Codebreakers Victory (14 page)

The
Scharnhorst
and the
Tirpitz,
the last two of Germany's battle cruisers, were hiding out in Norwegian harbors, ready to sail out and ravage convoys headed for the USSR. At Christmastime in 1943 the Germans decided to unleash
Scharnhorst
for an attack on convoy JW55B. Donitz, succeeding Raeder as commander in chief, was sensitive to the plight of German soldiers now being battered on the Russian front and wished desperately to stanch the flow of supplies to the Soviets. He believed he could commit the precious battleship because he had lulled Britain into more relaxed convoy protection by allowing recent sailings to pass through unmolested. Bletchley decrypts, however, warned of his plans. Although key German messages relating to the
Scharnhorst
were in the Offizier code, whose doubled encipherment slowed decryption, and were of little tactical value, BP did inform the escort fleet when the
Scharnhorst
put to sea. Further, the decrypts guided the British warships in placing themselves to intercept the German battleship when she did try to attack the convoy. In the early hours of December 26, a star shell fired from a British cruiser lit up the
Scharnhorst
instants before a salvo from the fleet's battleship, HMS
Duke of York,
slammed into her. Left burning, she was finished off by torpedoes from swarming destroyers. Of her crew of more than two thousand, only thirty-six men were rescued from the Arctic waters.

The final chapter of warfare against Germany's surface raiders was not written until November 1944. This was the struggle against the
Tirpitz.
Fear of this capital ship had caused the British to attempt repeatedly to put her out of commission. In March 1941 a commando raid against Saint-Nazaire succeeded in seriously damaging the only dry dock on the Atlantic coast capable of handling repairs of the massive battleship. In October 1942 the Admiralty sent across the North Sea a Norwegian naval officer in a fishing boat that had two manned torpedoes slung beneath it. The idea was to enter the fjord where the
Tirpitz
was berthed and aim the torpedoes at the ship. The scheme went awry when the boat encountered a squall and lost both the torpedoes. In September 1943 a fleet of six midget submarines was towed into position to glide in close to the
Tirpitz
and her escort vessels and detonate explosives beneath their keels. Three of the tiny subs made it through and, as Enigma decrypts later confirmed, made hits on the
Tirpitz,
so badly damaging her that the Germans did not expect to have her ready for action until mid-March of 1944.

When, repaired, the ship again became a danger, she was attacked and once more damaged, this time by carrier aircraft. A second carrier-planned sortie in July, meant to finish her off, met with increased antiaircraft fire and made no hits. But on September 15, 1944, RAF bombers operating from north Russia again put her out of action.

With Ultra decrypts carefully monitoring every stage of the big ship's latest repairs, the finale came when
Tirpitz
was once more reported ready for raiding. On the twelfth of November, thirty-two British bombers, each carrying a single twelve-thousand-pound bomb, took off from Scotland. At least two of the bombs hit the
Tirpitz
and capsized her. German sailors, hopelessly trapped within the inverted hull, were heard singing the German national anthem, "Deutschland Uber Alles," to their last breaths. "What a tragedy," one observer commented, "that men like that had to serve the Nazi cause."

Removal of this last threat of the surface raiders enabled the Admiralty to dispatch warships to the Pacific for the war against Japan.

 

 

Bletchley Copes with Shark

 

In February 1942, when everything had been going so well, Hut 8's intelligence feast abruptly ended. Up until then, both the surface ships and the U-boats had used a common cipher, called Dolphin by GC&CS. Now the U-boat command gained its own cipher, which the British dubbed Shark. It was not only a new code; it involved a change in the design of the U-boats' Enigma machines. This was a thinned reflector that allowed a fourth rotor to be added in its slot. Applied to the machines Donitz used in his communications with his Atlantic and Mediterranean U-boats, Shark plunged Bletchley into a ten-month blackout. During those long months, Hut 8 penetrated the new cipher on only three days—and each of these times only because of a German error in sending a message in both the Dolphin and Shark ciphers. Banburismus no longer worked. Turing's
EINS
catalogs were of no avail. The Submarine Tracking Room reported, "Little can be said with any confidence in estimating the present and future movement of the U-boats."

What made those ten months doubly frustrating was that by breaking codes other than Shark, BP knew a great deal about the U-boats: the commissioning of new craft and their trial runs in the Baltic, their expected performance, their armament, the experience levels of their commanders, their transfers to the west of France, even the times of their departures for active duty and their arrivals back in port. What was lacking was the most important information, in Hinsley's words, what happened "between the time they left harbour and the time they returned from patrol."

To make this long blackout period still more disastrous, B-Dienst was again gaining the upper hand in the contest of which antagonist was breaking the other's codes. The British Admiralty had switched to a new nonmachine code, but B-Dienst was readily reconstructing it. Donitz knew the schedules of the North Atlantic convoys and the courses they would take.

The Sigint seesaw had peremptorily swung back to the German side—at a time when Reich production was delivering increasing numbers of U-boats into Donitz's hands. In addition, he was receiving large "milk cow" supply submarines, each of which could deliver seven hundred tons of spare fuel and torpedoes, saving the U-boats the forty-six-hundred-mile round-trip back to their bases.

The consequences were muted for a while by the fierce winter of 1941-42, for its violent seas decreased the U-boats' effectiveness. When the weather moderated, however, Donitz and his commanders made up for lost time. They steadily increased their sinkings, while their losses of U-boats declined. The first half of 1942 resulted, again in Hinsley's words, in the U-boats' "greatest sustained period of success in the whole course of the war."

In view of the sudden inability of the convoys to steer clear of wolf packs coinciding with a change in code, the U-boat command might well have been tipped off that their earlier codes had been broken, if not for one momentous change in the war's course: the entry of the United States into the conflict. Four days after Pearl Harbor, Hitler had honored his Tripartite pledge to the Japanese by declaring war on the U.S. All that American shipping he had placed off-limits to the U-boats in order not to provoke the U.S. now became fair game.

As a result, instead of continuing to send his boats against the Atlantic convoys and finding them suspiciously vulnerable, Donitz directed his boats against the coasts of the U.S. and Canada. He did not have as many to dispatch as he would have liked. Many had to be diverted to the Mediterranean to help protect the supply lines to Rommel in North Africa. In addition, Hitler, still fearing a flank attack through Scandinavia, had ordered other U-boats to patrols in Norwegian waters. For attacks on U.S. shipping, the German admiral had only a "handful of boats, but they were the large, long-range Type IX craft now being supplied by German boatyards.

American unpreparedness enabled him to make the most of what he had. The U.S. could assemble few vessels suitable for escort duty, and the ones available were not assigned to convoy protection. The navy's head, Admiral Ernest King, did not approve of convoys; he preferred to go after the U-boats in open-sea hunts. These forays, however, proved fruitless. The U-boats simply hid out on the bottom until King's patrols had passed before rising to continue their slaughter of the busy traffic along the eastern coast. U.S. coastal cities, resisting the inconvenience and possible trade loss that would ensue from blackouts, kept their lights undimmed, providing the German prowlers neatly silhouetted targets. In just two weeks the U-boats sank twenty-five ships totaling more than two hundred thousand tons, a high percentage of them tankers, and continued the sinkings at roughly one a day. Crowds of watchers along the coasts witnessed the deadly pyrotechnics of exploding ships. Another "happy time" for the U-boats had begun.

If Dönitz's approach to sea warfare had a fault, it was in his belief that what mattered most was the tonnage sunk by his subs. Despite knowing that choking off British supplies in the North Atlantic was the real key to German victory, he was unable to resist the opportunities to pile up tonnage records elsewhere. His impressive statistics, it must be remembered, made for status-saving, job-preserving reports to Hitler. Yet while his U-boats were scoring easy points in U.S. waters, massive convoys were passing through to Britain almost unmolested.

Not until the summer of 1942 did the situation begin to change. By then Admiral King had given up the hunt missions and agreed to convoys. Coastal cities were blacked out. Plus, the navy established what it called its "bucket brigade." Tankers and merchant ships traveled up the coast in protected convoys by day and holed up in sheltered ports at night. The British helped by sending over escort corvettes and a squadron of RAF Coastal Command planes. Guided by visiting Britons, the U.S. Navy had begun setting up a Submarine Tracking Room similar to that of the Royal Navy. The happy time came to an end.

Dönitz rerouted his wolf packs to the North Atlantic. With few U-boat losses and strong inflows of new boats, his fleet had grown four times as large as when Shark had been introduced. Also he had found a chink in the Allies' defensive armor. This was the "Air Gap," a distance of three hundred miles between the extremity of air cover from Newfoundland and Iceland and that extending from the British Isles. In this gap he formed his boats into "picket lines." Aided by B-Dienst's decrypts, the pickets could detect approaching convoys and alert other subs to swarm in for the kill. Before Shark, when BP was breaking the naval Enigma, only one in ten convoys was sighted by the wolf packs. Now with BP blind, they found one of every three.

The carnage in the North Atlantic marked the second powerful German surge toward victory. In the first of the new round of convoy battles, eleven out of thirty-three ships went down. In the two months of September and October 1942, forty-three ships were sunk. By November the losses soared to 743,321 tons, the highest figure for any month in the entire war. During 1942 more than eight thousand merchant sailors were killed. Two of the ships sunk were carrying U.S. servicemen to England, adding to the lives lost.

The same grim story held true for convoys trying to deliver armaments and supplies to the Soviet Union. Grimmest of all was the fate of convoy PQ17, which set out from Iceland on June 27, 1942. The convoy was attacked in the Barents Sea by U-boats and aircraft. At that time the
Tirpitz
was still available as a raider. The convoy was given the misguided order to scatter. It didn't matter that the
Tirpitz
never got into the action. The U-boats and planes picked off the dispersed merchant ships one by one. Of the thirty-seven ships in the convoy, only thirteen reached Russian ports. As a result of the disaster, all convoys to Russia were suspended during the spring and summer of 1943.

The mounting destruction by the U-boats cast a pall of despair over news of the war that was otherwise turning in the Allies' favor. The British Eighth Army had defeated Rommel at El Alamein. The Allied landings in northwest Africa had surprised the Germans. The Germans' decision to occupy the whole of France had prompted the Vichy government to scuttle the French fleet at Toulon. But without Ultra's help, the situation in the North Atlantic was threatening to undo all the other triumphs.

Breaking Shark, Turing saw, required four-wheel bombes. Tabulating Machine Company engineers worked on their development, introducing some limited use of electronic tubes to speed their operation and race through the increased number of permutations introduced by the fourth rotor. Until these bombes could be delivered, Hut 8 could only wait. Luckily, an even harsher winter than the one preceding it slowed the U-boats in January and February 1943.

In March, however, they stormed back in force. During just the first twenty days, ninety-seven ships were sunk, with over half a million tons of supplies sent to the bottom. The official Admiralty verdict was that "the Germans never came so near to disrupting communications between the New World and the Old" as in those twenty days.

Behind the scenes, though, important changes were occurring. For one, the sheer productive might of the U.S. was tipping the scales. The Ships for Victory program was turning out standardized Liberty ships at a rate of three per day, enabling the Allies to produce more vessels than the Germans were sinking. The American merchant craft were faster, ensuring that convoys could move more swiftly. Escort patrol ships, aircraft carriers, destroyers and larger warships were being delivered by American shipyards. Recon aircraft with ever greater ranges were issuing from American factories in unprecedented numbers. Long-range American B-24 bombers were joining with British bombers to extend air cover over the convoys and close the Air Gap.

In addition, convoys were benefiting from British and American technology. Radiotelephones were installed to improve communications between ships and to coordinate their maneuvers. Escort vessels were equipped with their own direction-finding equipment to help them home in on lurking U-boats. Some larger freighters were fitted with airplane catapults, from which game pilots took off knowing they would, after their search-and-destroy missions, have to reach a land base or ditch near an Allied vessel in the hope of being picked up. Airborne radar and powerful new searchlights enabled Allied planes to detect and swoop in on U-boats traveling on the surface at night.