The moment England’s supply routes are severed, she will be forced to capitulate.i
I don’t remember ever having decoded a message from start to finish to see what it said. I was much more interested in the methodology for getting German out of a coded message.ii
In World War II there was no more vital theatre of conflict than the waters of the Atlantic Ocean, and here, as in every place where the opposing sides sought to outwit each other, the use of codes (and the breaking of enemy codes) was of huge importance to the outcome of the contest. Knowledge of British Admiralty codes initially gave the German U-boats such opportunities for sinking Allied shipping that their crews referred to this period of pre-eminence as ‘the happy time’. Subsequent Allied use of signals decrypted from the German naval Enigma turned the tables completely, making the mid-Atlantic a killing ground for submarines. On this vast ocean, so different from other arenas in which the Allies and the Germans fought, Ultra was as vital as ever. Through their incomplete but decisive mastery of German naval signals traffic, the Bletchley staff enabled Allied armies to cross the Atlantic and the English Channel without hindrance and to take the war on to the European mainland.
By the summer of 1940, German armies had overrun northern and western Europe. The only remaining belligerent, Great Britain, was an island that did not have sufficient food or raw materials to sustain an all-out war effort. Its only recourse was to depend on imports, and the majority of these came east across the Atlantic from Canada and the United States or, in the case of oil, from the Caribbean and the Gulf of Mexico. If the transatlantic lifeline could be severed, even temporarily, by sinking enough of the merchant ships that carried these cargoes, Britain would be unable to carry on fighting. The Germans thus possessed, in their submarine fleet, a highly effective means of defeating Britain quickly and without heavy casualties. Lieutenant Commander DE Balme of the Royal Navy, who was to play a heroic part in the battle, recalled that:
The Germans recognised that the Atlantic was the vital artery for Britain to obtain supplies of food (we had let our agriculture decline between the wars, so that we could only grow about one-third of our food), fuel (we had coal but no oil) and raw materials for our factories. If they could cut that line, they could win the war.
The importance of this supply route remained paramount until the end of the European war. It did not matter that America and Russia had now joined Britain in the fight, or that Allied armies were accumulating victories in North Africa, Italy, Eastern Europe or France. Unless the Atlantic shipping routes were secure, Britain would starve and the men and materiel needed to defeat Hitler would not reach the battlefields. It is small wonder that Churchill was to comment:
The Battle of the Atlantic was the dominating factor all through the war. Never for one moment could we forget that everything happening elsewhere, on land, at sea or in the air, depended ultimately on its outcome, and amid all other cares we viewed its changing fortunes day by day with hope or apprehension.
He was later to admit:
The only thing that really frightened me during the war was the U-boat peril.
In this, history was repeating itself. In World War I the enemy’s surface fleet had made no lasting contribution, but its submarines had proved a considerable menace. Germany itself had been blockaded by the Royal Navy and its warships had largely been unable to leave the Baltic, but U-boats had had the freedom of the North Sea and the Atlantic. They had set out to strangle Britain by attacking the ships that fed and supplied it. The Allies had responded by introducing the convoy system, in which merchant vessels sailed in batches, guarded by warships. While this undoubtedly saved many lives and cargoes, the German submarines had nevertheless proved effective, for in the course of the war they had sent to the bottom a total of 7,500 vessels, representing 11 million tons of shipping. The price of this success, however, had proved too high. With the approval of the country’s parliament, the German High Command had adopted a policy of ‘unrestricted submarine warfare’, which meant that not only the vessels of belligerent countries but also those of any nation deemed likely to be assisting the enemy could be attacked and sunk without warning or explanation. This tactic had brought Germany immense international odium. It had also brought the United States into the war in 1917, and thus ensured Allied victory.
Following its defeat in World War I Germany had been forbidden, under the terms of the peace treaty, to retain a submarine fleet. Its navy, however, had continued to build and to train in secret. The expertise of German engineers and submariners had been in demand among nations that were developing fleets of their own and so, while fulfilling this consultancy role in Spain, Turkey or Finland, Germany’s officers and crews had been able to keep their own skills up to the mark. Meanwhile its U-boats had been built in the yards of these countries. In 1935, with Germany well on the way to resuming Great Power status and with the United Kingdom anxious to appease Hitler, a naval agreement had been signed between the two nations that allowed Germany a submarine fleet 35 per cent the size of Britain’s. From that moment, German submariners had begun to train in earnest for the coming war. Like other branches of Hitler’s armed forces, they had also acquired useful experience through supporting Franco’s cause in the conflict in Spain.
The Type VIIC U-boat, developed in 1938, was the world’s most advanced submarine. With continuous modification, it was to be the basis of Germany’s fleet for most of the war. It displaced 871 tons underwater, carried a crew of 44 and had a top speed when submerged of 7.5 knots, with an operational range of 8,500 miles. It was armed with an 88mm deck gun but its ‘teeth’ were its 14 torpedoes, fired from four tubes in the bow and one in the stern. Germany had 56 U-boats of this type in service at the start of World War II.
They made an impact at once, for the ‘Battle of the Atlantic’ began on the day that Britain entered the war. On 3 September 1939, a U-boat sank the liner Athena, which was on its way from Canada to England, having mistaken it for a troopship. (The 118 passengers who died included 22 Americans; Hitler, who feared offending the neutral United States, was furious.) A month later U-47, commanded by the legendary Günther Prien, torpedoed the battleship HMS Royal Oak at its anchorage inside Scapa Flow with a loss of over 800 crew. In the first three months of conflict, despite the introduction of convoys, U-boats accounted for 114 merchant ships. Hitler was convinced by the spectacular success of his submarine fleet that they represented the best means of putting Britain out of the war, though he remained somewhat indecisive about inflicting a crushing defeat on a country that he still hoped would become an ally.
The following year brought fresh disaster for the Royal Navy, when the aircraft carrier HMS Glorious and two escorting destroyers were sunk in the North Sea by the battleship Scharnhorst. What made this event worse was the fact that it could have been avoided. Harry Hinsley, one of the young men working at Bletchley, specialized in naval codes. Though he had no access to naval Enigma messages (that version had not yet been broken), he had studied the volume of signals traffic, and in June 1940 he concluded that German ships were about to leave the Baltic. He warned the Admiralty, in the shape of its OIC (Operational Intelligence Centre), but it took no action. The OIC regarded Bletchley as untested and Hinsley as an amateur, a civilian, and too young to be taken seriously – he still looked every inch the undergraduate that he had recently been. It was only after this sinking, and even then only gradually, that the Admiralty began to accept that the academics at ‘BP’ might after all have something to offer.
In this first phase of the war, the German navy was the most formidable enemy faced by Britain. The B-Dienst, its intelligence service, had broken the Royal Navy’s Number 3 cipher, which was used to organize convoys, and the detailed knowledge of routes, gathering places and sailing times that this offered gave the U-boats a huge advantage in the Atlantic. For long months there was no corresponding British access to German naval codes, which were more complex than those of the other services. At the start of the war there were 13 separate codes and there would ultimately be 40, some of which Bletchley would never succeed in breaking. AEGIR was the code for ships of the surface fleet, HYDRA was for operational U-boats and TETIS for those that were undergoing training in the Baltic. The staff at Bletchley also came up with their own nicknames: ‘Dolphin’, for instance, was the term for the U-boats’ ‘home waters’ code.
The Enigma machines used by the German navy were more complex than those of the other services. They had up to eight wheels and thus the number of possible wheel-orders was 336. Alan Turing, with the help of Peter Twinn and a staff of Wrens, set up a specialist cryptographic section (‘Hut 8’) to concentrate energies on this vital area, and Turing managed to break into the cipher, though only for a short time, in April 1940.
IJ Good described the purpose of Hut 8 and the head-spinning complexity of the work they were trying to do:
Our job was to carry out certain cryptanalytic work and thus to prepare jobs for the machine known as the Bombe, which was housed in another building. The Enigma was used both by the German Navy and the German Army. In Hut 8 we were only concerned with the Naval Enigma. The U-boat version had four rotors after a time instead of only three so it was more difficult to break.
The particular set of rotors in a machine was determined by daily keys. For example, the three rotors for the Mediterranean Enigma were selected from a set of eight, of permanently fixed wiring. Since the order in which they are put in the machine is relevant, the number of possible wheel orders was 8 × 7 × 6. The wheel order was fixed for two days at a time. The number of initial settings was about 26 = 17,576 and moreover there was the additional plugboard which had 26 possible initial states, changed daily. Thus, the number of possible initial states of the machine at the beginning of the message was about 9 × 10. For the U-boats it was 10.
One means by which the codebreakers tried to crack the naval settings was through the use of what came to be known as ‘Banburismus’. This process, invented by Turing, took its name from the long printed sheets – delivered from a printer in Banbury, Oxfordshire – on which the calculations were made. The sheets were almost a foot wide and several feet long. On each one was a series of vertically printed alphabets, with the letters divided by horizontal lines.
Clerks punched holes in these sheets that corresponded with enciphered messages; the first enciphered letter would be punched in the first alphabet column, the second in the second, and so forth. Once a large number of sheets had been prepared in this way, they would be stacked in a pile and examined against a dark background to determine where holes, and therefore letters, were repeated. This enabled the sequences used in signalling to be studied, and similarities to be found in the encoding. Turing’s colleague Peter Twinn explained the two alternatives that could be attempted by those working on the complexities of the code:
You can either find out the wiring of a brand new wheel or you can work out with a reasonable degree of accuracy what the messages might be saying.
Though apparently crude and time-consuming, Banburismus enjoyed a degree of success – at any rate until the beginning of February 1941, when the introduction of a fourth wheel to the naval Enigma made the process suddenly redundant.
For all the brilliance of their hunches and deductions, there was no substitute for solid evidence of German encoding practices, and Hut 8 had been able to begin work in earnest because in the same month that Turing first read the cipher (April 1940), there had occurred the first of a series of captures – ‘pinches’, as they came to be known – that arguably were to make a greater contribution to winning the Battle of the Atlantic than the painstaking work of the mathematicians. Like Admiral Hall in the previous war, the codebreakers knew how much time and trouble could be saved by seizing enemy code books. The importance of these pinches was therefore impressed on the commanders and crews of British vessels. Wherever opportunity offered, boarding parties needed to be ready to clamber on to captured or sinking enemy craft and make straight for the communications equipment. Enigma machines were screwed to tables and so time might not allow them to be dismantled and removed, but failing this any loose parts, together with all possible paperwork, must be gathered up and passed (probably by human chain) to the boat. In these circumstances papers frequently became wet through and largely illegible. Fortunately, one of the Bletchley boffins had previously been on the staff of the Natural History Museum in London, and had considerable expertise in paper restoration. In the first pinch in April 1940, cipher forms picked up aboard a German patrol boat provided the enciphered version of plain text messages. Further pinches, this time from U-boats, produced two of the wheels for the naval Enigma.
Organizing pinches became a preoccupation for one man. Ian Fleming, later to win fame as the author of the James Bond novels, spent the war years working at the Admiralty as an officer in Naval Intelligence. He conceived the notion of ‘Operation Ruthless’, a highly colourful attempt to steal a code book. Andrew Lycett, a biographer of Fleming, described the plan:
The Germans had begun operating a new air-sea rescue boat out of Denmark. Ian was convinced this would carry the latest German code books. If he and a few others could don some German uniforms and wait in a boat in the Channel, pretending to have ditched, the rescue boat would come to pick them up. The British could then overpower the Germans and capture the boat and its valuable contents.
Ian suggested the following strategy to secure ‘the loot’:
1. Obtain from the Air Ministry an air-worthy German bomber.
2. Pick a tough crew of five, including a pilot, W/T (wireless/telegraph) operator and word-perfect German speaker. Dress them in German Air Force uniform, add blood and bandages to suit.
3. Crash plane in the Channel after making SOS to rescue service in P/L (plain language).
4. Once aboard rescue boat, shoot German crew, dump overboard, bring rescue boat back to English port.
The scheme was taken seriously by the OIC and by Turing, who looked forward to the result. A crashed Heinkel bomber was reconditioned and captured Luftwaffe uniforms were provided. Fleming became more ambitious, deciding that the hoax should be played on a Channel minesweeper, since that would offer richer pickings. Having stipulated that the group should be led by a ‘tough bachelor, able to swim’, he was very keen to go but was forbidden to have any active part in the mission, because his knowledge of secrets made his capture too risky. He therefore became the operation’s director rather than its hero – M rather than Bond. It came to nothing, however, because weeks went by and no suitable German vessel appeared; postponement therefore turned to cancellation.
After the fall of France in the summer of 1940, the U-boats had access to French ports, such as Lorient and St Nazaire, on the Atlantic coast. This meant they no longer had to make lengthy voyages from the Baltic and could extend their operational range as far as Newfoundland and America’s eastern seaboard. With much of Britain’s navy and air force kept at home in anticipation of a German invasion, Atlantic shipping became more vulnerable, and that year losses amounted to a massive 3,991,641 tons.
In 1941 the statistics worsened: the year’s total would be 4,228,558 tons. Winston Churchill demanded that the Atlantic become an absolute priority in the planning and waging of the war, with top-level conferences held at the Admiralty every week. In some respects, the situation was already improving. Neutral America offered Britain 50 destroyers (a foretaste of the later Lend-Lease agreement) and agreed to provide escorts for convoys as far as Iceland. Britain’s own resources once again became available when it was clear that Hitler’s invasion plan would not be carried out. Nevertheless, as noted by Commander Balme, the difficulty was in replacing the continuing losses of shipping:
The Battle of the Atlantic was a ‘tonnage war’. Could the U-boats sink ships faster than we could replace them? Happily, a high proportion of our ships’ crews were rescued after sinking, but in 1941 we just could not replace them fast enough.
In the event, losses were less crippling than had been predicted. Although U-boats took a heavy toll, large percentages of the merchant fleets of occupied countries remained at large and joined the Allies. This was especially true of Greece, whose sizeable merchant marine became available when that country was overrun in 1941.
The U-boats’ method of operation was to sail for a designated area – usually a set of map coordinates in mid-ocean – and to patrol this for a period of weeks, awaiting any shipping that passed through it, while also awaiting orders to assemble en masse or to attack. They would return to port only when their fuel or ammunition ran out. By 1941, their missions could be extended through the presence of fuel tankers nicknamed ‘milk cows’, which loitered around the Azores (an area too far south to be within range of Allied aircraft). Though they began the war patrolling as single vessels, they developed a trademark tactic that was known as: the ‘wolf pack’: they would gather in groups of between 10 and 20 in the path of a convoy and then attack it under cover of darkness, with each boat choosing its own target.
On occasions in the 1914–18 war, U-boat commanders had behaved chivalrously. They would attack by surfacing and ordering the crew of the target into the lifeboats, giving them time to get clear before their torpedoes were fired. In the new conflict this practice was seen as sentimental and counter-productive. Hitler and Admiral Karl Dönitz, the commander of the German navy’s submarine arm, knew that trained crews were even less easy to replace than ships, and demanded that they share the fate of their vessel. A month after the U-boat campaign began, Dönitz issued this order:
Rescue no one and take no one with you. Have no care for the ship’s boats. Weather conditions or the proximity of land are of no account. Care only for your own boat. We must be hard in this war.
Despite the risks run by ships on the Atlantic routes, life on board was monotonous, and the notoriously rough North Atlantic could be challenging, to say the least. Eric Marshall, who served aboard a naval vessel in these waters, described conditions that would have been extremely common for much of the year:
We were battered by the seas, many waves sweeping right across us, damaging and carrying away quite heavy gear. Travelling anywhere on deck was hazardous and choosing the right moment to move was not easy, particularly at night. Lifelines were always rigged in these circumstances but I could never make up my mind whether it was better to make a slow crawl using them or a quick dash and get it over as quickly as possible.
Marshall was a Coder and he and his colleagues worked in both Morse and radio. Their equipment included sets of code books, to which they were constantly referring and which they were trained to throw over the side if there were any danger of their vessel being captured. The books were deliberately weighted with lead for this purpose:
Work in the sea-cabin with heavily weighted code books crashing about was frustrating, and even sitting at the desk having to brace oneself against violent movement was exhausting.
When not engaged in his specialist work Marshall was an ordinary member of the ship’s company, taking his turn at other tasks, and was expected to help on the bridge (because it was next to his office) in stressful moments. Recalling the type of quiet interlude that could sometimes be snatched away from his desk, he provided a glimpse of a Coder’s life at sea:
While still dark during either the middle watch (midnight to 4 a.m.) or morning watch (4 a.m. to 8 a.m.) and if W/T traffic allowed, I would go into the wheel-house and have a chat with the helmsman and perhaps have a spell at the wheel, which in our case was not discouraged bearing in mind the duties that a Coder on watch might be required to undertake in an emergency. With one leg drooped over a spoke of the large, fixed wheel, an eye on the compass ahead fastened from the deckhead, one ear for any orders which may come down via the voice pipe from the Bridge and the other for any call from Mac through the door behind me busy with the continuously chattering Morse from his W/T sets, I was able to experience an unusual sense of calm.
His links with the world beyond the ship’s bulkheads made him popular with the rest of the crew, for he could provide gossip and diversion:
As Coders we were generally welcome wherever we went, for we were a useful source of information, not only from the routine less confidential messages we received, but also from the BBC news, which at sea could only be received through the sets in the wireless cabin. One of our official jobs was to prepare a daily news sheet for pinning up in the wheel-house.
Occasional relaxation notwithstanding, the atmosphere aboard an escort vessel was more usually characterized by taut nerves. The ships had to travel at the slow speed of the lumbering freighters. They had to steer an evasive course to present a more difficult target for pursuing submarines. Their crews had to scan the sea day and night for the telltale white wake of a periscope. Commander Balme remembered one such convoy:
The most tiring time of all was at night (for in the winter months night was 16 hours out of 24). We had 40 to 50 merchant ships and 8 to 10 escort vessels and we would zig-zag night and day at a speed of only 8 knots. On the bridge was an officer of the watch, a signalman and two lookouts.
The enemy was often not far away. Single U-boats might be following a ship or a convoy, but it was also likely that a group of them was gathering.
With its access to British naval code, the B-Dienst was listening to as many as 2,000 Admiralty signals a month during the first half of 1940, and could thus build up a detailed picture of shipping movements in the Atlantic (until the Admiralty changed its code, ending this intensive eavesdropping at a stroke). It would pass on to U-boat commanders by coded Morse radio signals the map references for the route being followed by a convoy. The predators could then decide where to rendezvous and set up an ambush, opting for mid-ocean so that they would be within the ‘air gap’ beyond the range of either British or Canadian escort aircraft. The horizon would then be searched by the submarine’s crew – either with binoculars from its conning tower or through the periscope – for the far-off wisps of smoke that heralded the arrival of its quarry in the hunting ground.
Commonly, a single vessel or a pack of submarines might follow the ships for days, waiting until enough of them had assembled before attacking. In turn the convoy and its escorts would naturally be searching the seas for any sign of the U-boats’ presence and so the wolf packs would keep both depth and distance between themselves and their prey, usually waiting until dark before moving in for the kill.
Aboard the convoys, the tension mounted palpably each evening. At dusk the crews of freighters would go to action stations, remaining at their posts until dawn. On a voyage lasting a week or more, they could expect to be attacked on consecutive nights by the same enemy submarines, and though the timing of these incidents might be predictable, nothing could be done except to remain alert and hope that the accompanying naval vessels, with their detection devices and depth charges, would spot them. Danger increased once they reached the air gap. S France remembered the anxiety, and the horror, of those long nights:
After two days and nights, the aeroplanes and corvettes [reached the limits of their range]. They could go no further so the convoy was left with nothing but the clear blue skies and the rolling waves of the Atlantic.
On the third night at 10.00 p.m. exactly, the U-boats struck among the ships of the convoy. There were loud explosions and the ships were lit up like an inferno. By daybreak there was silence and the damage done was quite visible. There were broken and battered ships scattered about. The ships that were intact kept moving steadily ahead throughout the daytime. They just sailed ahead and, as before, 10.00 p.m., the U-boats struck and again there were explosions.
On the third night at 10.00 p.m. the same destructive chorus opened up with the usual sounds and the heavens blazing red from the fires on the sea. As the stricken ships exploded one ship spilled out liquid all over [the water] and as it became alight the ships were all travelling through waves of flaming fire. The sea was so brilliantly lit that the whole scene was like a well-lit stage. The crew on board a burning ship formed a queue and a priest placed the Holy Sacrament into each man’s mouth, made the sign of the cross, then each man, after he had taken the Sacrament, jumped overboard right into the flames. The priest was the last man; he also swallowed the Sacrament, then, clasping his hands together, he too dived into the flames …
The wolf packs did not have things all their own way, however. Sailing with another North Atlantic convoy, Ordinary Seaman CJ Fairrie, a Bridge look-out aboard the destroyer escort vessel Bulldog, witnessed U-boat attacks over a period of three days. He described the ensuing action:
In the evening about 2100 we received a contact on our ASDIC submarine detecting outfit [an electronic probing device, formulated by the Anti Submarine Detection Investigation Committee, hence its name], however it was ignored – whales had been in the vicinity all day. At 2115 explosions were heard and two merchant ships in the rear of the convoy were seen to be sinking. The larger of the two, believed to be carrying whisky, was on fire. Small boats and rafts put off from both vessels, and it was later confirmed that no lives were lost.
Meanwhile ‘Action Stations’ had been sounded (I was Port Action Lookout on the bridge). The Amazon and escort vessel Rochester, together with Bulldog, dropped patterns of depth charges while the other escort vessels proceeded with the convoy. The U-boat encounter was eventually abandoned and the prey believed to be sunk owing to the severity of the attack. However the search went on throughout the night. Praise must be given to the U-boat commander for his daring attack, which was carried out at short range – he had contrived to pierce the defences of the escort vessels and had got among the convoy itself. After the U-boat attack, several contacts were registered – these stopped at 2325. It is said that 130 depth charges were dropped – what underwater craft could survive such a bombardment?!
The following day 1201. Ship noticed to be giving off white clouds of steam. Convoy moves off to port – some ships go to starboard. Smoking vessel settles low in the water – bows and stern seem to be coming up to meet. Another ship – larger than the other (in fact the largest in the convoy) is seen to be dipping her bows among the waves. The silence of the attack is eerie. Broadway (destroyer) and Aubretia (corvette) counter-attack. Three more ships in the meantime are torpedoed! The Esmond (the large merchant packet) is seen to have received a hit beneath the bridge.
The sea is rougher today and soon bobbing black objects are seen among the waves as boats and rafts lay off. One ship blows up amid a huge mass of flame and smoke. It appears that we have run into a nest of U-boats and the convoy is broken up. Armed trawlers stand by to pick up survivors.
Once a vessel had been hit, there was a set of procedures for evacuating those aboard and for destroying any materials that could be of value to the enemy. Captain Eric Monckton of the freighter Empire Starling, carrying beef from South America to Britain, remembered vividly his actions after his ship was torpedoed near the ‘Serpent’s Mouth’ off Trinidad:
After throwing the weighted bag over the side and getting rid of all secret papers, I made for the boat deck and gave orders for the crew to take to the boats and stand by one ship’s length astern. On going to the radio room, the Operator informed me that he had got away the SOS twice on the emergency set.
The Chief Officer and Chief Steward informed me that all their staffs were mustered and getting away in the boats. The Radio Operator had thrown the radio codes and secret orders over the side and came to inform me of it.
Before leaving, I went to the crews’ quarters and shouted for anyone who might have gone unnoticed in the muster for the lifeboat. There was no response and, all secrets and codes being disposed of, I made my way to the lifeboat.
The attackers too experienced apprehension as they stalked their prey, aimed at the target and then waited for retribution (in the form of depth charges) to descend on them from above, for a horrific fate might await them amid acrid fumes and claustrophobic darkness if their craft went to the bottom. Ironically, and in spite of Dönitz’s orders, Captain Monckton was captured by the U-boat that sank his ship and spent weeks aboard the U163. He witnessed the moment that this vessel discovered another potential target:
An American cruiser and an accompanying destroyer were sighted on the bow. The U163 dived hurriedly to periscope depth and closed for action, everyone on board being chased to their attack stations. All electric fans were turned off and amongst the crew there was great tension and excitement. The heat inside the submarine was unbearable and the perspiration just poured off me in streams. All was deathly quiet, except for the occasional sharp orders through the repeaters which were placed in each compartment of the hull.
I heard the torpedo being fired, the hiss caused by the compressed air used to initially send out the torpedo causing a definite pressure on the eardrums. Less than a minute after the torpedo had been fired, I heard a slight ‘ping’ as it struck the ship. Later, I learned that two torpedoes had been fired simultaneously.
Later the U163 took on a ‘down by the head’ position (e.g. with the bow pointing downward) and it was evident that we were going deeper. Some ten minutes after this, I could hear a noise like the rush of an express train and then the explosion of the ‘ashcans’ raining down and severe shakings of U163. We remained very still for about an hour. After remaining still and quiet for several hours and the hot atmosphere inside the submarine being just unbearable, we rose to periscope depth and after a careful look round through the two periscopes and seeing nothing, we broke surface.
The sending of reports and receiving of orders was, of course, carried out by radio, using the naval settings of the Enigma code. Captain Monckton noticed the regularity with which this was done:
Every night at a certain time, the U163 was in touch with Berlin and other German Base Stations, and if not on the surface could pick up [signals] from periscope depth via the 36-foot retractable tapered receiving mast which was mounted on the deck of the conning tower, and so received orders for her next day’s operating area. The charts used on the U163 were all marked out in numbered squares for easy reference purposes.
If Allied Intelligence could break the naval Enigma code and decipher U-boat radio traffic, the onslaught on the Atlantic convoys could be significantly hampered. In the early summer of 1941, Harry Hinsley of the Bletchley staff conceived of a possibility. The enemy was monitoring the weather in the North Atlantic from trawlers that sailed the waters around Iceland. These did not report their findings through Enigma, but they did use it to receive messages from Germany and must therefore have code books aboard. If one of these unprotected vessels could be boarded, the result might be a vital intelligence breakthrough.
The chosen target was the München, a trawler that would be at sea during May and June. An armed naval party would board the vessel, but it was highly likely that the crew would dump overboard any materials regarded as secret or sensitive. The Enigma settings were changed every month and the May ones were expected to go over the side. The June settings, however, would be kept somewhere secure and the boarding party would gamble on capturing the boat before the captain could reach them.
The Admiralty approved the plan, and a sizeable force was sent in search of the trawler. Aboard the flagship HMS Edinburgh was Colin Kitching, then an Ordinary Seaman. He remembered that:
On May 5th the 18th Cruiser Squadron (HMS Edinburgh, Manchester and Birmingham, with five destroyers) sailed from Scapa Flow and headed north.
The operation (codenamed EB) had been mounted with the specific aim of intercepting and capturing the München. Using surprise and speed, Admiral Holland intended to capture and board the vessel; all being well, an immense prize might be secured – a set of coding tables enabling the enemy’s naval cipher system, Enigma, to be read immediately for the first time.
At 1707 on May 7th the München was sighted between Edinburgh and [the destroyer HMS] Somali. The latter fired warning shots which caused most of the München’s crew to take to the boats. Somali closed at speed and boarded the ship. A prize crew and boarding party from HMS Edinburgh then went over in a cutter, which also carried a man in civilian clothes.
I made an inconspicuous contribution to the capture of the München. I was a member of the Edinburgh’s boarding party and escorted the mysterious ‘civilian’ to the vessel and back again. (Many years later, when this most hush-hush mission was at last declassified, it was revealed that he was Captain J.R.S. Haines, RN, of Naval intelligence.)
For the first time in my life I was equipped with a revolver and we – the boarding party – were under orders to fight our way on board the München if necessary. But the Somali was alongside and most of the München’s crew had quickly abandoned ship, leaving – as I remember – only the captain, another officer and a couple of ratings to receive us, which they did with great courtesy. Indeed one of them kindly helped me over the guardrail. The boarding party had to search the München in case the Germans had laid scuttling charges in the bowels of the vessel. I was somewhat handicapped by the fact that I didn’t know what a scuttling charge looked like. As it happened, there were none.
The München’s captain had thrown the Enigma machine and the May coding tables over the side as Somali approached, but the settings for June were in his desk; these were duly collected by Captain Haines, who knew exactly what he was looking for. Some of München’s crew were taken on board Edinburgh. Somali escorted the captured vessel to Scapa. HMS Nestor took Captain Haines to Scapa at speed; he was flown to London and reached Bletchley Park on May 10th.
At almost exactly the same time another prize was seized by the Royal Navy when a German submarine, U110, was boarded in the Atlantic after its crew surrendered. Though the vessel itself was later lost while being towed in rough seas, the finds made on board proved a priceless treasure for the Admiralty and for Naval Intelligence. This was a tremendous coup. The settings were precisely what the Bletchley codebreakers needed, for from the beginning of June they made it possible for the first time to read current U-boat messages within about six hours of receiving them. It had previously taken an average of ten days. As with the München, the German authorities had no idea that the Enigma machine with its coding materials had been captured.
The boarding of U110 became one of the most celebrated events in the intelligence war, for the combination of circumstance and courage made it an exciting story as well as a highly significant achievement. It was seen from the Bridge by Ordinary Seaman CJ Fairrie aboard the destroyer HMS Bulldog, which was escorting the convoy. Parts of his account were clearly written with hindsight: few of those who waited aboard, or manoeuvred the ship’s whaler through pitching seas toward the U-boat, would have known anything about German code books or realized at the time the importance of the finds. Nevertheless, there is about his memories a breathless immediacy that conveys the excitement of capturing one of these elusive enemy vessels:
About 1230, my opposite number lookout suddenly sights what appears to be a conning tower rising up out of the waves. It is! A surrendering U-boat brought up owing to damage received from Aubretia’s depth charges. At first sight I was astonished at what appeared to be a gasometer surfacing, and then the whole structure came into view. The starboard lookout yelled ‘U-boat surfacing!’ before I could open my mouth!
[The destroyer ] Broadway swings round and bears down on the U-boat. The latter’s crew are pouring out of the conning tower. Broadway prepares to ram but at the last minute turns away – but not without damage to herself – a glancing blow on her stern which puts one of her screws out of action. She fires point-blank into the conning tower. Bulldog turns, increases speed and prepares to ram. About 40 yards off the captain thought better and the Bulldog swung round to starboard. Previously, our 4.7s and 3-inch [guns] had opened up, but our fire fell short. Our pom-poms later sprayed the U-boat decks. Tommy guns, fired from the bridge, also joined in. A man clutched his stomach and fell forward into the water. Another with face covered in blood dived from the U-boat decks – spray and blood mingled together. A third was seen to have stopped a pom-pom bullet which took his head off, and he stood fountaining blood before pitching into the sea. Twice the crew tried to man their forward gun, but were driven back. The after-deck of the U-boat was awash. By now the majority of the crew were floating about in the water. Their facial expressions were inexplicable: no sign of fear. Resigned and unquestioningly calm. One raised an arm and cried ‘Kamerad!’ This was greeted by jeers and the brandishing of fists. Another Nazi was seen to be supporting a dying companion in his arms.
On the side of the conning tower was a monogram – a leering dog. One ear cocked and the other drooping. Beneath this was a gaping hole in the armour plating. Two officers clung to the conning tower amid a hail of murderous fire. At last they too jumped into the sea. The order ‘Cease fire’ was given. In spite of my previous humanitarian ideas, I could summon up no feeling for those men in the water. On previous convoys I had witnessed oil tankers hit and the sea on fire, choking and burning survivors, making rescue impossible. U-boats did not wait around to pick up survivors. I remembered the tale of the destroyer captain who, when he received orders to pick up U-boat survivors, raised his glasses to the sky and said ‘I can see no survivors’ and steamed on.
Previously a man believed to be the captain stood on the U-boat deck and semaphored to our bridge – unintelligible. It is said that he was trying to say that his was the only U-boat operating. What a tale! He was later identified as Fritz-Julius Lemp, who on the first day of the war had torpedoed and sunk the passenger liner Athena.
Bulldog lowered a whaler, and with Sub Lieut. Balme in charge, it went alongside the U-boat. They boarded the half-submerged vessel, and signalled to say she was watertight below and could be towed. The Broadway and the corvette [Aubretia] stood by screening our activities from attack. Meanwhile corvette picks up German survivors. She already had merchant ship survivors on board – a good mixture!
Our whaler buffeted by waves breaking against side of submarine, was damaged, broke loose and sank. Broadway’s whaler joins the fellows on the U-boat. Secured for towing about 1530, but had to loose again owing to fouling of screws. Secured again about 1700. Charts, codes, names of spies, U-boat bases, knowledge of movements of our convoys – an enormous coup – turning point in the Battle of the Atlantic! Materials seized from the U-boat [were] passed up from hand to hand. Among them was a wooden box that looked like a typewriter [though he added later: ‘At no time were we aware that a German Enigma machine had been captured’]. Meanwhile Amazon after dropping depth charges sees patches of oil and bubbles – claims another U-boat. A third U-boat is also supposed to have been sunk. The nest is losing its chicks!
We head back for Iceland with U-boat in tow. The disabled Broadway is our escort; both almost devoid of depth charges! We are open targets, proceeding at 5 knots! A signal has been sent calling for two tugs but they will not arrive until the following night – maybe later!
A coded signal is sent to HQ: ‘Have Primrose in tow, consider petals to be of great value.’ The following Thursday an answering signal is received from A.V. Alexander, 1st Lord [of the Admiralty]: ‘To Bulldog from Admiralty. Hearty Congratulations The petals of your flower are of rare beauty.’
When towing operation began we were approx. 420 miles from Iceland. No further signals are sent out owing to the possibility of our position being detected (whilst the securing of the U-boat was being done, lookouts reported a periscope on our starboard side – after 5 secs it disappeared and no more was seen of it).
Early next morning a signal came through to say that the convoy had run into another U-boat nest. Imagine our feelings – the seas are getting rougher, our speed is below 5 knots and we are a sitting bull[’s eye] to enemy action. It is hard to sleep and everyone is jumpy and nervy – will we get our prize home? If only the tugs would arrive and we could take over the escort duties from the crippled Broadway.
Saturday 10th May. Seas choppy, high wind. 1055 U-boat sank. Relief felt, in spite of our losing a grand coup. Wires are cut and we speed at 20 knots back to Iceland.
Another surviving account is that of the man who led the boarding party. Sub Lieutenant (later Commander) Balme had had no preparation for his role in capturing Enigma. He and his shipmates had not practised boarding submarines, or even launching their ship’s boat. Balme was the gunnery-control officer aboard HMS Bulldog and at the time was concentrating on his task of directing the ship’s guns as they raked the submarine. On the bridge of Bulldog the Commander of the 3rd Escort Group, Joe Baker-Cresswell, saw the potential of the situation and decided to take immediate action. There was a heart-stopping moment as the destroyer Broadway appeared to be trying to ram the U-boat and sink it. Baker-Cresswell immediately ordered the nearest available officer to take a party of men and get aboard the U-boat. Balme rose to the challenge. His account began by setting the scene:
On the 9th of May, 1941, we were attacked at noon. I had been on watch from 0400 to 0800, and after a bath and breakfast I was on the bridge. It was a sunny day, moderate wind but the usual Atlantic swell.
Suddenly, at noon, two ships were hit by torpedoes and we went to action stations. We turned the convoy 45 degrees away from the attack and Bulldog went full speed to the likely position of the U-boat.
The corvette Aubretia gained contact with the U-boat and attacked with depth charges. The U-boat surfaced 400 yards from us and we opened fire with every gun.
The noise was deafening and especially from our Lewis machine-guns which were being fired from the bridge over our heads by anyone who could pick them up. However it was undoubtedly the noise of all the shells and bullets hitting the U-boat which panicked the German crew, who all jumped overboard as fast as they could without successfully scuttling the U-boat. Thus the order went out: ‘Away armed boarding party.’ The captain ordered me to take the boarding party and get what I could out of the U-boat.
He then described the adventure itself:
The Gunner’s Mate was issuing revolvers and ammunition to me and the crew of the seaboat. We were 8 men and the seaboat was the traditional 27 foot wooden whaler pointed at both ends. We got out the oars and began rowing over to the U-boat. As speed was essential, I steered the boat to the nearest side which was to windward with the rollers breaking against the hull.
He ventured along the foredeck and climbed down the ladder inside the conning tower:
There were no Germans on deck or in the conning tower, and surprisingly the watertight hatch was closed. The worst moment was going down the last vertical ladder to the control room. Going down bottom-first, I felt a very vulnerable target to any German still down below.
The most eerie feeling was the complete silence except for an ominous hissing sound which was either from the batteries or a leak in the hull. The secondary lighting gave a rather dim ghostly effect. The U-boat had a 15-degree list to port and there was a plopping noise as she rolled against the Atlantic swell. This swell eventually broke up our whaler and we were then supplied with a motor boat from the destroyer Broadway.
I walked forward and aft through the two watertight doors out of the control room and decided that the Germans really had abandoned ship. I called my sailors down and told the signalman to semaphore back to Bulldog that she was deserted.
Balme and his men demonstrated immense bravery in searching methodically a vessel that was slowly sinking and whose scuttling-charges could have gone off at any time. Their comrades could do nothing to assist them – except see to it that their problems did not include hunger. The notion of providing snacks for men working in such danger strikes an oddly prosaic note amid the drama:
Speed in searching the U-boat was now essential, as I felt sure that the scuttling-charges would go off sooner or later, especially as there were continuous explosions around us from our depth charge attacks on other U-boats. This was a most unpleasant and frightening noise. We formed a human chain up the two ladders and began passing up books, charts and wireless equipment.
The great thing was for all the boarding party to be kept busy, passing out the items, including the Enigma cipher machine which was found in the wireless office. It was unscrewed from the table and so began its fateful journey up the conning tower into the motor boat of Bulldog. Thence to Iceland, then to Scapa Flow and from there to Bletchley.
Time was marching on. We boarded U110 at 1230 and were glad to receive sandwiches from Bulldog during the afternoon. Throughout these hours our escort vessels were attacking U-boats with depth charges and my fear was that their explosions, which felt very close, would set off the detonating charges.
Having got most of the books, charts and moveable wireless and other instruments out of the U-boat, I now thought I should have an engineer to try and get the engines working. So I semaphored Bulldog and in due course our Engineer Officer came over with a few stokers, as they were still called. But with everything written in German and nobody having ever served in submarines, we decided we would do more harm than good by turning the cocks to get her under way.
Meanwhile, on deck, Bulldog came in close and we tried to secure a towing wire. The first one parted and then Bulldog had to leave to investigate and attack a reported U-boat contact.
This was indeed a desolate and awful moment. There was I, with my boarding party, aboard U110 in the middle of the Atlantic, alone with no ships in sight and the wind and sea gradually increasing. This must have been about 4 p.m. There were not really any more books or moveable gear we could collect, so I battened down the watertight hatches and we waited. Happily, Bulldog returned and we set about securing a tow. This held and thus at about 6.30 p.m. we evacuated the U-boat and returned to Bulldog, having spent 6 hours in U110.
The findings aboard U110 were, in intelligence terms, a sort of Tutankhamen’s tomb. Together with the Enigma machine there was a stack of code books that gave the key to reading the U-boats’ short signals and weather reports. There was a set of bigram tables that confirmed, and expanded, the knowledge of these that Bletchley staff had already attained. Most significantly, perhaps, there were the ‘Offizier’ settings for June. These were a means of doubly enciphering particularly important messages. Sensitive material was first encoded using the ‘officer’ settings, and then again using the general ones. The ability to read this traffic made an immense difference to the Allied war effort, especially since changes to the naval Enigma were often announced via the Offizier code.
There were charts among the booty that indicated the positions of German minefields as well as the clear channels within them (this knowledge was to prove invaluable in planning Allied raids at St Nazaire and elsewhere). There were also charts for fixing the positions of U-boats in the Atlantic and indicating the locations of the ‘milk cows’ that refuelled them, 15 of which were to be sunk in the following weeks (unlike the U-boats themselves, their hulls were not designed for quick submersion).
All those involved in the operation were sworn to secrecy, and without exception kept silence for decades afterwards, but at Bletchley and Whitehall the excitement was intense. The U110 captures enabled the Hydra code to be read by the Allies almost as swiftly as by the Germans themselves. They were able to build up a detailed knowledge of U-boat tactics, patrol routes, operational routines, supply arrangements, and plans for attacks. From Bletchley the U-boat radio traffic, once deciphered, was forwarded to the Admiralty’s Submarine Tracking Room from which the war against the U-boats was organized, and which would now be able to route convoys away from the concentrations of U-boats.
A third coup, this time in the Mediterranean off the coast of Egypt, brought further secrets into the possession of the Allies but at a steep cost. In October 1942 a U-boat was forced to the surface by destroyers. Two members of a three-man boarding party in search of coding materials – Lieutenant Francis Fasson and Able Seaman Colin Grazier – lost their lives and received, posthumously, the George Cross for their bravery. The third member of the party, a 16-year-old canteen boy named Tommy Brown, remained on the U-boat’s conning tower to receive the items while the others went aboard. He survived the sinking and was awarded the George Medal. The incident is described, using the words of the citation, in Sir John Smyth’s history of the GC. Neither at the time nor when this history was published in 1968 could the nature of the finds or their relevance to the war effort be revealed. Both Fasson and Grazier very nearly received the Victoria Cross, but the Honours and Awards Committee decided, regretfully, that they were not quite eligible because ‘the service cannot be held to have been in the face of the enemy’. The George Cross is, nevertheless, evidence of truly outstanding bravery, and its award to men involved in pinches reflects the significance attached to the results of these daring raids:
The U-boat had been sighted on the surface by a British aircraft on a dawn patrol, which at once alerted the Destroyer Flotilla. After a lengthy search of the area the submarine’s approximate position was ascertained. Depth charges were dropped which forced the submarine to the surface, when she was immediately holed by gun fire from the destroyers. The crippled submarine at once surrendered and her crew were taken off. It was however important that the submarine’s papers and documents should be recovered, and HMS Petard came alongside her for this purpose. Lieutenant Fasson, who had given valuable assistance in tracking down the submarine, at once boarded her, taking with him Able Seaman Grazier. They were both fully aware that in the darkness, with the water rising rapidly in the sinking submarine, time was not on their side. They continued to produce and hand over instruments and papers until the submarine suddenly sank like a stone, taking them both to their death.
It was not always the naval Enigma that enabled the Allies to achieve victories at sea. On one occasion it was the air force version that provided information vital to the snaring of a major prize. In May 1941, the battleship Bismarck was heading for the French port of Brest. Bletchley knew that the ship was heading south, but did not know its destination. This was given away when a signal was intercepted from the Luftwaffe Chief of Staff, General Hans Jeschonnek, who wished to know Bismarck’s movements because a relation of his was on board. Once this knowledge was passed to the Royal Navy, Bismarck was ruthlessly hunted by ships and aircraft. On 26 May it was cornered and its rudder disabled in a bombing attack by planes from HMS Ark Royal. It sank shortly afterwards. The news provided an immense boost to morale at Bletchley, where the clerks and codebreakers could appreciate the part they were playing in winning the war.
Though findings of German coding materials were of great importance to the Royal Navy, they did not ‘turn the tide’ in the Battle of the Atlantic. There had been successes before the breakthroughs with the Enigma machine and there were disasters afterwards. One of these, in February 1942, was the replacement of Hydra with a new code (dubbed ‘Shark’ by the Allies) based on the addition of another wheel to the machine, which caused shipping losses to soar again.
The ability to read German signals was of vast importance to the Allies, but it was only one of a series of factors that brought gradual success. In March 1941 Günther Prien, regarded as Germany’s leading U-boat ace since he had sunk the Royal Oak in 1939, was lost with his entire crew when U47 was sunk by a depth charge. Only days later another legend, Karl Schepke, perished with his crew after being rammed by a British ship. A third famous submariner, Otto Kreschmer, was captured after his boat was sunk. Nevertheless, German submarine production was steadily increasing: at the beginning of 1942 there were 249 U-boats in service; by 1943 this would increase to 393 and by 1944 (production having been slowed by Allied bombing) to 436. In addition, changes in naval Enigma again left Allied codebreakers groping in the dark for some months.
The Allies learned from the costly experiences of the war’s earlier phase and slowly but steadily put new resources into place. The introduction of aircraft with a longer patrol range of 800 miles, as well as the use of aircraft carriers, closed the air gap. More sensitive radar was developed, and the introduction and improvement of ‘Huff-Duff’ (high-frequency direction-finding equipment) meant that the Allies could pinpoint the positions of U-boats with greater accuracy. Initially based ashore, Huff-Duff was later carried aboard ships. For attacking submarines the ‘hedgehog’ was developed – a 24-barrelled rocket launcher whose bombs detonated on impact with a U-boat’s hull, and was thus deadlier than depth charges. Most importantly, the team in Hut 8 broke Shark, enabling the naval planners to reroute convoys away from U-boat packs, and confirming that the Germans had been reading the Admiralty’s own Number 3 code; after March 1943 they were no longer able to do so. As a result of this knowledge and the subsequent measures taken by the Allies, almost 100 U-boats were sunk during the first months of 1943.
Dönitz, whose son was lost aboard a U-boat during this period, was astonished by the success of Allied convoys in avoiding his submarines. He realized that, somehow, the enemy must be gaining access to his vessels’ communications, but the notion that Enigma codes had been broken was not taken seriously. It was therefore assumed that the problem was caused by some superior form of radar. There seemed to be little that could be done about this, and no attempt was made to change the Triton code.
As the North Atlantic became more dangerous for submarines, they sought softer targets and found them in the seas off the Americas; and the fact that they were hunting elsewhere did much to save British shipping during the spring and summer of 1942. Though the United States was now at war, the American coast was not subject to blackout and neither was its shipping. Oil tankers and other merchant vessels did not travel in convoy. The constant traffic from the oil refineries of Texas and Trinidad provided a target too tempting to ignore and the U-boats took full advantage. There were so many of them in the western Atlantic that their wolf packs often comprised 20 boats – twice the number that had been common further north. The early part of 1942 became a second ‘happy time’ as three million tons of shipping went to the bottom in the first half of the year, a rate of sinking four times higher than in the Atlantic. Germany’s official history of the naval war, published many years later, commented that:
Convoys in the Caribbean and on the Brazilian and African coasts were not only less strongly escorted, but the escort vessels themselves were regarded by U-boat crews as being ‘harmless’ in comparison with those in the North Atlantic. A single U-boat had more chance of firing torpedoes at a convoy sighted in these areas than had a whole group of boats against a US–UK convoy.
Though these easy victories gave the submarine crews a certain amount of euphoria, they were clearly not enough. The vastness of America’s resources meant that it could continually replace losses, and even the destruction of its merchant shipping was not proving fatal. US shipyards embarked on an accelerated programme of construction in which ‘Liberty ships’ were assembled by skilled teams from prefabricated sections. The fastest recorded time in which such a vessel was built was 80 hours 30 minutes. The average was longer, but the ships were so simple in design that they could be completed in less than two weeks and were soon being built at the rate of 140 a month. Germany’s senior naval officer, Grand Admiral Reader, had told Hitler: ‘The sinkings of the U-boat war are a race with merchant ship construction.’ He had estimated that, in order to cripple the Allies, German submarines would need to sink 800,000 tons a month. Only once – in November 1942, when the figure was 802,000 – was this ever achieved. In 1943 the Allies lost 3.22 million tons through enemy action, but built 43.59 million tons. This was a contest that Germany could not possibly win.
In the meantime, other Allied advantages steadily grew. America’s entry into the war after the attack on Pearl Harbor in December 1941 had meant that half of the US Navy was now assigned to the Atlantic, and the number of available escorts therefore vastly increased (it was estimated that to ensure success there must be two escort vessels for every U-boat). RAF Coastal Command received more aircraft and some of these, such as the Sunderland flying boat, were specifically designed for U-boat hunting. Aircraft also targeted the Bay of Biscay, through which submarines had to travel when leaving or returning to their home ports, and this small area quickly became a killing ground that was feared by U-boat crews. In 1943 the Allies occupied the Azores, gaining a strategic base in mid-Atlantic.
These factors made the U-boat campaign increasingly expensive and the month of May 1943 brought the highest price yet. By 23 May, 47 U-boats had been lost – a rate of more than two a day. Dönitz conceded defeat. He knew that such a casualty rate could not be sustained and withdrew his fleet from the offensive. It was no longer worth spending lives in large-scale attacks when the odds were so steeply against success. For the remainder of the war, the U-boats concentrated on tying down Allied resources to keep ships and aircraft away from the coasts of Europe.
By 1944 the stream of Allied shipping across the ocean had become a torrent. The vessels now carried human cargoes, as well as freight, for the Allies were building up armies in England for the invasion of Europe. Their control over the Atlantic was by that time so overwhelming that not a single troop-carrying vessel was sunk. U-boats were deployed in a defensive role during Operation Overlord (13 of them were sunk in the Channel during the invasion) but as the Allies overran France the Atlantic ports from which the submarines had sailed were either captured or cut off, and the fleet was obliged to retreat to the Baltic, to help Germany’s increasingly desperate rearguard action against the Russians, or to Norway.
They were never, however, defeated entirely. In 1944 the introduction of a snorkel device made it a great deal more difficult to detect U-boats, for they could travel submerged for much longer; combined with a practice of keeping total radio silence during missions, this added considerably to their effectiveness. In the last year of the war two entirely new models appeared. The Type XXI and the Type XXIII were the most advanced submarines yet produced. Equipped with snorkels and with a speed of 17 knots (10 knots faster than the Type VII) they could have made a considerable difference to the German war effort if they had been introduced sooner and in greater numbers. They were preparing for a new offensive, as if unaware that the Third Reich was collapsing around them. They were, of course, too late. The U-boat war ended with the surrender of Germany on 8 May 1945.
And the role of the codebreakers in the Battle of the Atlantic? Their work had been vital in keeping supplies of raw materials flowing to Britain, thus preventing capitulation and complete German victory before the US became a belligerent. It had seriously hampered the efforts of the enemy submarine fleet and had saved, according to Hinsley’s estimate, about 350 vessels – one and a half million tons of shipping – from destruction.