By March 1944 Germany’s U-boats in the Atlantic had turned from predator to prey, pursued by patrol aircraft: A Royal Canadian Air Force Sunderland has bracketed U-625 with six depth charges and has begun machine gunning (splashes to starboard).
By the beginning of January 1944 losses at sea had reduced the U-boat Arm to 168 operational boats. This was only about two-thirds of its strength at its peak nine months previously, despite a continuous flow of replacements. However, a total of 268 newly built U-boats were undergoing trials during the month. The colossal bombing campaign by RAF Bomber Command and the US Eighth Air Force had done little to limit U-boat production. Although great swathes of residential districts in Kiel, Wilhelmshaven, Bremen, Vegesack and Hamburg had been destroyed, the effect on manufacturing areas and dockyards had been far less severe. Many more U-boats were being built than in the earlier years of the war.
Many of the best commanders and crews in the U-boat Arm had been lost, although there were plenty of newcomers to take their places. Most of these were volunteers but some were drafted from other branches of the Kriegsmarine. The trainees first underwent a three-month course during which discipline was the key ingredient. Then they were split up to train in their specialist trades, which took varying lengths of time. A few were trained as commanders, first watch officers or engineering officers. Others became helmsmen, diesel mechanics, electro mechanics, torpedo mechanics or cooks, etc. Some duties in a U-boat were common to several men, such as keeping lookout or steering. After qualification, a few were sent to join operational U-boats as apprentices, but the majority were posted to the newly built boats for familiarisation and further training. Again, the length of training time depended on each function. All knew that they would experience very cramped and uncomfortable conditions on their war cruises.
Some of these newcomers may have guessed that they would probably meet the fate of many of their predecessors, although most of them probably believed that they would somehow survive the war. The truth was that the majority would end their young lives entombed in shattered hulls somewhere on the bottom of the sea, although a few of the luckier ones would be picked up by the Allies and spend most of the rest of the war in PoW camps. The U-boat Arm was operating with reduced numbers of operational boats and by then was without its Italian allies. Its war was being fought in great areas of the world’s oceans and seas – the North Atlantic, the South Atlantic, the Arctic Ocean, the Mediterranean and the Indian Ocean, with a handful of boats in the distant waters of the Far East. However, the men were buoyed up with the hope that new developments would enable them to regain some advantage over an increasingly powerful enemy.
The ideal would have been a U-boat that could remain submerged throughout its war cruise, and indeed such a boat had already been designed by Professor Hellmuth Walter in combination with Germaniawerft of Kiel. Known as a ‘Type V boat’, it consisted of two hulls, one on top of the other. The top hull contained a turbine engine and the crew with their controls, while the lower hull was simply a huge fuel tank containing concentrated hydrogen peroxide. Such a boat could travel underwater at the extraordinary speed of 30 knots, faster than most Allied escort vessels, but it was impractical for two main reasons. One was that there were inadequate facilities in Germany to provide the enormous quantities of fuel required, while the other was that the Type V boat could be produced at only about half the rate of conventional U-boats.
Although the project to manufacture the Type V boat was abandoned, there was a simple adaptation that could be produced rapidly. This was the ‘Schnorkel’ breathing tube, which was fitted to conventional U-boats and came into service in early 1944. There was nothing new in the concept of an underwater breathing tube, for one had been designed centuries before by Leonardo da Vinci, although this was intended to be attached to a diving suit in which a man would walk across the Venetian sea bed and cause underwater damage to any Turkish galleys which invaded the port. Various efforts had been made in more recent times to fit a ventilation tube to submarines, culminating in a development by the Royal Netherlands Navy before the Second World War. With the destruction of so many of their boats in 1943, the method was approved as a defensive measure by the U-boat Arm in the summer of that year. In essence, it was devised as a simple retractable tube with a ballcock valve to prevent water from being washed into the boat.
In use, the Schnorkel could enable U-boats to avoid enemy warships and aircraft, as well as allowing them to remain underwater to recharge their batteries or sometimes during submerged attacks on vessels, but it had serious disadvantages. The underwater speed was reduced and movement within the boat had to be limited to avoid upsetting the trim. Exhaust fumes restricted the vision of those within the boat, while these fumes could be spotted by keen-eyed crew members of Allied aircraft. If waves happened to close the cutoff valve, the diesel engines sucked up the available air within the boat, so that the crew began to suffocate and then suffered agonies with their eardrums when air rushed in again. Long periods underwater also created foul conditions, since food waste and the contents of toilets could not be disposed of so readily. The invention did not seem to provide the expected protection, and indeed the first boat to attempt a war cruise with it, the Type VIIC U-264, was sunk in the North Atlantic on 19 February 1944.
In the event, the massacre of the U-boats continued into 1944. They sank only thirteen merchant vessels totalling about 18,500 tons in January, from an overall total of 123,500 tons lost by the Allies. In return, fourteen U-boats were sunk, almost all in the North Atlantic, where they sank only five of the thirteen merchant vessels lost. By this time the Allied shipbuilding programme had forged ahead, reaching a total of about 32 million gross tons since the beginning of the war, with the rate of production far exceeding the rate of sinkings.
February was even worse for the U-boats. Despite sinking eighteen merchant ships totalling about 93,000 tons from Allied losses of 117,000 tons, they lost twenty of their own number, primarily in the North Atlantic campaign. In March they sank twenty-three merchant ships totalling about 123,000 tons from the 158,000 tons lost by the Allies, but twenty-three U-boats went down to attacks by aircraft and escort vessels. Three of these U-boats were lost attacking Arctic convoys but once again most of them were destroyed by escort vessels and aircraft in the North Atlantic.
By the end of March the battleship Tirpitz was seaworthy again, following repairs to the damage inflicted on her by the X-craft of the Royal Navy on 22 September 1943. Enigma decrypts revealed that she was about to put to sea from Kaa fjord for trials in the adjoining waters of Alten fjord. This timing coincided with the running of two Russian convoys, the eastbound JW57 and the westbound RA57, giving the Admiralty the opportunity to launch a huge airborne attack from warships which sailed under the guise of protecting the convoys. These were the fleet carriers HMS Victorious and HMS Furious, accompanied by three escort carriers.
The attack was launched in the early morning of 3 April by two waves of Fairey Barracuda bombers, some of which carried a single 1,600 lb armour-piercing bomb while others carried three 600 lb anti-submarine bombs. Their fighter escorts consisted of Supermarine Seafires, Vought Corsairs, Grumman Wildcats and Hellcats, which were given the additional task of raking the gun positions and deck of the battleship. The attack achieved complete surprise when Tirpitz was weighing anchor. She was hit by fourteen bombs, some of which penetrated the upper armoured deck and burst below, but none penetrated the lower 8 inch armoured deck. The crew suffered 122 dead and 336 wounded, and the battleship was so badly damaged that she was out of action for three more months. Two Barracudas failed to return.
The earlier attack on Tirpitz by the X-craft midget submarines of the Royal Navy had shocked the Kriegsmarine and resulted in the formation of the Kleinkampfverbande (K-Verband) or ‘Small Battle Unit Command’. Its main purpose was to combat Allied vessels in any invasion force crossing the narrow waters of the English Channel. The simplest of the units which formed part of the new command were manned torpedoes. One of these, which entered service in March 1944, was named Neger (Nigger). It was fitted with rudimentary controls and could travel only on the surface for short distances. Another was Marder (Pine Marten), which was similar to Neger but included a diving tank and a pump for compressed air. This entered service in June 1944. The K-Verband was also equipped with Linsen (Lentil) motor boats, which operated in units consisting of one control boat and two carrying explosive charges. The explosive boats were steered by pilots who jumped out after directing them against targets,and then hoped to be picked up by the control boats. The chances of the pilots surviving attacks in all these vessels were rated as no more than 50 per cent and all the crews were volunteers for what became suicide missions.
In addition, midget submarines were rapidly designed and put into production. One of these was Hecht (Pike), also known as the Type XXVIIA, which began to enter operational service in May 1944. This was a three-man submarine, capable of travelling underwater as well as on the surface, and armed with a single torpedo. The Biber (Beaver) was a one-man submarine which could also operate both on the surface and submerged, and carried a single torpedo. It began to enter operational service in June 1944. A version with a shorter range, designed solely for coastal work, was the Molch (Salamander), which entered service at around the same time. Yet another was Seehund (Seal) or the Type XXVIIB, with a crew of two and capable of carrying two torpedoes, but this did not begin entering service until November 1944.
On their roughly one-to-one basis of sinkings against losses, the ocean-going U-boats were not justifying their existence. However, replacements continued to arrive steadily and by the beginning of April 1944 the operational strength stood at 166, with 278 more undergoing training and trials. The inexperienced crews were being prepared almost like lambs for the slaughter. U-boats sank only nine merchant ships totalling 62,000 tons in April, from the 82,000 tons lost by the Allies, but nineteen of their own number were sunk.
The ratio of successes against losses became even worse for the U-boat Arm in May. This was one of its worst months of the war, for only four merchant vessels totalling 24,500 tons were sunk, while twenty-two U-boats were picked off and went to the bottom of the sea. No area was safe for the U-boats, except perhaps the Baltic – but even there one was lost in a collision in May.
The anticipated invasion of Europe by the Western Allies began on 6 June, when airborne troops dropped inland and spearheads of seaborne forces stormed the beaches of Normandy, escorted by Allied warships and covered by an overwhelming number of Allied aircraft. The German defences were caught off guard by forecasts of unfavourable weather issued by their own meteorologists. Even then, the location of this invasion was believed to be an Allied diversionary tactic by Hitler and the Wehrmacht, who were fooled by Allied deception measures. They continued to believe for several weeks that the main thrust would be made across the narrows of the English Channel to the Pas de Calais.
Dönitz was on leave with his family at Badenweiler, a holiday resort in the Black Forest, when D-Day began. Alerted by telephone, he hastened back to his headquarters near Berlin to chair a conference on the situation. Meanwhile the commander of Marinegruppe West, Vizeadmiral Theodor Krancke, issued his orders. Thirty-six U-boats in the Biscay bases and twenty-two in Norwegian ports had been put on full alert. Five others from France already heading for the North Atlantic were recalled and seven dispatched from Norway were to await new orders. Seventeen based at Brest were then ordered to attack the western flank of the Allied invasion force and all set course on D-Day. Nineteen others based at Lorient, St-Nazaire and La Pallice were ordered to form a patrol line in the Bay of Biscay, for it was believed from Allied deception measures that other landings would be made on the western coast of France.
Movement of German surface vessels also took place, but none of the heavier warships was available to assist in repelling an invasion from the west. The pocket battleships Admiral von Scheer and Lützow were engaged in the Baltic, as were the heavy cruisers Admiral Hipper and Prinz Eugen, where their main tasks were in support of the German armies facing the advance of the Red Army. The crews of the few surface vessels available were enjoined to attack the enemy ‘regardless of cost’ and they did their best with very limited results. Four torpedo boats (the size of small destroyers) left Le Havre and sank a Norwegian destroyer before slipping back into port. Three destroyers in the Gironde were ordered to the English Channel but they were intercepted on D-Day near Belle Ile by Beaufighters of Coastal Command and two were so badly damaged that all three put into Brest while repairs were carried out. Eighteen Schnellboote (known as E-boats by the British) were available to attack the eastern flank of the invasion force. After an abortive attempt during daylight, when no torpedo hits were scored, these began to operate at night.
The U-boats were hunted remorselessly by aircraft of Coastal Command. They sank two on D-Day plus one, two on the following day, one on the next day, and another on the day after that. It was another miserable month for the U-boat Arm, for twenty-five boats were lost in all waters and their only achievements were the sinking of eleven merchant vessels amounting to about 58,000 tons, from a total of 104,000 tons lost by the Allies.
The ‘human torpedoes’ suffered huge losses during the early weeks of the invasion. They were transported by road to ports near the Normandy beaches. Bletchley Park was aware of their location but could not forecast the days of attack. Twenty-six of the Neger class set off on 5 July. Two suffered mechanical problems and fifteen others were lost to Allied gunfire or other hazards. The other nine managed to sink two minesweepers. Twenty-one others left on 7 July and sank a minesweeper as well as damaging a cruiser, but all of these were sunk by surface vessels or aircraft.
Those of the Marder human torpedo class and the Linsen motor boats did not begin attacking until the night of 2/3 August, when fifty-eight of the former and twenty-two of the latter were dispatched against Allied shipping off the Normandy coast near Courseuilles-sur-Mer. The Marder began the attack and one managed to hit a cruiser with a torpedo. Then a major engagement took place, in which they sank a destroyer, a minesweeper and a Liberty ship but forty-one of the attackers were eventually sunk. The Linsen then joined in the attack, sinking a minesweeper, a motor launch and a landing craft, for the loss of fourteen of their own number. Twenty-eight Linsen were sent out on 8/9 August but they sank no ships and twenty were lost.
Yet another attack took place on 16/17 August when forty-two of the Marder set off for the eastern flank of the Allied invasion fleet. They sank a barrage balloon vessel but lost twenty-six of their own number. The midget submarines failed to make any effective attack in these waters before the Allied advances overran the French ports from which they could operate. This type of attack on the invasion area, by either ‘human torpedoes’, motor launches or midget submarines, became impossible by the end of August.
Meanwhile, replacements built up the number of operational ocean-going U-boats to 188 by the beginning of July, with 246 more undergoing training and trials, but their achievements continued at a dismal level during July. They sank only twelve merchant ships totalling 63,500 tons, but lost twenty-three of their own number. Aircraft were the main cause of these losses, which included three destroyed during a heavy raid on Kiel by RAF Bomber Command.
The Western Allies planned another seaborne landing in August, this time on the southern coast of France, under the codename operation Dragoon. Ten U-boats were still operating in the Mediterranean, from the bases of Toulon in France or Pola in Yugoslavia. Their main targets were the convoys which brought supplies and reinforcements to the Allied troops fighting their way up the peninsula of Italy, or which were passing through the Mediterranean to the Suez Canal and thence to the Allied forces in India. The Allies decided to eliminate these U-boats by utilising the immense Allied air and sea superiority in an operation which was aptly named ‘Swamp’. So many of these Allied forces were available that it was possible to pursue a U-boat so intensively that it was likely to be spotted when it was eventually forced to surface.