11

The Waves of Air and Sea

1939–1945

Such is the U-boat war – hard, widespread and bitter, a war of groping and drowning, a war of ambuscade and stratagem, a war of science and seamanship.

Winston Churchill in the House of Commons, 26 September 19391

The British politician the 2nd Viscount Hailsham once said that ‘The one case in which I think I can see the finger of God in contemporary history is Churchill’s arrival at the premiership at that precise moment in 1940.’2 Another candidate for the intervention of the Almighty in the Second World War might be the Allied cracking of the German Enigma codes, producing a stream of decrypts known by their British special security classification, Ultra. This allowed the Allies for much of the war to read many of the communications sent and received by the OKW, OKH, Wehrmacht, Luftwaffe, Kriegsmarine, Abwehr, SS and Reichsbahn (railways), amounting in total to several million items of intelligence.3 From the correspondence of the Führer himself right down to that of the harbour-master of Olbia in Sardinia, messages were routinely decoded by the Allies. It made the Second World War, as Michael Howard has put it, ‘like playing poker with marked cards, albeit against an opponent with a consistently better hand than you’. Its importance can be gauged from the jokey acronym ‘BBR’ that the Americans gave to Ultra, which stood for Burn Before Reading.

For those who would prefer other explanations to divine intervention, the story of the cracking of the Enigma machine is also full of secular miracles. The design was patented by a Dutchman, H. A. Koch, in 1919, and by 1929 had been bought by the German Army and Navy (which used different versions of it). Looking like a normal typewriter but with three, four or five twenty-six-spoke rotor wheels attached, as well as lights and plugs that resembled a telephonist’s board, the machine had the ability to transform a typed message into a code so complicated that the Germans assumed it could never be broken. ‘To give an idea of how secure these machines are,’ General Franco’s intelligence officer Commander Antonio Sarmiento wrote in a 1936 report, when the Nationalists were buying ten Enigma machines from the Germans at the start of the Spanish Civil War, ‘suffice to say that the number of combinations is a remarkable 1,252,962,387,456.’4

The technical side of the Enigma story is ferociously complex, and involves specialist terms such as the Banburismus procedure, Caesar reflector, Dolphin, Porpoise, Shark and Triton nets (that is, sub-codes), the Eins catalogue, Cillis, the Herivel Tip, codes-within-the-code, Gamma wheels, perforated sheets and plugboard connections, rodding, Bigram tables, bombes, cross-ruffing, straight-cribs and a related code entitled Geheimschreiber (secret writer).5 The cracking of Enigma and its related codes – such as the Japanese diplomatic cipher Purple which was transformed into decrypts codenamed Magic – was a genuine Allied operation, involving the secret services of Poland, France, Britain, Australia and the United States. It began as early as 8 November 1931, when a traitor working in the German Cipher Office called Hans Thilo Schmidt allowed the French Deuxième Bureau (secret service) to photograph the Enigma operating manuals, which he had momentarily spirited out of a safe in the War Ministry. The French told the British, who subsequently told the Poles about the machine, but none could crack the code without building a replica of the machine itself. This was achieved by the Polish cryptographer Marian Rejewski in December 1932, although the Poles did not initially inform the French and British that this had happened. From that point on, the Poles could read Wehrmacht and Kriegsmarine radio traffic, although when in 1937 the latter changed its Enigma indicating key (the setting on a vital cog) the naval side fell silent, and was to remain so for the next three crucial years. Changes in the machines instituted by the Germans in December 1938 (installing an extra two rotor wheels, bringing the total to five) and January 1939 (doubling the number of plugboard sockets) also plunged the Poles into darkness. In late July 1939 they finally told the French and British secret services that they had been reading the German traffic until late 1938.

Ultra was not the sole means by which the Allies gathered intelligence, of course. Prisoners were captured and interrogated; simpler signals intelligence (sigint) codes used by front-line communications were eavesdropped upon and decoded by a British organization known as the Y Department; aerial photo-reconnaissance was interpreted at Medmenham on the Thames; resistance groups in Occupied Europe passed on information; SIS produced human intelligence (humint) from its own sources, although many were compromised early on in the war during the disastrous incident when in November 1939 two SIS officers, Captains Payne and Best, were kidnapped at Venlo on the Dutch–German border by Gestapo agents posing as Resistance figures; German generals in British captivity were eavesdropped upon when they discussed important subjects such as rocketry. Nonetheless, Ultra was by far the most important intelligence source and, because of its direct nature, the least corruptible in analysis. The Bletchley code-breakers were, as Churchill put it, ‘the geese who laid the golden eggs’ and who, just as importantly, ‘never cackled’. They were also almost all amateurs, recruited from civilian life, although their contribution was far to outweigh that of the career intelligence officers of the day.6

After the invasion of Poland in September 1939, several senior Polish cryptographers escaped with their replica Enigma machine and were installed by the Deuxième Bureau in a château near Paris, where they began – with British and French help – to decode messages, although at the time it took them two months to do so, meaning that the information they divulged had usually been long superseded by events. On 12 February 1940, however, the German submarine U-33 was attacked off the west coast of Scotland and two of the extra rotor wheels used by the naval Enigma were captured. Five weeks later, a brilliant, eccentric, accident-prone, homosexual Cambridge mathematics don called Alan Turing installed something known as a bombe machine, an electro-mechanical device which made hundreds of computations every minute, at the Government Code and Cypher School at Bletchley Park in Buckinghamshire, 40 miles north-west of London. Other heroes of Bletchley were to include the mathematicians Stewart Milner-Barry and Alfred Dilwyn (‘Dilly’) Knox. In modern computing parlance, while the Poles provided the Enigma hardware, the assorted civilian geniuses stationed at Bletchley provided the software that produced Ultra.

Far from being a school, Bletchley was a department of SIS, operating from a Victorian mansion that housed 150 workers in 1939, before expanding into huts in the grounds to fit 3,500 people by 1942 and no fewer than 10,000 by the end of the war. (Several of the huts can still be seen today, including the ones where the most important work was done, along with captured Enigma machines and the bombe predecessors of the computer.) Huts 6 and 3 deciphered, translated, annotated and passed on Wehrmacht and Luftwaffe signals, while Huts 4 and 8 (run by Turing and subsequently the chess champion Hugh Alexander) did much the same thing for the Kriegsmarine, sending reports to the Naval Intelligence Division of the Admiralty. Hut 4 also analysed sudden increases and decreases of signals traffic volume, which could suggest possible enemy intentions. On 4 April 1940, five weeks before Hitler unleashed Blitzkrieg on the West, same-day decoding of the German Army codes first became possible, but on 1 May the British at Bletchley and Poles in France were ‘blinded’ for three weeks when the Germans altered their indicating systems.7 Overall, however, Wehrmacht and Luftwaffe signals were decoded between three and six hours after they were sent, and naval signals during the battle of the Atlantic could be read as swiftly as one hour after transmission.8

Before May 1940 the cracking of the codes depended upon chance factors such as the transmission of flaws and errors, as with one German unit reporting every morning the same phrase, Verlauf ruhig (situation unchanged), thus giving the Cambridge mathematics don in Hut 6, Gordon Welchman, who had improved Turing’s bombe machine in 1940, a vital clue about several letters.9 The major expansion of the Luftwaffe before the war meant that its signallers were generally less well trained and disciplined, and more sloppy, than their Army and Navy counterparts. The fact that there were only twenty-six letters in the alphabet, the key flaw in the machine that no letter could represent itself in the code, and the absence of number keys meaning that every number had to be spelt out, also encouraging replication, were the major aids to decryption. The vast number of permutations – just under 1,253 trillion – that the Enigma code depended upon could therefore be narrowed down considerably by Turing’s and Welchman’s bombes.

It was not until the beginning of April 1941 that the German naval Enigma codes were broken – except for a very brief period in April 1940 – although there had been no shortage of plans to try to obtain German codebooks to help the process along, with the scheme of the intelligence officer and future Bond author Ian Fleming to crash a captured aircraft into the English Channel, and then ambush the rescue boat, being the most hare-brained.10 It turned out to be the capture off Norway of the German trawler Krebsthat yielded up the vital settings list that Bletchley needed to operate Turing’s Banburismus procedure for decryption. Although all German skippers were under strict instructions to destroy or throw overboard all codebooks at all costs, with the capture by HMSBulldogand HMS Broadway of soaking codebooks from Julius Lemp’s U-110 on 9 May 1941 by Sub-Lieutenant David Balme – they were dried over a stove on a British destroyer by Lieutenant Allon Bacon from the Naval Intelligence Division – Bletchley was able to discover future settings, the so-called Offizier procedure. This meant it could pick up announcements of future settings changes. By the autumn of 1941, evasive routing of convoys due to Ultra meant that the U-boats were sinking far fewer merchantmen; and as one historian has put it, ‘Bletchley Park had gone from being stymied by maddening cryptanalytic obstacles to being overwhelmed by its own success.’11 Yet it was not to last long.

Although the Abwehr set up regular investigations into the security of Enigma, and the commander of the U-boat branch of the German Navy, Karl Dönitz, had himself questioned whether it could have been broken, the Germans only continued to refine the existing machine settings rather than institute a brand-new communications system. Geheimschreiber, for example, was a non-Morse cipher that had up to ten rotary wheels, against the Enigma’s maximum of five. Its product was codenamed Fish at Bletchley and was far harder to crack, but it was not universally employed. Had a suspicious Reich turned to it instead of relying upon Enigma, the story of the Second World War might have been very different. Sir Harry Hinsley, the historian of British wartime intelligence, calculated that without Ultra the Normandy landings could not have been launched until 1946 at the earliest.12

Although the Allies could not be seen to rely on it too much, for fear that the Germans would realize it had been compromised, information gleaned from Ultra was used to great advantage at many key moments of the war – for example, it brought about the battle off Cape Matapan, enabled the sinkings of the Bismarck and Scharnhorst, disclosed Rommel’s weaknesses and shortages prior to El Alamein, simplified Montgomery’s advance into Tunisia in March 1943, made the planning for the invasions of Sicily and southern France much easier, exposed the whereabouts of German divisions before D-Day and revealed Hitler’s orders for a counter-attack at Falaise in August 1944. (The day before the Mediterranean battle of Cape Matapan, Admiral Cunningham strode ashore at Alexandria carrying his golf clubs, so as to lull the suspicions of the Japanese consul-general there. The next day, 28 March 1941, he sank three Italian destroyers and two cruisers whose whereabouts and intentions he knew from the Ultra decrypts he had received.)13 Yet it was undoubtedly in the battle of the Atlantic that Ultra was put to greatest use. Hut 8 of Bletchley Park succeeded in decoding about 1.12 million of the 1.55 million Kriegsmarine signals that were intercepted during the Second World War.

The battle of the Atlantic has been described as ‘one that really did threaten Britain’s survival just as surely as would panzer divisions roaming through the Home Counties’.14 In his memoirs Churchill wrote: ‘The only thing that ever really frightened me during the war was the U-boat peril… I was even more anxious about this battle than I had been about the glorious air fight called the Battle of Britain.’15 The UK had to import two-thirds of all her food during the war, 30 per cent of her iron ore, 80 per cent of her soft timber and wool, 90 per cent of her copper and bauxite, 95 per cent of her petroleum products and 100 per cent of her rubber and chrome.16 It is a moot point whether, in the event of the U-boats closing down her imports completely, Britain’s armaments industry would have ground to a halt before or after mass starvation struck every urbanized area. Yet that was unlikely to happen, for Hitler saw only too late the potential war-winning capacity of the U-boat, despite its almost bringing Britain to her knees in 1917. If the Nazis had started the war with as many submarines operational in September 1939 as they had in March 1945 – that is, 463 instead of only 43 – they might have won it. As it was, they did not come close to strangling British imports at any point, and once they had invaded Russia instead of the Middle East, and declared war against the United States, Britain was effectively safe from a naval and supply point of view. ‘The decisive point in warfare against England lies in attacking her merchant shipping in the Atlantic,’ Dönitz had long argued, but he believed he needed a minimum of 300 U-boats to be sure of victory, and he had less than one-sixth of that total in 1939.17 Once Hitler finally recognized their potential, a huge increase in U-boat production took place, but it was too late to win the all-important battle of the Atlantic. With only one-third of submarines operational at any one time, the others needing crew training and boat refitting, a massive building effort should have been instituted by Hitler by 1937 at the very latest, but he missed the opportunity.

Churchill agreed with Dönitz’s thesis, writing after the war: ‘The U-boat attack was our worst evil. It would have been wise for the Germans to stake all on it.’18 However, Dönitz was not the important figure when war broke out that he later became (indeed he ended the war as Führer of Germany). Although he was Führer der Untersee-boote at the outbreak of war, he only held the same rank as a cruiser captain.19 Born in September 1891 at Grünau near Berlin, he served as first watch officer under the U-boat ace Walter Forstmann in the Great War, before being given his own command in the Mediterranean, only for his boat to surface out of control while attacking a convoy. As a POW aboard a British cruiser in Gibraltar, he witnessed the armistice celebrations on the Rock in November 1918, and gestured to the ship’s captain at all the flags of the Allied powers flying from the ships, before asking what pleasure could be gained ‘from a victory attained with the whole world as allies’. The Briton replied pathetically, ‘Yes, it’s very curious,’ thus missing out on teaching Dönitz a valuable lesson about what would happen when Germany declared war against a global alliance.20

Karl Dönitz became a proponent of submarine warfare long before the moment when the Reich threw off its restraints under the Versailles Treaty, which banned it from having any submarines. Under the 1935 London Treaty, all signatories, including Germany, agreed to build a submarine fleet of no more than 52,700 tons, with no individual boat of more than 2,000 tons, but Germany used Spanish and Finnish yards to circumvent these restrictions. Yet Germany needed a tonnage vastly larger than she was building even illegally in order to destroy British maritime trade in wartime; and even if Dönitz had held greater sway in the German Naval Ministry than he actually did, it would probably have made little difference, as Admiral Erich Raeder was also making these arguments, with only intermittent interest from Hitler. ‘On land I am a hero,’ the Führer once said, ‘but at sea I am a coward.’21

Hitler was fascinated by the great surface ships such as the battleships Bismarck and Tirpitz, the pocket battleships Deutschland, Admiral Graf Spee and Admiral Scheer, the battle cruisers Scharnhorst and Gneisenau and the heavy cruiser Prinz Eugen, but he understood very little of naval strategy and the influence of sea-power. He certainly failed to spot the potential of a massive U-boat campaign, and largely ignored his admirals’ pleas for more ships and submarines during 1940, preferring to concentrate resources on the Wehrmacht and Luftwaffe. It was to be one of his greatest blunders of the war.

The deeply religious, handsome Dr Erich Raeder was born in Hamburg, the son of a languages teacher. He had been the navigation officer aboard the Kaiser’s yacht Hohenzollern, then served as a Staff officer under Admiral von Hipper during the Great War. He took an honours doctorate from Kiel University afterwards, writing a dissertation on cruiser warfare that he later published as a book. Naval chief of staff from 1928 and commander-in-chief of the Kriegsmarine from 1935, Raeder’s naval building programme, Plan Z, presupposed a war that began in 1944, which implies very poor co-ordination with the Führer. When it actually began five years too early, the German Navy did not yet have the balance – specifically in the areas of aircraft carriers and U-boats – to deliver victory against the Royal Navy. On the outbreak of war, Germany had only two modern battle cruisers – Scharnhorst and Gneisenau – three pocket battleships, two heavy cruisers, six light cruisers, twenty-two destroyers and only forty-three submarines, so on 24 September 1939 Raeder spent several hours trying to persuade the Führer of the attractions of a major, immediate U-boat building programme.22 Hitler said that he sympathized, but the necessary manpower and steel were not subsequently allotted to the Kriegsmarine in anything like the quantities required.

After a series of sharp engagements against the Royal Navy, by the end of 1940 Germany only had twenty-two U-boats left, and only twenty were built between the outbreak of war and the summer of 1940. Yet the twenty-five U-boats that were operating in the Atlantic by then had sunk no less than 680,000 tons between them.23 On 17 October 1940 a group of seven U-boats attacked Convoy SC-7 near Rockall, which numbered thirty-four merchantmen but had only four escorts. No fewer than seventeen ships were sunk, and no U-boat was damaged. U-boat captain Otto Kretschmer chalked up sinkings in the Atlantic that were to amount to more than a quarter of a million tons. As a result, Hitler slowly recognized the submarines’ potential and on 6 February 1941 he issued Führer Directive No. 23, which emphasized that ‘The wider employment of submarines… can bring about the collapse of English resistance within the foreseeable future… It must therefore be the aim of our further operations… to concentrate all weapons of air and sea warfare against enemy imports… The sinking of merchantmen is more important than attack on enemy warships.’24 Yet by then he was already deep into the planning stage for Operation Barbarossa, which was severely to undermine the U-boat offensive. Had he concentrated on knocking Britain out of the war first, he could then have turned eastwards at his leisure, with all the forces of the Reich and no prospect of having to draw off forces into Africa or the Mediterranean, and no aid coming to Russia from Britain either.

The Kondor was the Focke-Wulf 200 maritime reconnaissance bomber and had a range of up to 2,200 miles; it carried a 4,626-pound bomb load, flew at 152mph but lacked significant armour. It could be an invaluable spotter for U-boats, but when Dönitz asked Göring for more Kondors he was refused them, and for all the inspiring language of Directive No. 23 he had to rely on the twelve Kondors of Squadron KG40. These were nothing like enough, and as he later noted: ‘Here the flaw in the conduct of the war was revealed with painful clarity.’25 The call-up of 25,000 skilled dockyard workers to fight on the Eastern Front was another blow to Raeder and Dönitz, and when two years later Hitler announced the total scrapping of the capital-shipbuilding programme, Raeder resigned, to be replaced by Dönitz.

The battle of the Atlantic was a grim affair. ‘Seas the size of houses would come from every side,’ recalled one who fought in it, ‘so that on duty or off one could rarely rest, was always bracing the body, bending body and knees like some frozen skier to meet the motions of the ship.’26 Able Seaman Edward Butler, who served on an Atlantic convoy escort ship, told of how cold the crossings could get, when the ice was ‘freezing everything on the upper deck and the captain had to turn all hands to chip it off because it was becoming over top weight and there was a very severe danger of the ship capsizing. So we had to work during the night, in complete darkness, to get the ice off.’27 The best fictional account of the battle is Nicholas Monsarrat’s 1951 autobiographical novel The Cruel Sea, which was later made into a fine movie starring Jack Hawkins and Denholm Elliott. The story of the 1,000-ton, 88-man corvette HMS Compass Rose, from her commissioning in 1940 to her torpedoing in 1942, and then of the frigate HMS Saltash, the book covers the U-boat war, the Murmansk convoys and D-Day. Monsarrat particularly expresses his unstinting admiration of the men of the merchant marine who sailed in oil-tankers: ‘They lived, for an entire voyage of three to four weeks, as a man living on top of a keg of gunpowder: the stuff they carried – the life-blood of the whole war – was the most treacherous cargo of all; a single torpedo, a single small bomb, even a stray shot from a machine-gun, could transfer their ship into a torch.’28 The logistics of organizing a convoy were also well described; at any one time there might be more than 500 British ships at sea in a dozen or so convoys, and each ship:

would have to be manned, and loaded at a prescribed date, railage and docking facilities notwithstanding… their masters would have to attend sailing conferences for last-minute orders: they would have to rendezvous at a set time and place, with pilots made available for them: and their readiness for sea would have to coincide with an escort group to accompany them, which itself needed the same preparation and the same careful routing. Dock space had to be waiting for them, and men to load and unload: a hundred factories had to meet a fixed dispatch-date on their account: a railway shunter falling asleep at Birmingham or Clapham could spoil the whole thing, a third mate getting drunk on Tuesday instead of Monday could wreck a dozen carefully laid plans, a single air raid out of the hundreds that had harassed the harbours of Britain could halve a convoy and make it not worth the trouble of sending it over the Atlantic.29

A major problem with British strategy at the start of the war was that too much attention was paid to taking the offensive against the U-boat threat, and not enough to protecting convoys, which the Great War had proved was the best way of keeping the sea-lanes open. ‘Instead of employing the maximum number of vessels in the escort role,’ Vice-Admiral Sir Peter Gretton believed, the Royal Navy ‘wasted a great deal of energy in hunting for submarines in the open ocean’.30 When the captain of the unarmoured, converted passenger liner HMS Jervis Bay, Edward Fogarty Fegen, bravely but suicidally attacked the pocket battleship Admiral Scheer in November 1940, thereby allowing convoy HX-84 to scatter in a smokescreen at dusk, she had been the only escort vessel accompanying thirty-seven merchantmen. (Scheer nonetheless sank five of them. Fegen won a posthumous Victoria Cross.)

It was not until May 1941 that convoys were escorted all the way across the Atlantic, and very often they were woefully under-protected even then. Although Liberator bombers from Britain had the range to search the Eastern Atlantic for enemy submarines on the surface, and then attack them before they could dive to safety, Bomber Command would release only six squadrons to Coastal Command, which was not enough to make a serious difference. Air cover was generally scanty, and completely non-existent in the mid-Atlantic ‘Ocean Gap’, the area several hundred miles wide which planes could not reach from Iceland, Britain or Canada. (The Gap was closed in 1943 by the introduction of Very Long Range Liberators.) RAF Coastal Command entered the war badly under-equipped, under-staffed and under-trained, considering that its main role was to search for surface ships rather than submarines. There was also an absurd rivalry between the Admiralty and the Air Ministry that stymied efficiency in the opening stages. The Americans took even longer to institute a proper convoy system. On the eastern seaboard of the United States, failure to douse lights in the ports, and the relocation of much of the US Navy to the Pacific after Pearl Harbor, led to the sinking of no fewer than 485 ships totalling 2.5 million tons by August 1942.31

The battle of the Atlantic provided some nerve-wracking moments for British strategists: in March 1941 alone, U-boats sank forty-one ships. Yet that same month three of Dönitz’s best U-boat captains were neutralized. Germany’s top ace Otto Kretschmer – who had sunk forty-six ships totalling 273,000 tons – was captured after his U-99 was depth-charged and forced to the surface. Günther Prien, who had torpedoed the British battleship Royal Oak in Scapa Flow in October 1939, was killed when his U-47 was sunk by the destroyer HMS Wolverine. Finally Joachim Schepke was killed in an attack by an escort group commander, Captain Donald MacIntyre. An even greater blow fell that month when – in an escalation of ‘neutral’ America’s aggression – the United States announced that the waters between Canada and Iceland would thenceforth be protected by her Navy, thus allowing the Royal Navy to concentrate on protecting convoys. In September 1941, Roosevelt gave American ships permission to fire on German submarines wherever they saw them. ‘So far as the Atlantic is concerned,’ the American Chief of Naval Operations Admiral Harold Stark noted privately of the shooting war, ‘we are all but, if not actually, in it.’

After Enigma had been cracked in April 1941, between July and December 1941 Allied convoys were re-routed so expertly that not one was intercepted in the North Atlantic.32 Although there were still significant losses – over 720,000 tons were sunk in that period – experts calculate that more than 1.6 million tons were saved. Of course, if the Germans had started the war with enough U-boats, thereby closing the gaps in the ocean between them, no amount of re-routing could have saved the convoys. In May 1941 Churchill warned Roosevelt that if 4.5 million tons of shipping were lost during the next year, with the USA building 3.5 million and Britain 1 million, they would be ‘just marking time and swimming level with the bank against the stream’.33 Yet that month was the first that a west–east convoy was given escorts that sailed the whole way across the Atlantic with them. By September 1941, however, Hitler’s belated submarine-building programme had started to bear fruit, and Dönitz now had no fewer than 150 U-boats in commission, with which he would try to wrest victory in the battle of the Atlantic.

When the war broke out, both the British and German Admiralties assumed that the great German surface ships would be crucial in deciding whether Britain survived or starved. It was thought by London and Berlin that if these capital ships could dominate the Ocean Gap, the New World would be incapable, to adopt Churchill’s phrase in his ‘fight on the beaches’ speech, of stepping ‘forth to the rescue and liberation of the Old’. If, on the other hand, the Royal Navy and its Canadian and later American counterparts could sink these huge vessels, the danger was thought to be far less great. On the outbreak of war Graf Spee and Deutschland were already stationed to attack the trade routes, and Scharnhorst and Gneisenau put to sea in November 1939.

As recounted in Chapter 1, the forced scuttling of Graf Spee outside Montevideo harbour on 17 December 1939, the victim of a brave naval action at the battle of the River Plate but also a brilliant British deception operation, dented the myth of invincibility that had begun to surround the big German raiders. Similarly, although it was successful the German invasion of Norway in April 1940 cost the German Navy dear – almost half its entire destroyer force. But the fall of France in June allowed the Kriegsmarine to establish itself right along France’s Atlantic seaboard, with major bases at Lorient, Brest, La Rochelle and Saint-Nazaire. October 1940 saw Admiral Scheer break into the Atlantic Ocean, followed two months later by the heavy cruiser Admiral Hipper. The British Admiralty seemed incapable of preventing German raiders from sailing through the Denmark Straits between Greenland and Iceland. ‘For the first time in our history,’ Vice-Admiral Günther Lütjens told the crews of Scharnhorst and Gneisenau in January 1941, as they passed through the Faeroes–Iceland gap, ‘German battleships have today succeeded in breaking through the British blockade. We shall now go forward to success.’34 He was right in the short term: in two months the two ships together sank 116,000 tons of Allied shipping.

Yet both Admiralties were wrong in assuming that the big battleships would be decisive. In fact, it very soon became clear that the U-boats posed the primary threat, especially during what their crews were later to dub ‘the happy times’ of 1939–41. U-boats were often faster than their prey, averaging 17 knots on the surface, where they often sailed at night (they managed only 3 knots when submerged). Long after the war, Dönitz enumerated the advantages of the U-boat, which were more manoeuvrable than their Great War predecessors and:

had only a small silhouette consisting only of the conning tower and that is why the submarine could only be seen with difficulty during a night attack. Gradual development in communications meant the submarines were no longer obliged to fight alone, but they could attack together. This enabled us to develop the ‘wolf-pack’ tactics that became very useful against the convoys.35

After April 1941 Dönitz pioneered Rudeltaktik (herd tactics), by which the first U-boat to spot a convoy shadowed it while sending out signals to headquarters and other U-boats in the area, prior to a concerted night-time, surface, close-range torpedo attack by them all, acting as a wolf-pack. Monsarrat described how the U-boats took the upper hand in 1941:

The enemy was planning as well as multiplying. At last, the U-boats were co-ordinating their attack: they now hunted in packs, six or seven in a group, quartering a huge area of the convoy route and summoning their full strength as soon as a contact was obtained. They had the use of French, Norwegian and Baltic ports, fully equipped for shelter and maintenance: they had long-range aircraft to spot and identify for them, they had numbers, they had training, they had better weapons, they had the spur of success.36

By March 1941 the Allies had lost over 350,000 tons of shipping in the Atlantic, but the following month this rose to 700,000 tons. Since in 1939 Britain’s entire merchant marine totalled a gross tonnage of 17.5 million, the largest in the world, the danger to her from losing more than 1 million tons in two months was obvious.37 Setting up the Battle of the Atlantic Committee on 6 March 1941 to co-ordinate ministers, civil servants and the services, Churchill announced that ‘the Battle of the Atlantic has begun… We must take the offensive against the U-boat and the Focke-Wulf wherever we can and whenever we can. The U-boat at sea must be hunted, the U-boat in the building yard or in the dock must be bombed.’38

Yet it was the Germans who took the initiative, unleashing the battleship Bismarck and the new heavy cruiser Prinz Eugen into the Atlantic shipping lanes, in the hope of asphyxiating Britain and forcing her to sue for peace. Bismarck had been launched in Hamburg by the Iron Chancellor’s granddaughter, Dorothea von Löwenfeld, on 14 February 1939, and Göring, Goebbels, Hess, Ribbentrop, Himmler, Bormann, Keitel and of course Raeder were all present; the Führer gave a speech. The ship was one-sixth of a mile long, recalled the British writer Ludovic Kennedy, who was a junior reserve lieutenant when he took part in the operation to try to sink her,

120 feet wide, designed to carry eight 15″ guns and six aircraft, with 13″ armour made of specially hardened Wotan steel on her turrets and sides. Listed as 35,000 tons to comply with the London Treaty, she would in fact be 42,000 tons standard displacement and over 50,000 tons fully laden. There had never been a warship like her: she symbolized not only a resurgent Navy but the whole resurgent German nation… Warships combine uniquely grace and power, and Bismarck, massive and elegant, with the high flare of her bows and majestic sweep of her lines, the symmetry of her turrets, the rakish cowling of her funnel, her ease and arrogance in the water, was then the most graceful, most powerful warship yet built. No German saw her without pride, no neutral or enemy without admiration.39

Furthermore she had twelve boilers, her four gun turrets each weighed 1,000 tons – they were nicknamed Anton, Bruno, Caesar and Dora – she could sail at 29 knots and her crew numbered 2,065. Prinz Eugen, meanwhile, displaced 14,000 tons, had eight 8-inch guns and a speed of 32 knots.

These two warships left port at Gotenhafen (present-day Gdynia) at 21.30 hours on Sunday, 18 May 1941 in Operation Rheinübung (Rhine Exercise), a break for the Atlantic. Because several Polish labourers had been killed by oil fumes while cleaning her tanks,Bismarck sailed 200 tons of fuel short, something which her captain, Ernst Lindemann, was later bitterly to regret. Bismarck and Prinz Eugen skirted as far as possible away from the major British naval base of Scapa Flow and sailed through the Denmark Straits, where on the afternoon of Friday, 23 May they were shadowed with radar by the Royal Navy heavy cruisers HMS Norfolk and HMS Suffolk, until HMS Prince of Wales and HMS Hood were able to intercept them at dawn the next day. ‘If any one ship could be said to have been the embodiment of British sea-power and the British Empire between the wars,’ wrote Kennedy, ‘it was “The mighty Hood”, as Britain and the Navy called her.’ Built on Clydeside in 1916, she was, at 860 feet, 38 feet longer even than the Bismarck. Like Bismarck she had eight 15-inch guns in four massive turrets. With her maximum speed of 32 knots – she was the fastest ship of her size afloat – a ton of oil only got her half a mile. She had everything except upper-deck armour, because she had been built just before the battle of Jutland, when three British battle cruisers had been lost from shells falling vertically through their decks. Despite this, she had not been reconditioned.

When the Hood and Prince of Wales exchanged fire, at a range of 13 miles, with Bismarck and Prinz Eugen at 06.00 on Saturday, 24 May 1941, Norfolk and Suffolk were not close enough to provide support. In his fine memoir Pursuit: The Sinking of the Bismarck, Kennedy described how ‘For a moment the world stood still, then the guns spoke with their terrible great roar, the blast almost knocked one senseless, thick clouds of cordite smoke, black and bitter-smelling, clutched at the throat, blinded the vision, and four shells weighing a ton apiece went rocketing out of the muzzles at over 1,600 miles per hour.’40

Without the Norfolk and Suffolk to harry Bismarck from the rear, there was nothing to draw her fire from Hood, which was also taking fire from Prinz Eugen, and because the two German ships had swapped places since the last visual report, Hood was firing at the wrong target – Prinz Eugen rather than Bismarck – as the two looked alike at that distance despite their very different displacements.41 The Germans also had the weather gauge working in their favour, so that the British range-finders on the forward turrets were drenched with spray and other, less accurate instruments in the control tower had to be used instead. Furthermore, only the front turrets could be engaged as the British ships sailed towards the Germans, whereas their antagonists were able to deploy every high-calibre weapon they had.

Nonetheless, what happened next could not have been avoided whichever range-finders were used, whatever Norfolk and Suffolk had done, and however many guns Hood had managed to deploy. Only a thorough re-armouring of Hood’s upper deck in the inter-war years could have saved her. For a shell from Bismarck, in Kennedy’s phrase,

came plunging down like a rocket, hit the old ship fair and square between centre and stern, sliced its way through steel and wood, pierced the deck that should have been strengthened but never was, penetrated the ship’s vitals deep below the water-line, exploded, touched off the 4″ magazine which in turn touched off the after 15″ magazine. Before the eyes of the horrified British and incredulous Germans a huge column of flame leapt up from Hood’s centre.42

No one who witnessed that flame ever forgot it, as Hood exploded and then sank, with only three survivors out of a crew of over 1,400. Captain John Leach of the Prince of Wales continued firing at Bismarck, hitting her twice but only on the seventh salvo, yet once he was himself hit by German 5- and 8-inch shells, he was forced to escape under smoke cover. In an engagement lasting only twenty minutes, the Germans had sunk the maritime pride of the British Empire. Thereafter, their luck changed. One of the two 14-inch shells that the Prince of Wales landed on Bismarck had ruptured her fuel tanks, and she started leaking oil, which, because she had also sailed under-oiled and had not been resupplied when she might have been, meant that her skipper had to try to reach her supply ships and, he hoped, lead his antagonists into a wolf-pack.43 Meanwhile, Prinz Eugen broke off westwards, covered by an attack by Bismarck on Norfolk and Suffolk.

At sunset on 24 May, nine Fairey Swordfish torpedo-bombers from the aircraft carrier HMS Victorious braved Bismarck’s sixty-eight anti-aircraft guns and scored a hit with their 18-inch torpedoes. With the battleship still leaking oil steadily, it changed course for Brest. Then Enigma made its vital contribution, when a senior Luftwaffe officer in Athens using the Lufwaffe Enigma code enquired of his son serving in Bismarck where he was headed, and received the reply ‘Brest.’ Had it not been for Bismarck breaking radio silence in a code that Bletchley had cracked, she might have reached the port. She almost escaped anyway after her bearings were incorrectly plotted, but at 10.30 on 26 May she was spotted by a US Navy patrol pilot called Leonard Smith in a Consolidated Catalina flying-boat, part of RAF Coastal Command (and seven months before America entered the war).44

Force H, based in Gibraltar, and including the battle cruiser HMS Renown and the aircraft carrier HMS Ark Royal, attacked that afternoon. Planes from Ark Royal landed two hits with contact-detonating torpedoes, one of them entering the starboard steering compartment, exploding, and thrusting the starboard rudder against the central propeller. This jammed Bismarck’s steering and wrecked her chances of getting to Brest. Nevertheless, German aircraft and submarines operating out of French Atlantic ports might still have saved her, had it not been for the attacks made at 08.47 the following day, Tuesday, 27 May, by the battleships King George V and Rodney, firing at 16,000 yards, with Norfolk taking part too, and the cruiser Dorsetshire finished Bismarck off with torpedoes. At 10.36 she sank, killing all but 110 of her crew. It seems that she was also scuttled, evidence for which was discovered when she was found on the seabed 300 miles off south-west Ireland in 1989.

Hitler learnt the lesson of the vulnerability of great surface raiders to air attack. On 19 June 1943 he told Martin Bormann that although he had once ‘planned to construct the most powerful squadron of battleships in the world’ – which he was going to name after the great sixteenth-century poet–adventurers Ulrich von Hutten and Götz von Berlichingen – now ‘I am very pleased that I abandoned the idea.’ The reason was that ‘it is now the infantry of the sea which assumes the prime importance,’ and submarines, corvettes and destroyers ‘are the classes that carry on the fight’. To illustrate the point, the Führer said that although the Japanese had the greatest battleships in the world, ‘it is very difficult to use them in action. For them, the greatest danger comes from the air. Remember the Bismarck!’45

The sinking of the Bismarck – although of course it cost the Hood – saw the last of the German surface-fleet raiders threatening the Atlantic sea-lanes, and in that sense marked a major turning point in the battle. Bismarck’s and Prinz Eugen’s supply ships were immediately targeted, using the German Home Waters key of the naval Enigma code called Dolphin, and hardly any made it back to port.46 That meant that the Germans had henceforth to rely on underwater tankers and supply carriers, which had much smaller capacities and slower speeds.47 Although there were other major battles to be fought against vessels such as the battle cruiser Scharnhorst (sunk off the Northern Cape of Norway on 26 December 1943), Bismarck’s sister ship the Tirpitz (sunk by Lancaster bombers with 12,000-pound Tallboy bombs on 12 November 1944), the battle cruiser Gneisenau (scuttled at Gotenhafen on 28 March 1945) and the Prinz Eugen (which ended her days as a nuclear-test target in the Pacific), none of these ships posed the same level of danger during the battle of the Atlantic.

Tirpitz did, however, play a major – if not actually operational – part in the tragedy that overtook Convoy PQ-17 in July 1942. The Arctic convoys had started very soon after Operation Barbarossa. On 12 August 1941, even while Churchill and Roosevelt were still meeting at Placentia Bay in Newfoundland discussing how to help Russia, two squadrons of British fighters comprising forty aircraft left Britain on board HMS Argus bound for Murmansk, the first of the supplies shipped to Russia by the Arctic route. Under the command of a New Zealander, Wing Commander Ramsbottom-Isherwood, they reached the Soviet naval base at Polyarnoe, near Murmansk, which was to become a huge receiving depot for Allied supplies over the next four years. Although the RAF needed every aircraft it could get for home defences and North African operations in the summer of 1941, nonetheless it transported planes to help the USSR in its hour of trial.

The first regular convoys, which all had the codename PQ followed by a consecutive number, started out from Iceland to Murmansk and Archangel via Bear Island. On 28 September, PQ-1 set out packed with military supplies and large quantities of the vital raw materials that Stalin had asked for personally, including rubber, copper and aluminium. Soon afterwards, Churchill announced that Britain’s entire tank production for the month of September was going to be despatched to Russia. The tanks were badly needed, for on 2 October the Nazis launched Operation Typhoon on Moscow. The horrific winter of 1941/2, which did so much to destroy Hitler’s dreams of turning European Russia into an Aryan colony, also badly affected the Arctic convoys. The route taken was a hazardous one that comprised seventeen nerve-wracking days sailing around the Northern Cape above Norway and Finland, through the potentially lethal ice-floes, through German air strikes, U-boat attacks, marauding surface ships and the constant freezing Arctic storms. Monsarrat wrote: ‘One of the seamen, who’d taken off his gauntlets to open an ammunition locker, had torn off the whole of the skin of one palm and left it stuck to the locker like half a bloody glove, with him staring at it as if it were something hanging up in a shop. But that wasn’t as bad as what happened to the poor bastards that got dropped into the drink.’48 They froze to death within three minutes. By 1942, after three years of war, Monsarrat recalled how the sailors of the Royal Navy had:

developed – they had to develop – a professional inhumanity towards their job, a lack of feeling that was the best guarantee of efficiency: time spent in contemplating this evil warfare was time wasted, and rage or pity was something that could only come between them and their work. Hardened to pain and destruction, taking it all for granted, they concentrated as best they could on fighting back and on saving men for one purpose only – so they could be returned to the battle as soon as possible.49

One of the most serious setbacks of the naval war occurred on 4 July 1942, three days after Convoy PQ-17 had been spotted by German submarines and aircraft. It was hard to miss, comprising thirty-five merchant ships (twenty-two American, eight British, two Russian, two Panamanian and one Dutch), protected by six destroyers and fifteen other armed vessels. That same morning, four merchantmen were sunk by Heinkel torpedo-bombers, and, fearing that four powerful German warships – including the Tirpitz – were on their way, Admiral Sir Dudley Pound, the First Sea Lord, ordered the convoy to scatter, overriding the C-in-C Home Fleet Admiral Sir John Tovey and the Admiralty’s Operational Intelligence Centre. It was a virtual death sentence.

The German warships had indeed been ordered to intercept the convoy, but, unbeknown to Pound, Hitler had told them to turn back. Instead, the scattered convoy was picked off from the air and by submarines. Only thirteen ships reached Archangel; of the 156,500 tons loaded on board the convoy in Iceland back on 27 June, 99,300 tons were sunk, with the loss of no fewer than 430 of the 594 tanks and 210 of the 297 planes on board. It was astonishing that not more than 153 sailors were drowned. Further tragedy was to follow three days later, when the returning convoy QP-13 ran into a British minefield off Iceland through bad navigation, and a further five merchant ships were sunk. There were further serious setbacks during the war, including Convoy PQ-18, thirteen of whose forty ships were sunk in September 1942, although it did at least manage to take a severe toll on its attackers, destroying four German submarines and forty-one aircraft. This led to the War Cabinet temporarily suspending convoys to Russia altogether, an action which Churchill told the War Cabinet on 14 September had left the Russian Ambassador to Washington, Maxim Litvinov, ‘squealing’ but the Ambassador to London, Ivan Maisky, ‘plaintive’.50 It was not until late in 1943 that the Allies began to win the Arctic campaign: in November and December three eastbound and two westbound Arctic convoys reached their destinations without any loss.

Major scientific and technical developments during the war helped in the struggle against the U-boat. The Royal Navy used Asdic, the echo-sounding device for tracking U-boats, and 180 ships were fitted with it. It was not foolproof, however, so ships constantly zig-zigged hoping to escape submarines. As the battle of the Atlantic progressed, there were a number of factors that secured victory for the Allies, including the vast expansion of the Canadian Escort Force based at Halifax, Nova Scotia; side-firing as well as back-firing depth-charges; the new high-frequency, direction-finding (HF/DF) apparatus; Anti-Surface-Vessel radar, which the Germans greatly overestimated and often blamed for intelligence coups that actually derived from Ultra; Very Long Range bombers that reported U-boat positions, bombed them and closed off the Ocean Gap; powerful Leigh floodlights for spotting conning towers and periscopes; airborne centrimetric radar; and the alteration of the Royal Navy codes in June 1943 which plunged the German decrypters in the dark (although they were still able to read the Merchant Navy’s ciphers).

As so often it was the Commonwealth that played a vital, if largely unsung, part in winning the battle. The Royal Canadian Navy grew fifty-fold in the course of the conflict, and its anti-submarine arm, the Canadian Escort Force, contributed almost as much to victory as the Royal Navy. Protecting the HX (Halifax-to-Britain) and SC (Sydney-or Cape-Breton-to-Britain) eastbound convoys in one direction, and the westbound ONF (fast outbound-from-Britain) and the ONS (slow outbound-from-Britain) convoys in the other, they were invaluable.

Part of the explanation for the heavy losses on the Atlantic and Arctic convoys was that the British convoy code had been cracked by German intelligence, something that was not discovered until after the war. In February 1942 the German Beobachtungdienst (radio monitoring service) managed to crack about 75 per cent of Naval Cipher No. 3 which since June 1941 had routed convoys.51 The Germans were reading Royal Navy codes, although only 10 per cent of the intercepts could be used operationally because of the time taken to decipher them.52 Nonetheless, when the size, destinations and departure times of convoys did become known to the Germans, they could draw up an accurate picture of the whole operation. If they had achieved real-time decryption, as Turing was to do, it could have been potentially as decisive an advantage to the Germans as the cracking of the Enigma code was for the Allies. Instead of recognizing the danger, the Admiralty put the U-boats’ remarkable success in intercepting convoys down to the advanced hydrophone equipment they used, which it was thought could detect propeller noise for over 80 miles. When marvelling at the Germans’ continuing trust in Enigma, therefore, one must also consider the British faith in the Royal Navy’s own compromised codes. Naval Cipher No. 3 was not replaced with No. 5, which the Germans never cracked, until June 1943.

Coincidentally, the worst moment for the Allies in the battle of the Atlantic came in the same month as the Beobachtungdienst cracked Naval Cipher No. 3. On 1 February 1942, OKM (the Supreme Command of the Navy) introduced an extra rotor wheel to the Enigma machines used by U-boats in the Atlantic, thus enormously increasing the number of solutions to any Enigma-encrypted texts. The new code was dubbed Shark at Bletchley, and every effort was made to crack it, initially by producing four-rotor bombes.53Hitherto the Royal Navy had been able to foil ambushes and divert convoys away from danger areas. Suddenly, for more than ten months – almost for the whole of 1942 – Bletchley was thrust into the dark, its bombes producing only gibberish. With the Navy unable to re-route convoys away from peril, sinkings increased dramatically.

In 1940 U-boats had sunk 1,345 Allied ships totalling 4 million tons for the loss of twenty-four submarines, and in 1941 slightly more, 1,419 totalling around 4.5 million, for the loss of thirty-five. Yet in 1942, with Shark unbroken, U-boats sank 1,859 ships totalling over 7 million tons, albeit for the loss of eighty-six U-boats.54 In November 1942 alone over 860,000 tons of Allied shipping were sunk, 88 per cent of it by more than a hundred submarines that the Germans had at sea.55 Although the church bells were rung to celebrate the victory at El Alamein that month, they could just as well be tolling the news that the Allies were now for the first time in the war losing more tankers than they were building.

Yet salvation was at hand. At 22.00 hours on Friday, 30 October 1942, U-559 was forced to the surface after no fewer than 288 depth-charges were dropped on her by four British destroyers in the eastern Mediterranean. Her captain opened her stopcocks to scuttle the vessel and the entire crew abandoned ship, but Lieutenant Francis Fasson, Able Seaman Colin Grazier and a sixteen-year-old Naafiassistant Tommy Brown (who had lied about his age to join the Navy) from HMS Petard stripped off their clothes and swam over to it.56 Getting into the captain’s cabin, they used a machine gun to break into a locked cabinet and retrieve the codebooks and documents. After Brown had made three journeys delivering these to another party from the destroyer, the U-boat suddenly sank, drowning Fasson and Grazier. Although their gallantry had been up to the standard required for the Victoria Cross, as it was not ‘in the face of the enemy’ as the criteria stipulate they were awarded the George Cross posthumously, and Brown received the George Medal.

No decorations were more deserved: once Bletchley received the documents on 24 November they were found to include the all-important indicator list, code and weather tables that allowed the code-breakers to break into Shark on Sunday, 13 December. When the Shark code was used for weather signals, it was discovered, the fourth rotor was always set at neutral, so the old three-bombe rotor could be used to decrypt them, allowing the rest of the code to be reconstructed with relative ease.57 It was a massive breakthrough. ‘Although Dönitz did not know it,’ records an historian of the secret intelligence war, ‘the tide had turned, this time for good.’58 (Meanwhile, Tommy Brown GM was discharged from the Navy for volunteering while under age.)

There were other periods of the war when one or more codes – including Shark – went suddenly blank owing to the Germans upgrading or changing aspects of Enigma, but not for so long as to cause insuperable difficulties. Even though the Abwehr learnt from a captured Deuxième Bureau agent about the treachery of Hans Thilo Schmidt – who committed suicide in September 1943 – still they did not connect the facts and adopt a new communications system. Nor did they realize that the sinking of the Scharnhorst on 26 December 1943 had been partly the result of the reading of the Kriegsmarine’s codes. If at any stage the Germans had recognized the truth it could have proved catastrophic for the Allies, but the cracking of Enigma turned out to be the best-kept secret of the twentieth century.

At the Casablanca Conference in January 1943, Churchill and Roosevelt gave as high a priority to the defeat of the U-boat threat as they gave to the invasion of Sicily, their other immediate strategic objective. With seventeen new U-boats now being commissioned every month, Dönitz had no fewer than 400 by the spring of 1943, although only one-third were operational. Yet they were not to be enough, for in the first four months of 1943 the battle of the Atlantic turned heavily in the Allies’ favour. New tactics in dealing with U-boats, by peeling off escorts to attack in groups, once allied to scientific and technological advances, more aircraft and escort numbers, increasing ranges of bombers, the closing of the Ocean Gap, and the re-cracking of the Ultra naval code the previous December, all helped to tip the balance.

In 1943, the Germans sank only 812 ships totalling over 3 million tons, for the loss of 242 submarines.59

In the first five months of 1943 – the Schwerpunkt of the battle of the Atlantic – RAF Coastal Command and Royal Navy escort carriers managed to provide the all-important air support for convoys, and in April the battle was taken to Dönitz’s own bases in the Bay of Biscay with combined sea and air attacks. Ever since 1943 dawned there had been heavy bombing of the Biscay ports despite the effect on the civilian population, with Churchill summarized as telling the War Cabinet on 11 January that it was an ‘Important point of principle. The First Lord makes out his case… No doubt about gravity of the U-Boat War… Warn the French population to clear out. It is no longer touch and go with France.’60 Eden said he had gone into the issue, and ‘hitherto our policy was based on effect on French National Army if there was a great slaughter of French people. In this case we can’t possibly refuse. But they must have 3 or 4 days’ warning.’ Sir Charles Portal, Chief of the Air Staff, pointed out that warning the local population would greatly increase the risk to his bombing crews because of the increased anti-aircraft measures taken, which would leave the ‘effectiveness of attack imperilled’. Churchill thought a general warning ‘to leave coastal areas’ would suffice, and asked the service departments to get the co-operation of the United States over the policy. In naval matters, meanwhile, he said that the ‘Germans run away whenever they meet our surface ships… most discreditable in German history.’

Victory in the battle of the Atlantic was heralded by the fate of Peter Gretton’s Convoy ONS-5, which was attacked in atrocious weather off the south coast of Iceland during the spring of 1943. The convoy of forty ships had sailed out of Londonderry on 23 April at 7 knots in bad weather with an escort of two destroyers, one frigate and four corvettes, which went more slowly than surfaced U-boats. On 28 April the first U-boat attacked the convoy off the coast of Iceland, and for the next nine days there were constant running battles – on one night there were twenty-four separate attacks – until 09.15 hours on 6 May when Dönitz called off the action. In all fifty-nine U-boats from four wolf-packs – Group Star, Group Specht, Group Ansel and Group Drossel – had engaged the convoy, losing eight and with seven more damaged, for the loss of thirteen Allied merchantmen. ‘The convoy was still together,’ wrote Gretton later, ‘and the longest and fiercest convoy action of the war had ended with a clear-cut victory.’61 In his review of Dönitz’s memoirs, the naval historian Captain Stephen Roskill noted that the convoy’s struggle ‘is marked only by latitude and longitude and has no name by which it will be remembered; but it was, in its own way, as decisive as Quiberon Bay or the Nile’.62 In the single month of May 1943 forty-one U-boats – 30 per cent of the total force at sea – were sunk at a heavy cost in German lives (including that of Dönitz’s youngest son Peter on U-954).63

On 24 May Dönitz was forced to withdraw all his U-boats from the North Atlantic, and report to Hitler in Berlin. ‘There can be no let-up in submarine warfare,’ Hitler told him at a conference also attended by Keitel, Warlimont and Karl-Jesko von Puttkamer, the Führer’s naval adjutant, on 5 June. ‘The Atlantic is my first line of defence in the West, and even if I have to fight a defensive battle there, that is preferable to waiting to defend myself on the coast of Europe.’64 No longer did Germany see the Atlantic as a potential means of strangling Britain; now it was somewhere to hold off the coming invasion of north-west Europe. Yet Dönitz was powerless to obey his Führer – though he wisely did not admit as much then or subsequently – and on 24 June Allied ships capable of sailing 15 knots or faster were allowed to sail across the Atlantic without convoy protection for the first time in four years. June 1943 was the first month of the war in which not a single Allied convoy was attacked in the North Atlantic. June also saw the British introduce a new code for ship-to-shore radio traffic, Naval Cipher No. 5, to replace the one that the Germans had been listening into since 1941.

It was ironic that just as Albert Speer, who had been appointed armaments minister after the death in a plane crash of Fritz Todt in April 1942, found a way of rationalizing the manufacture of U-boats – using time-and-motion studies prevalent in the pre-war motor-car industries – down from forty-two weeks to only sixteen, there were fewer places for them to be deployed.65 Although twenty-eight U-boats did return to the North Atlantic in September 1943, they sank only nine of the 2,468 ships that crossed in the next two months. Despite large numbers of U-boats being put into service – there were never fewer than 400 between the summer of 1943 onwards, of which one-third were operational – the battle of the Atlantic had been decisively lost by Germany. Shipping losses of over 7 million tons in 1942 fell to 3 million in 1943.66 It was not negligible, but it was survivable. In August 1943 more U-boats were destroyed than merchant ships were sunk, ‘a piece of news which stirred a thousand hearts, afloat and ashore’, recalled Monsarrat. ‘For the first time in the war, the astonishing balance was struck.’67

Between January and March 1944 Germany lost twenty-nine U-boats while sinking only three merchantmen. They were thus incapable of interdicting the D-Day landings, although by the start of 1944 they had perfected the Schnorchel, a hinged air mast which permitted the U-boats’ diesel engines to suck in air and expel exhaust while fully submerged. Batteries could therefore be recharged underwater without having to surface and U-boats could increase their speed while submerged to 8 knots.68 Yet by August 1944 Dönitz had given up attempting to prevent resupply of the Allied armies on the Continent, especially after more than half of the U-boats in the Channel had been sunk.

In June 1944, just in time for the Normandy landings, Turing’s greatest invention of all, the Colossus II, came on stream. The world’s first digital electronic computer, it was able to decode Fish as well as Enigma messages in real time, and also decrypted the correspondence between OKW and the Commander-in-Chief West. As one who worked on Colossus, Donald Michie, has recalled: ‘At the end of hostilities 9 new-design Colossi were operational and 63 million characters of high-grade German messages had been decrypted.’69 Turing’s reputation for eccentricity seemed confirmed by his practices of bicycling around wearing a gas mask, and chaining his coffee mug to a radiator, but one of those who worked at Bletchley, WAAF Sergeant Gwen Watkins, later explained that ‘If you had a china mug and it was “borrowed”, you could replace it only by an enamel one, which made tea taste horrid. And cycling to work in your gas mask, if you had hay fever, was a good idea.’70 Eccentric or not, Turing’s contribution to victory was enormous, making his OBE a paltry reward and his cyanide-by-apple suicide in 1954 correspondingly tragic.

*

As the Russians made their way along the Baltic coast, the Germans had to relocate their U-boat fleet to Norway. Although their number peaked at the huge figure of 463 in March 1945, it was far too late for them to be able to make a difference. In total, throughout the war Germany deployed 1,162 U-boats, of which 785 were destroyed (over 500 by British ships and planes). Altogether they sank 145 Allied warships and 2,828 Allied and neutral merchantmen totalling 14,687,231 tons.71 In the course of the war, the Royal Navy lost 51,578 men killed and the Merchant Navy 30,248, mainly to U-boats.72 The U-boat crewmen were immensely brave, and at 75 per cent suffered among the highest death rates of any branch of service in the Reich, in what they themselves dubbed iron coffins. As the war progressed, the U-boat sailors’ life expectancy decreased, as is superbly portrayed in the German movie Das Boot. Furthermore, heavy Allied bombing of U-boat construction and marshalling yards meant that the newest-pattern U-boat – once hailed as a super-weapon – did not slide down the slipway until 3 May 1945, just as Dönitz was negotiating peace terms with the Allies.

For all that the battle of the Atlantic could have been disastrous for Britain had the Nazis built up a large submarine fleet before the war, nonetheless it was very unlikely that Britain could have lost, for the simple reason that the United States’ entry into the war meant that, even when the Shark code went suddenly silent in February 1942, the vast American production of merchant shipping was always ready to make up the losses, almost however bad. Thus whereas the amount of Allied tonnage sunk totalled 4.01 million against the 0.78 million built in 1940, and 4.355 million sunk against 1.972 million built in 1941, and the totals were almost equal at 7.39 million versus 7.78 million in 1942, in 1943 only 3.22 million were sunk against 15.45 million being built, in 1944 1.04 million were sunk against 12.95 million being built, and in 1945 0.437 million tons were sunk against 7.592 million being built.73 The overwhelming majority were being built by America, by a factor of over five to one.

Moreover, despite the losses, the size of the British merchant fleet stayed almost level throughout the war at between 16 and 20 million tons, making up tonnage through purchase, requisition, chartering from neutrals and other means. Even when the U-boats were sinking large quantities of shipping from 1939 to 1941, therefore, the British merchant fleet actually increased in size by three-quarters of a million tons. The statistics for U-boat and all other sinkings as a percentage of the net tonnage of incoming cargo docked in the United Kingdom are conclusive throughout: in 1939–40 it was 2.0 per cent; thereafter 1941: 3.9 per cent; 1942: 9.7 per cent; 1943: 2.7 per cent; 1944: 0.3 per cent and 1945: 0.6 per cent. Of course imports were wildly below the 91.8 million tons of pre-war levels – and were down to 24.5 million tons in 1942 – but by 1944 they had risen to 56.9 million tons.74 This means that, in the absence of a huge U-boat fleet in 1939 such as the one Germany belatedly had in 1945, and after America had entered the war, however vicious and bitter the battle of the Atlantic undoubtedly was Britain’s survival was never really in doubt, even though for most people on both sides it certainly did not look that way at the time.

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