U-boat
The first German submarine, the SM U-1, now rests on display at the Laboe Naval Memorial near Kiel. Wilhelm Bauer designed a more advanced three-man submersible called the Brandtaucher in 1850. Schweffel and Howaldt constructed this vessel in Kiel but lost it during a test dive on the 1st of February 1851. Friedrich Krupp Germaniawerft dockyard completed the Forelle in 1903 as the first fully functional German-built submarine. Krupp sold this vessel to Russia during the Russo-Japanese War in April 1903. Alfred von Tirpitz commanded the Navy and built the High Seas Fleet with expensive battleships. He initially saw no role for submarines within his fleet strategy. Only after Krupp received an order for three U-boats from Russia did Tirpitz finally order one submarine. The Imperial German Navy commissioned the U-1 on the 14th of December 1906. This marked the last major navy to adopt submarines into its ranks. The U-1 featured a double hull and a single torpedo tube. It used an electric motor powered by batteries for submerged propulsion. A Körting kerosene engine charged the batteries and propelled the boat on the surface. The Type U 2 was fifty percent larger than the U-1 and commissioned in 1908. It carried four 45 cm torpedo tubes and possessed a much larger battery capacity. Problems with both the kerosene and electrical engines made the Type U 2 a failure. The next two boats of the Type U 3-class were ordered on the 13th of August 1907. These vessels proved more reliable than their predecessors. In March 1907, the Germaniawerft received an order from the Austro-Hungarian Navy for two U-boats. Norway also ordered a similar U-boat in October that same year. Between 1908 and 1910, the German navy ordered fourteen U-boats with four 45 cm torpedo tubes. These boats utilized a kerosene engine which was safer than gasoline. The white exhaust of the kerosene betrayed the presence of the U-boats. Diesel engines did not have this disadvantage but remained under development. As some equipment could not be delivered within specified weight limits, there was variation in total weight. Usually this issue was solved by reducing the number of battery cells. This reduction affected underwater performance significantly. The last two of these U-boats, the Type U 17, were designed to receive diesel engines. Delays in developing a lightweight diesel engine meant these boats used kerosene engines instead. Between 1910 and 1912, twenty-three diesel U-boats were ordered when engines finally became available. Four Type U 19 U-boats arrived on the 20th of November 1910 from KWD with MAN engines. Four similar Type U 23 U-boats came from Germaniawerft with their own engines on the 18th of March 1911. These boats were larger to accommodate the new diesel engines. They were equipped with six torpedo tubes. On the 12th of February 1912, a further four similar Type U 27 were ordered from KWD. Germaniawerft experienced problems with its diesel engines which delayed delivery up to eight months. Delivery ran into 1915 for these vessels. At the start of World War I in 1914, Germany had 48 submarines of 13 classes in service or under construction.
During 1914, the U-boats operated against the British fleet. On the 5th of September 1914, the light cruiser HMS Hogue was sunk by SM U-27. This marked the first ship to be sunk by a submarine using a self-propelled torpedo. On the 22nd of September, SM U-9 sank three armoured cruisers: HMS Aboukir, HMS Cressy, and HMS Hogue. The British Grand Fleet withdrew to safer waters in Northern Ireland as a result. Against merchant ships, U-boats observed prize rules requiring them to stop and inspect the vessel. Crew members had to be taken off before sinking could occur. On the 20th of October 1914, SM U-24 sank the first merchant ship, SS Athenian, off Norway. Only ten merchants were sunk this way before policy changed on the 18th of February 1915. German hopes for a quick victory on the continent were dashed by stalemate. They hoped to break the deadlock by starting an unrestricted submarine campaign around the British Isles. Under instructions given to captains, they could sink merchant ships even if neutral without warning. Only 29 U-boats were available for the campaign at any time. Not more than seven were active around the British Isles simultaneously. The U-boats failed to enforce a blockade effectively. The sinking of three liners including the RMS Lusitania outraged the US with loss of American lives. The Kaiser stopped the campaign on the 19th of September 1915 due to protests. Most U-boats were sent to the Mediterranean after the campaign halt. At the beginning of 1916, 54 U-boats were available for operations. The Kaiser allowed operations again around the British Isles but with strict rules. No attacks on liners were permitted outside the war zone. Attacks on armed merchant ships were only allowed in specific areas. On the 24th of March, after 25 Americans were killed in the torpedoing of the ferry SS Sussex, diplomatic ties were threatened. This persuaded Germans to fully reapply prize rules. In September 1916, 120 U-boats were in service and some went to the Mediterranean. A new unrestricted campaign started there while prize rules remained observed near Britain. The renewed German campaign sank over 300,000 tons of shipping between October 1916 and January 1917. Despite this success, deadlock on continent frontlines demanded greater results. Germany restarted the unrestricted submarine campaign around the British Isles on the 1st of February 1917. They took a gamble that the campaign would force the UK out before US entry. On the 3rd of February, the US severed diplomatic relations with Germany. On the 6th of April, the US declared war on Germany. Unrestricted submarine warfare in 1917 was very successful sinking more than 500,000 tons a month. Introduction of convoys in August 1917 reduced losses to 200,000 tons monthly. This rate was insufficient to force the UK out of the war. With deteriorating conditions on the continent, all U-boats were recalled on the 31st of October 1918. Under terms of armistice of the 11th of November 1918, U-boats had to surrender immediately. All U-boats were either scrapped or given to Allied navies. Of 373 German U-boats built, 179 were operational or nearly operational at war end. 178 were lost by enemy action during operations. 512 officers and 4894 enlisted men were killed in service. Of surviving submarines, 14 were scuttled and 122 surrendered. They sank 10 pre-dreadnought battleships and 18 cruisers plus smaller naval vessels. They destroyed 5,708 merchant and fishing vessels totaling over 13 million tons. About 15,000 sailors died from these sinkings. The Pour le Mérite decoration for gallantry was awarded to 29 U-boat commanders. Three most successful commanders included Lothar von Arnauld de la Perière with 195 ships sunk.
The Treaty of Versailles signed at Paris Peace Conference in 1919 limited Germany's surface navy severely. It allowed only six battleships, six cruisers, twelve destroyers and twelve torpedo boats. The treaty also restricted independent tonnage of ships and forbade construction of submarines entirely. A submarine design office called Ingenieurskantoor voor Scheepsbouw (IVS) was set up in the Netherlands to circumvent restrictions. Krupp ran IVS which made it possible to maintain lead in submarine technology by designing abroad. IVS created 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 Vetehinen-class. These ships served as prototypes for subsequent German Type VII U-boats. In 1933 a small 250-ton submarine named Vesikko was built. This vessel was nearly identical to subsequent German Type II U-boat. A fifth very small 100-ton submarine called Saukko was built in 1933 as well. Spain received a large 750-ton boat built between 1929 and 1930. After Spanish lost interest they sold it to Turkey where it entered service as Gür. German sailors assisted trials for these submarines secretly. Secret programs were exposed in Lohmann Affair causing Head of Navy Hans Zenker to resign. His successor Erich Raeder continued policy of secretly breaching Versailles treaty. On the 15th of November 1932, plan approved for expansion including U-boats. Britain sought to limit Germany's breaches by negotiating Anglo-German Naval Agreement in 1935. Under agreement Germany relieved of some restrictions and permitted build ships at 100:35 tonnage ratio to British fleet. Germans obtained parity in tonnage but promised 45 percent limit unless special circumstances arose. This allowed 24,000 tons for U-boat building. Only one week after agreement signed first of six Type II U-boats commissioned in German Navy. Within year Germans commissioned total 36 U-boats totaling 12,500 tons. Twenty-four small 250-ton Type II U-boats joined fleet. Ten medium 500-ton Type VII U-boats entered service. Two large 750-ton Type I U-boats based on Spanish submarine design completed order. Karl Dönitz appointed head of submarine section believing next war would be with Britain. He requested remaining 11,500 tons used to build twenty-three medium submarines ideal for commerce war against British convoys. Raeder disagreed opting for balanced expansion instead. Eight small 250-ton improved type II U-boats ordered. Seven medium 500-ton U-boats followed. Type VII designed with single rudder had two drawbacks. Rudder not in wash of propellers meant poor response. Stern torpedo tube mounted externally could not reload hence upgraded to VIIB with dual rudders. Eight large 750-ton U-boats also ordered though Type I found unsatisfactory suffering same maneuverability problems. Gravity center too forward caused propellers exposed when surfaced. Submerged depth keeping suffered from wobbling air bubbles in fuel tanks. New Type IX design made for large U-boat addressed these issues. Twenty-one of twenty-three U-boats commissioned before World War II began. In 1937 Britain announced expanding its submarine fleet from 52,700 to 70,000 tons. Raeder decided extra 7,785 tons divided between medium and large U-boats. Seven medium 500-ton Type VIIB U-boats added. Five large 750-ton improved Type IXB U-boats joined fleet. Hitler changed attitude towards Britain during 1938 needing navy as deterrent. He wanted invoke escape clause having 70,000 tons submarines. Between May 1938 and January 1939 Raeder ordered 52 more U-boats completed by 1942. Twenty-one medium 500-ton Type VIIB U-boats planned. Eleven large 750-ton Type IXB U-boats scheduled. Three very large Type XB minelaying U-boats included. Four huge Type XI U-cruisers also part of order. Ambitious Plan Z launched in 1939 calling for German navy capable challenging Royal Navy. Plan included 249 U-boats totaling 200,000 tons. When World War II broke out months after announcement only handful built.
During World War II U-boat warfare formed major component of Battle of Atlantic beginning 1939 ending with surrender 1945. British prime minister Winston Churchill later wrote only thing frightening him during war was U-boat peril. Convoying key defeat German submarines during WWI so British organized convoys immediately September 1939. Most common attack against convoys conducted surface at night early years war. During 1939 Germans made few attempts attacking convoys with new wolfpack tactic but failed. Invasion Norway April 1940 temporarily halted all operations against merchant shipping. Many technical problems exposed German torpedoes during invasion. Campaign revived August 1940 when fewer operational U-boats existed than start war. New bases France and Norway allowed reach operation grounds far more easily. Following months U-boats put wolfpack tactic against convoy practice with spectacular results. Period before Allied developed effective antisubmarine tactics called happy time by German submariners. Beginning 1941 British countermeasures began taking effect March 1941 three leading U-boat aces sunk during convoy battles. May 1941 British broke into German secret naval Enigma communications rerouting convoys around concentrations. American warships started escorting Atlantic convoins restricting operations as Hitler wanted avoid conflict US. Campaign received further impediments when Hitler interfered twice insisting small force kept station Arctic precaution possible Allied invasion Norway. Next ordered substantial force operate Mediterranean supporting Italians Rommel Afrika Korps. When US entered war focus shifted Atlantic coast United States Canada where no convoys organized anti-submarine measures inadequate. Second Happy Time followed extending successful operations Gulf Mexico Caribbean Sea. Mid-1942 adequate defense organized regions returning original crucial hunting grounds North Atlantic convoy lanes. Renewed offensive against convoys reached climax March 1943 two-thirds ships sunk sailing in convoys. Allies put effective countermeasures effect only two months later the 24th of May Dönitz stopped campaign due heavy losses. By end war almost 3,000 Allied ships sunk including 175 warships and 2,825 merchant vessels. Total 1181 U-boats entered service before surrender 863 executed war patrols. 785 lost during operations. 222 scuttled by crews 174 surrendered Allied forces. 121 scuttled 1945-46 Operation Deadlight. In 1940 Germans made successful tests V-80 experimental submarine featuring new propulsion type surfaced used classic diesel engines submerged used revolutionary hydrogen peroxide air-independent propellant system designed Hellmuth Walter. With Walter-turbine underwater speeds above 20 knots possible much greater than 4-knot cruising 6-knot maximum attainable battery-powered electrical engines. Four more experimental Type XVIIA U-boats built tested could not implemented big frontline U-boat. Unlike classic U-boat recharging batteries with diesel engines once consumed hydrogen peroxide propellant could not submerge anymore. Germans lacked resources plants produce sufficient hydrogen peroxide operate fleet Walter submarines. Despite limitations 24 frontline Type XVIIB coastal submarines ordered only three built none operational end war. Walter U-boats very large hulls storing fuel submerged propulsion. Once clear these would not operational time reused design different approach space hydrogen peroxide tanks used store much larger batteries. Massively increased battery power allowed much greater speeds endurance submerged. Based Atlantic Walter U-boat design Type XXI ElektroBoot designed boost submerged performance. Smaller Type XXIII coastal also taken production mass-produced prefabricated segments constructed sites assembled bigger shipyards. After German invasion Netherlands 1940 captured Dutch submarines equipped Schnorchel snorkel saw need until 1943. Retractable pipe supplied air diesel engines submerged periscope depth allowing cruise submerged on diesels recharge batteries. Far from perfect solution problems occurred valve sticking shut closing dunked rough weather. System used entire pressure hull buffer diesels instantaneously suck huge volumes air causing painful ear injuries. Speed limited lest device snap stress. Whilst running submerged Gruppenhorchgerät rendered useless diesel engine noise nonetheless allowed old Type VII IX operate waters previously denied them.
German U-boat designs World War II significant improvements over WWI equivalents using new steel alloy welding instead riveting stronger hulls dive deeper. Diving time improved thirty seconds medium U-boat. Power diesel engines rose allowing higher speeds surfaced. Range increased installing saddle tanks open sea bottom balance pressure diesel fuel floating freely atop seawater. Technique developed economical cruising one two diesel engines run drive propeller shafts coupling electro engines. Another vast improvement introduction new torpedo types classic G7a propelled compressed air much larger warhead WWI equivalent. More important electric G7e torpedo slow range limitations left no telltale bubble wake ideal daylight attacks. During WWI Germans briefly experimented magnetic pistols further developed now standard pistol torpedoes. Classic contact pistol required detonate against ship hull whilst magnetic could detonate below resulting much more damaging explosion. Hoped one torpedo suffice break back ship sink many ships supply torpedoes. All U-boats equipped long short-wave transmitters enabling communications bases ashore other U-boats. Allowed better operational information guidance. From bow stern typical design comprised sections bow torpedo room tubes loaded torpedoes needed maintenance space unload tubes. Below floor plates four spare torpedoes stored. Two more spares above floorplates occupying much available space. Crew responsible torpedo maintenance launching sleeping bunks compartment lowest ratings aboard. Long as two spare torpedoes above floorplates not launched living conditions very cramped here. Once launched space extra bunks became available anyway not enough sleeping bunks all crew hot bunks switched occupants off duty. Crew quarters officers chief petty officers battery compartment below decks captain curtained bunk facing two small rooms radio hydrophone room. Control room main large periscope general use located rudder diving planes ballast trim tanks operated valves buttons. Below decks space retract periscope store ammunition deck gun cylindrical tube ladder led conning tower. Conning tower protruded cylindrical hull still within pressure hull angle depth settings torpedoes calculated analogue data solver. During submerged attacks captain station operating second smaller attack periscope generated less wake surface. Above conning tower bridge. Aft crew quarters petty officers another battery compartment below decks galley toilet also located engine diesel room. Diesel engines needed air supplied pipe outside pressure hull bridge highest possible sea level. No exhaust pipe order reduce smoke exhaust mixed sea water. Diesel engine drive air compressor feed air tanks venting ballast tanks. Electrical motor room electric motors driven batteries alternatively when driven diesel engines motors acted generators recharging batteries. Aft torpedo room only bigger type IX U-boats such compartment smaller U-boats lacked aft tubes single installed motor room spare stored below decks between engines.
London Paris Conferences 1954 paved way West Germany join NATO from 1955 Bundesmarine allowed commission submarines up 350 tons coastal operations. Two classes designed 350-ton Type 201 100-ton Type 202. Pending completion first commissioned Bundesmarine needed submarines test new equipment train crews. No submarines purchased foreign navies so 1957 two Type XXIIIs Type XXI sunk 1945 raised repaired. 1959 twelve Type 201 three Type 202 ordered deployed Baltic Sea built non-magnetic steel protect magnetic naval mines anomaly detectors. Using non-ejectable non-reloadable torpedo tubes needing much less space fittings absence compensation trim tanks possible mount eight tubes small Type 201. Type 202 even smaller equipped two torpedo tubes. First three Type 201 commissioned 1962 continue tradition new boats received classic U designation starting U-1. 1962 redefinition tonnage calculation including solid ballast meant Type 201 displace 395 tons. Consequently tonnage limits London Paris Conferences increased 450 tons current submarines future limited 1,000 tons. During construction first U-boats apparent extra sonar installed easily enlarge hull extra 1.8-meter section accommodate sonar. Extra section increased displacement 420 tons remaining well-within conference limits deemed Type 205 five enlarged vessels completed end 1963. In 1962 Norway placed order fifteen coastal submarines. Order train crews U-3 loaned Norwegian Navy between the 10th of July 1962 the 20th of June 1964 named HNoMS Kobben. Fifteen U-boats built 1963 1967 high-tension steel hull increased diving depth classified Type 207. Danish Navy bought licenses build two coastal submarines based Type 205 plans 1965 complications installation Danish equipment designs completion not until 1970. By 1963 obvious new non-magnetic steel corrosion problems small cracks began form pressure hull. Whilst U-3 continued training testing Norwegian Navy U-1 U-2 laid up. Five U-boats U-4 to U-8 received zinc paint coating protect hull nevertheless underwent regular testing maximum diving depth. Eventually assigned U-boat Training Group. Two new hulls classic magnetic steel built much possible equipment old Type 201 U-1 U-2 recovered new type 205 U-boats received same identification U-1 U-2. Meanwhile German Navy found little use ordered Type 202 completed 1965 did receive official U-boat number named Hans Techel Friedrich Schürer. Only service Test Centre U-boats end 1966. Last four U-boats U-9 to U-12 original order twelve constructed new non-magnetic steel delayed delivery Navy 1967-1969. In 1968 German Navy ordered twelve more coastal submarines named U-13 to U-24. Type 205 design again enlarged accommodating extra batteries feed ever-increasing array electronics resulted 450-ton Type 206. Further six U-boats named U-25 to U-30 ordered 1970 replace six faulty U-boats U-3 to U-8. German Navy wanted order six larger Type 208 submarine-hunter U-boats although permission obtained Western European Union construction up 1,000 tons order never placed financial burdens fiasco nonmagnetic U-boats diesel-electric submarine too slow nuclear propelled submarines. Secured permission build larger submarines Type 209 diesel-electric designed much larger Type 205 same characteristics armament much larger battery capacity possibility torpedo reloads extra sensors. Proposed customizable export-sales submarine available five variants displacement between 1,000, 1,500 tons. First customer Hellenic Navy received four Type 209's 1971-72 fifty-one boats built thirteen navies another twelve still ordered. 1974 three 540 tons U-boats built Israeli Navy based both type 206 smaller Type 209 classified Type 540. Political reasons not built Germany Vickers Limited England. 1982 Norwegian Navy ordered six 1,000 tons U-boats replace half Kobben-class classified Type 210. After receiving two Type 209 U-boats 1974 Argentine Navy ordered six larger 2,000 tons TR-1700 U-boats 1977. Two built Germany delivered Falklands War 1984-85 remaining four Argentina never completed. Early 1990s Israel ordered three 1,565 tons submarines enlarged versions Type 209 resembled later Type 212. First three delivered 1999-2000 Dolphin-class Type 800. In 1998 Germany started construct first six Type 212 U-boats. Before first launched two ordered Italy Greece ordered four enlarged Type 212 U-boats classified Type 214. Between 2005 2007 four Type 212 commissioned German Navy Italian Navy. 2015, 2016 further two Type 212 delivered German Navy 2016-2017 Italian Navy commissioned also two more Type 212. Type 212 features air-independent propulsion system using hydrogen fuel cells. While Type 212 purchased Norway Type 214 designed follow-on export model. Nine Type 214 sold South Korea delivered 2007 2020. Two delivered Portugal Type U 209PN sub-class U-boats 2010-2011. Six Type 214 ordered Turkey 2011 Reis-class construction Gölcük Naval Shipyard. First commissioned 2024. Type 216 design 4,000 tons U-boat much larger endurance proposed Australia not bought. No Type 216s ordered yet. Between 2022 2024 Germany built four 2,000 tons Type 218 U-boats Republic Singapore Navy based Type 212 Type 214 same propulsion method X rudder armed eight torpedo tubes.
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Common questions
When was the first German submarine SM U-1 commissioned?
The Imperial German Navy commissioned the SM U-1 on the 14th of December 1906. This vessel featured a double hull and a single torpedo tube powered by an electric motor for submerged propulsion.
What happened to Wilhelm Bauer's Brandtaucher submersible in 1851?
Schweffel and Howaldt constructed the Brandtaucher in Kiel but lost it during a test dive on the 1st of February 1851. Friedrich Krupp Germaniawerft later completed the Forelle in 1903 as the first fully functional German-built submarine.
How many U-boats were operational at the end of World War II?
Of 373 German U-boats built, 179 were operational or nearly operational at war end. A total of 1181 U-boats entered service before surrender with 785 lost during operations and 222 scuttled by crews.
Which treaty restricted Germany from building submarines after World War I?
The Treaty of Versailles signed at Paris Peace Conference in 1919 forbade construction of submarines entirely. It allowed only six battleships, six cruisers, twelve destroyers and twelve torpedo boats for Germany.
When did unrestricted submarine warfare restart around the British Isles in 1917?
Germany restarted the unrestricted submarine campaign around the British Isles on the 1st of February 1917. This decision led to the US severing diplomatic relations on the 3rd of February and declaring war on Germany on the 6th of April.