Biber ( submarine ) The Biber ( German for " beaver " ) was a German midget submarine of the Second World War . Armed with two externally mounted 21 - inch ( 53 cm ) torpedo es or mines , they were intended to attack coastal shipping . They were the smallest submarines in the Kriegsmarine . The Biber was hastily developed to help meet the threat of an Allied invasion of Europe . This resulted in basic technical flaws that , combined with the inadequate training of their operators , meant they never posed a real threat to Allied shipping , despite 324 submarines being delivered . One of the class ' s few successes was the sinking of the cargo ship " Alan A . Dale " . A number have survived in museums including one example that has been restored to operational condition . Development . Construction of the first prototype began in February 1944 and was completed in less than 6 weeks . The initial prototype was officially titled " Bunteboot " ( but better known as " Adam " ) was heavily influenced by the British Welman submarine . It differed from the final design in a number of respects such as being nearly 2 meters shorter . Following testing on the Trave river on 29 May twenty four Bibers were ordered . Design . The hull was built in three sections composed of 3 mm thick steel with an aluminium alloy conning tower bolted to the top . The conning tower contained armoured glass windows to allow the pilot to see out . The hydroplanes and rudder were made of wood and trying to control them while tracking the depth gauge , compass and periscope made the craft hard to handle . Adding to the pilot ’ s difficulties , the craft lacked compensating and trimming tanks , making staying at periscope depth a near impossibility . The Biber had two diving tanks one in the bow section and one in the stern . The submarine could be armed with either two TIIIc torpedoes with neutral buoyancy ( achieved by limiting the number of batteries on board ) , mines or a mixture of the two . The Biber was powered on the surface by a Otto blitz petrol engine which was used despite concerns about the risks posed by the carbon monoxide the engine gave off . The engine had the advantage of being cheap and available in large numbers . Propulsion while submerged was provided by a 13 horse power electric motor powered by three Type T13 T210 battery troughs . Operation . Biber operations were carried out under the auspices of the K - Verband , a German naval unit which operated a mixture of midget submarines and explosive speedboats . The training of Biber operators was originally planned to take eight weeks , but the initial group of pilots was rushed through in just three weeks . Planning also called for flotillas of 30 boats and pilots with just under 200 shore support crew . Operations generally lasted from one to two days with pilots either using a drug known as DIX to stay awake on longer missions or caffeine - laced chocolate . The poor quality of the Biber ' s periscope meant that night attacks had to be carried out on the surface . Fécamp harbour . The first Biber operation was launched on 30 August 1944 from Fécamp harbour . Twenty - two boats were launched but only 14 were able to leave the harbour and of those fourteen only two managed to reach their operational area . The bibers were then withdrawn to Mönchengladbach . Operations in the Scheldt Estuary . In December 1944 it was decided to deploy Bibers against traffic to Antwerp in the Scheldt Estuary . The force was based at Rotterdam with forward bases at Poortershaven and Hellevoetsluis . The first attack took place on the night of the 22 / 23 of December . Eighteen Biber were involved of which only one returned . The only allied loss caused by the operation was " Alan A . Dale " . Further operations between the 23rd and the 25th achieved no success and none of the 14 submarines deployed survived . On the 27th the accidental release of a torpedo in the Voorneschen resulted in the sinking of 11 Bibers ( although they were later recovered ) . The 3 undamaged bibers later sailed again ; none returned . An operation on the night 29 / 30 January resulted in damage to ( much of it due to ice ) or loss of most of the remaining Bibers . Losses combined with RAF bombing prevented attacks from being mounted in February 1945 . The bombing had damaged the cranes used to move the Bibers into and out of the water . Reinforcements allowed operations to continue until April 1945 but no successes were achieved and the Biber flotillas continued to take a very high rate of losses . The last Biber mission was an attempt at mine laying and took place on the night of 26 April . Of the 4 Bibers that took part one ran aground and three were attacked by Thunderbolts which sank two of them . Attempted attack on Vaenga Bay . In January 1945 an attempt was made to mount an attack on Vaenga Bay in the Kola Inlet . The hope was either to attack one of the convoys that stopped there to refuel and take on ammunition or to attack the Soviet battleship " Arkhangelsk " ( HMS " Royal Sovereign " on loan to the USSR ) . As it happened neither the battleship nor a convoy were in the port at the time of the planned attack . The plan was for U - boats to carry the Bibers within range of the harbour . U - 295 , U - 318 and U - 716 set off from Harstad on 5 January with Bibers mounted on their casings . Vibrations from the U - boats ’ engines caused the Bibers stern gland s to leak allowing water to reach the machinery space and as a result the mission was abandoned . Further developments . Planning for two man versions ( Biber II and Biber III ) began but never got off the drawing board . a bottle hidden under the seat and inside was a document in English , which , romantic as it read , appeared to have some bearing : on upon the capture of the submarine , and possibly the explanation of why the pilot met his end . Surviving examples . Three more Bibers can be seen in the Netherlands ; one in Vlissingen , at Fort Rammekens , and another at the Overloon War Museum . The third Biber is privately owned and displayed outdoors at Sloten near Amsterdam , it has been painted red and white and serves as an advertising sign . Other Bibers are displayed at the Deutsches Museum in Munich , the Technikmuseum Speyer in Speyer , Germany . Two examples survive in Norway , one at the Royal Norwegian Navy Museum and another at the Haakonsvern naval base .