In the last two years of the Great War the British had learned that the most efficient way of moving vast quantities of supplies and manpower through U-boat-infested waters was to form their merchant vessels into protective convoys, numbering anywhere between thirty and seventy vessels, and then sail them across the ocean at almost a snail’s pace, zigzagging or rerouting as needed to avoid enemy submarines. The upside was increased security for these vessels: packed together and sailing with a naval escort of destroyers and corvettes (later joined by aircraft and aircraft carriers), there was safety in numbers. If warned in advance, the entire complement of ships could avoid a single U-boat (or a group of submarines working together as a wolf pack) or, in some cases, prepare for a fight. The downside was lost time—not only the slow passage but the wait to form the convoy, unload all the ships once they reached their destination, and regroup them for the return voyage. The convoy system certainly reduced the number of trips each ship could make in a year, but the British were willing to pay that price.
The Americans, however, stubbornly chose to send ships individually and without escort, leaving them at the mercy of roving U-boats and with little means of defence. Stifled by their own antiquated strategy, the United States Navy had initially rejected the convoy system, opting for speed rather than safety. Compounding this vulnerability, the Americans lacked sufficient air cover along the U.S. coast and were still lax about implementing the basic precaution of blacking out bright lights in cities and seaside communities along the Atlantic coast, making it easy for seasoned hunters like Bleichrodt to pick out their victims as they steamed past the shore, perfectly silhouetted. As Dönitz would later boast:
The U-boats found that conditions there were almost exactly those of normal peacetime. The coast was not blacked-out, and the towns were a blaze of bright lights … The lights, both in lighthouses and on buoys, shone forth, though perhaps a little less brightly than usual. Shipping followed the normal peacetime routes and carried the normal lights. Although five weeks had passed since the declaration of war, very few anti-submarine measures appeared to have been introduced. There were, admittedly, anti-submarine patrols, but they were wholly lacking in experience. Single destroyers, for example, sailed up and down the traffic lanes with such regularity that the U-boats were quickly able to work out the time-table being followed.1
It was a painful beginning to the war at sea for the Americans, while the German U-boat crews called it their “Second Happy Time.” But even harder times lay ahead after the Allies experienced that new kind of blackout they had been dreading: the silence that followed the introduction of the four-rotor naval Enigma to the Atlantic U-boat fleet on February 1, 1942.
Blissfully unaware of the submarine only 1,300 yards to starboard, Master Robert George, the captain of the Tacoma Star, believed that his ship led a semi-charmed life.2 Already sunk once in Liverpool harbour by a German bomb during the Blitz in 1940, she had lived to fight another day after being raised, repaired and relaunched.3 Now, as she steamed towards Liverpool on her way home from Buenos Aires with her cargo holds full and ninety-three souls on board, her legendary luck ran out. In just under three minutes, two of U-109’s three torpedoes fired from essentially point-blank range struck the forward hold and the engine room amidships, engulfing her in a giant detonation cloud that smothered the vessel for a long time. When she finally emerged, the mortally wounded vessel turned hard to starboard and settled fast by the bow.4 Sinking in less than four minutes, the steamer had the dubious honour of becoming the first of nearly one thousand Allied merchant vessels, totalling an unprecedented 7.1 million tons of vital shipping, sunk during the four-rotor blackout that lasted from February to December 1942.5
According to the report from U-109, the captain and his crew made it to their lifeboats, but in the panic before they abandoned ship they sent the wrong coordinates in their frantic distress call. Never seen again, the ninety-three souls on board the Tacoma Star joined close to ten thousand others whose names appear in the sombre lists of the missing and dead from the Battle of the Atlantic.
To boast of his success and arrange a rendezvous to restock dwindling fuel supplies, Bleichrodt sent a triumphant message to Ernst Kals, the captain of the nearby U-130, which, if Bletchley Park had been able to decipher it, would have provided near-perfect intelligence. “Just sank Tacoma Star,” he reported. “Please meet me earlier in CB 4965 at 0900 hours.” Kals quickly replied, “Can’t reach rendezvous point before 1500 hours.”6
Only twenty-four hours earlier, when the three-rotor Enigma was still in use on Dönitz’s submarines, the contents of these messages would have been gold for the Submarine Tracking Room. Located in the basement of the Admiralty Citadel, the brown fortress-style bunker attached to the Old Admiralty Building in London, the tracking room formed one annex of the Operational Intelligence Centre. There, women from the Royal Naval Service, the Wrens, placed coloured markers tracking the location of each German U-boat and every Allied ship or convoy at sea on giant wall-mounted map boards showing the world’s sea lanes. If they had been privy to the positions of U-109 and U-130, these U-boats would have appeared on the wall as well. Immediately, the analysts there would have sent messages to Western Approaches Command in Liverpool, and the alarm would have been repeated to tracking rooms in Canada and the United States. Other vessels could be rerouted or an “incidental” ambush by anti-submarine forces orchestrated, turning the hunters into the hunted.7 But without the intelligence, nothing happened.
In hindsight, the failure to take immediate and direct action against the potential threat posed by the four-rotor naval Enigma is likely the greatest miscalculation made by both John Godfrey’s NID at the Admiralty in London and Frank Birch’s Naval Section at Bletchley Park during the entire war. The combined effects of wishful thinking and a “wait and see” approach—something Godfrey railed against in others—led to a near catastrophe on the seas that rivalled, at least in material terms, the massive land battles of attrition on the western front during the First World War. The U-boats exacted a bloody toll on merchant shipping in much the same way that the machine gun and heavy artillery shattered the flesh and bones of infantrymen caught in a no-man’s land between trench lines. With high casualties incurred (and for what appeared to be little reciprocal gain in sunken U-boats), this stage of the Battle of the Atlantic stirred up the ghost from the brutal charnel-house land battles of Verdun, the Somme and Passchendaele a generation before.
Looking back on the struggle after the war, Winston Churchill noted: “I am sure that no one knows so much about dealing with U-Boats … as the British Admiralty, not because we are cleverer or braver than others but because, in two wars, our existence has depended upon overcoming these perils [and] when you live for years on end with mortal danger at your throat, you learn in a hard school.”8 The learning curve was steep. One week after the changeover from the three- to the four-rotor Enigma, few if any of the colourful submarine-shaped markers used to denote the position of individual U-boats on the map board in the Submarine Tracking Room remained. One by one, the Wrens returned them to their cabinet drawers alongside the Special Intelligence dockets marked Shark, which were no longer stuffed and sagging. Dönitz’s submarines had begun to fade from sight in the most vital of all theatres—the Atlantic Ocean.
Godfrey would later write: “The tracking of U-Boats is perhaps the most important of NID’s functions.” The demanding job of the talented analysts toiling in the dungeon-like atmosphere of the tracking room was to stay on top of current events and predict the future. Their ability to “foresee, day, week, month or even longer ahead” was their sole purpose.9 In addition, they had to know what was happening with their own warships, convoys, aircraft and enemy U-boats. Their work relied on piecing together countless clues and scraps of information to create a background of knowledge against which to judge and weigh probabilities. When available, Special Intelligence served them well, and indeed it had quickly formed the backbone of th
eir work. Now, with the four-rotor naval Enigma in place, the analysts had little current intelligence to draw from, which left them gravely disheartened, particularly when the sombre distress signal from a stricken Allied tanker, troopship or merchant ship, such as the Tacoma Star, became their only source material.10
The four-rotor was not the only problem facing Alan Turing and the cryptanalysts at Bletchley Park. The Germans had also introduced a new weather code book just days before the four-rotor appeared, and they followed that up all through February with new editions of other codes and ciphers as well. Cumulatively, these new versions of the lesser codes blocked Bletchley’s “backdoor approach” and, for the time being, effectively shut them out of cribs. From this point onward, there was a steady fade to black. It began with a “grey-out” in February, darkened quickly, and spread like a cancer, leaving the Submarine Tracking Room, the Operational Intelligence Centre and the Naval Intelligence Division to rely on an “estimate and guess” approach—or, in the term Godfrey coined, a “Working Fiction”—rather than the solid base provided by Special Intelligence that had served the English so well.11
During this “depressing period,” as the future head of Hut 8, A.P. Mahon, wrote, any message enciphered by the Germans on the new four-rotor device withstood the intellectual and electromechanical probes from the cryptanalysts at Bletchley Park.12 Nothing, at least in the immediate future it seemed, could fix the problem. Lamenting the situation, Mahon recorded, “Clearly we had lost the most valuable part of the traffic, and no form of cryptographic attack was available to us.”13 Shaun Wylie, who worked with Alan Turing in the hut as a crib specialist, recalled:
We knew it was coming. But it was a grim time. We were very much frustrated; the things that we’d hoped to use went bad on us. We realised that our work meant lives and it ceased to be fun. We did what we could, of course, and we got on with what there was, but we kept an eye out for any possibility on Shark [the new key introduced for the U-boat fleet] that might present itself. There was a lot of pressure and we were trying all we could but we didn’t have many opportunities. We had to get Dolphin [the principal key used by naval Enigma] out, but Shark was the prime target, the focus of our interest.14
When Rolf Noskwith, a German Jew who had escaped from Nazi Germany a decade earlier and a fellow crib specialist, was asked years later if the relative impotence and the resulting loss of life created a sense of guilt among the cryptanalysts, he soberly recalled:
While we knew the seriousness of the situation, I cannot say that we felt guilty. First, we genuinely felt that, without more captured material, there was no short-term solution. Secondly, we knew that there was a long-term solution because of plans, in collaboration with the Americans, to build more powerful Bombes capable of breaking the four-wheel machines. Thirdly, we were still regularly breaking Dolphin.15
With the exception of a few odd days in March, when Bletchley took advantage of cribs supplied by an operator’s mistake to decrypt already stale traffic (ironically, a message announcing Dönitz’s promotion to full admiral), Shark would remain impenetrable until a heroic chance pinch of material from the U-559 in the last days of October 1942.
Through that warm and unusually dry summer, the Bletchley Park cryptanalysts worked literally round the clock to break the four-rotor Enigma in the same way they had succeeded with earlier versions of the machine, but with no success. Although they attempted to solve their dilemma with the less-sophisticated three-wheeled Bombes they had in their arsenal, these proved much too slow to outwit the four-rotor Enigma. Even when the German operators’ occasional transmission mistake provided Bletchley with a few cribs, it took six of the three-wheeled Bombes working together for seventeen straight days to decrypt the settings for just one day of traffic, providing messages more than a month out of date. This usage was a nonsensical waste of valuable resources for little, if any, gain; the few precious three-wheeled machines were desperately needed to decipher message traffic encrypted on three-rotor Enigma machines from other theatres of war (at this point, the German high command had put the four-rotor machine into operation only in the Atlantic), so it made no sense to devote their time to a task that offered little chance of success.
The only solution was to race against time to build a four-rotor Bombe. But even then, until the British could pinch the new code books for the four-rotor machine and regain a flow of cribs, the four-rotor Bombes would be of little use against Shark.16
The reaction from Godfrey at the Admiralty, from Bletchley Park and from the Operational Intelligence Centre in London in the short term was to fall back on the still-breakable German home waters key (Dolphin) and on lower-level codes and ciphers. As the history of the OIC records, Special Intelligence may have been “by far the most important information received,” but at least for now experts there maintained the ability “to read German local signals relating to local moves or tugs, escorts, minesweepers, repair and supply facilities … [and] had knowledge of new construction, completions and exercises in the Baltic.”17 However, they knew that, as use of the four-rotor Enigma machine spread more widely throughout the German navy, these lower-level codes and ciphers would likely disappear incrementally in the intelligence equation. To meet that possibility, the OIC attempted to rely on other sources to fill in the blanks—aerial reconnaissance, for example, and other signals intelligence technologies and techniques the English were fast developing.
The most promising sources in lieu of cryptography for the Operational Intelligence Centre were high-frequency direction finding (HF/DF or Huff Duff) and very high frequency direction finding (VHF/DF) technologies, in either their shore- or ship-based forms.
These technologies could detect the general location of a vessel by intercepting its radio signals, but they could not pinpoint the specific location. Unfortunately, because the Germans suspected that the Allies employed such measures, they drastically restricted their radio time on air to the absolute minimum to limit the chances of being found. Even if they were located, the information would quickly grow stale unless Allied ships or aircraft were in the immediate area to take action, and after a few hours it likely became useless. In addition, the radio intercepts could not establish the direction in which the vessel was travelling; only if the Allies picked up subsequent transmissions could they confirm that they came from the same vessel and thereby know the direction of travel. All this sleuthing was more art than science—and to round out and properly interpret the findings, the cryptanalysts required a consistent corpus of evidence to draw on as needed.18
Bletchley Park also enjoyed limited success with the techniques of radio finger printing (RFP, where they identified specific transmitters by photographing the particular wave form) and TINA (where they analyzed the characteristics of the radio operator himself). On their own, as Godfrey noted, these techniques were “without operational value as far as the U-Boat war was concerned,” but they paid dividends with regard to large surface vessels such as cruisers and battleships.19 Combining these two sources of SIGINT—signals intelligence—offered a much better chance of identifying a particular boat and inferring from its movements its possible intentions, though again, Godfrey complained, “neither RFP or TINA was precise.”20 Moreover, all these methods lay at the mercy of ionospheric conditions and were further crippled by the fact that U-boats generally maintained radio silence. They used their radios only when they were near Allied ships or convoys, meaning that by the time the British picked up a signal, it was far too late for the hunted vessels to implement the avoidance strategies that had been so successful in the latter half of 1941.21
The other promising cryptographic weapon was something the British called “Tunny”—a dual code name given to the deciphered message traffic passed by non-Morse teleprinters called Hellschreiber and Geheimeschreiber and to the first analogue device developed in an attempt to decipher the encryption machines. Unlike the Enigma, which was widely distributed throughout the German army, navy and a
ir force, these teleprinters were rare and provided a direct and “secure” link for only the most sensitive strategic material passed between Hitler’s headquarters and his diplomats and commanders in the field, such as Dönitz.22 Eventually, Bletchley Park, much to Ian Fleming’s delight no doubt, would take the analogue machine light years ahead and develop the world’s first programmable computer, a monstrosity code-named Colossus. Used to break into various Tunny channels, Colossus and its forerunners produced what Bletchley called “Fish” traffic, which on certain levels was cryptographic and intelligence gold that surpassed even Enigma and played a pivotal role in the Allied successes from 1943 onwards. However, in the late spring of 1942, when the blackout was hitting its peak, Tunny was still in the developmental stage, leaving Godfrey, who was at the cutting edge of SIGINT development, to lament that “the bulk of the traffic is non-naval.”23
Potent as all these alternative sources would become later in the war, in the spring and summer of 1942 they had yet to reach maturity as consistent intelligence weapons. Meanwhile, the three-rotor Dolphin key, combined with the lower-level dockyard cipher, continued to produce a limited amount of intelligence. Reports of ship movements in home waters, the Baltic training grounds and Norway, along with details of the inner workings of U-boat bases on the west coast of France, allowed the Operational Intelligence Centre to track the comings and goings of U-boats from their ports. Using a combination of methods, it could glean intelligence regarding the commissioning of new craft and their trial runs, the names of their commanders, their new armaments, and even their departure from and return to port through the Bay of Biscay. Crucially, however, the OIC remained in the dark as to the location of submarines while at sea. As the Submarine Tracking Room reported, “Little can be said with any confidence in estimating the present and future movement of the U-boats.”24
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