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U-boat is the anglicised version of the German word U-Boot [ˈuːboːt] ( ), a shortening of Unterseeboot, which means "undersea boat". While the German term refers to any submarine, the English one (in common with several other languages) refers specifically to military submarines operated by Germany, particularly in World War I and World War II. Although at times they were efficient fleet weapons against enemy naval warships, they were most effectively used in an economic warfare role (commerce raiding), 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 Canada, the British Empire, and the United States to the islands of the United Kingdom and (during World War II) to the Soviet Union and the Allied Countries in the Mediterranean. Austro-Hungarian submarines of World War I (and before) were also known as U-boats.
The first submarine built in Germany was the three-man submarine Brandtaucher, which sank to the bottom of Kiel harbor during its first test dive. The vessel was designed in 1850 by the inventor and engineer Wilhelm Bauer and built by Schweffel & Howaldt in Kiel for the Imperial German Navy. Brandtaucher was later rediscovered during dredging operations in 1887, and subsequently raised sixteen years later and placed in a museum in Germany, where it remains today.
This was followed in 1890 by WW1 and WW2, built to a Nordenfelt design. In 1903, Germaniawerft dockyard in Kiel completed Germany's first fully functional submarine, Forelle which was sold to Russia during the Russo-Japanese War in April 1904. The SM U-1 was a completely redesigned Karp-class submarine and only one was built. It was commissioned by the Imperial German Navy on 14 December 1906. It had a double hull, was powered by a Körting kerosene engine and was armed with a single torpedo tube. The fifty percent larger SM U-2 had two torpedo tubes. A diesel engine was not installed in a German navy boat until the U-19 class of 1912–13. At the start of World War I, Germany had 48 submarines of 13 classes in service or under construction. During the First World War the SM U-1 was used for training and was retired in 1919. It is currently on display at the Deutsches Museum in Munich.
At the start of World War I, Germany had twenty-nine U-boats; in the first ten weeks, five British cruisers had been lost to them. On 5 September 1914, HMS Pathfinder was sunk by SM U-21, the first ship to have been sunk by a submarine using a self-propelled torpedo. On 22 September, U-9 sank the obsolete British warships HMS Aboukir, HMS Cressy and HMS Hogue (the "Live Bait Squadron") in a single hour.
In the Gallipoli Campaign in early 1915 in the eastern Mediterranean, German U-boats, notably the U-21, prevented close support of allied troops by 18 pre-Dreadnought battleships by sinking two of them.
For the first few months of the war, U-boat anti-commerce actions observed the "prize rules" of the time which governed the treatment of enemy civilian ships and their occupants. On 20 October 1914, SM U-17 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, even potentially neutral ones, without warning.
In February 1915, a submarine was rammed and sunk off Beachy Head by the collier SS Thordis commanded by Captain John Bell RNR after firing a torpedo. On 7 May 1915, SM U-20 sank the liner RMS Lusitania with a single torpedo hit, although it is debated whether a second explosion was due to flammable cargo or another torpedo. 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 passenger ship was attacked. According to the ship's manifest, Lusitania was carrying military cargo, though none of them were classified as ammunition since they were classed as small arms and had bulk of non-explosives. This widely made the ship a non-military target. In fact, Lusitania had been carrying small arms for years prior to the sinking in 1915. It was not until the sinking of the ferry SS Sussex that there was a widespread reaction in the USA.
The initial U.S. response was to threaten to sever diplomatic ties, which persuaded the Germans to issue the Sussex pledge that re-imposed 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 on Germany in April 1917.
Unrestricted submarine warfare in the spring of 1917 was initially very successful, sinking a major part of Britain-bound shipping. Nevertheless with the introduction of escorted convoys shipping losses declined and in the end the German strategy failed to destroy sufficient Allied shipping. 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 destroyed.
Under the terms of the Armistice, all U-boats were to immediately surrender. Those in home waters sailed to the British submarine base at Harwich. The entire process was done quickly and in the main without difficulty, after which the vessels were studied, scrapped, or given to Allied navies. Stephen King-Hall wrote a detailed eyewitness account of the surrender.
At the end of World War I, as part of the Paris Peace Conference, 1919, the Treaty of Versailles restricted the total tonnage of the German surface fleet. The treaty also restricted the independent tonnage of ships and forbade the construction of submarines. However, a submarine design office was set up in the Netherlands and a torpedo research program was started in Sweden. Before the start of World War II, Germany started building U-boats and training crews, labeling these activities as "research" or concealing them using 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.
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 tons each), six cruisers and 12 destroyers. Prime Minister Winston Churchill wrote "The only thing that really frightened me during the war was the U-boat peril."
In the early stages of the war, the U-boats were extremely effective in destroying Allied shipping, initially in the mid-Atlantic, where there was a large gap in air cover. There was an extensive trade in war supplies and food across the Atlantic, which was critical for Britain's survival. This continuous action became known as the Battle of the Atlantic, as the British developed technical defences such as ASDIC and radar, and the German U-boats responded by hunting in what were called "wolfpacks" where multiple submarines would stay close together, making it easier for them to sink a specific target. Later, when the United States 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. The U.S. military engaged in various tactics against German incursions in the Americas; these included military surveillance of foreign nations in Latin America, particularly in the Caribbean, in order to deter any local governments from supplying German U-boats.
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 more ship-like hull design reflects the fact that these were primarily surface vessels which had the ability to submerge when necessary. This contrasts with the cylindrical profile of modern nuclear submarines, which are more hydrodynamic underwater (where they spend the majority of their time) but less stable on the surface. Indeed, while U-boats were faster on the surface than submerged, the opposite is generally true of modern subs. The most common U-boat attack during the early years of the war was conducted on the surface and at night, see submarine warfare. 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."
The U-boats' main weapon was the torpedo, though mines and deck guns (while surfaced) were also used. By the end of the war, almost 3,000 Allied ships (175 warships; 2,825 merchant ships) were sunk by U-boat torpedoes. Early German World War II torpedoes were straight runners, as opposed to the homing and pattern-running torpedoes which were fielded 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 change in the 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, the depth-keeping equipment and magnetic and contact exploders were notoriously unreliable in the first eight months of the war. Torpedoes would often run at an improper depth, detonate prematurely, or fail to explode altogether—sometimes bouncing harmlessly off the hull of the target ship. This was most evident in Operation Weserübung, the invasion of Norway, where various skilled U-boat commanders failed to inflict damage on British transports and warships because of faulty torpedoes. The faults were largely due to a lack of testing. The magnetic detonator was sensitive to mechanical oscillations during the torpedo run and at high latitudes fluctuations in the Earth's magnetic field. These were eventually phased out, and the depth-keeping problem was solved by early 1942.
Later in the war, Germany developed an acoustic homing torpedo, the G7/T5. 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. 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. The Germans in turn countered this by introducing newer and upgraded versions of the acoustic torpedoes, like the late war G7es, and the T11 torpedo. However, the T11 torpedoes did not see active service.
U-boats also adopted several types of "pattern-running" torpedoes which ran straight out 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.
During 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 and the Type IX boats which were larger versions of the VII but specifically designed for long-range patrols, some traveling as far as Japan and the east coast of the United States. With the increasing sophistication of Allied detection ans subsequent losses, German designers began to fully realise the potential for a truly submerged boat. The Type XXI "Elektroboot", was designed to favor submerged performance both for combat effectiveness and survival. It was the first true submersible. The Type XXI featured an evolutionary design that combined several different strands of the U-Boat development program, most notably from the Walter U-boats, the Type XVII, which featured an unsuccessful yet revolutionary hydrogen peroxide propulsion system. These boats featured a streamlined hull design, which formed the basis of the later USS Nautilus nuclear submarine, and was adapted for use with more conventional propulsion systems. The larger hull design allowed for a greatly increased battery capacity, which enabled the XXI to to cruise submerged for longer periods and reach unprecedented submerged speeds for the time.
Throughout 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, as well as more AA guns. However, by early/mid 1943 the Allies switched to centimetric radar (unbeknownst to Germany) which rendered the radar detectors ineffective. U-boat radar systems were also developed, but many captains chose not to use them for fear of broadcasting their position to enemy patrols and lack of sufficient electronic countermeasures.
The Germans experimented with the idea of the Schnorchel (snorkel) from captured Dutch submarines, early on but didnt see the need for them 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, as is today, 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 that the Schnorchel mast itself could be detected beyond visual range.
Several other pioneering innovations included, acoustic and electro absorbent coatings to make them less of an ASDIC or RADAR target. The germans also developed active countermeasures such as facilities to release artificial chemical bubble-making decoys, 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), the use of mystery ships, 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 793 U-boats and about 28,000 submariners (a 75% casualty rate, the highest of all German forces during the war).
At the same time, the Allies targeted the U-boat shipyards and their bases with strategic bombing.
The British had a major advantage in their ability to read some German naval Enigma codes. An understanding of the German coding methods had been brought to Britain via France from Polish code-breakers. Thereafter, code-books and equipment were captured by raids on German weather ships and from captured U-boats. A team including Alan Turing used special purpose "Bombes" and early computers to break new German codes as they were introduced. The speedy decoding of messages was vital in directing convoys away from wolf-packs and allowing interception and destruction of U-boats. This was demonstrated when the Naval Enigma machines were altered in February 1942 and wolf-pack effectiveness greatly increased until the new code was broken.
The German submarine U-110, a Type IXB, was captured in 1941 by the Royal Navy, and its Enigma machine and documents were removed. U-559 was also captured by the British in October 1942, three sailors boarded her as she was sinking, and desperately threw all the code books out of the submarine. Two of them, Able Seaman Colin Grazier and Lieutenant Francis Anthony Blair Fasson continued to throw code books out of the ship as it went under water, and went down with it. Further code books were captured by raids on weather ships. U-744 was boarded by crew from the Canadian ship HMCS Chilliwack on 6 March 1944, and codes were taken from her, but by this time in the war most of the information was known. The U-505, a Type IXC, was captured by the United States Navy in June 1944. It is presently a museum ship in Chicago at the Museum of Science and Industry.
Two events in the battle took place in 1942 when German U-boats attacked four allied ore carriers at Bell Island, Newfoundland. The carriers SS Saganaga and the SS Lord Strathcona were sunk by U-513 on 5 September 1942, while the SS Rosecastle and PLM 27 were sunk by U-518 on 2 November with the loss of 69 lives. When the submarine launched a torpedo at the loading pier, Bell Island became the only location in North America to be subject to direct attack by German forces in World War II.
Operation Deadlight was the code name for the scuttling of U-boats surrendered to the Allies after the defeat of Germany near the end of the war. Of the 154 U-boats surrendered, 121 were scuttled in deep water off Lisahally, Northern Ireland or Loch Ryan, Scotland in late 1945 and early 1946.
From 1955, the West German Bundesmarine was allowed to have a small navy. Initially two sunken Type XXIIIs and a Type XXI were raised and repaired. In the 1960s, West Germany re-entered the submarine business. Because Germany was initially restricted to a 450 tonne displacement limit, the Bundesmarine focused on small coastal submarines to protect against the Soviet threat in the Baltic Sea. The Germans sought to use advanced technologies to offset the small displacement, such as amagnetic steel to protect against naval mines and magnetic anomaly detectors.
The initial Type 201 was a failure because of hull cracking; the subsequent Type 205, first commissioned in 1967, was a success, and 12 were built for the German navy. To continue the U-boat tradition, the new boats received the classic U designation starting with the U-1.
With the Danish government's purchase of two Type 205 boats, the German government realized the potential for the submarine as an export. Three of the improved Type 206 boats were sold to the Israeli Navy becoming the Gal-class. The German Type 209 diesel-electric submarine was the most popular export-sales submarine in the world from the late 1960s into the first years of the 21st century. With a larger 1,000-1,500 tonne displacement, the class was very customizable and has seen service with 14 navies with 51 examples being built as of 2006.
Germany has brought the U-boat name into the 21st century with the new Type 212. The 212 features an air-independent propulsion system using hydrogen fuel cells. This system is safer than previous closed-cycle diesel engines and steam turbines, cheaper than a nuclear reactor and quieter than either. While the Type 212 is also being purchased by Italy, the Type 214 has been designed as the follow-on export model and has been sold to Greece, South Korea and Turkey.
In July 2006, Germany commissioned its newest U-boat, the U-34, a Type 212.
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