Type XXI submarine

<h2 id="description">Description</h2>
The main features of the Type XXI were the hydrodynamically streamlined hull and <a href="/facts/Conning_tower/tX2VzTHz">conning tower</a> and the large number of battery cells, roughly triple that of the <a href="/facts/Type_VII_submarine/arrhGLbm">Type VII submarine</a>. This gave these boats great underwater range and dramatically reduced the time spent on or near the surface. They could travel submerged at about 5 <a href="/facts/Knot_(unit)/Sho0TF2y">knots</a> (9.3 km/h; 5.8 mph) for about 75 hours<a class="footnote-ref" id="fnref:3" href="#fn:3">3</a> before recharging batteries, which took less than five hours using the <a href="/facts/Submarine_snorkel/je7hKxVp">snorkel</a> due to the new super-charged diesel engines. Being designed primarily for submerged use, the Type XXI's maximum surface speed (15.6 knots) was lower than that of the <a href="/facts/Type_IX_submarine/nxmEseJ5">Type IX</a> (18.2 knots) but its submerged speed was more than twice that of the Type IX (17.2 knots versus 7.7 knots) because they were equipped with much more powerful electric drive motors and had less drag.<a class="footnote-ref" id="fnref:4" href="#fn:4">4</a><a class="footnote-ref" id="fnref:5" href="#fn:5">5</a>
The Type XXI was also much quieter than the VIIC, making it more difficult to detect when submerged, and the design eliminated protruding components that had created drag in earlier models. The new, streamlined hull design allowed submerged speed of 17.2 <a href="/facts/Knot_(unit)/Sho0TF2y">kn</a> (19.8 <a href="/facts/Miles_per_hour/6a9Rbe8M">mph</a>; 31.9 <a href="/facts/Kilometres_per_hour/maSjyKdr">km/h</a>), versus 7.6 <a href="/facts/Knot_(unit)/Sho0TF2y">kn</a> (8.7 <a href="/facts/Miles_per_hour/6a9Rbe8M">mph</a>; 14.1 <a href="/facts/Kilometres_per_hour/maSjyKdr">km/h</a>) for the Type VIIC.<a class="footnote-ref" id="fnref:6" href="#fn:6">6</a> The ability to outrun many surface ships while submerged, combined with improved dive times (also a product of the new hull form), made the Type XXI much more difficult to pursue and destroy.<a class="footnote-ref" id="fnref:7" href="#fn:7">7</a> It also provided a sprint ability when positioning itself for an attack. Older boats had to surface to sprint into position. This often revealed a boat's location, especially after aircraft became available for convoy escort. The Type XXI was also equipped with a pair of electric "creep motors" for silent running.<a class="footnote-ref" id="fnref:8" href="#fn:8">8</a>
The Type XXI was equipped with six bow torpedo tubes (instead of the more common four in German submarines) and carried 23 torpedoes.<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a> 
It featured an electric <a href="/facts/Torpedo/RLLPpktk">torpedo</a>-reloading system that allowed all six bow torpedo tubes to be reloaded faster than a Type VIIC could reload one tube.<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a> The Type XXI could fire 18 torpedoes in less than 20 minutes. The class also featured a very sensitive passive <a href="/facts/Sonar/245ooRW7">sonar</a> for the time, housed in the "chin" of the hull.
The Type XXIs also had better facilities than previous U-boat classes, with much roomier crew berths, and a <a href="/facts/Freezer/TGb5ozLY">freezer</a> to prevent food spoilage.<a class="footnote-ref" id="fnref:11" href="#fn:11">11</a> The increased capacity allowed for a crew of 57.<a class="footnote-ref" id="fnref:12" href="#fn:12">12</a><a class="footnote-ref" id="fnref:13" href="#fn:13">13</a>
A post-war assessment of the Type XXI by the <a href="/facts/United_States_Navy/xYK0fUou">United States Navy</a> concluded that while the design had some admirable features, it was seriously flawed.<a class="footnote-ref" id="fnref:14" href="#fn:14">14</a> The submarines' engines were underpowered, which limited the surface speed and increased the time required to charge the batteries. The hydraulic system was unduly complex, and its main elements were located outside the pressure hull. This made the system highly vulnerable to corrosion and damage. The <a href="/facts/Submarine_snorkel/je7hKxVp">snorkel</a> was also badly designed, and difficult to use in practice.<a class="footnote-ref" id="fnref:15" href="#fn:15">15</a>

<h2 id="construction">Construction</h2>

This was the first U-boat to be constructed of modular components to allow for the manufacture of the various components in different factories and subsequent assembly at the shipyard.<a class="footnote-ref" id="fnref:16" href="#fn:16">16</a>
Between 1943 and 1945, 118 boats were assembled by <a href="/facts/Blohm_%2526_Voss/4vA6j4Lg">Blohm & Voss</a> of <a href="/facts/Hamburg/kmAAsYtT">Hamburg</a>, <a href="/facts/AG_Weser/lMYLxXUr">AG Weser</a> of <a href="/facts/Bremen_(city)/y56P3Pyk">Bremen</a> and <a href="/facts/Schichau-Werke/3rvtF93p">Schichau-Werke</a> of <a href="/facts/Danzig/a6VNPK28">Danzig</a>. Each hull was constructed from nine prefabricated sections with final assembly at the shipyards. This new method allowed for a hypothetical construction time of less than six months per vessel, but in practice all the assembled U-boats were plagued with severe quality problems that required extensive post-production work and time to rectify.<a class="footnote-ref" id="fnref:17" href="#fn:17">17</a> One of the reasons for these shortcomings was that sections were made by companies having little experience with shipbuilding, after a decision by <a href="/facts/Albert_Speer/VMYu0WaU">Albert Speer</a>. As a result, of 118 Type XXIs constructed, only four were fit for combat before the Second World War ended in Europe. Of these, only two conducted combat patrols and neither sank any Allied ships.<a class="footnote-ref" id="fnref:18" href="#fn:18">18</a> Post-war assessments by the US Navy and British <a href="/facts/Royal_Navy/Xdy8YCH7">Royal Navy</a> also found that the completed submarines had poor structural integrity due to the manufacturing problems. This rendered the submarines highly vulnerable to <a href="/facts/Depth_charge/bLMx1yF9">depth charges</a>, and gave them a lesser maximum diving depth than earlier U-boat designs.<a class="footnote-ref" id="fnref:19" href="#fn:19">19</a>
It was planned that final assembly of Type XXI boats would eventually be carried out in the <a href="/facts/Valentin_submarine_pens/1uTxn1A1">Valentin submarine pens</a>, a massive, bomb–hardened concrete bunker built at the small port of <a href="/facts/Farge/qa6Iw1Pl">Farge</a>, near Bremen.<a class="footnote-ref" id="fnref:20" href="#fn:20">20</a> The pens were constructed between 1943 and 1945, using about 10,000 concentration camp prisoners and prisoners of war as forced labour.<a class="footnote-ref" id="fnref:21" href="#fn:21">21</a> The facility was 90% completed when, during March 1945, it was heavily damaged by Allied bombing with <a href="/facts/Grand_Slam_bomb/c5QUNEbD">Grand Slam</a> "earthquake" bombs and abandoned. A few weeks later the area was captured by the British Army.<a class="footnote-ref" id="fnref:22" href="#fn:22">22</a>
Due to the combination of design and construction problems, historian <a href="/facts/Clay_Blair/G1X1vC3d">Clay Blair</a> judged that "the XXI could not have made a big difference in the <a href="/facts/Battle_of_the_Atlantic/PV9uF2Jw">Battle of the Atlantic</a>.<a class="footnote-ref" id="fnref:23" href="#fn:23">23</a>

<h2 id="sensors">Sensors</h2>
<h3>Radar detector</h3>
The FuMB Ant 3 Bali radar detector and antenna was located on top of the snorkel head.

<h3>Radar transmitter</h3>
The Type XXI boats were fitted with the <a href="/facts/Hohentwiel_(Radar)/HLo2jV0K">FuMO 65 Hohentwiel U1</a> with the Type F432 D2 radar transmitter.

<h2 id="wartime-and-post-war-service">Wartime and post-war service</h2>
<h3>Germany</h3>

<a href="/facts/German_submarine_U-2511/b08CNH6x">U-2511</a> and <a href="/facts/German_submarine_U-3008/MbRBDYVK">U-3008</a> were the only Type XXIs used for war patrols, and neither sank any ships. The commander of U-2511 claimed the U-boat had a British cruiser in his sights on 4 May when news of the German cease-fire was received. He further claimed he made a practice attack before leaving the scene undetected.<a class="footnote-ref" id="fnref:24" href="#fn:24">24</a>
During 1957, <a href="/facts/German_submarine_Wilhelm_Bauer/RW2bQlyb">U-2540</a>, which had been <a href="/facts/Scuttling/kDeqTHM7">scuttled</a> at the end of the war, was raised and refitted as <a href="/facts/Research_vessel/7T7NsS7I">research vessel</a> Wilhelm Bauer of the <a href="/facts/Bundesmarine/gPB0Nrba">Bundesmarine</a>. It was operated by both military and civilian crews for research purposes until 1982. During 1984, it was made available for display to the public by the <a href="/facts/Deutsches_Schiffahrtsmuseum/lEASx8mv">Deutsches Schiffahrtsmuseum</a> (German Maritime Museum) in <a href="/facts/Bremerhaven/oWEkkt3D">Bremerhaven</a>, Germany.

<h3>France</h3>
<a href="/facts/French_submarine_Roland_Morillot_(S613)/ABB75RgK">U-2518</a> became <a href="/facts/French_submarine_Roland_Morillot_(S613)/ABB75RgK">French submarine Roland Morillot</a>. It was used for active service during the <a href="/facts/Suez_Crisis/mlfbUT51">Suez Crisis</a> in 1956, and remained in commission until 1967. It was scrapped in 1969.

<h3>Soviet Union</h3>
Four Type XXI boats were assigned to the USSR by the <a href="/facts/Potsdam_Agreement/7yWhoYWV">Potsdam Agreement</a>; these were <a href="/facts/German_submarine_U-2529/AvVsuM9m">U-2529</a>, <a href="/facts/German_submarine_U-3035/b2n1GvAs">U-3035</a>, <a href="/facts/German_submarine_U-3041/K9CnSQFm">U-3041</a>, and <a href="/facts/German_submarine_U-3515/T8L8uwN2">U-3515</a>, which were commissioned into the <a href="/facts/Soviet_Navy/t2buEMEK">Soviet Navy</a> as B-27, B-28, B-29, and B-30 (later B-100) respectively. However, Western intelligence believed the Soviets had acquired several more Type XXI boats; a review by the <a href="/facts/United_States_Joint_Intelligence_Community_Council/vACLcvR6">U.S. Joint Intelligence Committee</a> for the <a href="/facts/Joint_Chiefs_of_Staff/Uvqu4MJ1">Joint Chiefs of Staff</a> during January 1948 estimated the Soviet Navy then had 15 Type XXIs operational, could complete construction of 6 more within 2 months, and could build another 39 within a year and a half from prefabricated sections, since several factories producing Type XXI components and the assembly yard at Danzig had been captured by the Soviets at the end of World War II. U-3538 — U-3557 (respectively TS-5 – TS-19 and TS-32 – TS-38) remained incomplete at Danzig and were scrapped or sunk during 1947. The four boats assigned by Potsdam were used in trials and tests until 1955, then scuttled or used for weapon testing between 1958 and 1973. The Type XXI design formed the basis for several Soviet design projects, Projects 611, 613, 614, 633, and 644. These became the submarine classes known by their NATO codes as <a href="/facts/Zulu-class_submarine/ueGFbAvs">Zulu</a>, <a href="/facts/Whiskey-class_submarine/5QV1Stlz">Whiskey</a> and <a href="/facts/Romeo-class_submarine/9dAc3mYz">Romeo</a> submarine classes.<a class="footnote-ref" id="fnref:25" href="#fn:25">25</a>

<h3>United Kingdom</h3>

<a href="/facts/German_submarine_U-3017/Pbxppky5">U-3017</a> was commissioned into the <a href="/facts/Royal_Navy/Xdy8YCH7">Royal Navy</a> as <a href="/facts/German_submarine_U-3017/Pbxppky5">HMS N41</a>. It was used for tests until being scrapped during November 1949.

<h3>United States</h3>
The United States Navy acquired <a href="/facts/German_submarine_U-2513/WKHq1kpG">U-2513</a> and <a href="/facts/German_submarine_U-3008/MbRBDYVK">U-3008</a>, operating them both in the Atlantic Ocean. During November 1946 President <a href="/facts/Harry_S._Truman/2E2LmMoB">Harry S. Truman</a> visited U-2513; the submarine dived to 440 feet (130 m) with the President aboard.<a class="footnote-ref" id="fnref:26" href="#fn:26">26</a> U-2513 was sunk as a target on 7 October 1951; U-3008 was sold for scrap on 15 September 1955.

<h2 id="survivor">Survivor</h2>

The only boat to survive intact is <a href="/facts/German_submarine_Wilhelm_Bauer/RW2bQlyb">Wilhelm Bauer</a> (ex-U-2540), at the <a href="/facts/German_Maritime_Museum/lEASx8mv">German Maritime Museum</a> in Bremerhaven.<a class="footnote-ref" id="fnref:27" href="#fn:27">27</a> Records indicate that this sub was scuttled by her crew in 1945, salvaged in 1957 and refurbished for use by the West German Bundesmarine until retirement in 1982. She was then modified to appear in wartime configuration for exhibition purposes.<a class="footnote-ref" id="fnref:28" href="#fn:28">28</a>

<h2 id="notable-wrecks">Notable wrecks</h2>
The wrecks of several Type XXI boats are known to exist. During 1985, it was discovered that the partially scrapped remains of <a href="/facts/German_submarine_U-2505/E0QCPGjN">U-2505</a>, <a href="/facts/German_submarine_U-3004/110rHnQC">U-3004</a>, and <a href="/facts/German_submarine_U-3506/Iedxjy1j">U-3506</a> were still in the partially demolished "Elbe II" U-boat bunker in <a href="/facts/Hamburg/kmAAsYtT">Hamburg</a>. The bunker has since been filled in with gravel, although even that did not initially deter many souvenir hunters who measured the position of open hatches and dug down to them to allow the removal of artifacts.<a class="footnote-ref" id="fnref:29" href="#fn:29">29</a> The wrecks now lie beneath a car park (parking lot), making them inaccessible.<a class="footnote-ref" id="fnref:30" href="#fn:30">30</a>
<a href="/facts/German_submarine_U-2513/WKHq1kpG">U-2513</a> lies in 213 feet (65 m) of water 70 nautical miles (130 km) west of <a href="/facts/Key_West/JvtQRdTn">Key West</a>, Florida. The boat has been visited by divers, but the depth makes this very difficult and the site is considered suitable for only advanced divers. Four other boats lie off the coast of Northern Ireland, where they were sunk during 1946 as part of <a href="/facts/Operation_Deadlight/WaKVCLue">Operation Deadlight</a>. Both <a href="/facts/German_submarine_U-2511/b08CNH6x">U-2511</a> and <a href="/facts/German_submarine_U-2506/C0EoNuaE">U-2506</a> were found by nautical archaeologist <a href="/facts/Innes_McCartney/QUQrNGHL">Innes McCartney</a> during his Operation Deadlight expeditions between 2001 and 2003.<a class="footnote-ref" id="fnref:31" href="#fn:31">31</a><a class="footnote-ref" id="fnref:32" href="#fn:32">32</a> Both were found to be in good condition. In April 2018 the wreck of <a href="/facts/German_submarine_U-3523/bduWoGul">U-3523</a> was found north of Skagen in Denmark.<a class="footnote-ref" id="fnref:33" href="#fn:33">33</a>

<h2 id="influences">Influences</h2>
The Type XXI design directly influenced advanced post-war submarines, the <a href="/facts/Greater_Underwater_Propulsion_Power_Program/tQupwLW4">Greater Underwater Propulsion Power Program</a> (GUPPY) improvements to the <a href="/facts/United_States/P0sCdLe5">United States</a> <a href="/facts/Gato-class_submarine/1YXIP7p5">Gato</a>, <a href="/facts/Balao-class_submarine/YfIyG8jH">Balao</a>, and <a href="/facts/Tench-class_submarine/dARahGWJ">Tench</a>-class submarines,<a class="footnote-ref" id="fnref:34" href="#fn:34">34</a> and the <a href="/facts/Soviet_Union/m7wWsPto">Soviet</a> submarine projects designated <a href="/facts/Whiskey-class_submarine/5QV1Stlz">Whiskey</a>, <a href="/facts/Zulu-class_submarine/ueGFbAvs">Zulu</a>,<a class="footnote-ref" id="fnref:35" href="#fn:35">35</a> and <a href="/facts/Romeo-class_submarine/9dAc3mYz">Romeo</a> <a href="/facts/NATO_reporting_name/GL1ptqxy">by NATO</a>. The Chinese-built Romeo-class submarines, and the subsequent <a href="/facts/Ming-class_submarine/7zPgaaVS">Ming class</a>, were based on Soviet blueprints.

<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/List_of_Type_XXI_submarines/Mz45PDQI">List of Type XXI submarines</a></li>
<li><a href="/facts/British_R-class_submarine/SdU2hq8J">British R-class submarine</a></li>
<li><a href="/facts/I-201-class_submarine/KKRqDe0b">I-201-class submarine</a></li></ul>
<h2 id="notes">Notes</h2>

<ul><li>Blair, Clay (2000). Hitler's U-boat War: The Hunters 1939-1942. London: Cassel & Co. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 0304352608.</li>
<li>Breyer, Siegfried (1999). German U-Boat Type XXI. Translated by Force, Ed. Atglen, PA: Schiffer. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-0-7643-0787-4.</li>
<li>Fitzsimons, Bernard, general editor. The Encyclopedia of 20th Century Weapons and Warfare (London: Phoebus Publishing Company, 1978), Volume 24, p. 2594, "'Whiskey'", and p. 2620, "'Zulu'".</li>
<li>Gröner, Erich; Jung, Dieter; Maass, Martin (1991). German Warships 1815–1945, U-boats and Mine Warfare Vessels. Vol. 2. Translated by Thomas, Keith; Magowan, Rachel. London: Conway Maritime Press. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-0-85177-593-7.</li>
<li>Kohl, Fritz; Eberhard Rossler (1991). The Type XXI U-boat. Conway Maritime. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-1-55750-829-4.</li></ul>
<h2 id="external-links">External links</h2>

Wikimedia Commons has media related to Type XXI submarines.

<ul><li><a href="http://ipmsstockholm.org/magazine/2003/11/detail_uboot_xxi.htm">U-Boot Type XXI in Detail</a> <a href="https://web.archive.org/web/20070927034240/http://ipmsstockholm.org/magazine/2003/11/detail_uboot_xxi.htm">Archived</a> 2007-09-27 at the <a href="/facts/Wayback_Machine/nmQ3a6JC">Wayback Machine</a> with photos.</li>
<li>Helgason, Guðmundur. <a href="http://www.uboat.net/types/xxi.htm">"Type XXI"</a>. German U-boats of WWII - uboat.net. Retrieved 20 April 2015.</li>
<li><a href="http://www.uboataces.com/uboat-type-xxi.shtml">Type XXI</a> on www.uboataces.com</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">Jones, Marcus O. (2014) "Innovation for Its Own Sake: The Type XXI U-boat", Naval War College Review, Vol. 67, No. 2, Article 9 https://digital-commons.usnwc.edu/nwc-review/vol67/iss2/9%7C[permanent dead link] p10 "Early Type XXI hulls suffered from defective diesel-engine superchargers, faulty hydraulic torpedo-loading systems, trouble-prone steering systems..." <a href="https://digital-commons.usnwc.edu/nwc-review/vol67/iss2/9%7C" target="_blank">https://digital-commons.usnwc.edu/nwc-review/vol67/iss2/9%7C</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">H I Sutton (7 March 2021). "World-Submarine-Family-Tree". Covert Shores. <a href="http://www.hisutton.com/World-Submarine-Family-Tree.html" target="_blank">http://www.hisutton.com/World-Submarine-Family-Tree.html</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">Gordon Williamson (February 5, 2005). Wolf Pack: The Story of the U-Boat in World War II. Osprey. p. 59. ISBN 978-1841768724. Retrieved October 12, 2018. <a href="978-1841768724" target="_blank">978-1841768724</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">"German Type IX U-Boat - history, specification and photos". <a href="http://www.uboataces.com/uboat-type-ix.shtml" target="_blank">http://www.uboataces.com/uboat-type-ix.shtml</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">Gordon Williamson (February 5, 2005). Wolf Pack: The Story of the U-Boat in World War II. Osprey. p. 58. ISBN 978-1841768724. Retrieved October 12, 2018. <a href="978-1841768724" target="_blank">978-1841768724</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">"History, U-Boot Wilhelm-Bauer". Museum Harbour of Bremerhaven. October 2, 2015. Archived from the original on October 12, 2018. Retrieved October 11, 2018. <a href="https://web.archive.org/web/20181012054022/https://u-boot-wilhelm-bauer.de/en/history.html" target="_blank">https://web.archive.org/web/20181012054022/https://u-boot-wilhelm-bauer.de/en/history.html</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">Gordon Williamson (February 5, 2005). Wolf Pack: The Story of the U-Boat in World War II. Osprey. ISBN 978-1841768724. Retrieved October 12, 2018. <a href="978-1841768724" target="_blank">978-1841768724</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">Gordon Williamson (February 5, 2005). Wolf Pack: The Story of the U-Boat in World War II. Osprey. ISBN 978-1841768724. Retrieved October 12, 2018. <a href="978-1841768724" target="_blank">978-1841768724</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">Gordon Williamson (February 5, 2005). Wolf Pack: The Story of the U-Boat in World War II. Osprey. p. 59. ISBN 978-1841768724. Retrieved October 12, 2018. <a href="978-1841768724" target="_blank">978-1841768724</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">Breyer 1999, pp. 18–19. - Breyer, Siegfried (1999). German U-Boat Type XXI. Translated by Force, Ed. Atglen, PA: Schiffer. ISBN 978-0-7643-0787-4. <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">Gerken, Louis (1989). Torpedo Technology (Illustrated ed.). United States: Pennsylvania State University. p. 57. ISBN 978-0961716325. Retrieved 30 June 2017. <a href="978-0961716325" target="_blank">978-0961716325</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">Gardiner, Robert (1990). Warships - 1990. London, UK: Conway Maritime Press. p. 183. ISBN 978-0851775470. <a href="978-0851775470" target="_blank">978-0851775470</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
<li id="fn:13">Gordon Williamson (February 5, 2005). Wolf Pack: The Story of the U-Boat in World War II. Osprey. p. 60. ISBN 978-1841768724. Retrieved October 12, 2018. <a href="978-1841768724" target="_blank">978-1841768724</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></li>
<li id="fn:14">Blair 2000, p. x. - Blair, Clay (2000). Hitler's U-boat War: The Hunters 1939-1942. London: Cassel & Co. ISBN 0304352608. <a href="#fnref:14" class="footnote-back-ref">↩</a></li>
<li id="fn:15">Blair 2000, p. xi. - Blair, Clay (2000). Hitler's U-boat War: The Hunters 1939-1942. London: Cassel & Co. ISBN 0304352608. <a href="#fnref:15" class="footnote-back-ref">↩</a></li>
<li id="fn:16">Gordon Williamson (February 5, 2005). Wolf Pack: The Story of the U-Boat in World War II. Osprey. ISBN 978-1841768724. Retrieved October 12, 2018. <a href="978-1841768724" target="_blank">978-1841768724</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></li>
<li id="fn:17">Gordon Williamson (February 5, 2005). Wolf Pack: The Story of the U-Boat in World War II. Osprey. ISBN 978-1841768724. Retrieved October 12, 2018. <a href="978-1841768724" target="_blank">978-1841768724</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></li>
<li id="fn:18">Tooze, Adam (2006). The Wages of Destruction. London: Penguin Books. pp. 616–618. ISBN 978-0-14-100348-1. <a href="978-0-14-100348-1" target="_blank">978-0-14-100348-1</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></li>
<li id="fn:19">Blair 2000, p. x. - Blair, Clay (2000). Hitler's U-boat War: The Hunters 1939-1942. London: Cassel & Co. ISBN 0304352608. <a href="#fnref:19" class="footnote-back-ref">↩</a></li>
<li id="fn:20">Flower, Stephen (2004). Barnes Wallis' Bombs. Tempus. p. 350. ISBN 978-0-7524-2987-8. <a href="978-0-7524-2987-8" target="_blank">978-0-7524-2987-8</a> <a href="#fnref:20" class="footnote-back-ref">↩</a></li>
<li id="fn:21">Marc Buggeln. "Neuengamme / Bremen-Farge". Holocaust Encyclopedia. United States Holocaust Memorial Museum. Retrieved 29 January 2011. <a href="http://www.ushmm.org/wlc/en/article.php?ModuleId=10007390" target="_blank">http://www.ushmm.org/wlc/en/article.php?ModuleId=10007390</a> <a href="#fnref:21" class="footnote-back-ref">↩</a></li>
<li id="fn:22">Flower, Stephen (2004). Barnes Wallis' Bombs. Tempus. p. 351. ISBN 978-0-7524-2987-8. <a href="978-0-7524-2987-8" target="_blank">978-0-7524-2987-8</a> <a href="#fnref:22" class="footnote-back-ref">↩</a></li>
<li id="fn:23">Blair 2000, p. x. - Blair, Clay (2000). Hitler's U-boat War: The Hunters 1939-1942. London: Cassel & Co. ISBN 0304352608. <a href="#fnref:23" class="footnote-back-ref">↩</a></li>
<li id="fn:24">Van der Vat, Dan (1994). Stealth at Sea. London: Orion. p. 353. ISBN 978-1-85797-864-3. <a href="978-1-85797-864-3" target="_blank">978-1-85797-864-3</a> <a href="#fnref:24" class="footnote-back-ref">↩</a></li>
<li id="fn:25">Polmar, Norman; Kenneth J. Moore (2004). Cold War Submarines: The Design and Construction of U.S. and Soviet Submarines. Brassey's. pp. 23–24. ISBN 978-1-57488-594-1. <a href="978-1-57488-594-1" target="_blank">978-1-57488-594-1</a> <a href="#fnref:25" class="footnote-back-ref">↩</a></li>
<li id="fn:26">"Truman Dives 440 Feet In German Sub", The Pittsburgh Press, November 21, 1946, p9 <a href="https://news.google.com/newspapers?id=p1kbAAAAIBAJ&sjid=1EwEAAAAIBAJ&pg=3101,1930838&dq=truman+sub&hl=en" target="_blank">https://news.google.com/newspapers?id=p1kbAAAAIBAJ&sjid=1EwEAAAAIBAJ&pg=3101,1930838&dq=truman+sub&hl=en</a> <a href="#fnref:26" class="footnote-back-ref">↩</a></li>
<li id="fn:27">Hitler's U-boat Bases (2002), Jak P Mallmann Showell, Sutton Publishing ISBN 0-7509-2606-6 <a href="/wiki/ISBN_(identifier)" target="_blank">/wiki/ISBN_(identifier)</a> <a href="#fnref:27" class="footnote-back-ref">↩</a></li>
<li id="fn:28">Gordon Williamson (2002). Kriegsmarine U-boats 1939–45. 841763640. ISBN 9781780966618. <a href="9781780966618" target="_blank">9781780966618</a> <a href="#fnref:28" class="footnote-back-ref">↩</a></li>
<li id="fn:29">Hitler's U-boat Bases (2002), Jak P Mallmann Showell, Sutton Publishing ISBN 0-7509-2606-6 <a href="/wiki/ISBN_(identifier)" target="_blank">/wiki/ISBN_(identifier)</a> <a href="#fnref:29" class="footnote-back-ref">↩</a></li>
<li id="fn:30">"3 Type XXI boats in the Elbe II in Hamburg". uboat.net. <a href="http://uboat.net/history/hamburg_elbe2.htm" target="_blank">http://uboat.net/history/hamburg_elbe2.htm</a> <a href="#fnref:30" class="footnote-back-ref">↩</a></li>
<li id="fn:31">"Uboat.net Operation Deadlight dives 2001". <a href="http://www.uboat.net/gallery/DivingE/" target="_blank">http://www.uboat.net/gallery/DivingE/</a> <a href="#fnref:31" class="footnote-back-ref">↩</a></li>
<li id="fn:32">"Uboat.net Operation Deadlight dives 2002". <a href="http://www.uboat.net/gallery/DivingF/" target="_blank">http://www.uboat.net/gallery/DivingF/</a> <a href="#fnref:32" class="footnote-back-ref">↩</a></li>
<li id="fn:33">Ritzau (13 April 2018). "Rare wreckage of groundbreaking nazi submarines found in the Skagerrak". tv2.dk (in Danish). Retrieved 13 April 2018. <a href="/wiki/Ritzau" target="_blank">/wiki/Ritzau</a> <a href="#fnref:33" class="footnote-back-ref">↩</a></li>
<li id="fn:34">Friedman, Norman (1994). U.S. Submarines Since 1945: An Illustrated Design History. Annapolis, Maryland: United States Naval Institute. pp. 23–28, 35, 40–43. ISBN 1-55750-260-9. <a href="1-55750-260-9" target="_blank">1-55750-260-9</a> <a href="#fnref:34" class="footnote-back-ref">↩</a></li>
<li id="fn:35">Fitzsimons, Bernard, general editor. The Encyclopedia of 20th Century Weapons and Warfare (London: Phoebus Publishing Company, 1978), Volume 24, p.2594, "'Whiskey'", and p.2620, "'Zulu'". <a href="#fnref:35" class="footnote-back-ref">↩</a></li>
</ol>

Type XXI submarine open-in-new

Type XXI submarine