U-boats arenaval submarines operated by Germany, especially duringWorld War I andWorld War II. The term is ananglicized form of the German wordU-Boot[ˈuːboːt]ⓘ, a shortening ofUnterseeboot (lit. 'under-sea boat').Austro-Hungarian Navy submarines were also known as U-boats.
U-boats are especially known for their use inunrestricted submarine warfare in both world wars, attempting todisrupt merchant traffic towards the UK and force the UK out of the war. InWorld War I, Germany intermittently waged unrestricted submarine warfare against theUK: a first campaign in 1915 was abandoned after strong protests from the US but in February 1917 the Germans, facing deadlock on the continent, saw no other option than to resume the campaign. The renewed campaign failed to achieve its goal mainly because of the introduction ofconvoys. Instead the campaign ensured final defeat as the campaign was a contributing factor to the entry of theUS in the First World War.[1]
InWorld War II,Karl Dönitz, supreme commander of theKriegsmarine's U-boat arm (Befehlshaber der Unterseeboote), was convinced the UK and its convoys could be defeated by newtactics, and tried to focus onconvoy battles.[2] Though U-boat tactics initially saw success in theBattle of the Atlantic, greatly disrupting Allied shipping, improved convoy and anti-submarine tactics such ashigh-frequency direction finding and theHedgehog anti-submarine system began to take a toll on the German U-boat force. This ultimately came to a head in May 1943, known asBlack May, in which U-boat losses began to outpace their effect on shipping.
A more advancedsubmersible, the three-manBrandtaucher, was designed byWilhelm Bauer in 1850 and constructed bySchweffel and Howaldt inKiel. It was lost on 1 February 1851 during a test dive.[a][5][6]
Some 50 years later in 1903, theFriedrich Krupp Germaniawerft dockyard in Kiel completed the first fully functional German-built submarine,Forelle,[7] whichKrupp sold to Russia during theRusso-Japanese War in April 1903.[8]
At this time, the German commander of the NavyAlfred von Tirpitz was building theHigh Seas Fleet with which he intended to challenge the supremacy of the UKRoyal Navy. He focused on expensivebattleships and there was no role for submarines in his fleet.
Only when Krupp received an order for threeKarp-class U-boats from Russia, did Tirpitz order one submarine.[9][10] TheSM U-1 was a completely redesignedKarp-class and when theImperial German Navy commissioned it on 14 December 1906,[11] it was the last major navy to adopt submarines.[9]
TheU-1 had a double hull and a single 45 cm (18 in) torpedo tube. It used anelectric motor powered by batteries for submerged propulsion and aKörtingkerosene engine for charging the batteries and propulsion on the surface.[12] The 50%-largerSM U-2 was commissioned in 1908,[13] had four 45 cm torpedo tubes and a much larger battery capacity. But the boat was a failure due to problems with both the kerosene and electrical engines. The next two U-boats of theType U 3-class, ordered on 13 August 1907, were more reliable.[12]
In March 1907, the Germaniawerft received an order from theAustro-Hungarian Navy for two 237 t (233 long tons) U-boats and in OctoberNorway ordered a similar U-boat.
These foreign U-boats were based on an improvedU-1 design.[14] Between 1908 and 1910, the German navy ordered fourteen 500 t (490-long-ton) boats with four 45 cm torpedo tubes and two reload torpedoes. These boats used a kerosene engine which was safer thangasoline and more powerful thansteam, 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.[15] As some equipment could not be delivered within the specified weight limits, there was some variation in the total weight of each U-boat. Usually this was solved by reducing the number of battery cells, which affected underwater performance.[16] The last two of these U-boats, theType U 17, was designed to receive diesel engines but due to delays in developing a lightweight diesel engine, these U-boats were equipped with kerosene engines.[17]
Between 1910 and 1912, twenty-three diesel U-boats were ordered[15] when diesel engines finally became available: four 650 t (640-long-ton)Type U 19 U-boats on 20 November 1910 fromKWD withMAN engines and four similarType U 23 U-boats from Germaniawerft with Germaniawerft engines on 18 March 1911. These boats were larger to accommodate the diesel engines, and were equipped with 50 cm (20 in) torpedo tubes. On 12 February 1912 a further four similarType U 27 were ordered from KWD, and although Germaniawerft experienced problems with its diesel engines, it received an order for elevenType U 31 U-boats. Due to these problems, delivery of these U-boats was delayed up to eight months and ran into 1915.[18]
At the start of World War I in 1914, Germany had 48 submarines of 13 classes in service or under construction.[15]
| U-boats built by Germany for the German Navy | |||||||
|---|---|---|---|---|---|---|---|
| Type | Nbr built | In service | Displacement surface | Speed surface | Speed submerged | Engines surface[20] | Engines submerged[20] |
| U 1 | 1 | 1906 | 238 t (234 long tons) | 10.8 knots (20.0 km/h; 12.4 mph) | 8.9 knots (16.5 km/h; 10.2 mph) | 2 x 200 hp (150 kW) Korting | 2 x 200 hp (150 kW) |
| U 2 | 1 | 1908 | 341 t (336 long tons) | 13.2 knots (24.4 km/h; 15.2 mph) | 9.0 knots (16.7 km/h; 10.4 mph) | 2 x 300 hp (220 kW) Daimler | 2 x 315 hp (235 kW) |
| Type U 3 | 2 | 1909 | 421 t (414 long tons) | 11.8 knots (21.9 km/h; 13.6 mph) | 9.4 knots (17.4 km/h; 10.8 mph) | 2 x 300 hp (220 kW) Korting | 2 x 515 hp (384 kW) |
| Type U 5 | 4 | 1910-11 | 505 t (497 long tons) | 13.4 knots (24.8 km/h; 15.4 mph) | 10.2 knots (18.9 km/h; 11.7 mph) | 4 x 225 hp (168 kW) Korting | 2 x 520 hp (390 kW) |
| Type U 9 | 4 | 1910-11 | 493 t (485 long tons) | 14.2 knots (26.3 km/h; 16.3 mph) | 8.1 knots (15.0 km/h; 9.3 mph) | 2 x 225 hp (168 kW) Korting + 2 x 300 hp (220 kW) Korting | 2 x 580 hp (430 kW) |
| Type U 13 | 3 | 1912 | 516 t (508 long tons) | 14.8 knots (27.4 km/h; 17.0 mph) | 10.7 knots (19.8 km/h; 12.3 mph) | 2 x 250 hp (190 kW) Korting + 2 x 350 hp (260 kW) Korting | 2 x 600 hp (450 kW) |
| U 16 | 1 | 1911 | 489 t (481 long tons) | 15.6 knots (28.9 km/h; 18.0 mph) | 10.7 knots (19.8 km/h; 12.3 mph) | 2 x 242 hp (180 kW) Korting + 2 x 358 hp (267 kW) Korting | 2 x 600 hp (450 kW) |
| Type U 17 | 2 | 1912 | 564 t (555 long tons) | 14.9 knots (27.6 km/h; 17.1 mph) | 9.5 knots (17.6 km/h; 10.9 mph) | 4 x 350 hp (260 kW) Korting | 2 x 560 hp (420 kW) |
| Type U 19 | 4 | 1913 | 650 t (640 long tons) | 15.4 knots (28.5 km/h; 17.7 mph) | 9.5 knots (17.6 km/h; 10.9 mph) | 2 x 850 hp (630 kW) MAN | 2 x 600 hp (450 kW) |
| Type U 23 | 4 | 1913-14 | 669 t (658 long tons) | 16.7 knots (30.9 km/h; 19.2 mph) | 10.3 knots (19.1 km/h; 11.9 mph) | 2 x 900 hp (670 kW) GW | 2 x 600 hp (450 kW) |
| Type U 27 | 4 | 1914 | 675 t (664 long tons) | 16.7 knots (30.9 km/h; 19.2 mph) | 9.8 knots (18.1 km/h; 11.3 mph) | 2 x 1,000 hp (750 kW) MAN | 2 x 600 hp (450 kW) |
| Type U 31 | 11 | 1914-15 | 685 t (674 long tons) | 16.7 knots (30.9 km/h; 19.2 mph) | 9.8 knots (18.1 km/h; 11.3 mph) | 2 x 925 hp (690 kW) GW | 2 x 600 hp (450 kW) |
| Type U 43 | 8 | 1915-16 | 725 t (714 long tons) | 15.2 knots (28.2 km/h; 17.5 mph) | 9.7 knots (18.0 km/h; 11.2 mph) | 2 x 1,000 hp (750 kW) MAN | 2 x 600 hp (450 kW) |
| U-boats built by Germany for foreign Navies | ||||||||
|---|---|---|---|---|---|---|---|---|
| Type | Nbr built | In service | Displacement surface | Speed surface | Speed submerged | Bow tubes | Stern Tubes | Deck gun |
| Forelle | 1 | 1904 | 16 t (16 long tons) | 5.5 knots (10.2 km/h; 6.3 mph) | 5.5 knots (10.2 km/h; 6.3 mph) | 2 x 45 cm | -- | -- |
| Karp-class | 3 | 1907 | 210 t (210 long tons) | 10 knots (19 km/h; 12 mph) | 8.5 knots (15.7 km/h; 9.8 mph) | 1 x 45 cm | -- | -- |
| U-3-class | 2 | 1909 | 421 t (414 long tons) | 12 knots (22 km/h; 14 mph) | 8.5 knots (15.7 km/h; 9.8 mph) | 2 x 45 cm | -- | -- |
| Kobben | 1 | 1910-11 | 505 t (497 long tons) | 11.9 knots (22.0 km/h; 13.7 mph) | 8.9 knots (16.5 km/h; 10.2 mph) | 2 x 45 cm | 1 x 45 cm | -- |
| Atropo[21] | 1 | 1912 | 231 t (227 long tons) | 14.7 knots (27.2 km/h; 16.9 mph) | 8 knots (15 km/h; 9.2 mph) | 2 x 45 cm | -- | -- |
During 1914, the U-boats operated against the British fleet: on 5 September 1914, thelight cruiserHMS Pathfinder was sunk bySM U-21, the first ship to be sunk by a submarine using a self-propelled torpedo. On22 September,U-9 sank thearmoured cruisersHMS Aboukir,HMS Cressy, andHMS Hogue. As a result, the BritishGrand 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.[22]
| Surface warships | 55 |
| Mines | 48 |
| Submarines | 18 |
| Q-ships | 11 |
| Merchant ships | 7 |
| Aircraft | 1 |
| Accidents | 19 |
| Unknown | 19 |
| Total | 178 |
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 shippingblockades. Under the instructions given to U-boat captains, they could sink merchant ships, even neutral ones, without warning.[22] 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 the sinking of three liners including theRMS Lusitania,[b] with loss of American lives, outraged the US so that theKaiser had to stop the campaign on 19 September 1915.[24] After the stop of the campaign, most of the U-boats were sent to the Mediterranean.[23]
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, after 25 Americans were killed in the torpedoing of the ferrySS Sussex the US threatened to severdiplomatic ties, which persuaded the Germans to fully reapply prize rules.[23]
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 1,400,000 GRT 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, theUS declared war on Germany.[23] Unrestricted submarine warfare in 1917 was very successful, sinking more than 500,000 GRT a month. With the introduction of convoys in August 1917, shipping losses declined to 300,000 GRT 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.[25] Under the terms ofarmistice of 11 November 1918, U-boats were to immediately surrender. All U-boats were either scrapped or given to Allied navies.[26]
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.[27] 512 officers and 4894 enlisted men were killed. Of the surviving German submarines, 14 U-boats werescuttled and 122 surrendered. They sank 10pre-dreadnought battleships, 18 cruisers, and several smaller naval vessels. They further destroyed 5,708 merchant and fishing vessels for a total of 11,108,865 GRT and the loss of about 15,000 sailors.[28] ThePour le Mérite, the highest decoration for gallantry for officers, was awarded to 29 U-boat commanders.[29] The three most successful U-boat commanders wereLothar von Arnauld de la Perière (195 ships with 453,869 GRT), followed byWalter Forstmann (149 ships with 391,607 GRT ), andMax Valentiner (144 ships with 299,482 GRT ).[30]
When the German Army captured three ports on the Belgian coast in the opening stages of the war, the German navy ordered coastal submarines to be operated from these ports against the English coast. As the war was then expected to end in a matter of months, only very small 130 t (130 long tons) U-boats could be designed with an expected building time of four months. On 15 October 1914 fifteenType UB I U-boats were ordered, and based on that design, on 23 November a further fifteenType UC I coastal minelaying U-boats were ordered.[31] Given the weakness of theAustro-Hungarian Navy and the need to help theirTurkish Allies, the German Navy sent some of these U-boats to theDardanelles andBlack Sea.[32]
In the spring of 1915 it became clear that the war would continue well into 1916 and more coastal U-boats were ordered. The Type UB I and UC I had fullfilled the expectations but were underpowered. Thirty U-boats of the successingType UB II were ordered, which were with around 270 t (270 long tons) double in size. As with the cessation of unrestricted U-boat warfare in September 1915, mine warfare became more prominent, a record number of 64Type UC II minelaying U-boats were ordered, which allowed for the first time for the mass-production of a U-boat. The Type UC II proved to be an ideal combination of mine and torpedo armament: on the same patrol it could lay minefields and attack shipping on the way to its target.[33]
On the resumption of the U-boat campaign in 1916, it was realized that not enough large U-boats could be built in time, and as a compromise it was decided to build an enlargened coastal U-boat capable of patrolling in theWestern Approaches. The hull of the Type UC II was taken as a basis, the forward mineshaft room was replaced with a torpedo room, more powerfull diesel engines provided better surface speed and larger fuel tanks extended the range. On 2 May 1916 the first twenty-fourType UB III were ordered and as the war prolonged, more than 200 were ordered but only 96 were commissioned before the armistice.[34][35]
| standard U-boat types | Type U 51,Type U 57,Type U 63,Type U 66,Type U 81,Type U 87,Type U 93 |
| U-cruisers and merchant U-boat types | Type U 139,Type U 142,Type U 151,Type UD 1 |
| UB coastal U-boat types | Type UB I,Type UB II,Type UB III,Type UF,Type UG |
| UC coastal minelaying U-boat types | Type UC I,Type UC II,Type UC III |
| UE ocean minelaying U-bot types | Type UE I,Type UE II |
TheTreaty of Versailles ending World War I signed at theParis Peace Conference in 1919 limited the surface navy of Germany's newWeimar Republic to only sixbattleships, sixcruisers, twelvedestroyers and twelvetorpedo boats. The treaty also restricted the independent tonnage of ships and forbade the construction of submarines.[36] In order to circumvent the restrictions of the treaty, a submarine design office calledIngenieurskantoor voor Scheepsbouw (IVS) was set up in theNetherlands[37] 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.[38] The IVS made designs for small 250-ton U-boats, medium 500-ton U-boats and large 750-ton U-boats.[39]
The IVS constructed three 500-ton medium submarines in Finland between 1927 and 1931, known as theVetehinen-class. These ships were the prototypes for the subsequent GermanType VII U-boat. In 1933 a small 250-ton submarine, theVesikko was built. This submarine was nearly identical to the subsequent GermanType II U-boat. A fifth very small 100-ton submarine, theSaukko 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 asGür. German sailors assisted in the trials for these submarines. These secret programs were exposed in theLohmann Affair and as a result the Head of theReichsmarine,Hans Zenker, had to resign. His successorErich 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.[40]
In 1935, Britain sought to limit Germany's increasingly apparent breaches of the Versailles treaty, negotiating theAnglo-German Naval Agreement. Under the agreement, Germany was relieved of some Treaty of Versailles restrictions and permitted to build ships in a 100:35 tonnage ratio to the British fleet. For submarines the Germans obtained parity in tonnage, but promised a 45 percent limit unless special circumstances arose.[41] This allowed 24,000 tons for U-boat building. Only one week after the agreement was signed, the first of six Type II U-boats,U-1 was commissioned in the German Navy, which changed name fromReichsmarine (Imperial Navy) toKriegsmarine (War Navy).[42] Within the year, the Germans commissioned a total of 36 U-boats for a total of 12,500 tons:[43]
Karl Dönitz was appointed as head of the submarine section of theKriegsmarine. 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. He requested the remaining 11,500 tons be used to build twenty-three medium submarines, which he considered ideal for a commerce war against British convoys. Raeder disagreed, and opted for a more balanced expansion of the submarine fleet:[43]
Twenty-one of these twenty-three U-boats were commissioned before 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:[45]
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During 1938, Hitler changed his attitude towards Britain. Whilst he still hoped that Britain would not interfere in his foreign policy, 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:[46]
In 1939, the ambitiousPlan 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.[46]
When World War II started, Germany had 56 U-boats commissioned, of which 46 were operational and 22 having sufficient range for Atlantic operations; the other 24 were limited toNorth Sea operations.[47]
German U-boat designs of World War II were significant improvements over their World War I equivalents. By using new steel alloy andwelding instead ofriveting, they had stronger hulls and could dive deeper. The diving time was improved to thirty seconds for a medium U-boat. The power of diesel engines rose, allowing higher speeds while surfaced. Range was increased by installingsaddle tanks, which were on open to the sea on the bottom in order to balance pressure, with the diesel fuel floating freely atop the seawater. 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.[48]
Another vast improvement was the introduction of new torpedo types for the U-boats: the classicG7a torpedo propelled by compressed air had a much larger warhead than its WWI equivalent, but more important was the introduction of the electricG7e torpedo.[49] Though slow with range limitations, it left no telltale bubble wake, making it ideal for daylight attacks.[48] During WWI, the Germans had briefly experimented withmagnetic 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.[50][51]
All U-boats were now also equipped with long- and short-wave transmitters, enabling communications with bases ashore and with other U-boats. This allowed for better operational information and guidance.[50]
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 ministerWinston Churchill later wrote "The only thing that really frightened me during the war was the U-boat peril."[56]
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. Theinvasion of Norway in April 1940 temporarily halted 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 asthe happy time (die glückliche Zeit).[57]
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 tobreak into German secret navalEnigma communications and could henceforth reroute convoys around U-boat concentrations.[58] When American warships started to escort Atlantic convoys, the U-boats were restricted in their operations as Hitler wanted to avoid conflict with the US.[59] 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 theArctic as a precaution against a possible Allied invasion in Norway,[60][61] and next, he ordered a substantial force of U-boats to operate in the Mediterranean in order to support the Italians andRommel'sAfrika Korps.[62]
When the US entered the 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 aSecond Happy Time when U-boats could extend their successful operation to theGulf of Mexico and theCaribbean Sea.[63] By mid-1942 an adequate defense was organized in these regions; U-boats returned to their original and crucial hunting grounds on the North Atlantic convoy lanes.[64] The renewed offensive against convoys reached its climax in March 1943, when two-thirds of all ships sunk had been sailing in convoys.[65] 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.[66]
By the end of the war, almost 3,000 Allied ships (175 warships; 2,825 merchant ships) had been sunk by U-boats.[67] In total, 1181 U-boats entered service before the German surrender, of which 863 executed war patrols, and 785 were lost.[68][69] 222 U-boats were scuttled by their crews and 174 surrendered to Allied forces.[70] 121 U-boats were scuttled in 1945-46 duringOperation Deadlight.[71]
In 1940 the Germans made successful tests with theV-80 experimental submarine featuring a new type of propulsion: surfaced, it used the classic diesel engines, but submerged it used a revolutionaryhydrogen peroxideair-independentpropellant system designed byHellmuth Walter. With this Walter-turbine, underwater speeds of above 20 knots were possible, much greater than the 4-knot cruising and 6-knot maximum speeds attainable through battery-powered electrical engines. Four more experimentalType XVIIA U-boats with Walter turbines were built and tested but could not be implemented into a big frontline U-boat.[72][73] 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.[74]
The Walter U-boats had very large hulls to store 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 massively increased battery power, U-boats enjoyed much greater speeds and endurance when submerged.[75] Based on the design of an Atlantic Walter U-boat, theType XXI "Elektroboot" was designed to boost submerged performance. SmallerType XXIII coastalElektroboote were also taken into production. TheseElektroboote were mass-produced, with prefabricated segments constructed at different sites and then assembled at the bigger shipyards.[76][77]
After theGerman invasion of the Netherlands in 1940, the Germans captured some Dutch submarines equipped with aSchnorchel (snorkel) but saw no need for them until 1943. TheSchnorchel was a retractable pipe that supplied air to the diesel engines while submerged atperiscope depth, allowing the boats to cruise submerged on diesel engines and recharge their batteries.[78] 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, often causing painful ear injuries. Speed was limited to 8 knots (15 km/h), lest the device snap from stress. Whilst running submerged with theSchnorchel, theGruppenhorchgerät was rendered useless by diesel engine noise. TheSchnorchel nonetheless allowed old Type VII and IX U-boats to operate in waters that previously denied to them.[79]
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TheLondon and Paris Conferences in 1954 paved the way forWest Germany to joinNATO, and from 1955 the West GermanBundesmarine was allowed to commission submarines up to 350 tons for coastal operations. Two classes were designed: the 350-tonType 201 and the 100-tonType 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 theBaltic Sea, they were built innon-magnetic steel to protect against magneticnaval mines andmagnetic 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 tubes in the small Type 201. The Type 202 was even smaller and equipped with two torpedo tubes.[80]
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 withU-1. In 1962, a redefinition of the tonnage calculation to include solid ballast meant the Type 201 would displace 395 tons. Consequently, tonnage limits established in the London and Paris Conferences were increased to 450 tons for current submarines and future U-boats 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 sonar. This extra section increased displacement to 420 tons, remaining well-within conference limits. Deemed theType 205, five of these enlarged vessels would be completed by the end of 1963.[81]
In 1962, Norway placed an order for fifteen coastal submarines. In order to train crews,U-3 was loaned to theNorwegian Navy, between 10 July 1962 and 20 June 1964, she was named HNoMSKobben.[82] The fifteen U-boats built between 1963 and 1967 had a high-tension steel hull for increased diving depth and were classified asType 207.[83] TheDanish 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 designs, construction was not completed until 1970.[84]
By 1963, it became obvious that the new non-magnetic steel had corrosion problems when small cracks began to form in the pressure hull. Whilst U-3 continued training and testing in the Norwegian Navy,U-1 andU-2 were laid up. The five U-boatsU-4 toU-8 received zinc paint coating to protect the hull, but nevertheless had to undergo regular testing of their maximum diving depth.[85] 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 201U-1 andU-2 was recovered for these new type 205 U-boats, which received the same identificationU-1 andU-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 namedHans Techel andFriedrich Schürer. They were only in service with the Test Centre of U-boats until end of 1966. The last four U-boatsU-9 toU-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.[86]
In 1968, the German Navy ordered twelve more coastal submarines, namedU-13 toU-24. The Type 205 design was again enlarged, accommodating extra batteries to feed the ever-increasing array of electronics. This resulted in the 450-tonType 206. A further six of these U-boats namedU-25 toU-30 were ordered in 1970 to replace the six faulty U-boatsU-3 toU-8. The German Navy wanted to order six larger Type 208 submarine-hunter U-boats, and although permission was obtained from theWestern 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.[87]
Having secured the permission to build larger submarines, theType 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 theHellenic Navy, which received four Type 209's in 1971-72. As of 2002[update], fifty-one boats had been built for thirteen navies, with another twelve still ordered.[88][89] In 1974, three 540 tons U-boats were built for theIsraeli Navy. Based both on the type 206 and as a smaller Type 209, these three U-boats were classified as theType 540. For political reasons these U-boats were not built in Germany but byVickers Limited in England.[90][91] In 1982, the Norwegian Navy ordered six 1,000 tons U-boats, to replace half of the Kobben-class submarines, these were classified as theType 210.[92] After receiving two Type 209 U-boats in 1974,[93] theArgentine Navy ordered six larger 2,000 tonsTR-1700 U-boats in 1977. Two of these were built in Germany and delivered after theFalklands War in 1984-85, the remaining four were to be built in Argentina, but these were never completed.[94] 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 theDolphin-class or Type 800.[95]
In 1998, Germany started to construct the first of sixType 212 U-boats. Before the first was launched, two were ordered by Italy, and Greece ordered four enlarged Type 212 U-boats, which were classified asType 214.[96] Between 2005 and 2007, the four Type 212U-31,U-32,U-33 andU-34 were commissioned in the German Navy[97] and two in the Italian Navy.[98] In 2015–2016, a further two Type 212U-35 andU-36 were delivered to the German Navy,[97] and in 2016-2017, the Italian Navy commissioned also two more Type 212.[98] The Type 212 features an air-independent propulsion system usinghydrogenfuel cells.[96][97] While the Type 212 is also being purchased by Norway,[99] 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 asType U 209PN sub-class U-boats in 2010-2011.[100] Six Type 214s were ordered by Turkey in 2011 as theReis-class for construction at theGölcük Naval Shipyard.[101] The first was commissioned in 2024.[102]
TheType 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[update], no Type 216s have been ordered.[103] Between 2022 and 2024, Germany built four 2,000 tonsType 218 U-boats for theRepublic 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.[104]
