Elektroboot An elektroboot ( " electric boat " in German ) was the first submarine designed to operate entirely submerged , rather than as submersibles that could submerge as a temporary means to escape detection or launch an attack . History . Even before the second world war the rocket designer Hellmuth Walter had been advocating the use of hydrogen peroxide ( known as " perhydrol " ) as a fuel . His engines were to become famous for their use in rocket - powered aircraft — notably the Me 163 Komet — but most of his early efforts were spent on systems for submarine propulsion . In these cases the hydrogen peroxide was reduced chemically and the resulting gases used to spin a turbine at about 20 , 000 rpm , which was then geared to a propeller . This allowed the submarine to run underwater at all times , as there was no need for air to run the engines . The system also used up tremendous amounts of fuel , and any boat based on the design would either have to be absolutely huge , or have terribly limited range . Thus the system saw only limited development even though a prototype was running in 1940 . But when problems with the existing U - boat designs became evident in 1942 , the work was stepped up . Eventually two engineers came up with a simple solution to the problem . Instead of running the submarine 100 % on the perhydrol , they used it strictly for bursts of speed when needed . Most of the operations would then be carried out as with a normal boat , using a diesel engine to charge batteries . However while a conventional design would use the diesel as the primary engine and the batteries for short periods of underwater power , in this case the boat would run almost all the time on batteries in a low - speed cruise , turning on the perhydrol during attacks . The diesel was now dedicated entirely to charging the batteries , which it needed only three hours to do . The perhydrol design suffered from several design flaws which were not fixed before the end of the war . As an intermediate solution , the perhydrol propulsion system was dropped in favour of a conventional diesel / electric solution , but retaining the streamlined hull - shape . The battery capacity was increased significantly along with fuel stores , and the boat was designed to operate underwater for long periods . Electric U boats . The result was the " Elektroboot " series , the Type XXI U - boat and a short range Type XXIII U - boat , finalized in January 1943 but with production only commencing in 1944 - 1945 . When under water , the Type XXI managed to run at , faster than a Type VII running full out on the surface and almost as fast as the ships attacking her . After the war , tests carried out by the United States Navy on two captured Type XXIs showed they could outrun some ASW ships by going in the direction of heavy seas . ( The US Navy ' s first nuclear - powered submarine , , used a modified Type XXI hull shape . ) For most of the trip it ran silently underwater on batteries , surfacing only at night , and then only to snorkel depth . Weapons were likewise upgraded , with automated systems allowing the torpedo tube s to be reloaded in less than one - fourth of the time , firing homing torpedoes that would attack on their own . Even the interior was improved : it was much larger and fitted with showers and a meat refrigerator for long patrols . The design was to be produced in two versions , primarily the Type XXI , and lesser numbers of the smaller Type XXIII . Both were much larger and more difficult to build than the existing designs , the Type XXI taking some 18 months . Mass production of the new type did not really get started until 1944 and subsequently only one combat patrol was carried out by a Type XXI before the war ended . This patrol is considered controversial . According to some sources , the did not make any contact with the enemy . Another version suggests that the U - boat did make a contact with of the Royal Navy , but did not fire as the captain had already received orders of surrender . A number of boats were commissioned into Allied navies after the war for research purposes , and one into the " Bundesmarine " of post - war Germany .