German Type VII submarine Type VII U - boats were the most common type of German World War II U - boat . The Type VII was based on earlier German submarine designs going back to the World War I Type UB III , designed through the Dutch dummy company " Ingenieurskantoor voor Scheepsbouw den Haag " ( I . v . S ) which was set up by Germany after World War I in order to maintain and develop German submarine technology and to circumvent the limitations set by the Treaty of Versailles , and was built by shipyards around the world . The Finnish " Vetehinen " class and Spanish Type E - 1 also provided some of the basis for the Type VII design . These designs led to the Type VII along with Type I , the latter being built in AG Weser shipyard in Bremen , Germany . The production of Type I was cut down only after two boats ; the reasons for this are not certain and range from political decisions to faults of the type . The design of the Type I was further used in the development of the Type VII and Type IX . Type VII submarines were the most widely used U - boats of the war and were the most produced submarine class in history , with 703 built . The type had several modifications . The Type VII was the most numerous U - boat type to be involved in the Battle of the Atlantic . Type VIIA . Type VIIA U - boats were designed in 1933 - 34 as the first series of a new generation of attack U - boats . Most Type VIIA U - boats were constructed at Deschimag AG Weser in Bremen with the exception of U - 33 through U - 36 , which were built at Germaniawerft , Kiel . Type VIIA U - boats were generally popular with their crews and much more powerful than the smaller Type II U - boat s they replaced , with four bow and one external stern torpedo tubes . Usually carrying 11 torpedoes on board , they were very agile on the surface and mounted the 88 mm fast - firing deck gun with about 220 rounds . Ten Type VIIA boats were built between 1935 and 1937 . All but two Type VIIA U - boats were sunk during World War II ( and , both scuttled in Kupfermühlen Bay on 4 May 1945 ) . The boat was powered on the surface by two MAN AG , 6 cylinder , 4 - stroke M6V 40 / 46 diesels giving a total of at 470 to 485 rpm . When submerged it was propelled by two BBC GG UB 720 / 8 electric motors giving a total of at 322 rpm . Type VIIB . The VIIA had limited fuel capacity , so 24 Type VIIB boats were built between 1936 and 1940 with an additional 33 tons of fuel in external saddle tank s which added another of range at surfaced . They were slightly faster than the VIIA , and had two rudders for greater agility . The torpedo armament was improved by moving the aft tube to the inside of the boat . Now an additional aft torpedo could be carried below the deck plating of the aft torpedo room ( which also served as the electric motor room ) and two watertight compartments under the upper deck could hold two additional torpedoes giving it a total of 14 torpedoes . The only exception was , which lacked a stern tube and carried only 12 torpedoes . Type VIIBs included many of the most famous U - boats of World War II , including ( the most successful ) , Prien ' s , Kretschmer ' s , and Schepke ' s . On the surface the boat was powered by two supercharged MAN , 6 cylinder , 4 - stroke M6V 40 / 46 diesels ( except for " U - 45 " to " U - 50 " , " U - 83 " , " U - 85 " , " U - 87 " , " U - 99 " , " U - 100 " , and " U - 102 " which were powered by two supercharged Germaniawerft 6 - cylinder , 4 - stroke F46 diesels ) giving a total of 2 , 800 to 3 , 200 bhp ( 2 , 400 kW ) at 470 to 490 rpm . When submerged , the boat was powered by two AEG GU 460 / 8 - 276 ( except in " U - 45 " , " U - 46 " , " U - 49 " , " U - 51 " , " U - 52 " , " U - 54 " , " U - 73 " to " U - 76 " , " U - 99 " and " U - 100 " which retained the BBC motor of the VIIA ) electric motors giving a total of 750 shp ( 560 kW ) at 295 rpm . Type VIIC . The Type VIIC was the workhorse of the German U - boat force , with 568 commissioned from 1940 to 1945 . The first VIIC boat commissioned was the in 1940 . The Type VIIC was an effective fighting machine and was seen almost everywhere U - boats operated , although its range of only 6 , 500 nautical miles was not as great as that of the larger Type IX ( 11 , 000 nautical miles ) , severely limiting the time it could spend in the far reaches of the western and southern Atlantic without refueling from a tender or U - boat tanker . The VIIC came into service toward the end of the " First Happy Time " near the beginning of the war and was still the most numerous type in service when Allied anti - submarine efforts finally defeated the U - boat campaign in late 1943 and 1944 . Type VIIC differed from the VIIB only in the addition of an active sonar and a few minor mechanical improvements , making it 2 feet longer and 8 tons heavier . Speed and range were essentially the same . Many of these boats were fitted with snorkels in 1944 and 1945 . They had the same torpedo tube arrangement as their predecessors , except for , , , , and , which had only two bow tubes , and for , , , , , and , which had no stern tube . On the surface the boats ( except for , and to which used MAN M6V40 / 46s ) were propelled by two supercharged Germaniawerft , 6 cylinder , 4 - stroke M6V 40 / 46 diesels totaling at 470 to 490 rpm . For submerged propulsion , several different electric motors were used . Early models used the VIIB configuration of two AEG GU 460 / 8 - 276 electric motors , totaling with a max rpm of 296 , while newer boats used two BBC ( Brown Boveri & Co ) GG UB 720 / 8 , two GL ( Garbe Lahmeyer ) RP 137 / c electric motors or two SSW ( Siemens - Schuckert - Werke ) GU 343 / 38 - 8 electric motors with the same power output as the AEG motors . Perhaps the most famous VIIC boat was , featured in the movie " Das Boot . " U - flak " Flak Traps " . The concept of the " U - flak " or " Flak Trap " originated the previous year , on 31 August 1942 , when was seriously damaged by aircraft . Rather than scrap the boat , it was decided to refit her as a heavily armed anti - aircraft boat intended to combat the losses being inflicted by Allied aircraft in the Bay of Biscay . Two 20 mm quadruple " Flakvierling " mounts and an experimental 37 mm automatic gun were installed on the U - flaks ' decks . A battery of 86 mm line - carrying anti - aircraft rockets was tested ( similar to a device used by the British in the defense of airfields ) , but this idea proved unworkable . At times , two additional single 20 mm guns were also mounted . The submarines ' limited fuel capacities restricted them to operations only within the Bay of Biscay . Only five torpedoes were carried , preloaded in the tubes , to free up space needed for additional gun crew . Four VIIC boats were modified for use as surface escorts for U - boats departing and returning to French Atlantic bases . These " U - flak " boats were , , , and . Conversion began on three others ( , , and ) but none was completed and they were eventually returned to duty as standard VIIC attack boats . The modified boats became operational in June 1943 and at first appeared to be successful against a surprised Royal Air Force . Hoping that the extra firepower might allow the boats to survive relentless British air attacks in the Bay of Biscay and reach their operational areas , Donitz ordered the boats to cross the bay in groups at maximum speed . The effort earned the Germans about two more months of relatively limited freedom , until the RAF modified their tactics . When a pilot saw that a U - boat was going to fight on the surface , he held off attacking and called in reinforcements . When several aircraft had arrived , they all attacked at once . If the U - boat dived , surface vessels were called to the scene to scour the area with sonar and drop depth charges . The British also began equipping some aircraft with rockets that could sink a U - boat with a single hit , finally making it too dangerous for a U - boat to attempt to fight it out on the surface regardless of its armament . In November 1943 , less than six months after the experiment began , it was discontinued . All U - flaks were converted back to standard attack boats and fitted with " Turm 4 " , the standard anti - aircraft armament for U - boats at the time . ( According to German sources , only six aircraft had been shot down by the U - flaks in six missions , three by " U - 441 , " and one each by " U - 256 , " " U - 621 , " and . ) Type VIIC / 41 . Type VIIC / 41 was a slightly modified version of the VIIC and had the same armament and engines . The difference was a stronger pressure hull giving them a deeper test depth and lighter machinery to compensate for the added steel in the hull , making them slightly lighter than the VIIC . A total of 91 were built ; all of them from onwards lacked the fittings to handle mines . Today one Type VIIC / 41 still exists : is on display at Laboe ( north of Kiel ) , the only surviving Type VII in the world . List of Type VIIC / 41 submarines . There were 91 Type VIIC / 41 submarines commissioned . Type VIIC / 42 . The Type VIIC / 42 was designed in 1942 and 1943 to replace the aging Type VIIC . It would have had a much stronger pressure hull , with skin thickness up to 28 mm , and would have dived twice as deep as the previous VIICs . These boats would have been very similar in external appearance to the VIIC / 41 but with two periscopes in the tower and would have carried two more torpedoes . Contracts were signed for 164 boats and a few boats were laid down , but all were cancelled on 30 September 1943 in favor of the new Type XXI , and none was advanced enough in construction to be launched . It was powered by the same engines as the VIIC . Type VIID . The type VIID boats , designed in 1939 and 1940 , were a lengthened - by - version of the VIIC for use as a minelayer . The mines were carried in , and released from , three banks of five vertical tubes just aft of the conning tower . The extended hull also improved fuel and food storage . On the surface the boat used two supercharged Germaniawerft , 6 cylinder , 4 - stroke F46 diesels delivering 3 , 200 bhp ( 2 , 400 kW ) at between 470 to 490 rpm . When submerged the boat used two AEG GU 460 / 8 - 276 electric motors giving a total of 750 shp ( 560 kW ) at 285 rpm . Only one ( " U - 218 " ) managed to survive the war ; the other five were sunk , killing all crew members . Type VIIF . The Type VIIF boats were designed in 1941 as supply boats to rearm U - boats at sea once they had used up their torpeodes . This required a lengthened hull and they were the largest and heaviest type VII boats built . They were armed identically with the other Type VIIs except that they could have up to 39 torpedoes onboard and had no deck guns . Only four Type VIIFs were built . Two of them , and , were sent to support the Monsun Gruppe in the Far East ; and remained in the Atlantic . Type VIIF U - boats used the same engines as the Type VIID class . Three were sunk during the war , the last was scuttled after the war along with the majority of the surrendered U boats