Tough to Sink

S.S. Laurentic before her conversion to armed merchant cruiser in 1939 (u-boat.net)

S.S. Laurentic before her conversion to armed merchant cruiser in 1939 (u-boat.net)

It has long been the practice in wartime for the British government to requisition civilian vessels for war service. Often these vessels are used in the logistics role supporting the Royal Navy at sea or the British Army and Royal Air Force in foreign lands. The practice has been used as late as the 1982 Falklands War where perhaps most famously the ocean liner Queen Elizabeth II was used to ferry over 3000 troops to the South Atlantic. Using civilian ships in wartime is a precarious business at best. They are seldom designed with the same level of protection a warship is afforded making them very vulnerable and their vital role in supporting the war effort makes them highly prized targets for the enemy.

One such civilian ship taken over for use by the Royal Navy was the Cunard White Star Line passenger ship the Laurentic. Requisitioned by the Admiralty a week before Germany invaded Poland on September 1st 1939 the vessel was put in to dock for conversion to an armed merchant cruiser which was completed in a remarkably short space of time. HMS Laurentic F51 was accepted in to service on October 15th 1939. As part of her conversion she was armed with seven Breech Loading 5.5inch (140mm) Mk I guns and three QF 4inch (102mm) Mk.XVI naval guns. She was also fitted with a quantity of depth charges for use against submarines.

The vessel was, like many of her kind, primarily employed on patrol and escort duties; armed merchant cruisers were effectively the last line of defence with the Royal Navy’s main fleet and aircraft being the first. Her start to the war was relatively uneventful but all that changed on the evening of November 3rd 1940. A little after 2140 hours her commanding officer, Capt E.P. Vivian RN, was informed that the radio room had received a distress call from an unescorted merchantman, the Casanare, stating it had been attacked by a U-Boat. Along with another armed merchant cruiser, HMS Patroclus, Laurentic raced to the scene west of Ireland at a place called Bloody Foreland.

A sister-ship to Casanare (wrecksite.eu)

A sister-ship to Casanare (wrecksite.eu)

Unknown to Captain Vivian and his men they were about to face off against one of Germany’s greatest U-Boat aces, the brash and skilled Kapitänleutnant Otto Kretschmer (known as “Silent Otto”) and his crew of U-99. Kretschmer’s attack had been a textbook example of U-Boat warfare, catching the Casanare completely by surprise. The torpedo struck just aft of the vessel’s bridge and she began to list heavily enough for the crew to begin abandoning ship. The wireless operator aboard U-99 suddenly found his headset alive with messages between their victim and the two approaching ships all of which were transmitted uncoded and in plain language.

Kretschmer continued to shadow the sinking Casanare while surfaced and it was not long before he detected the two ships coming to its aid. Picking his moment carefully, Kretschmer waited for the Laurentic to come in to his sights and at 2250hrs he unleashed his deadly arsenal on his second unsuspecting victim of the night (this early in the war few ships had radar to detect a surfaced U-Boat at night but by 1945 this kind of operation would have been suicide for a U-Boat commander). Launched from a distance of one and a half kilometres and incredibly while the U-Boat was turning the torpedo struck the Laurentic amidship near the boiler room tearing open a gaping hole in her side. Kretschmer watched the ship expecting it to sink and indeed a number of her crew had leapt overboard in the chaos of the blast but as the smoke dissipated the Laurentic proved that she was not done for yet and remained stubbornly afloat.

Kretschmer made two more attacks on the Laurentic, one at 2320hrs and another at 2330hrs with the range now having decreased to just 250m. The crew of the Laurentic briefly spotted the U-Boat on the surface and began shelling the submarine which quickly slipped away. The Laurentic was now heavily damaged and was riding much lower in the water than it should be convincing Kretschmer that the ship was finally done for and so he turned his U-Boat away to assess his situation.

hms patroclus

HMS Patroclus (u-boat.net)

In the meantime, HMS Patroclus had arrived on station and began efforts to rescue the crew of the Laurentic many of whom were abandoning the ship. The Patroclus’ Captain, William Wynter, ordered that two depth charges be launched over the side in an effort to frighten the U-boat away. He couldn’t have known that Kretschmer was still on the surface unseen in the night. Believing he had successfully drove off the U-Boat, Wynter’s crew began to rescue their comrades but Kretschmer had come about and at 0022hrs the Patroclus was hit by a torpedo from U-99 killing an unknown number of men aboard a lifeboat from the Laurentic that was being hauled aboard at the time. Like the Laurentic the Patroclus refused to sink and twenty minutes later at 0044hrs a second torpedo was launched in to the ship. The torpedo malfunctioned and missed its aim point hitting below the foremast. No doubt gritting his teeth Kretschmer fired a third torpedo at 0118 hrs but as he did so the British lookouts spotted the U-Boat and Kretschmer found his vessel taking fire forcing him to flee yet again.

Dumbfounded by his enemy’s refusal to sink, Kretschmer searched for his first target, the Casanare, to confirm it had indeed sunk. Two lifeboats bobbing in the water at her last known position offered the proof he was looking for when suddenly the air around him growled with the sound of aeroengines as an RAF Shorts Sunderland flying boat appeared over the scene. Kretschmer ordered his U-Boat to dive and the RAF aircraft was unable to launch its weapons but remained on station trying to locate the submarine.

Kretschmer used his time submerged wisely and reloaded the torpedo tubes. With the sound of the Sunderland’s engines dissipating he felt confident enough to surface at 0330 hours. Rather arrogantly he went back to the site of his attack on the two armed merchant cruisers and saw that Laurentic and Patroclus had still yet to sink! At 0435hrs he fired a fourth torpedo at Laurentic which struck astern. The blast ignited the depth charges stored in that area resulting in a huge explosion. The Laurentic’s luck ran out and the ship began to sink by the stern disappearing forever.

Kretschmer then turned on the Patroclus but as he did so his own lookouts spotted a destroyer, HMS Hesperus, approaching on the horizon. Rather than be satisfied with sinking the Casanare and the Laurentic he made a hasty attack on the Patroclus. At 0516hrs a fifth torpedo struck the ship fired from U-99 but the British ship refused to go down one last time prompting Kretschmer to fire a sixth torpedo. That was the end of the Patroclus and the hull crumbled into pieces before finally sinking. 114 sailors had been killed in the whole incident.

Kretschmer and the crew of U-99 celebrate in late 1940 (commons.wikimedia)

Kretschmer and the crew of U-99 celebrate in late 1940 (commons.wikimedia)

Kretschmer immediately ordered his U-Boat to dive as the destroyer zeroed in on him. Kretschmer and his men now paid for their victory as they were repeatedly depth charged by the Hesperus but the destroyer failed to score a direct hit and Kretschmer returned to Germany a hero.

So just what was the secret behind the Laurentic and the Patroclus that kept them afloat for so long? Was it excellent damage control techniques? Perhaps it was superb craftsmanship in the construction of the two vessels? Actually it was neither. It was in fact the placing of thousands of empty oil drums inside the hull of the ship. This dramatically increased the overall buoyancy of the vessels which meant that despite several gaping holes in the hull the barrels kept the vessels afloat making them very tough to sink.

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The Only Underwater Submarine-to-Submarine Kill in History

HMS Venturer

Even in the 21st century the submarine remains one of the stealthiest weapons of war. Advances in sonar technology and magnetic anomaly detectors have done much to improve the chances of detecting submarines but the advantage is still very much on the side of the submariner even when he is facing another submarine. Submarines are in a much better position to detect other submarines than surface vessels as their hydrophone detectors can take advantage of underwater currents carrying the sound or sonar ping from a nearby submarine. Nevertheless, one of the most difficult missions in warfare remains sub-versus-sub combat whilst both are submerged. In the history of submarine warfare there has so far only been one occasion where a submarine successfully carried out an attack on another while both were underwater.

While the story of anti-submarine warfare is remembered as akin to a game of chess between surface ships and their elusive elusive quarry, submarines have actually fought one another ever since the type went to war in 1914. British submarines were heavily involved in providing a defensive screen against German submarines that tried to attack the troop ships crossing the English Channel at the outbreak of war. The Germans spotted the British submarine screen and the two sides tried to lure one another in to combat but all in vain. Nevertheless, the British submarines still achieved their mission by keeping the Germans away from the vital troop ships carrying the British Army to France.

HMS E3

HMS E3 (commons.wikimedia)

On the 18th of October 1914 the British submarine HMS E3 under the command of Lieutenant Commander George Cholmney was conducting a patrol in the North Sea off Borkum, an island off North West Germany. During the course of the day the E3 spotted a small flotilla of German destroyers and began stalking them however the destroyers had the advantage of speed and the E3 was not able to get in to a good firing position. Cholmney therefore elected to hide his submarine in a nearby bay believing the German destroyers would either return or disperse thus allowing him a second chance to engage.

Unbeknown to Cholmney the bay was already occupied. The sleek lines of U-27 under the command of Kapitänleutnant Bernd Wegener slid through the waters with its lookouts atop the coning tower scouring the horizon. They quickly spotted what they suspected to be a buoy floating by in the distance but there wasn’t supposed to be one there and on closer inspection Wegener realised that it was in fact a British submarine. He immediately ordered his crew to diving stations and he closed on the target expertly positioning his submarine between E3 and the afternoon sun in order to make spotting his periscope more difficult to see in the glare on the water.

Having pursued the E3 for nearly two hours the distance between the U-27 and the still oblivious E3 had closed to 656 yards (600m) and Wegener decided it was time to engage the enemy vessel. He dispatched two G6 torpedoes at the British submarine and after travelling for twelve seconds they struck the stern of the submarine blowing it clean off from the rest of the submarine’s forward hull. There were no survivors from HMS E3 which has the unfortunate distinction of being the first submarine to be sunk in action by another.

Throughout World War I and World War II submarine versus submarine actions were infrequent and often resembled that of the sinking of E3; one submarine spots another on the surface and fires at it. While naval Anti-Submarine Warfare (ASW) technology advanced on both sides it was the aircraft that would prove the biggest threat to submarines and remains so to this day. The thought of using submarines to hunt down other submarines while submerged however was a concept that still appeared to remain confined to the realms of fiction.

ASDIC

ASDIC

There were a number of obstacles that stood in the way of World War II submarines trying to hunt each other down in the depths of the world’s oceans. First of all detecting the other submarine was still a challenge. Hydrophone technology was still very primitive and while they could give advanced warning of a surface vessel pushing its way through the waves above, a submerged submarine made less noise and so was less detectable. The sea did more than keep a submarine hidden from view as well. Sound waves don’t travel very well in colder waters making the passive hydrophone system less effective in hearing the enemy sub. ASDIC, an early form of sonar, sent out a sonic pulse to detect an object but again low temperatures hindered its effectiveness. Unsettled water also disrupted the pulse degrading its strength but the biggest problem with ASDIC was that while it could give a direction it couldn’t give a depth.

Even if a submarine could detect another submarine engaging it in combat presented its own problems. Firstly the torpedoes themselves had to be set to a neutral buoyancy rather than their usual run depth which in World War II was just below the waterline of a ship. If this wasn’t achieved then the launched torpedoes would rise upwards rather than straight on towards the target. By World War II the first primitive targeting computers were being installed in submarines for aiming the torpedoes but these were designed for attacking surface based targets. They therefore operated in a two-dimensional capacity (forward and to the left/right of the attacking submarine) as opposed to the three-dimensions required for fighting below the surface (forward, left/right and above/below the attacking submarine).

Given all these factors it is no wonder that only once has a successful attack on a submerged submarine by another submerged submarine been carried out in military history. The story begins in the twilight of World War II and has all the hallmarks of a Tom Clancy thriller. As 1945 dawned the fate of Nazi Germany seemed sealed. The allies were now marching eastwards across western Europe and north through Italy while in the east the massive juggernaut of the Soviet Union was bearing down to complete the ever tightening noose around the neck of Hitler’s Third Reich. In the Pacific theatre the almost paper ally of Germany, Japan was in a similarly dire state but unlike Germany Japan still had distance on its side. It was clear that Japan was not going to be defeated before Germany and that the war in the Pacific would likely last another few years as only a handful of people knew of the awesomely destructive weapon the Manhattan project was developing that would ultimately bring about peace. As part of the alliance with Japan, Germany promised to supply advanced weapons and technologies to its Far East ally that would help keep the Americans at bay. This policy continued throughout the war and even in the dark days of 1945 the Germans were sending this advanced technology to Tokyo.

U-boat pen like that at Bergen, Norway (uboataces.com)

U-boat pen like that at Bergen, Norway (uboataces.com)

Naturally, intercepting these shipments became a high priority for the allies and in December 1944 British codebreakers intercepted communications between Germany and Japan of an upcoming shipment expected to leave Norway via U-boat. The overwhelming strength of allied air and naval power meant that U-boats now offered the only chance of getting through to Japan as merchant ships would almost certainly be detected and sunk. On the 5th of February 1945 U-864 slipped its moorings at the Bergen U-boat bunker in Norway under the command of Korvettenkapitän Ralf-Reimar Wolfram with its destination being Japan. The departure had been repeatedly delayed due to first a faulty snorkel and then again after the U-boat ran aground attempting to leave Kiel in Germany forcing it to Bergen for repairs. Whilst in Bergen it was again damaged this time in a visit by the Royal Air Force’s famous No.617 Squadron and their Lancasters carrying 12,000lb “Tallboy” bombs. The U-boat pen was damaged and this in turn damaged U-864 and delayed repairs further. Now however despite the fact that Germany’s situation was growing ever direr in Europe the mission, codenamed Operation: Caesar, was to go ahead.

Wolfram’s U-boat was crammed with material destined to aid Japan’s fight against the allied nations in the east. This included 61 tons of metallic mercury which was a material growing increasingly scarce in Japan and used in bomb trigger construction. Perhaps of greater concern to the allied cause were numerous boxes containing engine parts for the Junkers Jumo 004 jet engine that powered the Messerschmitt Me262 jet fighter. The intention was for Japan to reverse engineer these components in order to build their own jet fighters that could counter the devastating B-29 Superfortress raids that were bringing Japan to its knees. Other boxes contained guidance systems for the V-2 rocket again for use by the Japanese in developing their own rocket program although this was at a significantly less advanced stage than in Germany.

U-864 was carrying personnel and equipment for Japan's jet fighter program

U-864 was carrying personnel and equipment for Japan’s jet fighter program

The U-boat also included four passengers. Tadao Yamoto was a Japanese acoustic torpedo expert who had travelled to Germany to compare notes and inspect German efforts in developing the first guided torpedoes. Toshio Nakai was an expert in the manufacture and employment of different fuel and was most likely involved in examining the fuel systems of the Me262 for use in Japan’s jet fighter project. Finally, emphasizing just how important the jet fighter project in Japan was to the Japanese, two Messerschmitt engineers were also aboard. The U-boat’s mission therefore was given the highest of priorities and conducted in the strictest secrecy.

Somewhat ironically it was this level of secrecy that betrayed the U-boat for the codebreakers at Britain’s famous Bletchley Park intelligence operation had cracked the German codes and learned of the mission. The Admiralty was immediately alerted about the U-boat and quickly went in to action to intercept it. Among the assets available was HMS Venturer, a V-class patrol submarine, under the captaincy of Lieutenant Jimmy Launders. Launders was known to have a brilliant mathematical mind that made him an ideal submarine commander and in the coming engagement this mathematical prowess would manifest itself in spectacular fashion. Venturer had already made a name for itself when it came to fighting other U-boats having sunk U-771 the previous November with torpedoes while it recharged its batteries on the surface.

HMS Venturer crestRoyal Navy Submarine Command, using the best information it had available to it, ordered Launders and the Venturer to patrol near the island of Fedje off Norway’s southwest coast in the belief that this was the most likely place where U-864 would be transiting in its attempt to break out. Venturer was one of an increasing number of British submarines that had been fitted with its own ASDIC system but the calculative Launders reasoned quite correctly that if Venturer went about sending out ASDIC pings to hunt for the U-864 it would alert the Germans to his presence and even invite attack. Venturer therefore stalked the waters around the island silently listening for the sound of a U-boat with its hydrophone equipment. Unfortunately for Venturer U-864 had already passed the island and had apparently escaped but as often is the case in war luck was about to play its part.

Wolfram was having problems with U-864’s engines. While they appeared to be functioning properly they were generating a great amount of noise indicating there was a problem deep inside the engine block. Afraid of breaking down hundreds of miles from a friendly port Wolfram elected to reverse his course and cancel the mission yet again. It must have been extremely frustrating for Wolfram and his men who unknown to them were now sailing back towards Venturer’s hunting ground.

Given his calculating mind Launders had begun to reason that they had indeed missed U-864 as he continued his patrol on the morning of February 9th 1945. Then suddenly he was informed by his hydrophone operator that he was detecting a sound in the distance. When asked what the sound was the hydrophone operator responded by saying that it sounded like a fishing boat’s diesel engine had started up. Launders suspected that it was more than a simple fishing boat’s engine. He reasoned that it was quite likely to be a submarine surfacing to charge its batteries since the noise seemed to appear out of nowhere. He therefore ordered his submarine to head for the sound of the diesel engine.

U-boat snorkelling (weberswarships.ca)

U-boat snorkelling (weberswarships.ca)

As they closed on the source of the noise the officer of the watch aboard Venturer raised the periscope and reported sighting another periscope cutting through the water. In actual fact he had spotted U-864’s snorkel which allowed the U-boat to run its diesel engines while submerged by feeding in outside air and ejecting the exhaust fumes. Snorkels were a relatively new invention and were only on German U-boats at this point hence the officer’s mistake. Launders now formulated a plan of attack. While the noisy diesel engines aboard U-864 were running he knew that the U-boat’s own hydrophone system would have a difficult time detecting his vessel and so the element of surprise was still on his side. Launders believed that the U-boat would have to surface soon not realizing what the snorkel was and the advantage it offered to the U-boat. He planned to stalk the U-boat until it surfaced and then attack it with torpedoes as it had done when attacking U-771 in the previous November.

For several hours Venturer followed U-864 which was zig-zagging from side to side as it made its way back to Norway; a common tactic to reduce an enemy submarine’s ability to acquire a firing solution with a high chance of scoring a hit. Time was quickly running out for Launders however as his own engine room reported that Venturer’s batteries were being drained rapidly by the pursuit and she would have to surface to charge them before long. Realizing that U-864 was not about to surface anytime soon Launders was faced with a choice; attack while the U-boat was submerged or break off the pursuit.

Launders’ mind began running numbers as he contemplated the chances of a successful engagement. He had a rough estimate of how deep the U-boat was thanks to the fact he could see its periscope (snorkel) but that didn’t guarantee accuracy. Launders reasoned that his best chance of success was to ripple fire all four of his forward torpedoes in to a kill-zone around the U-boat’s estimated position. Each torpedo would be fired independently at 17;5 second intervals and each successive torpedo would be directed differently assuming that if the first torpedo missed then the U-864 crew would be alerted to Venturer’s attack and take evasive action. Launders was calculating the first three dimensional submarine attack in history.

He had precious little battery life left and so he moved his submarine in to the most optimal attack position he could attain. Launders and his men knew their chances of success were low but they pressed on anyway determined, in that defiant spirit of the submarine service, to give it their best shot. The first torpedo left its tube and began its run while Launders counted down on his stopwatch towards the launching of the second torpedo. The frantic sounding whirl of the torpedo did indeed alert the crew of U-864 which quickly began efforts to take evasive action but the large U-boat was no ballerina and in order to submerge further to the protection of the deep the diesel engines had to be shut down and the electric motors started up all of which took time. Nevertheless the first torpedo was off target and missed as did the second.

After 53 seconds the third torpedo raced out of its tube and began its run. The fourth and final torpedo left the submarine 17.5 seconds later and with none left to fire Launders ordered his submarine to go deep to avoid counter attack. The submarine began a steep dive down in to the depths below as Launders watched the seconds tick by. He knew that if the third torpedo had found the target then they would have heard the explosion by now and so he assumed that it had missed. Everything now lay on the final torpedo.

There was a deep booming sound in the ocean outside. The explosion sent a shockwave familiar to the crew of a successful submarine as that of an enemy vessel exploding. Through the hydrophones Launders could hear the sound of popping rivets and breaking bulkheads confirming that he had hit the target. U-864, in taking evasive action to avoid the third torpedo had actually turned in to the path of the fourth just as Launders had predicted and now both the U-boat and its precious cargo were being sent to the ocean floor below. It remains the most unique submarine action in history.