May 28, 2012

BATTLE OF THE ATLANTIC: Part 2: THE WOLF PACK



Der Deutsche U Boot Krieg im Atlantik (You Tube video)

The Nazi's called it Die Gl├╝ckliche Zeit, "Happy Time"  Hordes of German U boats emerged from their bunkers, stationed at Brest, Lorient, La Pallice and La Rochelle, on a nightly search-and-destroy mission. The first "Happy Time" took place in the period from June to October 1940 during which U-boats were able to sink over 282 Allied ships totalling 1,489,795 tons. It was the most daring and most successful naval campaign by the Germans during WW2 and the most humiliating and terrifying situation for the Allies. Britain desperately needed war material and supplies from the United States and Canada, and required massive quantities each week. And the Kriegsmarine knew how to cut the life-line. British vessels were literally sitting ducks. Were Germany to have continued at this rate, they would have easily been able to win the war by attrition.

The Atlantic Ocean and all connecting waterways were the Germans' hunting grounds but they were ordered to avoid the English Channel altogether - the Channel passage was much too shallow and heavily fortified with mine fields. What gave the U-boats such an enormous advantage was that the bases were 450 miles closer to the Atlantic than from other stations in the North Sea. It gave U-boats the added benefit of being able to attack much farther westward and prolong the hunt for longer periods of time. Enormous submarine pens were constructed in France allowing the entire fleet to be docked securely, and completely impervious to Allied bombing. As a result, the numbers of U-boats constructed had doubled.


WW2 Battle of Atlantic - U-boat bunkers at Lorient_France
U-boat bunkers at Lorient, France


CONVOY: DANGERS

On September 21, 1940 the British Convoy HX-72 was attacked by a pack of four German U boats and in the space of two consecutive nights, lost eleven ships and two damaged. The next month, Convoy SC-7, escorted by two sloops and two corvettes, were attacked by a wolf pack and lost 59% of its' vessels. Convoy HX-79 lost a fourth of its fleet despite strong presence of two Allied destroyers, four corvettes, three trawlers and a minesweeper. On December 1st Convoy HX-90 was ambushed by seven German U boats and three Italian submarines. They lost ten ships, three damaged. For the weeks and months which followed, similar attacks ensued, with rising loses for the British Navy and its Allies. The Italian fleet of 32 submarines, stationed at Bordeaux,  frequently accompanied the wolf pack on its missions to attack Atlantic-bound convoys. The Italian fleet, though smaller, managed to sink 109 ships totaling 593,864 tons. However they bore the brunt of heavy criticism from Donitz who considered the Italians to be undisciplined and uncooperative. Convoys were not only prone to attack by U boats but also by the Luftwaffe. Fw200 planes and Junkers Ju 290 flew reconnaissance and bombing raids. In early 1941, the Luftwaffe succeeded in destroying a total of 365,000 tons.






(7/12) Battlefield I: The Battle of the Atlantic Episode 3 (GDH) (00:10:00m)



Britain was nearing the breaking point. Desperate measures had to be taken to protect Allied convoys from further U boat attacks. Churchill proposed an "offensive strategy" by which British aircraft carriers would be deployed to patrol the shipping lanes and conduct anti-submarine hunting missions. In theory it appeared to have merit, but in reality the plan was destined to fail: a U-boat would always be able to spot a vessel approaching and quickly submerge before being detected. Even when aircraft carriers were able to spot a U-boat, their weapons were woefully inadequate to maneuver an attack. In any event, by the time an allied battleship or cruiser could reach the area in which a U-boat was last reported, it would have long since disappeared below the surface of the waves. Despite this flawed British strategy, the Royal Navy would continue repeating the same mistakes for the entire first year of the war.



THE WOLF PACK
 

Submarine warfare was not a novel concept. Reminiscent of WW1, the Germans once again relied on U-boats during WW2 to destroy Allied convoys and in the process strangle Britain militarily. But this time new tactics would be employed. Traditional naval doctrine required submarines to perform only as an auxiliary to surface fleets in their mission to attack enemy vessels. Warships were considered to be the ultimate commerce destroyers - not submarines. But Karl Donitz. who later would become Commander of the German Kriegsmarine, had other ideas. He strongly advocated in favor of converting the entire German fleet almost completely to that of U boats. Donitz was convinced that Germany, with a fleet of only 300 new Type VII U-boats, could easily destroy British oil tankers and starve the Royal Navy of supplies, thus winning the war.




German U-boat in action 1941 (Battle sequence) (00:02:30m)


The new tactic was called the "Wolf Pack", albeit a revised and much improved version of its WW1 predecessor.  Essentially it involved the formation of groups of several submarines, together which could swarm the enemy's defenses and utterly destroy them.  The reason it did not succeed during WW1 was due to technological limitations of German radio frequencies.  However,  during the interwar years, Germany developed two innovations that were almost certain to ensure her military invincibility: the development of ultra-high frequency radio transmitters, and the Enigma cipher machine. 


Two of the five U-Boats in the Eisbar (Polar Bar Group) wolf pack.


The Eisbar wolf pack together sank more than 100,000 tons
 of  shipping in just two weeks off the South African coast. (September and October 1942)

 
The Wolf Pack was a deadly force to contend with. The procedure was straightforward but very effective. A number of U-boats would be dispatched directly into the path where an allied convoy was expected to pass.  As soon as a ship was spotted, its course, speed, and composition would be signaled to German Naval Command. Meanwhile the U boat would continue to stalk the convoy reporting any changes as they occurred.  Upon the order of Command Base, the rest of the pack would close in to the first boat's position and, once in formation, move in for the "kill". The results were devastating and catastrophic.  By dawn, the mission having been completed, the wolf pack would disband, quietly submerging beneath the waves leaving one lone wolf to prowl the seas for the next sighting.   

However,  their tactics were not nearly as effective in the Atlantic since it was extremely difficult to spot convoys in the vast expanse of the ocean.  Consequently, the German Command began to dispatch aircraft on air reconnaissance missions - but even so,  it presented another set of problems stemming from perpetual internal conflicts raging between the Kriegsmarine land and sea divisions.

U-boat attacks were almost always conducted at night and always at the surface, or very near to the surface. It was an idea which Donitz had borrowed from Admiral Wilhelm Marschall who had originated the concept in the 1920s, but for which Donitz later claimed credit. The tactic had the additional advantage of making the submarine undetectable by ASDIC, (Anti-Submarine Detection Investigation Committee), or sonar as the Americans referred to it.  In the early part of the war, the British had not yet equipped their vessels with radar, and lacking any alternative method for effectively detecting U-boats, had to employ what resources they possessed at the time.



SECOND "HAPPY TIME"

War broke out between the United States and Germany on December 11, 1941, and immediately thereafter Donitz launched Operation Paukenschlag (Operation Drumbeat).  Now began the second phase of the Battle of the Atlantic in which German U-boats specifically targeted the eastern coastline  of North America, and what was termed as the "Second Happy Time"  lasting from January 1942 until August of the same year. Just like the first "Happy Time". German U-boats attacked and sunk numerous vessels, escaping virtually unharmed. By the end of Operation Drumbeat, the Kriegsmarine succeeded in destroying 609 ships totaling 3.1 million tons. This quantity was astounding, as it related to one fourth of all shipping stock destroyed by U-boats during the entire war. By the end of Operation Drumbeat, the Kriegsmarine had lost only 22 U-boats.
 
WW2 Battle of Atlantic - U.S. oiler SS Pennsylvania Sun torpedoed by the German submarine U-571 on 15 July 1942
U.S. oiler SS Pennsylvania Sun torpedoed by the German submarine U-571 on 15 July 1942
The SS Pennsylvania Sun was torpedoed  about 200 km west of Key West, Florida but was saved and returned to active service the following year.

In mid-December 1941, the first five Type IX U-boats left the confines of their bunkers in France, and set on their way to different targets of the North American coast. This mission was so secret that each U-boat received orders in sealed envelopes, only to be opened after passing 20°W.  No charts nor sailing instructions were provided.  Such haste was made for the mission, that the captain of U-123, Reinhard Hardegen, had been given, of all things,  two tourist guides to New York City, one in which included a crude fold-out map of the harbor.

Each of the U-boats, upon exiting the Bay of Biscay emitted routine signals, all of which were detected by the British Y-Service. These were Intelligence centres whose sole objective was to collect and analyze data concerning enemy traffic. Amateur ham radio operators even got into the act and provided British Intelligence with invaluable information. Thus they were able to track the progress of the U-boats crossing the Atlantic and dispatched a warning message to the Royal Canadian Navy and to U.S. Admiral Ernest King of a "heavy concentration of U-boats off the North American seaboard".  There were 21 in all.

The U-boats' target was the area from Maine to North Carolina, an area under the command of U.S. Rear-Admiral Adolphus Andrews.  Unfortunately Andrews had to deal with grossly outdated equipment and inexperienced sailors to operate them.  At his disposal were only 7 Coast Guard cutters, 4 converted yachts, 3 WW1 vintage patrol boats, 2 gunboats that pre-dated WW1, and 4 wooden submarine chasers. Though he had 100 aircraft available, they were relegated to training purposes only.  Though reports of the U-boat sightings were passed down the chain of command, hardly any American action was taken.

The first casualty of Operaton Drumbeat was the British freighter Cyclops, sunk by U-123 on January 12, 1941.  Two days later Hardegen reached New York harbor, and spotted the Norwegian tanker Norness off the coast of Long Island, launched torpedoes and sank her, however it took 5 hits to finish her off.   What gave the U-boat a decisive advantage was that coastal authorities had not instituted a black out.  U-boat navigation was made far too easy by the continuing glaring shore lights. The next day, Hardegen actually entered the harbor almost breaching the U-boat in the process and the crew got their first look at New York City in all its glory. They remained in the Harbor just long enough to sink the British tanker Coimbra and exited immediately thereafter.


 
animation of silhouette of vessel against night sky of NYC



The most successful German U-boat was U-221, a type VIIC vessel, under the command of Hans-Hartwig Trojer. She made a total of five patrols in the Atlantic and sank 11 Allied ships totalling 65,589 GRT (gross register tons) and damaged one ship.  The U-boat also destroyed 10 allied landing craft (9 LCMs and 1 LCT) which were aboard the British merchant ship Southern Empress when U-221 torpedoed and sunk her on October 14, 1942.  The U-221 suffered heavy damages, and the U-254 was destroyed altogether when they both collided at sea on December 8, 1942 amidst heavy fog. The collision disabled the U-boat which returned to St. Nazaire for repairs.  It finally met its fate in September 1943 when it was attacked with 8 depth charges released by the British Halifax bomber (58-B Squadron RAF Coastal Command of the southwestern coast of Ireland).  The U-221 sank but not before shooting down the Halifax bomber. All 50 crew members were killed.
 

ASDIC 

ASDIC was essentially a transmitter-receiver which emitted directional sound waves through the water.  Its ability to detect underwater objects (or U-boats) relied on the series of sound waves which bounced off an underwater object and reflected back to the receiver.  The range could easily be measured by recording the length of time it took to transmit and echo back, its visible manifestation demonstrated by a flickering light on the range scale.  The bearing of the target could be read when the transmitter head was maneuvered as if it were a searchlight, thereby making it possible to take a compass reading.


Despite the faith that the British initially held for this device, the ASDIC was not completely reliable.  It often gave false readings especially during bad weather, when ships were rolling, pitching and heaving. The level of noise had to be kept at low or moderate levels - anything over 18 knots created too much signal turbulence.  The transmitter head extended beneath the ship, enclosed inside a large metal dome which was filled with water, and through which the sound waves were transmitted.  It was supposed to minimize the noise made by the rushing water as the ship sped forward.




WW2 Battle of Britain - ASDIC -Canadian sailors operating ASDIC -Photo by William H. Pugsley- National Archives of Canada- PA-139273
Canadian sailors operating ASDIC -Photo by William H. Pugsley- National Archives of Canada- PA-139273

Screening operations were very laborious and took a great deal of time. The ASDIC operator had to search through an arc of about 45 degrees each side of the base course of the ship; and it had to be repeated at regular intervals and slow enough to permit the sound waves to return. The recognizable "ping" would be heard when the transmitter detected an object underwater. Otherwise the process had to continue, rotating the head up to 5 degrees each time.

The disadvantages of the ASDIC is that it would often detect all manner of underwater objects besides U-boats, that is, whales, schools of fish, even vertical sea currents and ships' wakes.  Much of the fault for false readings were due to the inexperienced operators, who unlike the veterans, could not make a clear distinction between bad signals and correct ones.

What made it even more frustrating is that the ASDIC often could not even detect the U-boat when it was nearby, due to rough seas, and the varying water temperature at different depths, all of which had an adverse affect on the transmission readings.  The German U-boats easily evaded detection merely by diving to greater depths.

What was remarkable about ASDIC is that it had the capacity to eavesdrop on the sounds of U-boat propeller noises, as well as the operation of machinery, in particular the use of compressed air in the ballast tanks that are responsible for changing the depths of the vessel.  Unfortunately, the opportunity rarely arose since the typical German tactic would be to dive quickly - below the thermal layers,  and move at speeds slow enough to maintain silent running.

It was often difficult for a vessel to maneuver an attack on a U-boat.. The attacking ship had to be certain where the U-boat was, and had to estimate where the U-boat would would be when depth charges were released. Therefore it would be imperative for the attacking ship to take a lead on the U-boat just as would a hunter on his prey.  Far too often contact was lost in as little as 300 yards distance.  It was basically a guessing game, or estimations based on range at which contact was lost.



U-BOAT TACTICS  AND EVASION

The mission of finding Allied convoys was delegated to the German U-boats rather than surface vessels. U-boats were best equipped to find and attack their targets, and escape virtually unharmed. But their capacity to track convoys had limitations; for one thing the bridge was too close to the surface of the water which made it difficult to establish clear visibility.  Consequently they relied on German code-breakers stationed at B-Dienst to decipher Allied radio communications and discover when and where Allied convoys were expected to arrive.  U-boats would spread out along those co-ordinates and shipmates would scan the horizon with binoculars looking out for ship masts, or smoke emissions. Hydrophones were also useful in detecting the sound of ship propellers. Whenever a convoy was spotted, a string of messages were transmitted to German Command as the U-boat proceeded to stalk its prey.  Headquarters would signal other U-boats in the area to head for the same coordinates and once having arrived, the fleet would converge simultaneously, ambushing the convoy.



WW2 Battle of Atlantic - German U-boat torpedoed allied vessel on the right (sinking)
German U-boat torpedoed allied vessel on the right (sinking)

Even more daring was the strategy devised by German commander Kretschmer by which U-boats would penetrate the convoy's escort screen and attack once positioned well within the columns of merchant ships in the convoy. British radar at the time was incapable of reading target discrimination and range.


U-boats easily out-maneuvered surface vessels, and were able to evade depth charges and Hedgehogs. Typical of the German U-boat tactics  were their tendency to provoke a chase, that is, "run away" from the Allied escort thereby provoking them on a stern chase and, pinging through the wake of the U-boat. (The objective was clearly to give the ASDIC system a hard time.)  And just at the moment in which ASDIC lost contact, the U-boat would take a sharp turn to the left or right, and escape from the line of attack.





A Destroyer Escort dropping a depth charge
 
British sailors loading platform with HedgeHogs
 
The Hedgehog was an anti-submarine weapon used by the British to great success.  It was deployed on convoy escort vessels and destroyers as an auxiliary to the depth charges.  Several small spigot mortar bombs would be fired from spiked fittings and, instead of working on a time or depth fuse, the Hedgehogs exploded on contact.  It resulted in a higher success rate, sinking U-boats more did the depth charges.  A depth charge, on the other hand, used explosives set off by a fuse to ignite at a pre-selected depth, and could be dropped by any vessel, or patrol aircraft.  If successful, the U-boat would be crippled or destroyed.



Leigh Light on RAF Liberator Feb 1944
Another evasive maneuver of the U-boat was to use full power while turning sharply - the intention of which was to create a great deal of noise and confuse ASDIC readings.  Other methods included the release of chemical pellets which when interacted with water would produce voluminous clouds of bubbles to reflect the sound waves transmitted by ASDIC. 

But the most common tactic was for the U-boat to dive very deep and below a thermal layer, or, below the depth at which depth charges would be able to explode.  They have been recorded as having dived as far as 200 meters (600 feet) depths.


Though German U-boats ran on diesel, they had to surface at night in order to recharge their batteries. While on the surface they were at increased risk of being exposed to ASV (Air to Surface Vessel) Radar. The ASV, in addition to use of the Leigh Light (a powerful search light rated at 22 million candela) made it exceedingly more difficult for the U-boats to conduct their night raids, much less recharge their batteries. The Allied trick was to approach the submarine using ASV and then turn on the searchlight at the very last moment. The U-boat had finally become the target, having no time escape.  In an effort to counter these measures, other U-boats attempted to recharge their batteries during daylight hours, when they could detect approaching aircraft.  It was an act of desperation by the Germans, and self-defeating on their part.



THE CHANGING TIDES OF FORTUNE

The Battle of the Atlantic began with a powerful burst of energy, but which over time, began to fizzle out.  Initially, Donitz' intention was to deploy the entire fleet of U-boats in an effort to exert the maximum impact. The plan was impractical because the logistics required to execute such an operation were too unwieldly. To make matters worse for the Germans, the winter of 1939-40 was unusually frigid and brought the entire operation to a complete standstill, leaving several U-boats trapped in ice. Even the German penchant for organization was not refined enough to anticipate this kind of outcome.



On April 9, 1940, the Kriegsmarine was gearing up again. Hitler launched Operation Weserubung, an attack on Norway and Denmark which lasted until mid-June of that year.  Throughout the campaign, German U-boats were suddenly confronted with numerous malfunctions: though they would target Allied ships, their torpedoes would strangely explode prematurely - or not at all.  In many instances, torpedoes would pass underneath the target vessels, leaving them virtually unscathed.  British ships would simply sail away as if nothing had happened.  The malfunctions were the result of interference of the magnetic field on torpedoes launched at such a high altitude. In addition to that, the torpedoes exhibited a slow leakage of high pressure air from the depth regulation gear - a flaw due perhaps to incorrect design or construction. Nevertheless, the Germans resolved this problem merely by capturing some British torpedoes (which were far superior in design, construction, and reliability) and copied its design.

The British scrambled to improve its' security.  After a disastrous first year, British Command finally decided to establish escorts on a permanent, and mandatory basis. It was immediately followed by a surge of new British and Canadian made vessels, as well as American,  Free French, Norwegian, Dutch and Polish. Though the Polish Navy was small in comparison to its more powerful allies, the contribution made by the Polish Navy was extremely vital to the war effort. (see Part 1)





(8/12) Battlefield I: The Battle of the Atlantic Episode 3 (GDH) (00:10m)


As war raged on, a new base was established at Tobermory, in the Hebrides, at which escort ships were put into training, under the command of Vice Admiral Gilbert O. Stephenson. Their only mission was to prepare the escort ships and the crews for the rigors of sea battle.  It was an objective greatly facilitated by the advent of new short-wave radar sets, introduced in 1941, and the co-ordination of supporting Allied aircraft. By spring of 1941, these cumulative changes had a direct effect on the success of Allied missions, most apparent when a U-boat failed to return from patrol. Two weeks later, the convoy HX 112 was able to hold off a U-boat attack: The convoy was protected from the newly formed escort group, which consisted of five destroyers and two corvettes.  In another daring sea battle, the HMS Vanoc was able to ram and sink the U-100, after having detected it on ship's radar.  And on and on it went, the Allies continuing to gain the advantage.  Within a short span of time, the Kriegsmarine had lost three of its top-rate U-boats.(Editors note: Apologies but details not available)

Even though the Allies benefited from the technological improvements, the Kriegsmarine found ways to counter Allied tactics. Donitz devised a new strategy.  In April he dispatched the U-boats further west in an effort to intercept them before escort ships could join the convoys. The plan worked.  Convoy SC26
was hit, and ten of their ships were sunk.  Only one U-boat lost.

By summer of 1941 the British scrambled to provide additional escorts that would accompany convoys throughout the Atlantic crossing, and not just within territorial maritime zones.  British Command called upon the Royal Canadian Navy to provide escorts to convoys in the western zone as well as establish a base at St. John's, Newfoundland.  Commodore Leonard Murray was appointed the Commodore of the Newfoundland Escort Force, under the Command of Western Approaches (Liverpool). The Canadian escort fleet consisted of 16 destroyers, 17 corvettes, and additional vessels of the Royal Navy (7 destroyers, 3 sloops and 5 corvettes), all of which escorted convoys from the Canadian ports to Newfoundland, and from there to Iceland. British escort groups then took over the rest of the way.

Over time it became apparent that the southern Atlantic was just as dangerous to unescorted American merchant vessels.  On May 21, the American ship SS Robin Moor was intercepted 750 miles west of Freetown, Sierra Leone, by U-69. The German captain gave the American passengers and crew 30 minutes to disembark into lifeboats, after which the Moor was torpedoed and sunk. Survivors drifted at sea for almost 18 days before being found by rescue.

Though the United States was cooperating with Britain during the Battle of the Atlantic, they increased their participation considerably. President Roosevelt had originally established the Pan-American Security Zone but soon it was extended it as far as Iceland.  American warships served as escorts to Allied convoys as far as Iceland and engaged in numerous battles with U-boats along the route. When America finally entered the war, a Mid-Ocean Escort Force was established, including American, Canadian and British destroyers and corvettes.



PAN-AMERICAN SECURITY ZONE

Before America entered the war, President Roosevelt, together with leaders of South American nations, and Canada, signed legislation declaring a specific area of the Atlantic to be designated as the Pan-American Security Zone and thereby expressed intolerance of any belligerent acts.  Though essentially neutral,  American ships escorted Allied convoys that were headed for Europe laden with tons of supplies for the British war effort. Initially this Zone extended between 300 and 1,000 nautical miles. (560-1,900 km; or 350-1,200 miles)


WW2 Battle of Atlantic - President Roosevelt
President Roosevelt
Early in 1941, the U.S. Navy began sending convoy escorts to ease the burden on British and Canadian fleets, and to report any U-boat sighting to British Command.  The Kriegsmarine was not pleased, but was instructed by the German admiralty to avoid any hostile acts that would give the United States cause to enter a declaration of war against Germany.  By spring of 1941, Roosevelt extended the security zone to a longitude of 26 degrees west, 2,300 nautical miles (4,200 km, or 2,600 miles), east of New York; and 50 nautical miles (93 km, or 58 miles) just short of Iceland.  The tiny island of Iceland thus became the central staging area for the largest naval convoy of the century.


ALLIED VICTORY


By 1943 the war began to turn against the Germans. Nevertheless, Donitz was confident that the increased construction of U-boats would once again tip the balance of power in Germany's favor.  By the end of WW2, the German submarine fleet was the most advanced in the world but failed to reassert itself.  Many factors had converged to destroy the supremacy of the Kriegsmarine. Perhaps a degree of responsibility lay with Donitz himself, who was known to be particularly anxious concerning the daily operation of the U-boats; his relentless questioning and the subsequent transmission of ciphers he demanded presented Allied intelligence with all the details they needed.


Numerous factors contributed to an Allied victory: improvement in Allied convoy tactics, the use of high frequency direction finding (the Huff-Duff), radar, active sonar (or ASDIC, in Britain), depth charges, ASW spigot mortars (called Hedgehogs), the introduction of the Leigh Light, coordination of escort aircraft (and escort carriers), the cracking of the German Naval Enigma Code, and most crucial of all - the full entry and participation of the United States.  By the end of the war, the Kriegsmarine lost a total of 793 U-boats and 28,000 men KIA, a casualty rate of 75%  - the highest rate among any of the German forces during WW2.  In addition, Allied strategic bombing successfully obliterated U-boat shipyards as well as their bases.




U-Boat sunk, 1943 - www.pastfinder.de (00:01:55m)





(12/12) Battlefield I: The Battle of the Atlantic Episode 3 (GDH) (00:05:07m)




WW2 Battle of Atlantic MAP of Convoy Routes March-December 1941




NEXT

(please click on the following link for part 3)







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