U-boat

U-boats were naval submarines operated by Germany, particularly in the First and Second World Wars. The term is an anglicized version of the German word U-Boot [ˈuːboːt] , a shortening of Unterseeboot (under-sea boat), though the German term refers to any submarine. Austro-Hungarian Navy submarines were also known as U-boats.
U-boats are most known for their unrestricted submarine warfare in both world wars, trying to disrupt merchant traffic towards the UK and force the UK out of the war. In World War I, Germany intermittently waged unrestricted submarine warfare against the UK: a first campaign in 1915 was abandoned after strong protests from the US but in 1917 the Germans, facing deadlock on the continent, saw no other option than to resume the campaign in February 1917. The renewed campaign failed to achieve its goal mainly because of the introduction of convoys. Instead the campaign ensured final defeat as the campaign was a contributing factor to the entry of the US in the First World War.
In World War II, Karl Dönitz, supreme commander of the Kriegsmarine's U-boat arm (Befehlshaber der Unterseeboote), was convinced the UK and its convoys could be defeated by new tactics, and tried to focus on convoy battles. Though U-boat tactics initially saw success in the Battle of the Atlantic, greatly disrupting Allied shipping, improved convoy and anti-submarine tactics such as high-frequency direction finding and the Hedgehog anti-submarine system began to take a toll on the German U-boat force. This ultimately came to a head in May 1943, known as Black May, in which U-boat losses began to outpace their effect on shipping.
The first submarine built in Germany, the three-man Brandtaucher, sank to the bottom of Kiel Harbor on 1 February 1851 during a test dive. Inventor and engineer Wilhelm Bauer had designed this vessel in 1850, and Schweffel and Howaldt constructed it in Kiel. Dredging operations in 1887 rediscovered Brandtaucher; she was later raised and put on historical display in Germany. The boats Nordenfelt I and Nordenfelt II, built to a Nordenfelt design, followed in 1890. In 1903, the Friedrich Krupp Germaniawerft dockyard in Kiel completed the first fully functional German-built submarine, Forelle, which Krupp sold to Russia during the Russo-Japanese War in April 1904.
At the beginning of the century, the German commander of the Navy Alfred von Tirpitz was building the High Seas Fleet with which he intended to challenge the supremacy of the Royal Navy. He focused on expensive battleships and there was no role for submarines in his fleet. Only when Krupp exported its submarines to Russia, Italy, Norway and Austria-Hungary did Tirpitz order one submarine. The SM U-1 was a completely redesigned Karp-class submarine and when the Imperial German Navy commissioned it on 14 December 1906, it was the last major navy to adopt submarines. The U-1 had a double hull and a single torpedo tube. It used an electric motor powered by batteries for submerged propulsion and a Körting kerosene engine for charging the batteries and propulsion on the surface. The 50%-larger SM U-2 (commissioned in 1908) had two torpedo tubes.
Between 1908 and 1910, fourteen big boats with four torpedo tubes and two reload torpedoes were ordered. These boats used a kerosene engine which was safer than gasoline and more powerful than steam, but the white exhaust of the kerosene betrayed the presence of the U-boats, robbing them of their primary asset, their stealth. Diesel engines did not have that disadvantage, but a powerful and reliable diesel engine was still under development. Finally, the U-19 class of 1912–13 had the first diesel engine installed in a German navy boat. Between 1910 and 1912, twenty-three diesel U-boats were ordered. At the start of World War I in 1914, Germany had 48 submarines of 13 classes in service or under construction. During that war, the Imperial German Navy used SM U-1 for training. Retired in 1919, she remains on display at the Deutsches Museum in Munich.
During 1914, the U-boats operated against the British fleet: on 5 September 1914, the light cruiser 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 armoured cruisers HMS Aboukir, HMS Cressy, and HMS Hogue. As a result, the British Grand Fleet had to withdraw to safer waters in Northern Ireland. Against merchant ships, U-boats observed the "prize rules" which meant they had to stop and inspect the ship, and take the crew off the ship before they could sink it. On 20 October 1914, SM U-17 sank the first merchant ship, SS Glitra, off Norway. Only ten merchants were sunk in that way before policy was changed on 18 February 1915. On the continent German hopes for a quick victory were dashed and a stalemate had settled on the front. The Germans hoped to break the deadlock by starting an unrestricted submarine campaign against shipping in the waters around the British Isles. This was also cited as a retaliation for British minefields and shipping blockades. Under the instructions given to U-boat captains, they could sink merchant ships, even neutral ones, without warning.
Only 29 U-boats were available for the campaign, and not more than seven were active around the British Isles at any time. The U-boats failed to enforce a blockade but three sinkings of liners, with loss of American lives, outraged the US so that the Kaiser had to stop the campaign in September 1915: on 7 May 1915 SM U-20 sank RMS Lusitania; on 19 August SM U-24 sank SS Arabic; and on 9 September SM U-20 sank RMS Hesperian. Most of the U-boats were sent to the Mediterranean. At the beginning of 1916, 54 U-boats were available, and the Kaiser allowed again operations around the British Isles, but with strict rules: no attacks on liners and outside the war zone around the British Isles attacks were only allowed on armed merchant ships. But on 24 March, 25 Americans were killed in the torpedoing of the ferry SS Sussex, which was mistaken for a troopship by SM UB-29. The US threatened to sever diplomatic ties, which persuaded the Germans to fully reapply prize rules. In September 1916, 120 U-boats were in service, and again some were sent to the Mediterranean. Whilst around British Isles prize rules were observed, in the Mediterranean a new unrestricted campaign was started. The renewed German campaign was effective, sinking 1.4 million tons of shipping between October 1916 and January 1917. Despite this, the deadlock situation on the continent frontlines demanded even greater results, and on 1 February 1917, Germany restarted the unrestricted submarine campaign around British Isles. Germany took the gamble that the U-boat campaign would force the UK out of the war before the US could effectively enter. On 3 February, the US severed diplomatic relations with Germany, and on 6 April, the US declared war on Germany.
Unrestricted submarine warfare in 1917 was very successful, sinking more than 500,000 tons a month. With the introduction of convoys in August 1917, shipping losses declined to 300,000 a month on average, which was not sufficient to force the UK out of the war. With deteriorating conditions on the continent, all U-boats were recalled on 31 October 1918. An armistice became effective on 11 November 1918. Under the terms of armistice, all U-boats were to immediately surrender. Those in home waters sailed to the British submarine base at Harwich, after which the vessels were studied, then scrapped or given to Allied navies.
Of the 373 German U-boats that had been built, 179 were operational or nearly operational at the end of the war. 178 were lost by enemy action. 512 officers and 4894 enlisted men were killed. Of the surviving German submarines, 14 U-boats were scuttled and 122 surrendered. They sank 10 pre-dreadnought battleships, 18 heavy and light cruisers, and several smaller naval vessels. They further destroyed 5,708 merchant and fishing vessels for a total of 11,108,865 tons and the loss of about 15,000 sailors.
The Pour le Mérite, the highest decoration for gallantry for officers, was awarded to 29 U-boat commanders. Twelve U-boat crewmen were decorated with the Goldenes Militär-Verdienst-Kreuz, the highest bravery award for noncommissioned officers and enlisted men. The most successful U-boat commanders of World War I were Lothar von Arnauld de la Perière (195 ships with 44,869 tons), followed by Walter Forstmann (149 ships with 391,607 tons), and Max Valentiner (144 ships with 299,482 tons).
The Treaty of Versailles ending World War I signed at the Paris Peace Conference in 1919 limited the surface navy of Germany's new Weimar Republic to only six battleships, six cruisers, twelve destroyers and twelve torpedo boats. The treaty also restricted the independent tonnage of ships and forbade the construction of submarines. In order to circumvent the restrictions of the treaty, a submarine design office called Ingenieurskantoor voor Scheepsbouw (IVS) was set up in the Netherlands The IVS was run by Krupp and made it possible to maintain a lead in submarine technology by designing and constructing submarines in Holland for other nations. The IVS made designs for small 250-ton U-boats, medium 500-ton U-boats and large 750-ton U-boats.
The IVS constructed three 500-ton medium submarines in Finland between 1927 and 1931, known as the Vetehinen-class. These ships were the prototypes for the subsequent German Type VII U-boat. In 1933 a small 250-ton submarine, the Vesikko was built. This submarine was nearly identical to the subsequent German Type II U-boat. A fifth very small 100-ton submarine, the Saukko was built in 1933 as well. In Spain a large 750-ton boat was built between 1929 and 1930. After the Spanish lost interest in the U-boat, they sold it to Turkey where it entered service as Gür. German sailors assisted in the trials for these submarines. These secret programs were exposed in the Lohmann Affair and as a result the Head of the Reichsmarine Hans Zenker had to resign. His successor Erich Raeder continued the policy of secretly breaching the Versailles treaty. On 15 November 1932, a plan was approved for an expansion of the German navy which included U-boats.
In 1935, Britain sought to control the increasingly apparent breaches of the Versailles Treaty and it concluded in 1935 the Anglo-German Naval Agreement. This ended officially the limitation of the Versailles Treaty and allowed Germany to build ships in a 100:35 tonnage ratio to the British fleet. For submarines the Germans obtained a parity in tonnage, but promised a 45 percent limit unless special circumstances arose. This allowed 24,000 tons for U-boat building. Only one week after the signature of the agreement, the first of six Type II U-boats, U-1 was commissioned in the German Navy, which changed name from Reichsmarine (Imperial Navy) to Kriegsmarine (War Navy). Within the year, the Germans commissioned a total of 36 U-boats for a total of 12,500 tons:
Karl Dönitz was appointed as head of the submarine section of the Kriegsmarine. He believed firmly that in spite of the Anglo-German Naval agreement and Hitler's policy of avoiding conflict with Britain, the next war would be with Britain. Based on these views, he requested that the remaining 11,500 tons be used for building twenty-three medium submarines, which were in his opinion the ideal type for the commerce war against British convoys. Raeder however did not share these beliefs and opinions and opted for a more balanced expansion of the submarine fleet:
Twenty-one of these twenty-three U-boats were commissioned before the start of World War II. In 1937, Britain announced it would expand its submarine fleet from 52,700 to 70,000 tons. Again, Raeder decided that the extra 7,785 tons would be divided between medium and large U-boats:
During 1938, Hitler changed his attitude towards Britain. Whilst he still hoped that Britain would not interfere in his foreign policy, it became clear to him that he needed a Navy that could act as a deterrent. Hitler wanted to invoke the escape clause of the naval agreement and to have 70,000 tons of submarines. Between May 1938 and January 1939, Raeder ordered 52 more U-boats to be completed by 1942:
In 1939, the ambitious Plan Z was launched. It called for the construction of a German Navy capable of challenging the Royal Navy. The plan included 249 U-boats for a total of 200,000 tons. But when World War II broke out only months after the plan was announced, only a handful of the planned U-boats ended up being built.
When World War II started, Germany had 56 U-boats commissioned, of which 46 were operational and only 22 had enough range for Atlantic operations, the other 24 were limited to operations on the North Sea.
Compared to their World War I equivalents, the German U-boat designs of World War II were greatly improved. By using a new steel alloy and by welding instead of riveting, they had stronger hulls and could dive deeper. The diving time was decreased to thirty seconds for a medium U-boat. The power of diesel engines was increased, so U-boats had a greater surface speed. Range was increased by installing fuel saddle tanks, which were on open to the sea on the bottom in order to balance pressure, with the diesel fuel floating freely on the seawater within the saddle tank. Also, a technique was developed for economical cruising where only one of the two diesel engines would be run and would drive the two propeller shafts through a coupling with the two electro engines.
Another vast improvement was the introduction of new torpedo types for the U-boats: the classic G7a torpedo propelled by compressed air had a much larger warhead than its WWI equivalent, but more important was the introduction of the electric G7e torpedo. This torpedo was slower and had less range, but it left no telltale bubble wake and was, hence, ideally suited for daylight attacks. During WWI, the Germans had briefly experimented with magnetic pistols and these were further developed now as the standard pistol for torpedoes. The classic contact pistol required a torpedo to detonate against the ship's hull, whilst a magnetic torpedo could detonate below a ship, resulting in a much more damaging explosion. Thus, it was hoped that one torpedo would suffice to break the back of a ship, and a U-boat could sink many more ships with its supply of torpedoes.
All U-boats were now also equipped with long- and short-wave transmitters, which enabled them to communicate with bases ashore and with fellow U-boats at sea. This allowed for better operational information and guidance.
From bow to stern, A typical U-boat design comprised these sections:
During World War II, U-boat warfare was the major component of the Battle of the Atlantic, which began in 1939 and ended with Germany's surrender in 1945. British Prime Minister Winston Churchill later wrote "The only thing that really frightened me during the war was the U-boat peril."
As convoying had been key in the defeat of German submarines during World War I, the British began organizing convoys at once in September 1939. The most common U-boat attack against convoys during the early years of the war was conducted on the surface and at night. During 1939 the Germans made a few attempts to attack convoys with their new 'wolfpack' tactic, but these were not successful. The invasion of Norway in April 1940 halted temporarily all U-boat operations against merchant shipping. During the invasion many technical problems with the German torpedoes were exposed and only in August 1940 could the campaign against convoys be revived. There were now fewer U-boats operational than at the beginning of the war, but thanks to the new bases in France and Norway U-boats could reach their operation grounds far more easily. During the following months the U-boats put their 'wolfpack' tactic against convoy in practice with spectacular results. This period, before the Allied forces developed truly effective antisubmarine warfare tactics, was referred to by German submariners as "die glückliche Zeit" or the First Happy Time.
In the beginning of 1941, British countermeasures began to take effect: in March 1941, the three leading U-boat aces were sunk during convoy battles. In May 1941, the British were able to break into German secret naval Enigma communications and could henceforth reroute convoys around U-boat concentrations. When American warships started to escort Atlantic convoys, the U-boats were restricted in their operations as Hitler wanted to avoid possible conflict with the US. The campaign against merchant shipping received further impediments when Hitler interfered on two occasions: first he insisted that a small force of U-boats be kept on station in the Arctic as a precaution against a possible Allied invasion in Norway, and next, he ordered a substantial force of U-boats to operate in the Mediterranean in order to support the Italians and Rommel's Afrika Korps.
When the US entered war, the focus of U-boat operations shifted to the Atlantic coast of the United States and Canada, where no convoys were organized and anti-submarine measures were inadequate. There followed a Second Happy Time when U-boats could extend their successful operation to the Gulf of Mexico and the Caribbean Sea. By mid 1942 an adequate defense was organized in these regions and then U-boats returned to their original and crucial hunting grounds on the North Atlantic convoy lanes. The renewed offensive against convoys reached its climax in March 1943, when two thirds of all ships sunk, were ships sailing in convoys. But the Allies put effective countermeasures into effect, and only two months later on 24 May, Dönitz had to stop the campaign due to heavy losses.
By the end of the war, almost 3,000 Allied ships (175 warships; 2,825 merchant ships) had been sunk by U-boats. In total, 1181 U-boats entered service before the German surrender, of which 863 had executed war patrols, and 785 were lost. 222 U-boats were scuttled by their crews and 174 surrendered to Allied forces. 121 U-boats were scuttled in 1945-46 during Operation Deadlight.
The U-boats' main weapon was the torpedo, though mines and deck guns (while surfaced) were also used. Early German World War II torpedoes were fitted with one of two types of pistol triggers – 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. Initially, the depth-keeping equipment and magnetic and contact exploders were notoriously unreliable. During the first eight months of the war, torpedoes often ran at an improper depth, detonated prematurely, or failed 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 to fluctuations in the Earth's magnetic field at high latitudes. These early magnetic detonators were eventually phased out. The depth-keeping problem remained problematic, not until January 1942 was the last fault discovered by accident: when ventilating the onboard torpedoes during maintenance, it was possible that the excess internal air-pressure in the U-boat offset the depth setting mechanism in the balance chamber of the torpedo.
In order to give U-boats better opportunities against well-defended convoys, several types of "pattern-running" torpedoes were developed. The FAT (Flächen-Absuch-Torpedo or Federapparat-Torpedo) and LUT (LageUnabhängiger Torpedo) was an electric torpedo which ran straight out to a preset distance, then traveled in either a circular or ladder-like pattern through the convoy lanes. This increased the probability of a hit. The torpedo had one setting to regulate the length of the prerun, after which one of four other possible settings kicked in and made the torpedo zigzag towards either left or right and either on short (1200 m; 2⁄3 nmi) or long (1900 m; 1 nautical mile) legs. When fired, the firing U-boat sent out a warning to the other U-boats in the vicinity so these could dive to avoid being hit by the random running torpedo. The FAT torpedo became available end of 1942 and was in regular use during the convoy battles of March 1943.
Germany also developed acoustic homing torpedoes. In February 1943, the first acoustic torpedo, the T4 "Falke", was tested on a small scale with moderate success, but this torpedo could only be used against large, slow ships. The acoustic torpedo ran straight to an arming distance of 1000 m and then turned toward the loudest noise detected. Its successor, the T5 "Zaunkönig", was designed to combat small and fast warships, and entered service in September 1943.
In 1940 the Germans made successful tests with the V-80 experimental submarine featuring a new type of propulsion: on the surface it used the classic Diesel engines but submerged it used a revolutionary hydrogen peroxide air-independent propellant system designed by Hellmuth Walter. With this Walter-turbine, a U-boat could achieve underwater speeds of more than 20 knots, much more than the 4-knot cruising and 6-knot maximum speed of electrical engines powered by batteries. Four more experimental Type XVIIA U-boats with Walter turbines were built and tested, but the Germans could not put this design in use for a big frontline U-boat. Unlike a classic U-boat that could recharge its batteries with the diesel engines, once a Walter U-boat had consumed its hydrogen peroxide propellant it could not submerge anymore. The Germans did not possess the resources and plants to produce sufficient hydrogen peroxide to operate a fleet of Walter submarines. Despite these limitations, 24 frontline Type XVIIB coastal submarines were ordered, but only three were built and none were operational before the end of the war.
The Walter U-boats had very large hulls in order to store the fuel for submerged propulsion. Once it became clear these Walter U-boats would not be operational in time, the Walter U-boat hull design was reused with a different approach: the space for the hydrogen peroxide tanks was used to store much larger batteries. With the much increased battery power U-boats were also able to reach much higher speeds and endurance when submerged. Based on the design of an Atlantic Walter U-boat, the Type XXI "Elektroboot" was designed to boost submerged performance. Smaller Type XXIII coastal Elektroboote were also taken into production. These Elektroboote were mass-produced, with prefabricated segments constructed at different sites and then assembled at the bigger shipyards.
After the German invasion of the Netherlands in 1940, the Germans captured some Dutch submarines equipped with a Schnorchel (snorkel) but saw no need for them until 1943. The Schnorchel was a retractable pipe that supplied air to the diesel engines while submerged at periscope depth, allowing the boats to cruise submerged on diesel engines and recharge their batteries. It was far from a perfect solution: problems occurred 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. Speed was limited to 8 knots (15 km/h), lest the device snap from stress. Whilst running submerged with the Schnorchel, the Gruppenhorchgerät was useless because of interference with the noisy diesel engines. But the Schnorchel allowed the old Type VII and IX U-boats to operate in waters which were previously denied to them.
The London and Paris Conferences in 1954 paved the way for West Germany to join NATO, and from 1955 the West German Bundesmarine was allowed to commission submarines up to 350 tons for coastal operations. Two classes were designed: the 350-ton Type 201 and the 100-ton Type 202. Pending the completion of the first of these U-boats, the Bundesmarine needed submarines to test the new equipment and to train crews. No submarines could be purchased from foreign navies; so in 1957, two Type XXIIIs and a Type XXI U-boats sunk in 1945 were raised and repaired. In 1959, twelve Type 201 and three Type 202 U-boats were ordered. As both types were designed to be deployed in the Baltic Sea, these U-boats were built in non-magnetic steel to protect against magnetic naval mines and magnetic anomaly detectors. By using non-ejectable, non-reloadable torpedo tubes which needed much less space because of smaller fittings and the absence of compensation trim tanks, it was possible to mount eight of these in the small Type 201. The even smaller Type 202 was equipped with two torpedo tubes.
The first three Type 201 U-boats were commissioned in 1962. To continue the U-boat tradition, the new boats received the classic "U" designation starting with the U-1. In 1962, a redefinition of the tonnage calculation which included the weight of the solid ballast meant that the Type 201 displaced now 395 tons. Consequently, the tonnage limits as agreed in the London and Paris Conferences was increased to 450 tons for current submarines and future U-boats were limited to 1,000 tons. During construction of the first U-boats, it became apparent that an extra sonar needed to be installed. Since the Type 201 was constructed in sections, it was easy to enlarge the hull with an extra 1.8-meter section to accommodate the extra equipment. This extra weight brought the displacement to 420 tons, still well within the conference limits. This enlarged version was classified as Type 205. Five U-boats of this type were completed before the end of 1963.
In 1962, Norway placed an order for fifteen coastal submarines. In order to train crews, U-3 was loaned to the Norwegian Navy, between 10 July 1962 and 20 June 1964, she was named HNoMS Kobben. The fifteen U-boats built between 1963 and 1967 had a high-tension steel hull for increased diving depth and were classified as Type 207. The Danish Navy bought the licences to build two coastal submarines based on the Type 205 plans in 1965. Due to complications with the installation of Danish equipment in these design, finishing of the construction was delayed until 1970.
By 1963, it became obvious that the new non-magnetic steel had corrosion problems. Small cracks started to form in the pressure hull. Whilst U-3 continued training and testing in the Norwegian Navy, U-1 and U-2 were laid up. The five U-boats U-4 to U-8 received zinc paint coating to protect the hull, but nevertheless these U-boats had to undergo regular testing of their maximum diving depth. Eventually, these five U-boats were assigned to the U-boat Training Group. Two new hulls in classic magnetic steel were built, and as much as possible equipment of the old Type 201 U-1 and U-2 was recovered for these new type 205 U-boats, which received the same identification U-1 and U-2. Meanwhile, the German Navy found little use for the two ordered Type 202 U-boats had been completed by 1965; these U-boats did not receive an official U-boat number but were named Hans Techel and Friedrich Schürer. They were only in service with the Test Centre of U-boats until end of 1966. The last four U-boats U-9 to U-12, from the original order of twelve U-boats were constructed with new non-magnetic steel which delayed their delivery to the Navy until 1967-1969.
In 1968, the German Navy ordered twelve more coastal submarines, named U-13 to U-24. The Type 205 design was again enlarged to accommodate extra battery capacity, needed to feed the ever-increasing array of electronic equipment. This resulted in the 450-tons Type 206. A further six of these U-boats named U-25 to U-30, were ordered in 1970, to replace the six faulty U-boats U-3 to U-8. The German Navy wanted to order six larger Type 208 submarine-hunter U-boats, and although permission was obtained from the Western European Union for construction up to 1,000 tons, this order was never placed because there were financial burdens with the fiasco of the nonmagnetic U-boats and since a diesel-electric submarine was too slow as a submarine hunter for nuclear propelled submarines.
Having secured the permission to build larger submarines, the Type 209 diesel-electric submarine was designed as a much larger Type 205, with the same characteristics and armament, but with much larger battery capacity, the possibility for torpedo reloads and extra sensors. It was proposed as a very customizable export-sales submarine, available in five variants with a displacement between 1,000–1,500 tons. The first customer was the Hellenic Navy, which received four Type 209's in 1971-72. As of 2002, fifty-one boats had been built for thirteen navies, with another twelve still ordered. In 1974, three 540 tons U-boats were built for the Israeli Navy. Based both on the type 206 and as a smaller Type 209, these three U-boats were classified as the Type 540. For political reasons these U-boats were not built in Germany but by Vickers Limited in England. In 1982, the Norwegian Navy ordered six 1,000 tons U-boats, to replace half of the Kobben-class submarines, these were classified as the Type 210. After receiving two Type 209 U-boats in 1974, the Argentine Navy ordered six larger 2,000 tons TR-1700 U-boats in 1977. Two of these were built in Germany and delivered after the Falklands War in 1984-85, the remaining four were to be built in Argentina, but these were never completed. In the early 1990s, Israel ordered three 1,565 tons submarines which were enlarged versions of the Type 209 but resembled more the later Type 212. The first three submarines were delivered in 1999-2000 as the Dolphin-class or Type 800.
In 1998, Germany started to construct the first of six Type 212 U-boats. Before the first one was launched, two were ordered by Italy, and Greece ordered four enlarged Type 212 U-boats, which were classified as Type 214. Between 2005 and 2007, the four Type 212 U-31, U-32, U-33 and U-34 were commissioned in the German Navy and two in the Italian Navy. In 2015-2016, a further two Type 212 U-35 and U-36 were delivered to the German Navy, and in 2016-2017, the Italian Navy commissioned also two more Type 212. The Type 212 features an air-independent propulsion system using hydrogen fuel cells. While the Type 212 is also being purchased by Norway, the Type 214 has been designed as the follow-on export model. Nine Type 214s have been sold to South Korea and were delivered between 2007 and 2020. Two were delivered to Portugal as Type U 209PN sub-class U-boats in 2010-2011. Six Type 214s were ordered by Turkey in 2011 as the Reis-class and will be built at the Gölcük Naval Shipyard, the first was commissioned in 2024.
The Type 216 was a design for a 4,000 tons U-boat with a much larger endurance. It was proposed to but was not bought by Australia. As of 2025, no Type 216s have been ordered. Between 2022 and 2024, Germany built four 2,000 tons Type 218 U-boats for Republic of Singapore Navy, which are based on the Type 212 and Type 214, with the same propulsion method and 'X' rudder, but armed with eight torpedo tubes.