Seehund The Seehund ( German : " seal " ) , also known as Type XXVII , was a successful series of German midget submarine s created during World War II . Designed in 1944 , and operated by two man crews , the submarines were used by the " Kriegsmarine " during the closing months of the war , sinking 9 merchant vessels and damaging an additional 3 , with 35 losses mostly attributed to bad weather . History . The origin of the " Seehund " began with the salvage of the two British X class submarine s HMS " X6 " and " X7 " which had been sunk during Operation Source , an attempt to sink the German battleship Tirpitz . " Hauptamt Kriegschiffbau " subsequently produced a design for a two - man submarine based on inspection of the British boats , designated Type XXVIIA and named " Hecht " ( " Pike " ) XXVIIA ( Hecht ) . Like the British X class boats , the Type XXVIIA was designed to carry explosive charges to be laid beneath enemy ships , but it was markedly smaller and had substantial differences from the X class . It dispensed with a dual diesel / electric propulsion system , relying instead solely on electrical power in the form of a 12 hp AEG torpedo motor , on the basis that since it would operate submerged there was no need for a diesel engine . However , this resulted in a very low endurance of at . Since the boat would need to be able to pass through anti - submarine nets and similar obstacles , it was designed without hydroplanes or fins , her trim being controlled with adjustable weights within the pressure hull . In practice this proved totally ineffective since the weights could not be moved quickly enough and hydroplanes and fins were subsequently fitted . Submerged control was still poor , since " Hecht " was not fitted with ballast tank s . Even though " Hecht " had been designed to transport an explosive charge , Karl Dönitz insisted that a torpedo be carried so that attacks could be carried out on vessels in coastal waters . Externally , " Hecht " resembled the British Welman submarine . The detachable explosive charge was fitted to the nose of the submarine , while the forward section held the battery and a gyrocompass , the first to be fitted to a German midget submarine and considered essential for navigation if the craft was to operate submerged . Behind this was the control compartment with seats for the two man crew arranged one behind the other on the centerline with the engineer in front and the commander behind him . The commander was provided with a periscope and a clear acrylic dome for navigational purposes . On 18 January 1944 , Dönitz discussed the new design with Adolf Hitler who expressed his approval , and on 9 March contracts were placed with Germaniawerft of Kiel for construction of a prototype , followed by a further contract for 52 submarines on 28 March . The 53 " Hechts " were constructed between May and August 1944 : in the event , none saw active service but were instead used to train " Seehund " crews . Type XXVIIB . As the orders were being placed , " Hecht " variants were under construction . The first was the Type XXVIIB , which had a greater range , could carry two G7e torpedo es , and had diesel / electric propulsion . The design was completed at the end of June 1944 and resembled " Hecht " but had a better boat - shaped external casing for improved seakeeping while surfaced , and saddle tanks . Additional room had been made inside the pressure hull by moving the batteries to the keel , while the two torpedoes were slung externally in recesses in the lower hull . A 22 hp diesel engine was fitted for surface use and was estimated to give a surfaced speed of , with a 25 hp electric motor providing a submerged speed of . The final variant of the Type XXVII was the Type XXVIIB5 , better known as the " Seehund " ( " Seal " ) or Type 127 . " Seehund " had a small raised platform midships with the air intake mast , magnetic compass , periscope , and a clear dome which could survive depths of . The submarine ' s fixed periscope incorporated lenses which let the commander check the sky above for aircraft before surfacing . Production . The first contract for " Seehund " construction was placed on 30 July 1944 . Enthusiasm for the submarine was so high that most of the contracts and hull numbers were allocated even before the design was completed . A total of 1 , 000 boats were ordered , Germaniawerft and Schichau - Werke to build 25 and 45 boats per month respectively . Other centers involved in " Seehund " production were CRD - Monfalcone on the Adriatic and Klöckner - Humboldt - Deutz at Ulm . However , Dönitz would not consent to the production of the Type XXVII U - boat being held up for " Seehund " construction , while shortages of raw material , labor and transport problems , and conflicting priorities in Germany ' s economy all combined to reduce " Seehund " production . In the end " Seehund " production was undertaken by Germaniawerft at Kiel using a facility which was no longer needed for Type XXI or Type XXIII production . A total of 285 " Seehunds " were constructed and allocated numbers in the range " U - 5501 " to " U - 6442 " . Operational service . From the Allied point of view the " Seehund " s small size made it almost impossible for Asdic to get a return from her hull , while her very quiet slow speed running made her almost immune to detection by hydrophone . As Admiral Sir Charles Little , Commander - in - Chief , Portsmouth put it , " Fortunately for us these damn things arrived too late in the war to do any damage " . " Seehunds " operated mainly around the German coast and in the English Channel , and could attack on the surface in turbulent weather , but had to be almost stationary for submerged attacks . From January to April 1945 " Seehunds " performed 142 sorties , during which they sank 8 ships for a total of 17 , 301 tons and damaged 3 for a total of 18 , 384 tons ; 35 " Seehunds " were lost in action . The last " Seehund " sorties took place on 28 April and 2 May 1945 , when two special missions were performed to resupply the cutoff German base at Dunkirk with rations , the boats carrying special food containers ( nicknamed " butter torpedoes " ) instead of torpedoes , and on the return voyage using the containers to carry mail from the Dunkirk garrison . The French navy received four units as war reparations , and commissioned them as " S 621 " , " S 622 " , " S 623 " and " S624 " . They were used until August 1953 . " S 622 " is preserved and on display at Brest naval museum . The U - 5075 is on display at the United States Naval Shipbuilding Museum , part of the Massachusetts Military Research Center , in Quincy , Massachusetts . Occasional amateur radio events are conducted by this museum ship , using the callsign WW2MAN .