G7e torpedo The G7e or more appropriately the G7e / T2 , G7e / T3 , and G7e / T4 Falke torpedo es were , with the exception of the T4 model , the standard torpedoes for Germany during World War II . All of the G7e models shared standardized dimensions for all German torpedoes designed for use by U - boat s during World War II , they measured 53 . 3 cm ( 21 inches ) in diameter , 7 . 16 m in length , and carried a " Schießwolle 36 " ( a mixture of explosives ) warhead of 280 kg . All were powered by 100 hp ( 75 kW ) electric motors and lead - acid batteries which needed constant maintenance to maintain their reliability . Additionally , the batteries of these torpedoes needed to be preheated to a temperature of 30 °C ( 85 °F ) to operate with maximum speed and range , though generally this was a non - issue as U - boats had the element of surprise and often had the advantage of firing the first shot . G7e / T2 . The T2 model of the G7e was in service with German U - boat fleets from the first day of World War II . In stark contrast with the G7a steam driven torpedo , the T2 left no visible stream of bubbles to alert ships they were under attack , and was virtually silent ; however , these were quite literally the T2 ' s only advantages over the G7a torpedo . In all other respects , the T2 was barely functional and performed abysmally when compared to the G7a . Its range was much shorter than the G7a ' s at only 3000 m , and it ran much slower at 30 kt ( 55 km / h ) . Poor range and speed were not the T2 ' s only problems . Both of its detonators were terribly flawed . The magnetic influence mechanism , designed to allow the torpedo to run under the keel of a ship and detonate , breaking the ship ' s back , was totally inconsistent ; often a T2 would detonate prematurely , or not at all . In the first engagement between a U - boat and a capital ship in the war , accurately fired three magnetically fused T3s at HMS Ark Royal , all of which detonated prematurely without effect and exposed her position to the British force , which promptly sank her . This led the BdU to order all G7e / T2 torpedoes be fired only for contact detonation . However , the contact pistol of the T2 was miserably flawed as well ; British battleship HMS Rodney managed to narrowly survive almost certain destruction when three perfectly targeted , impact - fused T2s from struck simultaneously on her keel and broke themselves without detonating . Captain Wilhelm Zahn of U - 56 was so depressed by the evident futility of his efforts that he needed to be briefly relieved of duty by Admiral Karl Dönitz in order to compose himself , while the civilian Naval Ordnance Corps , responsible for torpedo development and maintenance , continued to insist the U - boat captains were somehow at fault . Estimates of the failure rate of T2 torpedoes for one reason or another range between 20 % and 40 % , a staggeringly negligent figure considering the centrality of the torpedo to the U - boat ' s effectiveness , the criticality of the U - boats to the Battle of the Atlantic , and the requirement of winning the commerce war at sea in order to have any hope of defeating Britain in a prolonged war . Due to the complicated politics of the powerful German military - industrial establishment ( exacerbated by the internecine conflicts so common to Hitler ' s Germany ) , no one was ever held accountable or punished for these failures . Nevertheless , the German Navy , after many recriminations and counter - recriminations and much prodding by German U - boat Command ( BdU ) , eventually admitted and ( grudgingly ) invested resources into correcting the T2 ' s flaws . Gradually , it improved , and by the end of the Norwegian Campaign problems with the contact exploder and depth - keeping gear had been mostly solved , as well as significant strides made in improving the magnetic proximity feature . At the same time , the T2 ' s range was increased from 3000 m to 5000 m and eventually 7500 m . By that time , however , the T2 was already being phased out of production . G7e / T3 . Improvements in the design of the G7e / T2 were incorporated into the production of the next model of electric torpedo for Germany ' s U - boat fleet . Introduced in 1942 , the T3 represented a vast improvement over the early T2 . The faulty exploders from the T2 were scrapped in favor of a new design . The T3 had a range of 5000 m and could achieve 30 kt . With the improved design of the T3 and the new exploder , the G7a steam torpedo was totally superseded and was rarely used for the remainder of the war . Using the T3 ' s perfected proximity feature , U - boat captains could effectively fire under the keel of a ship and break the back of their targets with a single torpedo , increasing the overall effectiveness of the U - boat fleet . The T3 could be fitted with both the FaT ( " Flächenabsuchender Torpedo " ) and LuT ( " Lagenunabhänger Torpedo " ) pattern running systems for convoy attacks . Though many opportunities had been missed due to the defects of the T2 torpedo , with the new T3 U - boats were deadlier than ever . G7e / T4 " Falke " . The T4 Model was the adjunct of the earlier T3 model in nearly every way . The T4 was not an ordinary straight - running torpedo , however ; it was the world ' s first acoustic homing torpedo . It ran at 20 kt ( 37 km / h ) for 7500 m and was introduced in March 1943 . In early 1933 , Germany started development and testing of acoustic homing mechanisms for torpedoes . From the outset of submarine warfare , submariners had dreamt of being able to aim and fire torpedoes without surfacing or using a periscope . The periscope gives away the location of a submarine , and a hull - penetrating periscope greatly weakens a submarine ' s pressure hull and limits the depths to which it can dive . U - boats also had to come to very shallow depths to use their periscopes , generally about 15 m , leaving them greatly exposed to bombing , depth charging , and even gunfire . With the introduction of " Falke " , U - boats could remain more deeply submerged and fire at convoys with nothing to give away their position but the noise of their screws . Rather than aiming with a periscope , the torpedo could be roughly aimed at a sound contact as detected by a U - boat ' s hydrophones , and the homing mechanism could be trusted to find the target without the need for precise aiming . " Falke " worked much like a normal straight - running torpedo for the first 400 m of its run , after which its acoustic sensors became active and searched for a target . The sensitive sound sensing equipment in " Falke " required the torpedo be as quiet as possible , hence it ran at only 20 kt ( 37 km / h ) ; in addition , the firing U - boat was forced to stop its motors . " Falke " was intended to home on merchant targets , however , so its slow speed was not a great hindrance . Only known to have been fired in action by three U - boats , " U - 603 " , " U - 758 " , and " U - 221 " , although regarded as successful , resulting in the sinking of several merchants , and its performance rated satisfactory , " Falke " was rapidly phased out of service . It was replaced by the G7es / T5 " " Zaunkönig " " ( referred to by the Allies as GNAT , for German Navy Acoustic Torpedo ) , which was faster and better able to home onto the sound of fast moving warships as well as merchant traffic . Though its period of operational service was brief , " Falke " was a proof of concept for the acoustic homing torpedo . Its introduction occurred only two months before the U . S . Navy achieved its initial combat success with the Mark 24 FIDO " mine . " FIDO was not a mine , but a passive , acoustic - homing torpedo designed for use by long - range patrol aircraft . ( It was designated a mine for security reasons . ) The initial success with the Mark 24 occurred on 14 May 1943 , when a PBY - 5 from VP - 84 sank " U - 640 " with the new weapon . Most sources indicate that the Germans ' first combat success with the " Zaunkönig " ( GNAT ) did not occur until September 1943 . While the Allies became aware in September 1943 that the Germans had brought GNAT into operational service , it was not until the capture of " U - 505 " in June 1944 that they obtained reliable data on the German homing torpedo . See also . List of World War II torpedoes of Germany