The effect of the German submarines, or U-Boats, was a major shock to the British Royal Navy during the Great War, so it was not surprising that in the Peace Treaty of Versailles, Germany would not be allowed to have any submarines and its navy was greatly reduced in size. In fact, the potential of the submarine as a weapon seemed such a possible threat to Britain’s imports and thus, its economic survival, that there were some British politicians trying to ban submarines in general.
A new U-boat force
In Germany, the U-boat crews and commanders were well respected heroes of the Great War, so it is no wonder that even as early as 1922, they secretly kept tabs on the further developments of the submarine. In 1935, when Hitler felt strong enough politically to openly proclaim the rearmament of the German Wehrmacht, Admiral Erich Raeder began building a modern new U-boat force.
He envisioned a large submarine fleet. According to him, their true potential had been wasted in the Great War because Germany was unable to produce enough of them to be effective. But to his dismay, not only the Anglo-German Naval Agreement, but also Hitler’s own visions of mighty battleships and aircraft carriers, seriously limited his options. Raeder therefore tasked the acclaimed submarine captain from the Great War, now Admiral Karl Dönitz, to do the best with what he had at hand.
And that was little enough. By the outbreak of the Second World War, the Kriegsmarine had only 39 frontline submarines available. Dönitz and Raeder agreed that such a small force couldn’t achieve much, especially if Hitler kept insisting on playing by the rules of Prize Regulations. By late 1940, though, even after the Führer switched to all-out submarine warfare, only 13 new U-boats had been commissioned, not even enough to replace their losses.
Meanwhile, the Royal Navy was turning to the convoy system faster than expected. After the sinking of the passenger liner, Athenia, and the Battleship Royal Oak, right in the navy’s backyard at Scapa Flow, the British government insisted on grouping together large numbers of merchant ships that were to be escorted by the Royal Navy in convoys. The convoy system had been the major counter to the German submarines in the Great War, and now, Admiral Dönitz sought to overcome that problem by concentrating his submarines in the same way. The idea of the Wolfpack was born.
If Germany wanted to bring Britain to its knees, they had to win the tonnage war. They simply had to sink more ships and cargo than the British could reproduce. But it was a slow process. During the Norwegian campaign, the submarines had faulty torpedoes, which repeatedly jeopardised their missions. Even when in perfect position to take a shot, the German torpedoes could simply fail to explode or to find their target. This was not only frustrating but also dangerous to the then exposed submarines.
German scientists then came up with magnetic triggers instead of impact-fuses, which would detonate in the range of the vessels. By 1940, with the comfort of the French ports after the Battle of France, which eliminated the time consuming transit into the Atlantic and increased the effectiveness of the submarines by shortening repair times, the Wolfpacks seemed to be ready.
Falling prey to new tactics
Convoys heading out from Canada towards the British Isles were the first to fall prey to the new tactics. Like a real pack of wolves, the first vessel that located the convoy would inform the others of its coordinates via radio transmission and continue to shadow it. The commander of the group would come up with a plan of approach and coordinate the coming attack from his own submarine. Then, when in a favourable position, the Wolfpack would strike. If the convoy was not strongly protected or if a smaller group was separated by the rest due to bad weather or anything else, they engaged the enemy. If not, they waited for the dark of night.
U-Boats were hard to detect in any case, even with the advanced abilities of the Royal Navy. But under the cover of the night, after silently surfacing, they would be silhouetted by their commanders against the dark horizon or a strong wind, making detection many times harder. Then, they would strike, usually firing three, four or all torpedo tubes one after the other to minimise the risk of torpedo failure affecting targeting.
The convoy’s armed escort ship would usually react to the first attacker, which had to dive and take evasive action, but that led to the disruption of the convoy’s formation. As the convoy reacted, the second submarine would attack, hitting the group from a different angle, then evade and give another submarine the chance to shine. This way, they could maybe sink 5, 6, or even 7 ships on one approach and get away without losing a sub. If each convoy lost around 10% of its merchant ships this way, Britain would indeed lose the tonnage war. In fact, some early convoy losses were so high that British High Command kept the numbers from the public to avoid panic.
And because of the first positive results, Raeder and Dönitz were optimistic that by enlarging the submarine fleet, the tonnage victory was theirs for the taking. Britain could not use its mighty Navy to guard against invasion and protect its merchant fleet at the same time, could it? But once more, their pleas fell on deaf ears. This time it was Germany’s favourite uniform-fetishist, Hermann Göring, who, as the man who divided the resources, favoured his Luftwaffe over the Navy. Once more, the full potential of the Wolfpacks could not be unleashed.
Still, from June 1940 to March 1941, the German submarine fleet inflicted heavy losses on the convoys, but once the threat of a German invasion of Britain really faded, then the British began catching up with them. They outfitted their ships with air to surface radar systems, began using naval aircraft more efficiently in general, and organised hunting groups equipped with depth charges. Mid-1941 was a real low point for the German navy, as many of its submarine aces – those with five or more kills – were killed or sunk by the new aggressiveness of the British escorts. The exchange rate went to 5 British ships for 1 German submarine, and that was sustainable for Germany.
The Wolfpacks were still deadly, they just now had to be carefully deployed. Radio communication and coordination were key for that game, and as long as the Allies failed to crack their codes, the Wolfpacks were indeed invisible in their approach. But then, the British cracked their codes. Unknown to the Kriegsmarine, the capture of U-110 led to the cracking of the German coding machine, Enigma, at Bletchley Park, which now allowed the British to have a comprehensive picture of the German submarine deployment.
1942 began with a new British confidence that the Wolfpacks would soon be tamed or skinned. However, now that the US had joined the war, increasing transatlantic traffic was cause for new headaches. And Dönitz had shifted his attention further westward to intercept as much of it as possible.
On May 6, 1942, convoy ON 92, outbound from Britain to North America, 42 ships strong, left Liverpool guarded by the destroyer USS Gleaves, the cutter USCGC Ingham and 4 Canadian corvettes. It was a rather ill-equipped and inexperienced convoy. Only HMS Bury carried a High Frequency Direction Finder and only one other ship was equipped with a 10 cm radar system. To save as much time as possible, they took the Great Circle route, the shortest and most direct line across the North Atlantic, but also the most predictable. It didn’t take long for the Germans to intercept their radio traffic.
On May 11, U-569 spotted the convoy and alerted the rest of its pack. Wolfpack Hecht – Pike – was soon in pursuit. The Bury was quick to realise that they were shadowed, and not only by the U-569 but also by at least two other submarines. Now, a convoy usually had at least two basic options. To send out a hunting party in the hopes of driving the submarines away, or to quickly take evasive action and outrun them. Neither was really a possibility here, though, as the escorts were too few and the convoy too slow. And the somewhat outdated system of the Bury could only give a vague fix on enemy positions, and that position was closing in on them as night fell.
The Gleaves decided on a daring move, chasing the U-569 alone. This, however, was what the Wolfpack had hoped for. Just after the Gleaves’ left shortly before midnight, U-124 approached the convoy from the south, successfully torpedoing two of the outside ships, the Empire Dell and Llanover cargo vessels. The other ships fired illumination flares, hoping to catch the attacker, but that only diverted attention from U-94, who promptly sank the cargo ship, Cocle. Shortly after that, U-124 made a second run through the convoy undetected, sinking both the steamer Mount Pares and the Crystales cargo ship. With five ships reported sinking or burning, the Gleaves quickly came rushing back.
The next morning, the Gleaves and the corvettes – who had spent their time rescuing sailors from sinking ships, had an easier time preventing the Wolfpack from emerging in broad daylight, but then their luck ran out. Their evasive manoeuvres led them into a storm and also into the path of U-94, which was waiting for them. During the storm that night, U-94 torpedoed at least one, but possibly two merchant ships, the British Batna and the Swedish Tolken. Having lost 7 ships now, the convoy was in shambles but the Wolfpack was running out of fuel and torpedoes, so Dönitz called his pack back home, pleased with the results.
The Allies realised that, despite their earlier successes and improvements, the Wolfpacks were very much still alive and dangerous, and German Naval Command gained new hope that the battle for the Atlantic was a long way from being over.
If you’re interested in a more visual interpretation of the above story, watch our Sabaton History episode, Wolfpack – German U-boat Tactics:
“I am sure that no one knows so much about dealing with U-boats in the Atlantic and the mine menace around our shores and harbours of any kind as the British Admiralty, not because we are cleverer or braver than others, but because, in two wars, our existence has depended upon overcoming these perils. When you live for years on end with mortal danger at your throat, you learn in a hard school.” – Winston Churchill, 1951
When German submarines were once more sent to sea in 1935, many young sailors of the Kriegsmarine were reminded of the tales of the Great War. Back then, the German U-boat fleet had been a fearsome menace that sought to starve Britain out of the war. Their commanders nicknamed the first generation of U-boats “canoes” because of the old rudimentary equipment and the lack of a compartmentalised interior. Otto Kretschmer served on one of the new U-Boats that was sent into the Atlantic. U-35’s first mission was to intervene in the Spanish Civil War in 1937, by laying mines around the Bay of Biscay. The mission was rather uneventful, but it gave the crews a feel for the potential of the “grey wolves”, and why they had been so dreaded in the Great War. While everything seemed quiet and calm on the surface, deep down in the sea they silently lurked, waiting for their chance to strike.
War in the Atlantic
In June 1940, Kretschmer once more departed for war in the Atlantic. This time in personal command of a top-of-the-line TypeVII U-Boat. U-99 was an excellent submarine, sturdy and powerful enough to dive deep and prevail on the long hazardous journeys through the ocean. During the German campaign in the west, it was U-99s job to attack the Allied supply lines and cause as much damage as possible. The Atlantic was Britain’s Achilles heel and at the time, was rich with tankers and merchant ships. Although the Royal Navy had introduced the protective convoy system early on, their crews were still unfamiliar with anti-submarine techniques and Kretschmer’s attacks were extraordinarily daring. When a convoy was sighted, U-99 shadowed the unsuspecting ships from afar, often letting itself be overtaken by the guarding destroyers. In the dark of the night, it resurfaced and slipped into the formation unnoticed. Kretschmer then closed in on the biggest target to about 600m, the safest distance to launch a successful torpedo. Aimed right at the middle of the ship, just under the central keel plate, the ensuing explosion usually ripped any merchant ship apart. If not, the U-boat’s surface gun would punch more holes in. Like a fox in the henhouse, Kretschmer wreaked havoc from within the convoys themselves.
For the rest of the year, the German U-Boat scourge was on a seemingly unstoppable rampage. Operating from occupied France or Norway, they targeted inexperienced convoys, often travelling from as far away as South Africa or Australia towards the English Channel. Like the pilots in the skies, U-Boat commanders became aces, celebrated heroes of Nazi Propaganda. Together with Günther Prien of U-47 and Joachim Schepke of U-100, Otto Kretschmer was one of the three U-Boat darlings of the press. They were the three knights of the high seas, bestowed with the greatest honours, who would soon see Britain brought to her knees. After not even a year in service, Kretschmer, the night-raider, had sunk more tonnage than any other commander. Over 250,000 tons were now on the ocean floor, attributed to the Shiny Golden Horseshoe of U-99.
On February 22, 1941, U-99 went on a hunting expedition once again. Prien was already on his way, and Kretschmer was scheduled to meet with Schepke’s Wolfpack. Throughout March, the submarines were once more successful. U-99 was credited with sinking 8 ships in just 11 days. With his last torpedo fired, Kretschmer was heading home, but he was suddenly surprised by two British destroyers. U-99 made an emergency dive, but at 200m depth, the boat was suddenly shaken by explosions. The destroyers were dropping depth-charges and the men were thrown around. Lights were knocked out and the glass dials of the instruments sprung. Then water broke into the control room and the depth-meter stopped working.
Deeper and deeper they sank, the worst nightmare of every U-boat crew. There was a reason submarines were also known as “iron coffins”. In total darkness they sank to at least 500m, and the pressure tore at the ship’s hull. Any minute now, they would be crushed to death. Kretschmer had no choice. He blew the ballast tanks and the U-boat shot back up to the surface. They surfaced right in front of the destroyers. The British opened fire and machine gun bullets rattled off the hull. Kretschmer ordered everyone out of the tower, the official sign that the submarine was surrendering. Everyone except the officers who were busy destroying the secret papers and, most importantly, the coding machine, the Enigma. Kretschmer was among the last to escape the boat, which promptly sank back to the depths of the sea. The crew of U-99 went into captivity.
Over the coming weeks as he was interrogated, Kretschmer learned the bitter reality that the war had begun to turn against the German U-boats. Prien was dead, and so was Schepke. Kretschmer was surprised by the amount of intelligence the British had gathered about the German U-boat operations: “They knew everything. About Dönitz, our top personnel, the submarine captains, everything. We didn’t know anything about them except that they were the enemy.”
The loss of three of its most acclaimed U-Boat commanders in a single month was a major blow to the German Kriegsmarine. And it only went downhill from then on. After the British finally captured one of the enigmas intact, they were able to decipher the German codes. With new radar systems and more effective countermeasures now on nearly every ship, the war on the High Seas had taken a dangerous turn for the Germans.
In late August 1942, 5 German U-Boats left the submarine base of St. Nazaire to operate off the South African coast. The North Atlantic had become a dangerous place for U-boat aces, and to regain the initiative, the 5 submarines formed a battlegroup. The wolfpack under the codename Eisbär (Polar Bear) was to assist and support each other during the hunt for convoys in the far south.
Eisbär didn’t get far in its search for trouble. Near Ascension Island, U-156, under command of Werner Hartenstein, spotted the smokestacks of the former passenger liner Laconia. En route to Cape Town, the Laconia was now a passenger liner in name only. Armed with 10 guns, depth charges and a radar-system, the Laconia now served as a British troop ship. Shortly after 8 o’clock in the morning though, two of U-156’s torpedoes struck and a huge explosion rocked the ship. Seeing the Laconia sink, Hartenstein was just about to rejoin the Wolfpack, when he saw hundreds of people jumping from the ship. No one had expected a full troop ship travelling alone and unescorted on this route. It became clear why, as the pleas for help were not in English but were mostly in Italian. The Laconia had been transporting 1,500 Italian prisoners of war and 160 of their Polish guards. This changed everything. Hartenstein radioed back to Grand Admiral Dönitz, explaining the situation.
Two years earlier it would have been a matter of principle to stay and help, but this was 1942. Any moment, an Allied plane or warship could appear on the horizon. Still, the Wolfpack commanders could not stand idly by while hundreds of people – many of them even allies – drowned. Dönitz gave permission to mount a rescue operation as long as the Wolfpack was not endangered. Hartenstein opened his communication channel to the Allies. He declared in an unencrypted message what was going on, and that he would not attack any Allied ship that joined the rescue. To emphasise their intentions, the Wolfpack put bright red cross flags on their decks, as they began rescuing friend and foe alike. The operation took all day and night, and there was trouble. Many Italians accused their captors of being kept locked away while the ship sank, and that many were shot at or bayoneted as they tried to reach the lifeboats.
Despite the tensions, Wolfpack Eisbär was able to save at least 400 out the 1,500 Italians from immediate death. But just as the next day dawned, they spotted a plane flying towards them. It was an American bomber, who circled for several minutes high above them. Then suddenly the bombs fell. The first exploded right in the middle of the lifeboats. The fourth bomb fell close to U-156, causing light damage. This was the moment Hartenstein had feared. Without a choice, he ordered all British survivors to leave his boat and started the engines. The duty to his men and the Wolfpack came first. Again, they radioed High Command, who urged them to withdraw at once. Hartenstein was furious that neither his unencrypted rescue message nor the red-cross flag had been respected. With no other option, they loaded their boats with as many Italians as possible and dove for cover.
The sinking of the Laconia was, of course, one of many tragic events of the war. From the ruthless attack by the U-Boat, to the failed rescue attempt in the face of merciless bombing, helpless people were repeatedly caught up in it. From the depths of the sea to the heights of the sky, no place was safe from the war. The immediate consequence of the attack was that Grand Admiral Dönitz issued the infamous Laconia Order. From then on, all U-boat commanders were ordered to not undertake rescue operations of the enemy anymore. Rescue attempts, he stated, would contradict their most basic demands of the war: to destroy hostile ships and their crews. The order ended with a single demand: Be harsh!
Watch our second Sabaton History episode about the German U-boats, Wolfpack Pt. 2 – The Torpedoing, below: