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

by Kahn, David

  Meanwhile, Baker-Cresswell was reporting that he had captured a U-boat, that she appeared to be taking water, that he had no one who could read German to fix her, and finally that he was taking her in tow to bring her to Scapa. But just as he started to attach a 3½-inch cable, and while the boarding party was aboard the submarine, news came that two ships of the convoy, which by now had steamed out of sight in the decreasing visibility, had been torpedoed. The submarine that had done this was being attacked by the ships of Escort Group 3 that had remained with the convoy. Soon the Broadway and the Aubrietia obtained an asdic contact with a presumed submarine and began dropping depth charges. Then lookouts on Baker-Cresswell’s own Bulldog shouted that they had seen a periscope. Baker-Cresswell slipped the tow to the U-boat and searched for the new submarine, with no success.

  Gradually the excitement subsided, and the Bulldog resumed the tow. The U-boat seemed to keep turning to starboard, perhaps a consequence of the slow turning of her port motor. But this, though a nuisance, did not prevent the Bulldog from increasing speed to 4 knots. Baker-Cresswell ordered all watertight hatches and doors to be closed on the submarine and the boarding crew to rejoin his ship. At 6:30 all were back, and the towing speed was increased to 6 knots. By 7 the next morning, however, the wind had become a strong breeze of up to 30 miles per hour and blowing from slightly south of west as the Bulldog headed northeast in a lumpy sea. It proved impossible to hold this course, so Baker-Cresswell let the submarine head downwind, a position in which she seemed comfortable, and kept the towing wire taut. Suddenly, at 11 A.M., the U-110, which had been settling by the stern, started to sink more rapidly. Soon her bow reared to the vertical. Baker-Cresswell had the towing line cut with an ax, and the submarine slid beneath the surface.

  It was a terrible moment for Baker-Cresswell, who had badly wanted to bring his prize into port. He felt that the U-boat, having withstood so many shocks, should be able to stand the 400-mile tow to Iceland, then Scapa. But his disappointment was ameliorated when he examined the two packing cases of material from the boat that had been stored in his cabin. Of the many books and documents, he thought that the Kriegsmarine grid of the seas of the world was the most valuable. But he recognized the Enigma as “a typewriter for ciphering,” and he consoled himself for his disappointment about the submarine: “At least I’ve got the cipher.” It was what he had hoped for: a World War II Magdeburg.

  His satisfaction increased soon after his arrival at Scapa Flow. Bletchley sent two men with a single briefcase to examine what he had captured and to bring back the most important items. They were stunned at the quantity and ecstatic over the quality. “I never thought we’d get any of this,” one of them gloated to Balme. They dried off some of the documents and photographed the most important items, in case their plane crashed as they were bringing the originals back to Bletchley. They had special containers made because they had so much to take. On May 13 they gave the codebreakers of Hut 8 an unbelievable trove of cryptographic treasure: key tables not only for general-grade Enigma messages but also for officer-grade, the procedures for enciphering officer-grade and staff-grade messages, the indicators book, one of the books—codenamed BACH (“brook”)—for enciphering the indicator bigrams, the directions for the cue-word system for changing settings in case the originals were compromised or feared so, and the U-boat Short Signal Book.

  The value of these documents and those from the München was shown dramatically. On May 21, before the June keys took effect, Hut 4 was teleprinting translations to the O.I.C. with an average elapsed time from interception of eleven days. Luck or ability lowered this average to thirty-four hours on May 28. But then no translations were sent for the next three days, suggesting that no intercepts could be solved. When the seized keys came into force, however, the interception-to-teleprint time fell sharply. A German cryptogram intercepted at 18 minutes after midnight on June 1 was forwarded to Hut 8, deciphered there, translated in Hut 4, and sent to the O.I.C. by 4:58 A.M. And for the rest of the month, except for a few aberrations, the interception-to-teleprint time averaged around six hours. Thanks to the captures of the München and the U-110, the British were reading German naval messages practically as fast as the Germans themselves. But how long could this situation last?

  14

  “ALL THIS RUBBISH?”

  EVEN THE REMARKABLE SUCCESSES OF THE TWO SEIZURES—THE München planned, the U-110 a windfall—slake did not slake the needs of Naval Section. When the captured keys expired, the cryptanalysts would face delays of forty-eight hours in solutions. They enjoyed none of the shortcuts to solution, such as cillies, that the cryptanalysts of the Luftwaffe Enigma did, and almost all of their cribs had to be run on bombes, which were in very short supply. Yet they had to try to stay current. Harry Hinsley reluctantly concluded that another operation, similar to that against the München, would have to be mounted.

  He scanned the patrol rhythms and positions of the several isolated weather ships and concluded that the Lauenburg offered the most fruitful target. On June 19, he wrote that she had departed Trondheim during the night of May 27–28 to take over from the Sachsen, which had been on station for more than six weeks. “Evidence of her predecessor’s patrol suggests that Lauenburg intends to be out after the end of June,” he wrote. The “evidence of a tendency to overstocking with cypher material … suggests that Lauenburg, leaving in the last few days of May, will be carrying keys both for June and July.”

  According to the ship’s intercepted weather reports, she was working much farther to the northeast in the Norwegian Sea than the München had: along 72° north sliding between 1° and 4° west, within the German naval grid square AB 72, an area used by previous weather ships.

  For the German need for meteorological data from the Atlantic could not abate until Hitler’s forces had conquered Britain. The Kriegsmarine continued to convert fishing trawlers to mobile observation platforms. The Lauenburg was one of the newest—only three years old—a 136-foot-long motor-driven fishing vessel of 344 tons. She bore the proud name of the capital, 30 miles up the Elbe River from Hamburg, of an ancient former duchy.

  Retained as her captain when she entered naval service was Hinrich Gewald, fifty-eight. Corpulent, stolid, taciturn, he had always lived in the East Frisian village of Westrhauderfehn, on the flat German fenland not far from the Dutch border, a region that sent many of its sons to sea. He spoke the Plattdeutsch dialect, some of whose words are more like English than high German: German dass (“that”) became dat, Schiff (“ship”) became Schipp, gross (“big,” “great”) became grot.

  Like his father before him, Gewald became a fishing captain. In 1926 he gained a modicum of fame when he was mentioned in a book about fishing by Adrian Mohr, who had sailed aboard Gewald’s boat the Dortmund. It was probably the captain’s ability to navigate well in the far north, which poses special problems, his prowess in sailing among icebergs, and his World War I naval experience that commended him to the navy to continue to command the Lauenburg.

  His crew of twenty-two men included three petty officers and three sailors from the navy, among them Georg Klarman, twenty, who manned the 3.7-centimeter gun. The others manned guns, worked the radio, and made the weather observations. Many of the nonnaval crew members had, like their captain, served aboard civilian fishing vessels. The baker, Kurt Braun, born twenty-four years before in the East Prussian seacoast town of Frauenburg, had sailed aboard several other fishing vessels before coming to the Lauenburg. Morale was good aboard the ship, though its members had not shared the common experiences that weld a bunch of individuals into a team.

  Such were the vessel, the master, and the crew that sailed from Trondheim on May 25 (not on the twenty-seventh, as Hinsley had estimated). They reached their observation position within a few days. It was the Lauenburg’s first patrol, but she soon settled into her daily routine. The crew stood watch. Braun baked fresh bread daily. Lookouts watched for icebergs and other dangers, such as enemy ships. The meteorol
ogists transmitted their observations twice a day, between 6 and 6:40 A.M. and between 2:10 and 2:20 P.M., to the big radio station at Kootwijk, in central Holland. At 6:41 A.M. (British time) on June 27, she transmitted her first condensed weather report, prefixed with the required WW, on 12,040 kilocycles. The second, with the same prefix and on the same frequency, went at 2:11 P.M.—apparently the favored time, since for at least three days in a row she radioed at that same minute.

  From time to time Captain Gewald shifted the Lauenburg’s position. Between June 6 and 19 she moved west along the 72nd parallel from 1° to 4° west longitude, occasionally slipping up to the 73rd parallel. At that latitude, more than 300 miles north of the Arctic Circle, and at that season, only days before the summer solstice, the sun turned incessantly about the ship, never setting, merely dipping in the north. At times, brash and growlers and full-sized icebergs covered the sea. To the west and north, the Lauenburg’s crew could sometimes see the edge of the permanent ice pack, a low white line glinting on the horizon. The sailors did not spend all their time working. Some caught seals, some read the books that had been brought aboard for their entertainment; some looked at the pornographic postcards they had slipped under their pillows.

  Hinsley’s memorandum of June 19 about the Lauenburg, with its implied recommendation that the ship be the target of the next operation to seize cipher material, went to the Admiralty, perhaps via Captain Haines, the liaison officer. The concept passed rapidly through the normal channels of the Plans and Operations divisions, and soon orders were issued that a task force be created to board the Lauenburg and grab the secret documents. To make sure that no important documents aboard the target vessel were overlooked and to scan the captured papers not only for cryptographic documents but for any others that might be of value, B.P. assigned one of its staff, Royal Naval Volunteer Reserve Lieutenant Allon Bacon, to sail with the task force.

  Bacon was a member of naval intelligence’s Section 8G, which liaised between the Naval Section of B.P. and the Admiralty; he dealt particularly with captured documents. A yachtsman who had made his money in the City, London’s financial district, he was a friend of Commander Malcolm Saunders, the head of 8G. Before the war, he and Saunders had sailed his yacht to Kiel with a couple of Royal Navy radio operators belowdecks and had intercepted enough Kriegsmarine traffic to give British cryptanalysts more depth for an attack on some cryptosystem. Rangy, dark-haired, round-faced, and very handsome, he knew some German and something about the sea and got on well with naval officers; because of this ability, and because of his job specialty and his intelligence and resourcefulness, he was picked for the Lauenburg operation.

  The head of the Home Fleet assigned the task to the commander of the Tenth Cruiser Squadron, Rear Admiral H. M. Burrough, sailing in the Nigeria, and gave him another cruiser and three destroyers with which to accomplish it. Two were powerful Tribals—the Tartar and the Bedouin—and one an even newer vessel, the Jupiter, on which Bacon sailed. But a collision with another ship caused the second cruiser to return to base, so only three destroyers and the Nigeria participated. All were at Scapa Flow. Burrough met with the captains of the destroyers and agreed on a plan of action, including procedures for boarding. At 10 P.M. on Wednesday, June 25, they cleared the antisubmarine booms of Scapa and set course for the Faeroe Islands, to the northwest.

  At Skaalefiord, the flotilla topped up with fuel while commanding officers and the heads of the boarding teams held final conferences. At 9:30 P.M. on Thursday, Burrough took his force out into the North Atlantic in rapidly declining visibility. He headed north at 21 knots, passing to the east of Britain’s main Faeroes-Iceland minefield. As he approached the island of Jan Mayen, a forecast of fog and ice impelled him to pass to the south and east instead of the west and north to reach the trawler’s reported position. This position was now at 73° north latitude, 4° west longitude, or some 300 miles to the northeast of Jan Mayen. The flotilla swung around the island and steamed north toward its unsuspecting target.

  The Tartar’s skipper, Commander Lionel P. (Kim) Skipwith, had come aboard early in 1940. In his mid-thirties, Skipwith was an experienced destroyer commander: the Tartar was his seventh command. He was rather an individualist. For relaxation he embroidered. He painted the wood in his cabin canary yellow and its deck a pale green—a refreshing change from the expanse of gray outside. A craftsman, he once modeled the Tartar beautifully in wood. He hated the Germans: during attacks on U-boats, he would sometimes stick one finger in the air to signal the gunners “Get me one dead German” as evidence of success if the sub surfaced.

  Despite this, he was reasonable. Once he warned the chief gunner’s mate that his gunners were striking matches at night. The mate replied that it was cold and they had to smoke, whereupon Skipwith gave permission for the mate to put a coil of slow match—a fuse that burned a yard every eight hours—in a bucket for them to light their cigarettes with. Perhaps for acts like this, perhaps for a tendency to bend the rules to get things done right, his men adored him. The chief gunner’s mate, an experienced career sailor, thought him the finest captain he had ever served under.

  He captained a vessel that was called “Lucky Tartar” by her flotilla mates because of her eerie success in avoiding damage. During the German invasion of Norway, the Tartar came out unscathed during air attacks that sank or damaged other British vessels. A year later, during the Bismarck chase, she escaped untouched when Luftwaffe bombing sank a sister ship. But she spent much time based at Scapa Flow as part of the Home Fleet, to block any movement of German naval forces into the Atlantic. And Scapa was awful. The wind never stopped. Ships constantly dragged their anchors. In winter it was never light, in summer never dark. There was nothing to do ashore except to walk or fish or—for the ratings—drink beer in a club. When other ships came in, the officers sometimes went over to visit with their friends. Occasionally movies were shown. Skipwith once mentioned that he hadn’t been ashore for 100 days and a young officer rashly told him that he had him beat because he hadn’t been on land for 101; the next day the officer, realizing that prudence was better than valor when it came to his commanding officer, yielded the record to Skipwith: he went to one of the islands around the harbor and took a walk for twenty minutes.

  The Tartar also put in months of patrolling, “basically hammering back and forth in this unfriendly sea,” an officer said, speaking of months of “gales endured on the open bridge.” It was “very dull, soul-destroying” work. Soon the Tartar had established two records: she was the first destroyer to spend 200 days at sea in World War II, and she was the first to have run 100,000 nautical miles since the beginning of the war. This comforted the crew members but little. Thought one:

  You don’t know what it was like, what with the cold and the wet and all. Sometimes, every time you jumped out of your hammock you’d land in water up to your knees. You were cold and wet and tired and hungry and scared and sick. You were always being thrown about. Sometimes you couldn’t stand upright for weeks on end. It was awful. And you’d think, “I’ll never go back to this.” And when you were on leave, at home, and it was almost up, you’d think of your mates, and you’d think, “I can’t let them down”—and you’d go back.

  The raid on the Lauenburg was a change from the routine. “It was a welcome relief to be doing a particular thing,” one officer said. The men did not know their target’s name, or the secret purpose of the attack, only that they were going after a trawler.

  After skirting Jan Mayen, the four-ship flotilla turned due north at 2:40 A.M. on Saturday, June 28. A few hours later, it swung to northeast by east. At 11:15, the Nigeria, the flagship, tested its close-range weapons; the Tartar tested her antiaircraft pom-poms.

  Burrough, meanwhile, reconsidered his plans. He had intended a sweep from west to east, like the one that had worked so well with the München. But the position of a fog bank, and the presence of icebergs, meant that this course would require the ships to steam through the ice in t
hick fog. So Burrough decided instead on a south–north sweep, hugging the fog bank to port. At 12:08 P.M. he ordered the ships to form a line abreast west to east, guiding on the Nigeria, in this order: Jupiter, Nigeria, the Bedouin, Tartar. They were to spread out to the limit of visibility or to asdic range, whichever was greater. They were to close toward the Nigeria when fog was sighted ahead and to open out in clear spaces. If they did not find the trawler by the completion of the search—a time to be specified later—the Nigeria would signal a new course and speed and then start a new search. Burrough ordered that when the trawler was sighted, the shells fired should not be high-explosive but practice ones set to burst above the target, as these would persuade her crew to abandon ship while not endangering the precious documents that the British were working so hard to obtain. When Skipwith told the chief gunner’s mate, Thomas R. Kelly, a wiry, intelligent hand, that “I would like you to fire at the ship but not hit her,” Kelly cheekily replied, “Christ, that should be easy.”

  All the ships had boarding parties made up, with the men given belts and pistols and trained for the job. The Tartar’s was composed of some ten tough former merchant seamen who enjoyed a fight and who were under the command of an officer, with Kelly as second in command.

  At 1:50 P.M., the Nigeria altered course to due north. The destroyers followed. At 2:02 Burrough signaled the flotilla to “Spread as previously ordered” and to steer “Course 000 [due north] speed 18 knots” until the first sweep was to end, at 9:30. At 2:15, the destroyers spread out to visibility range—some 6 or 7 miles at the time—and the search began.

  Aboard the Tartar, Skipwith posted lookouts on the bridge and in the crow’s nest. He announced to his ship’s company, “We’re looking for a weather ship that’s giving the German bombers information to bomb your homes. So keep your eyes skinned for it.” The gunnery control officer, Lieutenant Henry Durrell, a former merchant service officer, offered a pound to the first member of the crew to spot the trawler. He was himself perched in the director tower, a housing high up on the mast for the range finder, and so had a good chance to win his own bet.