U-boat is the anglicized version of the German word U-Boot, itself an abbreviation of Unterseeboot (undersea boat), and refers to military submarines operated by Germany, particularly in World War I and World War II. Although in theory, U-boats could have been useful fleet weapons against enemy naval warships, in practice they were most effectively used in an economic-warfare role, enforcing a naval blockade against enemy shipping. The primary targets of the U-boat campaigns in both wars were the merchant convoys bringing supplies from the British Empire and the United States to the island of Great Britain. Austrian submarines of World War I were also known as "U-Boats". 
Kreigsmarine Unterseeboote - U-BOATS - Submarines of the German Navy ==========================================================================
The distinction between U-boat and submarine is common in English-language usage (where U-boat refers exclusively to the German vessels of the World Wars) but is unknown in German, in which the term U-Boot refers to any submarine.
The German Navy was very definite about their requirement of an Atlantic going U-boat. The most important offensive characteristics were surface speed, range, maneuverability and the number of torpedoes carried. Accordingly, since submerging was the primary escape method, dive speed and depth were definite desirable characteristics. With the advancement of technology, particularly in the field of electronic and optical advancement, this had allowed German engineers (and otherwise) to design far more effective U-boats than the U-boats of the First World War era.
The Kriegsmarine understood that given the limited underwater capabilities of the U-boat, it was not to be considered as a true submarine. Rather, a U-boat was principally considered as a torpedo boat, with the special capability to submerge for attack - or as a defensive measure. Thus a U-boat was short for Unterseeboot, or underwater boat.
Between 1919 until the end of the Second World War, Germany designed many U-boats ranging from special purpose tiny midget subs to the giant sea cow (seekuh) supply u-boat. Many were doomed to be nothing more than designs that never made it past the drawing board.
The U-boat was essentially a launch platform for its main weapon, the torpedo, though mines were also laid. By the end of the war, almost 3,000 Allied ships (175 warships; the rest were merchant ships) were sunk by U-boat torpedoes. Early German World War II torpedoes were straight runners, unlike the homers and pattern-runners of later in the war. They were fitted with one of two types of pistol trigger: impact, which detonated the warhead upon contact with a solid object, and magnetic, which detonated upon sensing a magnetic field within a few meters. One of the most effective uses of magnetic pistols would be to set the torpedo's depth to just beneath the keel of the target. The explosion under the target's keel would create a shock wave, and the ship could break in two. In this way, even large or heavily-armored ships could be sunk or disabled with a single well-placed hit. In practice, however, both the depth-keeping equipment and magnetic exploders were notoriously unreliable early in the war. Torpedoes would often run at an improper depth, detonate prematurely, or simply fail to explode. This was most evident in Operation Weserübung, the invasion of Norway, where various skilled Captains failed to inflict damage on British transports and warships because of faulty torpedoes. The faults were largely due to a lack of testing in the production of the torpedoes. The magnetic detonator was also affected by the Earth's magnetic field—the more so in higher latitudes. The magnetic exploder was eventually phased out, and the depth-keeping problem was solved in early 1942.
Later in the war, Germany developed an acoustic homing torpedo, the G7es. It was primarily designed to combat convoy escorts. The acoustic torpedo was designed to run straight to an arming distance of 400 meters and then turn toward the loudest noise detected. This sometimes ended up being the U-boat itself; at least two submarines may have been sunk by their own homing torpedoes. (Problems with steering mechanisms on normal torpedoes made them occasionally lethal to the firing boat as well). Additionally, it was found these torpedoes were only effective against ships moving at greater than 15 knots (28 km/h). At any rate, the Allies countered acoustic torpedoes with noisemaker decoys such as Foxer, FXR, CAT and Fanfare.
U-boats also adopted "pattern-running" torpedoes which ran to a preset distance, then traveled in either a circular or ladder-like pattern. When fired at a convoy, this increased the probability of a hit if the weapon missed its primary target.
In World War 2, as they did in World War 1, submarines were widely used by both sides as the ultimate weapon of naval blockade, sinking large numbers of both merchant ships and warships, resulting in either paralyzing the enemy's military industry and war effort by causing severe shortages of war materials and products and preventing maritime troop transfers, or forcing the enemy to dedicate enormous resources to anti submarine warfare in order to prevent that from happening, resources which could otherwise be used in the enemy's main war effort.
Either way, the submarine is the classic weapon of the war of attrition, where victory is achieved by the side which inflicts significantly more losses in men and material to the enemy than it suffers, and monthly ship tonnage loss counts reflect success or failure better than battle maps. The submarine's ability to attack almost anywhere and anytime, in total surprise and with devastating results, makes it a highly efficient weapon, in which a small crew of about 40 to 80 sailors can do more damage than 1000 sailors in a battleship, and for a fraction of the cost, and a much larger anti-submarine force is required in order to efficiently fight the submarine.
The same features of the submarine also make it the perfect blockade runner, capable of quietly smuggling secret agents and commandos, or small amounts of high importance cargo, to and from almost any enemy beach or a blockaded harbor, making the submarine one of the main vehicles of intelligence and special forces warfare.
Unlike the post war nuclear submarines, World War 2 submarines had quite limited underwater speed, range, and endurance. They usually sailed on the surface, especially at night, and submerged only when they had to, to avoid being detected and attacked. In the first years of the war, German submarines even made group night attacks while surfaced, as if they were surface torpedo boats. As RADAR and aircraft were more widely used to detect and attack submarines, they were forced to remain submerged most of the time, and new technical and electronic improvements were invented, mostly by the Germans, to significantly improve the submarine's underwater performance, and to enhance its awareness to nearby danger.
The first submarine built in Germany was the Brandtaucher, designed in 1850 by the inventor and engineer Wilhelm Bauer and built by Schweffel & Howaldt in Kiel for the German Navy.
This was followed in 1890 by W1 and W2, built to a Nordenfelt design. In 1904, Krupp's dockyard in Kiel completed a submarine which was sold to Russia. The first works were carried out by the Spanish engineer Raymondo Lorenzo d'Equevilley Montjustin (submarine 'Narval')
Despite their ultimate importance, the German Navy declined to take up the experiment with the submarine until 1904.
The first submarine for the German Navy was built in 1905. U-1 was delivered in December 1906, built by Krupps Germania in Kiel. This was the "Karp" class which had 238 ton displacement on the surface and 283 tons submerged. The paraffin engine developed 10 knots on the surface with a range of 1500 sm. Submerged, the ship could manage 50sm at 5 knots using battery electric propulsion. The ships followed a design by Laubeuf first used successfully in 1897, having a double hull and flotation tanks around the outside of the main crew compartments. The submarine had just one torpedo tube at the front and room for a total of three torpedos (the 50% larger U2 design having two tubes). The early Körting kerosene engines were noisy and smokey, so that a considerable boost to the usefulness of the submarine came with the introduction of quieter and cleaner diesel engines in 1910, which were much more difficult for an enemy to detect. At the start of World War 1 Germany had 48 submarines in service or under construction. These were of 13 different classes.
Admiral von Tirpitz later became the commander of the Navy. The main fighting forces of the navy were to become the High Seas Fleet, and the U-boat fleet. Smaller fleets were deployed to the German overseas protectorates, the most prominent being assigned to the East Asia Station at Tsingtao during WWI.
At the start of World War I, Germany had twenty-nine U-boats in active service; in the first ten weeks, five British cruisers had been lost to them. In September, U-9 sank the obsolete British warships Aboukir, Cressy and Hogue (the "Live Bait Squadron") in a matter of an hour.
For the first few months of the war, U-boat anti-commerce actions observed the current "prize rules" which governed the treatment of enemy civilian ships and their occupants. On 20 October 1914 the U-boat U17 sank the first merchant ship, the SS Glitra off Norway. Surface commerce raiders were proving to be ineffective, and on 4 February 1915, the Kaiser assented to the declaration of a war zone in the waters around the British Isles. This was cited as a retaliation for British minefields and shipping blockades. Under the instructions given to U-boat captains, they could sink merchant ships, potentially neutral ones, without warning. A statement by the U.S. Government, holding Germany "strictly accountable" for any loss of American lives, made no material difference.
On 7 May 1915, U-20 sank the liner RMS Lusitania with a single torpedo hit. The sinking claimed 1,198 lives, 128 of them American civilians, including noted theatrical producer Charles Frohman and Alfred Vanderbilt, a member of the prestigious Vanderbilt family. The sinking deeply shocked the Allies and their sympathizers because an unarmed civilian merchant vessel was attacked without any warning. According to the ship's manifest, Lusitania was carrying no military cargo. However, after further investigations, it has been confirmed that the Lusitania was in fact carrying bullets and ammunition for the allies to use against the Germans. However, this was not known at the time and the Lusitania was actually mistaken for a troopship. But it was not until the sinking of the ferry "Sussex" that there was a widespread reaction in the USA.
The initial U.S. response was to threaten to sever diplomatic relations, which persuaded the Germans to re-impose restrictions on U-boat activity. The U.S. reiterated its objections to German submarine warfare whenever U.S. civilians died as a result of German attacks, which prompted the Germans to fully re-apply prize rules. This, however, removed the effectiveness of the U-boat fleet, and the Germans consequently sought a decisive surface action, a strategy which culminated in the Battle of Jutland.
Although the Germans claimed victory at Jutland, the British Grand Fleet remained in control at sea. It was necessary to return to effective anti-commerce warfare by U-boats. Vice-Admiral Reinhard Scheer, Commander in Chief of the High Seas Fleet, pressed for all-out U-boat war, convinced that a high rate of shipping losses would force Britain to seek an early peace before the United States could react effectively.
The renewed German campaign was effective, sinking 1.4 million tons of shipping between October 1916 and January 1917. Despite this, the political situation demanded even greater pressure, and on 31 January 1917, Germany announced that its U-boats would engage in unrestricted submarine warfare beginning 1 February. On 17 March, German submarines sank three American merchant vessels, and the U.S. declared war in April 1917.
In the end, the German strategy failed to destroy sufficient Allied shipping, largely due to the introduction of escorted convoys, before U.S. manpower and materiel could be brought to bear in France. However, the main reason for the ending of the war was the effectiveness of the British blockade of Germany which brought about an economic collapse. An armistice became effective on 11 November 1918 and all surviving German submarines were surrendered. Of the 360 submarines that had been built, 178 were lost but more than 11 million tons of shipping had been sunk.
At the end of World War I, as part of the Paris Peace Conference, 1919, the German armed forces became subject to the stipulations of the Treaty of Versailles. The provisions of the Versailles Treaty restricted the German navy to 15,000 men and no submarines, while the fleet was limited to six pre-dreadnought battleships ("panzerschiffe"),six cruisers, twelve destroyers and twelve torpedo-boats.. The Treaty also stipulated that Germany could replace its armoured ships as needed, but with vessels that were not more than 10,000 tons displacement. With the scuttling of the majority of the High Seas Fleet at Scapa Flow, new construction was needed.
The Treaty of Versailles limited the size and armament of the Reichsmarine and prevented it from introducing new technologies. The restrictions were intended to prevent the German navy from becoming a threat to the Allied powers. On the other hand, the Allies had made certain that the Reichsmarine would be in the foreseeable future the strongest power in the Baltic Sea, in order to serve as a counterweight against the new Soviet Union, which was viewed with distrust by the Allies.
The Treaty of Versailles specifically forbade the construction of submarines. However, a submarine design office was set up in Holland and a torpedo research programme was started in Sweden. Before the start of World War II, Germany started building U-boats and training crews, hiding these activities as "research" or other covers. When this became known, the Anglo-German Naval Agreement limited Germany to parity with Britain in submarines. When World War II started, Germany already had 65 U-boats with 21 of those at sea ready for war.
NV Ingenieurskantoor voor Scheepsbouw (Dutch: engineer-office for shipbuilding), usually contracted to IvS, was a Dutch dummy company set up by the Reichsmarine after World War I in order to maintain and develop German submarine know-how and to circumvent the limitations set by the Treaty of Versailles. The company designed several submarine types for paying countries, including the Soviet S class submarine and the prototypes for the German Type II submarine and the German Type VII submarine.
The company was a joint venture by the German shipyards AG Vulcan and the Krupp-owned Germaniawerft in Kiel and AG Weser in Bremen. Design work was carried out at the facilities of these companies in Germany.
The company was funded by the German Navy. IvS first constructed two submarines for Spain, which were later sold to Turkey, both of which were launched in 1927 and were closely based on the Type UBIII of the Kaiserliche Marine. 1927-1933 five IvS submarine designs were build in Finland. One of them was CV 707, later Vesikko, which was the prototype of type IIA. The contracts were worded in such a way that IvS personnel were involved with crew training and selection, and were allowed to take part in boat service trials. The Germans — who were, at the time, tightly restricted from using their submarines for themselves — thus gained a first-hand knowledge of how their new prototypes worked in practice.
At the time of IvS, the Germans were bound by a Treaty that they had signed and sworn to uphold as a result of the Armistice in 1918. This treaty, among its other terms, demanded that all of the German U-boats were destroyed or given to other nations. Thus the German Navy was left without a submarine capacity, and IvS was created to get around these restrictions. IvS ultimately provided the foundations of the massive, thousands-strong navy that Germany developed for use in World War II.
In 1933 Germany established a school for training Unterseeboot crews, ironically under the title 'Anti-Submarine Defence School,' or in their tongue, Unterseebootsabwehrschule. This school was established in Kiel. This program involved provision for a small fleet of eight 500 ton submarines. This number was later doubled to 16.
Later, Germany developed plans for an actual navy. The projected designs for the boats that were to be the composition of this navy were referred to as 'Experimental Motor Boats'. Deutsche Werke in Kiel was elected to build the new submarines, and a new U-boat base was to be built at Kiel-Dietrichsdorf. There component materials were gathered surreptitiously, in preparation for the order to begin production.
When the Nazis came to power in 1933, Adolf Hitler soon began to ignore many of the Treaty restrictions and accelerated German rearmament. The Anglo-German Naval Agreement of 18 June 1935 then allowed Germany to build a navy equivalent to 35% of British surface ship tonnage and 45% of British submarine tonnage; battleships were to be limited to no more than 35,000 tons.
Following the 1938 crisis caused by the German occupation of Czechoslovakia, Germany abandoned all pretensions of adherence to treaty limitations on its navy.
Plan Z, the blueprint for the German naval construction program finalized in 1938, envisaged building a navy of approximately 800 ships to be completed between the period 1939 – 1947. This project never became a full reality. It is very questionable that German industry would have had the resources for such a construction program and that the other European Nations would stood still and not react to this program. The realization of the Z-Plan was implemented on January 29th, 1939. Two H-Class battleships (H-39) were laid down, three months later Germany quit the the fleet treaty with England and the dream "No more war against Britain" was gone. Then, only four months later, Germany attacked Poland and work on all Z-Plan projects was stopped. During the next months of the war, all incomplete ships of the Z-plan were scrapped and the material was used to build additional submarines.
Since the simultaneous and rapid build-up of the German army and airforce demanded substantial effort and resources, the planned naval program was not very far advanced by the time World War II began. Implementation only began in January 1939 when three H-class battleships and two M-class light cruisers were laid down. On September 1, 1939, the navy still had a total personnel strength of only 78,000, and it was not at all ready for a major role in the war. With expectations in Germany of a quick victory by land, Plan Z was essentially shelved and the resources initially allocated for its realization were largely redirected to the construction of U-boats.
By the start of World War II, much of the Kriegsmarine were modern ships: fast, well-armed and well-armoured. This had been achieved by concealment but also by deliberately flouting World War I peace terms and those of various naval treaties. However, the war started with the German Navy still at a distinct disadvantage in terms of sheer size with what were expected to be its primary adversaries-the navies of France and Great Britain. Although a major re-armament of the navy (Plan Z) was planned, and initially begun, the start of the war in 1939 meant that the vast amounts of material required for the project were diverted to other areas. The sheer disparity in size when compared to the other European powers navies prompted German naval commander in chief Grand Admiral Erich Raeder to write of his own navy once the war began "The surface forces can do no more than show that they know how to die gallantly."
The Kriegsmarine was involved in World War II from the start of the war and participated in the Battle of Westerplatte and the Battle of the Danzig Bay during the Invasion of Poland. In 1939, major events for the Kriegsmarine were the Battle of the River Plate, the sinking of the Battleship HMS Royal Oak, and the sinking of the Aircraft Carrier HMS Courageous. The Battle of the Atlantic started in 1939, although the German submarine fleet was hampered by the lack of good ports from which to attack Allied shipping.
In April 1940, the main action the German Navy was involved in was the invasion of Norway, where it suffered quite heavy losses, including the Heavy Cruiser Blücher sunk by the guns of Oscarsborg Fortress in the Oslofjord, ten destroyers lost in the Battles of Narvik and two light cruiser lost elsewhere during the campaign. The Kriegsmarine did however sink a number of British ships during this campaign, including the Aircraft Carrier HMS Glorious.
The losses in the Norwegian Campaign meant that only a handful of heavy ships were ready for action for the planned, but never executed, invasion of Britain (Operation Sealion) in the summer of 1940. There were serious doubts that the invasion sea routes could have been protected against British naval action. After the fall of France and the conquest of Norway, the German submarine fleet was brought much closer to the British shipping lanes in the Atlantic. At first, the British merchant convoys lacked radar equipped escorts; as such, the submarines were very hard to detect during their nighttime surface attacks. This year was for these reasons one of the most successful for the Kriegsmarine, as measured in terms of merchant shipping sunk compared to submarines lost (the First Happy Time).
The Italian and Japanese navies had large submarine fleets when the war began. The Italian submarine warfare was not very efficient, except in the operation of underwater divers, a highly efficient method of underwater warfare which they invented and excelled in. The Japanese built remarkable submarines, but misused them. They used submarines mostly in cooperation with surface warship groups and mostly against enemy warships, which are much harder targets than merchant ships. As a result, their submarine achievements were low.
British submarines were a secondary force in the large Royal Navy. They mainly attacked Axis warships, including sinking 39 German submarines, and participated in many intelligence operations, but their main strategic contribution was made by a small force of smaller coastal submarines which operated from the heavily attacked tiny island of Malta in the center of the Mediterranean Sea. This small force kept sinking the Italian supply ships which provided fuel and other equipment to the German-Italian forces which fought in North Africa, and the increasing shortages this caused limited the abilities of these Axis forces and eventually led to their defeat.
Italy entered the war in June 1940, and the Battle of the Mediterranean began: from September 1941 to May 1944 some 62 German submarines were transferred there, sneaking past the British naval base at Gibraltar. The Mediterranean submarines sunk 24 major Allied warships (including 12 destroyers, 4 cruisers, 2 aircraft carriers and 1 battleship) and 94 merchant ships (449,206 tons of shipping). None of the Mediterranean submarines made it back to their home bases as they were all either sunk in battle or scuttled by their crews at the end of the war.
During 1941, the Kriegsmarine and the United States Navy became de facto belligerents, although war was not formally declared, leading to the sinking of the USS Reuben James. The Japanese attack on Pearl Harbor and the subsequent German declaration of war against the United States in December 1941 led to another phase of the Battle of the Atlantic. In Operation Drumbeat and subsequent operations until August 1942, a large number of Allied merchant ships were sunk by submarines off the American coast as the Americans had not prepared for submarine warfare, despite clear warnings (this was the so-called Second happy time for the German navy). The situation became so serious that military leaders feared for the whole allied strategy.
The vast American ship building capabilities and naval forces were however now brought into the war and soon more than offset any losses inflicted by the German submariners. After the attack on Pearl Harbor, the US Navy initially had two main forces, the few aircraft carriers, and the submarines. While the aircraft carriers were given the task of destroying the Japanese Navy, especially the Japanese carriers, the main task of the American submarines, just like the German U-boats, was to suffocate Japan's military industry, cut its oil supply, starve it, and prevent mass troop movements by sea, all by sinking the Japanese merchant fleet on which it was so dependent as a nation of islands.
Initially the American submarines suffered severely from faulty torpedoes and other problems, but when the problems were finally fixed in mid 1943, the US Pacific submarine force had tremendous achievements, efficiently doing its job and also secondary tasks such as rescuing downed airmen. They sunk almost 1300 Japanese merchant ships, and many warships, for a loss of 52 submarines of a total of 288, a remarkable achievement which was aided by the fact that unlike the British, the Japanese neglected to properly escort and protect their merchant ships until the end of the war.
In 1942, the submarine warfare continued on all fronts, and when German forces in the Soviet Union reached the Black Sea, a few submarines were eventually transferred there.
The Battle of the Barents Sea was an attempt by a German naval force to attack an Allied Arctic convoy. However, the advantage was not pressed home and they returned to base. There were serious implications: this failure infuriated Hitler, who nearly enforced a decision to scrap the surface fleet. Instead, resources were diverted to the U-boats, and the surface fleet became a lesser threat to the Allies.
During World War II, U-boat warfare was the major component of the Battle of the Atlantic, which lasted the duration of the war. Germany had the largest submarine fleet in World War II, since the Treaty of Versailles had limited the surface navy of Germany to six battleships (of less than 10,000 tonnes each), six cruisers and 12 destroyers.
German U-boat success in World War 1 against British shipping was such that after its defeat Germany was not allowed to have any submarines. In 1935, Germany ignored the treaty and began to rebuild a new submarine force, under the command of a former World War 1 U-boat captain, Karl Doenitz. A brilliant, innovative, and experienced tactician and submarine commander, Doenitz advanced submarine warfare to new heights, trained highly skilled crews and captains, and developed devastating new tactics, mainly the Wolfpack tactic which allowed a group of submarines to efficiently coordinate and concentrate their effort instead of fighting alone.
In the Wolfpack tactic, the submarines first spread across a long stretch of ocean to enhance their probability of detecting passing enemy ships, and when one of the submarines detected a convoy of enemy ships, instead of immediately attacking it alone, it reported its position and course and followed it, and the other submarines first slowly regrouped to a position ahead of the enemy convoy, and only then attacked it together, preferably at night, overwhelming or even outnumbering the convoy's anti-submarine escort warships and sinking many more ships.
The devastating implementation of such tactics by the German U-boats, and systematic ongoing analysis of results and adaptation to changes, made Doenitz and his submarines the most formidable enemy Britain faced, more worrying even than the Luftwaffe. Winston Churchill said that the only threat that really worried him during World War 2 was "The U-boat peril".
The experienced Doenitz calculated that considering the submarines sailing to and back from the area of operations, submarines used for training new crews, and submarines being resupplied and repaired in German harbors, he needed 300 submarines in order to have 100 submarines active in the area of operations near Britain.
The only thing that saved Britain from being suffocated early in the war by the German U-boats, were Doenitz's superiors.
The German High Command, and mainly Hitler, were focused before and during the war on continental ground warfare. Hitler was also firmly confident before the war that Germany will not have to fight Britain in the near future. He said so himself in a letter to the U-boat captains just 5 weeks before the war.
The German Navy itself, like the British Navy, was dominated by Admirals who served in the big guns surface ships, and despite the successful experience of German submarines in World War 1, and the development of the aircraft as a powerful weapon against surface ships, they kept the submarines force as a secondary arm of the Navy, in terms of budget allocation.
As a result, Hitler and Roeder (head of the German Navy) confidently rejected Doenitz' pre-war warnings that Germany has too few submarines to achieve their task of cutting Britain's maritime life line, and instead of having 300 submarines at the beginning of the war as he wanted, he had just 55, and only 12 could be active in atlantic operations.
Even after the war started, it took a long time before the U-boats were allowed to fully exploit their devastating potential and before their rate of production was significantly raised to compensate for losses and increase their numbers. In 1943 Doenitz was also promoted to head of the German Navy and submarine production was dramatically increased, but it was too late. The German U-boats then faced much stronger anti submarine forces, which were equipped with new technologies, new tactics, a new commander, Admiral Max Horton, a former submarine captain and commander of the British submarine force, who knew best how to fight against submarines, and by then merchant ships were produced in America faster than the U-boats could sink them. In May 1943 Doenitz lost 41 U-boats in 3 weeks. The hunters became the hunted. The U-boat activity expanded to the South atlantic, to the US East coast, the Carribean, and the Mediterranean, but the main battlefield remained the North atlantic sea routes to Britain, and there they lost the battle.
The Battle of the Atlantic was the longest battle of the Second World War, beginning from the first day of hostilities and ending on the very last day of the war. It was also the most important battlefield during the entire Second World War because the success of every other campaign in every other theater of war depended upon its success. Many experts agree that defeat of the German U-Boats and control of the shipping lanes linking the Allied nations of Great Britain, United States and Canada was a key factor if the Allied nations were to invade occupied Europe and the heartland of Germany itself.
The Battle of the Atlantic was not about the most powerful navy; neither was it about glorious battles fought between battleships and submarines. But the Battle of the Atlantic was a commerce war waged by German U-Boats against Britain’s merchant marine. For nearly six years, Germany launched over 1,000 U-Boats into combat, in an attempt to isolate and blockade the British Isles, thereby forcing the British out of the war. It was a fight which nearly choked the shipping lanes of Great Britain, cutting off vital supplies of food, fuel and raw materials needed to continue fighting.
Which led to what was perhaps the longest ongoing battle to be fought in Europe during World War II, the attempted destruction of Hitler's French U-boat fortresses. The French naval bases at St. Nazaire and Lorient, occupied by the Germans in June 1940, quickly became the homes of massive U-boat fortresses - nearly indestructible submarine pens, built mostly by slave labour. From these bases, the U-boats struck merchant shipping at will from the Mediterranean to the North Sea. Thousands of vessels were lost, along with vital war materiel from the U.S. destined for Britain and the Soviet Union. The Royal Air Force began an all-out bombardment of the two ports. Despite their extensive efforts - and those of the Americans who joined them in 1942 - the fortresses would survive, surrounded by decimated French towns and countryside.
Until the end of 1942, the Germans sunk an average of 14 ships for each submarine lost. Since 1943, the rate dramatically reduced and submarines losses were very high. During the war they sunk a total of 3000 allied ships, mostly merchants, 14.5 million tons of shipping, and lost almost 800 submarines, which is about 80% of those which participated in operations, and 2/3 of the total of 1170 U-boats produced.
During 1943 and 1944, due to Allied anti-submarine tactics and better equipment the U-boat fleet started to suffer heavy losses. Radar, longer range air cover, improved tactics and new weapons all contributed. German technical developments, such as the Schnorchel, attempted to counter these. Also new U-boat types, the Elektroboote, were in development and, had these become operational in sufficient numbers, the Allied advantage would have been eroded.
By the end of the war, German U-Boats in the Battle of the Atlantic had sent over 2,900 ships and 14 million tons of Allied shipping to the bottom of the sea. In exchange, the Allies sank almost 800 U-Boats and over 30,000 of the 39,000 German sailors who put to sea, never returned – the highest casualty rate of any armed service in the history of modern war.
In the early stages of the war, the U-boats were extremely effective in destroying Allied shipping, initially in the gap between Canadian and British escorts. Later when the USA entered the war the U-boats ranged from the Atlantic coast of the United States and Canada to the Gulf of Mexico, and from the Arctic to the west and southern African coasts and even as far east as Penang. It is even rumored that one German U-boat managed to make it all the way down to Galveston Bay, Texas. Because speed and range were severely limited underwater while running on battery power, U-boats were required to spend most of their time surfaced running on diesel engines, diving only when attacked or for rare daytime torpedo strikes. The most common U-boat attack during the early years of the war was conducted on the surface and at night. This period, before the Allied forces developed truly effective antisubmarine warfare (ASW) tactics, was referred to by German submariners as "die glückliche Zeit" or the "happy time."
Germany had the largest submarine fleet during World War II. Due to the Treaty of Versailles limiting the surface navy, the rebuilding of the German surface forces had only begun in earnest a year before the outbreak of World War II. Expecting to be able to defeat the Royal Navy through underwater warfare, the German High Command pursued 'guerre de course' commerce raiding and immediately stopped all construction on capital surface ships save the nearly completed Bismarck class battleships and two cruisers, switching its resources to submarines, which could be built more quickly. Though it took most of 1940 to expand the production facilities and get the mass production started, more than a thousand submarines were built by the end of the war.
Germany put submarines to devastating effect in the Second Battle of the Atlantic in World War II, attempting but ultimately failing to cut off Britain's supply routes by sinking more merchant ships than Britain could replace. The supply lines were vital to Britain for food and industry, as well as armaments from the US. Although the U-boats had been updated in the intervening years, the major innovation was improved communications, encrypted using the famous Enigma cipher machine. This allowed for mass-attack tactics or "wolf packs" (Rudeltaktik), but was also ultimately the U-boats' downfall once the Allies cracked the code.
After putting to sea, U-boats operated mostly on their own, trying to find convoys in areas assigned to them by the High Command. If a convoy was found, the submarine did not attack immediately, but shadowed the convoy to allow other submarines in the area to also comverge upon the convoy. These were then grouped into a larger wolfpack strike force to attack the convoy simultaneously, preferably at night while surfaced.
The wolfpacks, known to the Germans as Rudeltaktik, were created by Karl Dönitz as a means to defeat the allied convoy system. He finally had enough U-boats and facilities to try his idea after the fall of France in 1940. The idea is simple enough; gather U-boats in patrol lines to scout for convoys. Once a convoy was spotted the first boat was designated "shadower" and would chase the convoy and report its heading and speed to BdU. This would allow other boats to form around it and attack, more or less all at once, usually on the surface at night.
This was meant to overwhelm the convoy escorts - and it sure did if the U-boats were manned by determined commanders. The wolfpacks were introduced in June, 1940 and proved an immediate success. Around 135 such groups were formed during 1940-1943, each one lasting up to 2 weeks. The number of U-boats in each wolfpack ranged from 3-4 on up to around 20 in the biggest groups.
From September 1939 to the beginning of 1943, the Ubootwaffe ("U-boat force") scored unprecedented success with these tactics, but were too few to have any decisive success. By the spring of 1943, German U-boat construction was at full capacity, but this was more than nullified by increased numbers of convoy escorts, aircraft, as well as technical advances like radar and sonar. Huff-Duff and Ultra allowed the Allies to route convoys around wolf packs when they detected them from their radio transmissions. The results were devastating: from March to July of that year, over 130 U-boats were lost, 41 in May alone. Concurrent Allied losses dropped dramatically, from 750,000 tons in March to only 188,000 in July. Although the Second battle of the Atlantic would continue to the last day of the war, the U-boat arm was unable to stem the tide of men and material, paving the way for Operation Torch, Operation Husky, and ultimately, D-Day. Winston Churchill wrote that the U-boat "peril" was the only thing that ever gave him cause to doubt the Allies' eventual victory.
Throughout World War II, the Kriegsmarine produced many different types of U-boats as technology evolved. Most notable are Type VII, known as the "workhorse" of the fleet, which was by far the most-produced type; Type IX boats were larger and specifically designed for long-range patrols, some traveling as far as Japan. With the Type XXI "Elektroboot", German designers realized the U-boat depended on submerged ability both for survival and lethality. The Type XXI featured a revolutionary streamlined hull design and propulsion system with a large battery which allowed it to cruise submerged for long periods and reach unprecedented submerged speeds. The large battery was because the space was originally intended for hydrogen peroxide storage with a Walter turbine, but this had proved unsuccessful on the Type XVII.
During the course of the war, an arms race evolved between the Allies and the Kriegsmarine, especially in detection and counter-detection. Sonar (ASDIC in Britain) allowed allied warships to detect submerged U-boats (and vice versa) beyond visual range but was not effective against a surfaced vessel; thus, early in the war, a U-boat at night or in bad weather was actually safer on the surface. Advancements in radar became particularly deadly for the U-boat crews, especially once aircraft-mounted units were developed. As a countermeasure, U-boats were fitted with radar warning receivers, to give them ample time to dive before the enemy closed in. U-boat radar was also developed, but many captains chose not to utilize it for fear of broadcasting their position to enemy patrols.
The Germans took the idea of the Schnorchel (snorkel) from captured Dutch submarines, though they did not begin to implement it on their own boats until rather late in the war. The Schnorchel was a retractable pipe which supplied air to the diesel engines while submerged at periscope depth, allowing the boats to cruise and recharge their batteries while maintaining a degree of stealth. It was far from a perfect solution, however. There were problems with the device's valve sticking shut or closing as it dunked in rough weather; since the system used the entire pressure hull as a buffer, the diesels would instantaneously suck huge volumes of air from the boat's compartments, and the crew often suffered painful ear injuries. Waste disposal was a problem when the U-boats spent extended periods without surfacing. Speed was limited to 8 knots (15 km/h), lest the device snap from stress. The schnorchel also had the effect of making the boat essentially noisy and deaf in sonar terms. Finally, Allied radar eventually became sufficiently advanced such that the schnorchel head itself could be detected. The U-boats had a radar detector but the Allies changed to centimetric radar which the Germans did not discover.
The later U-boats were covered in a sound-absorbent rubber coating to make them less of a torpedo target. They also had the facility to release a chemical bubble-making decoy, known as Bold, after the mythical kobold.
Advances in convoy tactics, high frequency direction finding (referred to as "Huff-Duff"), radar, active sonar (called ASDIC in Britain), depth charges, ASW spigot mortars (also known as "hedgehog"), the intermittent cracking of the German Naval Enigma code, the introduction of the Leigh Light, the range of escort aircraft (especially with the use of escort carriers), and the full entry of the U.S. into the war with its enormous shipbuilding capacity, all turned the tide against the U-boats. In the end, the U-boat fleet suffered extremely heavy casualties, losing 743 U-boats and about 28,000 submariners (a 75% casualty rate).
Between 1943 and 1945, a group of U-boats known as the "Monsun Boats" (Monsun Gruppe) operated in the Indian Ocean from Japanese bases in occupied Indonesia. As the Allied merchant convoys had not yet been organized in those waters, the initial sinkings were plentiful. However, this situation was soon remedied. During the later war years, the "Monsun Boats" were also used as a means of exchanging vital war supplies with Japan.
The Monsun Gruppe (or Monsoon Group) was a force of German U-boats (submarines) that operated in the Pacific and Indian Oceans during World War II.
The Indian Ocean was considered strategically important, the region not only contained India, Britain's most prized possession, but also the shipping routes and raw materials that the British vitally needed for its war effort. In the early years of the war German raiders and capital ships, operating in the Indian Ocean, had sunk a number of merchant ships, however as the war progressed it become more difficult for them to operate in the area and by 1942 most were either sunk or dispersed. From 1941, U-boats were also considered for deployment to this area but due to the successful periods known as the First and Second Happy Times, it was decided that sending U-boats to the Indian Ocean would be an unnecessary diversion. There were also no foreign bases in which units could operate from and be resupplied, hence they would be operating at the limits of their range. As a result the Germans concentrated their U-boat campaign in the North Atlantic.
Japan’s entrance into the war in 1941/42 led to the capture of European South-east Asian colonies such as British Malaya and the Dutch East Indies. In May-June, 1942, Japanese submarines began operating in the Indian Ocean and had engaged British forces in Madagascar. The British had invaded the Vichy controlled island in order to prevent it from falling into Japanese hands.
In 1943, the Germans agreed to send a number of U-boats to the Far East that would operate from Japanese occupied ports in the region against the then lucrative, relatively unprotected shipping in the area. The U-178 was the first, arriving at the former British seaplane base in Penang in August 1943. The idea of stationing U-boats in Malaya and the East Indies for operations in the Indian Ocean was first proposed by the Japanese in December 1942. As no supplies were available at either location the idea was turned down although a number of U-boats from the first wave operated around the Cape of Good Hope at the time. Penang, situated on the west coast of Malayan Peninsula was selected as the main U-boat base. A second base was established at Kobe, Japan, and small repair bases were located at Singapore, Jakarta and Surabaya. Eventually more than half a dozen U-boats operated from these bases. These U-boats were known as the "Monsun Gruppe" and were commanded by Captain Wilhelm Dommes. Altogether 41 U-boats of all types including transports would be sent, a large number of these however, were lost and only a small fraction returned to Europe.
The Italian Royal Navy (Regia Marina) converted four submaries into "transport submarines" in order to exchange rare or irreplaceable trade goods with Japan. They converted the Barbarigo, the Cappellini, the Giuliani, and the Torelli. After Italy quit the war in 1943, the Cappellini was taken over by the German Navy (Kriegsmarine) and re-named the UIT-24. When Germany surrendered in 1945, the UIT-24 was taken over bt the Imperial Japanese Navy and re-named the I-503. The Torelli shared a similar story.
The Japanese already started operating in the Arabian Sea by August 1943 and certain arrangements were made to avoid incidents between U-boats and Japanese submarines - attacks on other submarines were strictly forbidden. The Indian Ocean was the only place where German and Japanese forces fought in the same theatre.
The idea of stationing German U-boats in Penang or Sabang for operations in the Indian Ocean was first proposed by the Japanese in December 1942. As no supplies were available at either location the idea was turned down (although a number of U-cruisers from the first wave operated around the Cape at the time).
The idea was raised again in the spring 1943. Additionally, the Japanese requested 2 U-boats to be handed over for copying. Although Doenitz saw no point in such a handover, it was decided to give a type IXC boat.
As long as targets were available in the Atlantic, Doenitz considered sending U-boats on a large scale to the Far East as unprofitable. However, on 5 April, 1943 it was decided to send U-178 to Penang to establish the naval base there. U-511 sailed soon after to be eventually given to the Japanese in return for rubber.
It is also reported that U-511 arrived at Penang around 17 July, 1943 as the first German U-boat to enter the base (before U-178).
U-511 scored some success while on the passage to Japan. The boat carried Vice-Admiral Nomura (the Japanese Naval Attache) and in September 1943 was recommissioned as RO-500. U-511's crew was to be a spare crew for the boats which were later to operate from the Japanese-held bases.
After the May 1943 crisis it was decided to look for less strongly defended areas and the idea of sending boats to the Far East was finally approved. Indian Ocean was the only region with almost peace-time shipping arrangement and still with U-boats radius of action.
As the result arrangements were made to replenish U-cruisers still operating around the Cape and to send a new wave of boats for the attack in the Arabian Sea. The latter was scheduled for the end of September 1943 - right after the monsoon period. Because of this the group was named Monsun. The group was to sail in June 1943 at the latest.
Very few patrols with the intention to return back to the Far East bases were attempted by the Monsun boats.
One of the reasons for disappointing results was the quality and quantity of torpedoes available at Penang. They were derived from German armed merchant cruisers and blockade-runners and suffered badly from the long storage in the tropics. To make up for this special torpedo transports of type VIIF were sent with torpedoes and spares. Also further operational boats were systematically sent to the Far East:
It can be seen that the effort was gradually shifted from combat missions to transport missions. Some of the boats were even permanently converted to transports. How important the transport missions were can be judged from the fact that even in the spring 1945 U-boats were still sailing to the Far East. Some of them with interesting cargoes indeed - like well-known U-234. U-874 and U-875 were loading some 170 tons of mercury, lead and optical glass but never left European waters.
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NB: The above text has been collected / excerpted / edited / mangled / tangled / re-compiled / etc ... from the following online sources :
Naval history of Germany - wikipedia article #1
German U-Boats (Kriegsmarine Unterseeboot) - wikipedia article #2
NV Ingenieurskantoor voor Scheepsbouw (Dutch: engineer-office for shipbuilding) - wikipedia article #3
Kriegsmarine (War Navy of Nazi Germany) - wikipedia article #4
Plan Z (Nazi naval reconstruction plan) - wikipedia article #5
KM - Z-Plan(German fleet re-building program) - www.german-navy.de
List of Kriegsmarine U-Boats - wikipedia article #6
Submarines during WWII - wikipedia article #7
Uboat Wolfpacks - http://uboat.net/ops/
German U-boats - http://www.uboataces.com/ article # 1
German U-boats - http://www.uboataces.com/ article # 2
Commerce War - http://www.warcovers.dk/
Hitler's U-boat Fortresses - www.worldwartwobooks.com
World War 2 Submarines - www.2worldwar2.com
Anti-Submarine Warfare - wikipedia article #8
WW2 Submarine Warfare - wikipedia article #9
Monsun Boats - http://uboat.net/ops/
Monsun Gruppe - wikipedia article #10
