, her captain, Lieutenant Commander Hugh P. Price of the Royal Navy, a hydrographer, sailed a right triangle, one apex of which was near the rocky islet Ailsa Craig, which rises abruptly 1,100 feet from the sea to a conical summit. At 2:50 A.M., as the vessel was steaming on the due-south leg of the triangle, the seaman listening on the hydrophone reported hearing a strong sound from slightly off the Gleaner’s starboard bow. The officer on watch brought the 4-inch gun and the depth charges to the ready, altered course toward the object, which had moved to off the port bow at a range of almost 2 miles, and called Price.

  On the bridge, Price heard strong hydrophone noises that sounded tonk, tonk, tonk, tonk at a rate of about two a second. He swung toward the moving object and increased speed to 16 knots. At 3:16 the range increased slightly, but thereafter it decreased. He swung his vessel to bring his searchlight to bear.

  Aboard the U-boat, just after Schilling saw the shadow of the surface vessel, he and Dresky went below. “Prepare to dive” rang out. The U-33 submerged. A moment later Price, observing that the target bearing was rapidly drawing aft, had the searchlight switched on. He spotted something that looked white—possibly spray from the submarine—but it disappeared almost at once.

  The light was seen aboard the U-boat, which had apparently then not gone entirely under. After she submerged totally, the crew heard each beat of the ship’s screw passing overhead from starboard stern to port bow. Price knew he was passing over the target, but trouble with the depth charges led him to wait until he could fire a pattern instead of dropping the charges haphazardly. In the submarine, Dresky ordered a dive to 125 feet, but the vessel had reached only 80 feet when the Gleaner, which had circled around and made contact again at 3:53, fired a pattern of four depth charges that exploded at 150 feet, not far from the U-33.

  The detonations shook the U-boat. Its lights went out. With the booms, the crew members ducked their heads and hunched their shoulders. The emergency lighting came on but could barely penetrate the dust, thick as fog, that the explosions had kicked up. None of the men screamed; no one cried; no one dirtied his pants. Their earlier attacks had toughened them, and their comradeship sustained them. From all parts of the vessel then came the reports of damage. The rudder and diving plane indicators had failed. All depth indicators were broken. There were two leaks. The starboard electric motor was sparking. The gauges of the rear electrical control panel were burned out. The gyro compass had reversed itself. A welded seam had torn. But all in all, the damage was not great. The crew began to replace the broken light bulbs. Dresky ordered the crew to put on their escape apparatus, then: “Absolute silence in the boat. Put her on the bottom!” And the U-33 settled to the sea floor. The men took off their shoes and spoke only in whispers.

  On the Gleaner, the shock of the explosions briefly extinguished lights and caused her to lose contact with the submarine. The reloading party was having difficulty because the ship canted from side to side as Price turned her in giant figure 8’s to remain over the target. At 4:12 he fired another pattern. In the U-boat, extra machine parts were flung from their holders. More bulbs failed. Both diesel exhausts began to leak. Dresky asked Schilling what they should do; the engineer proposed trying to sneak away under water. When Schilling started the pumps to force water out of the ballast tanks to increase buoyancy, however, Dresky ordered them stopped because they made too much noise. But the submarine, with 2 tons of negative buoyancy, could not free herself from the bottom by her propellers alone.

  At around 4:40, the Gleaner approached for another attack. Schilling started the pumps, apparently thinking there was little to lose, but Dresky canceled the order. Five more depth charges rocked the submarine. The men remained unshaken. Lieutenant Johannes Becker, the second watch officer, sipped a beer in the torpedo room. “Water coming in!” was reported from astern. Rottmann went back to investigate. In the diesel room, the machinists were sitting on the equipment so their feet would not get cold. They looked at Rottmann’s face when he came in to get a clue as to the condition of the
boat. He put on a neutral expression so as not to frighten them. He need not have worried. Many seemed to have the same feeling that Machinist Ernst Masanek had about himself: “Don’t worry. You’ll get out of it all right.” Rottmann reported that only a connection between two internal tanks had been torn and that water was running into the bilges.

  Dresky then ordered Schilling to get the submarine off the bottom. There was no point in awaiting the next attack and the next and the next. But once the submarine was moving, then what? The man at the helm said that escape was not possible, that all they could do was save the crew. Schilling pointed out that traveling submerged in those narrow and shallow waters, which were streaming at 6 knots, was extraordinarily difficult. Dresky agreed and concluded that surface travel offered the best chance of escaping. He began preparing for this, ordering the first watch officer to ready the mines for discharge and the second watch officer, Becker, to prepare the secret materials for destruction.

  The most secret item was the Enigma cipher machine. Becker knew that the rotors were its heart and that the machine, if recovered by the British, would have little value without them. So he took the three in the machine and the five others in their wooden box and distributed them among a few crew members, including Rottmann, Lieutenant Karl Vietor, and Machinist First Class Fritz Kumpf. He instructed them to drop the rotors into the sea as soon as they went overboard. Meanwhile the crew members prepared themselves for immersion in the frigid water by dressing in as many layers of clothing as possible. This would tend to hold the water that was warmed by their bodies near them and prevent their being chilled by cold water flushing past their skin. Rottmann put on, over his underwear, his pullover and service trousers, a coverall, a leather jacket, leather pants, fur pants, and his escape apparatus.