The two Explorer class submarines were experimental vessels built for the Royal Navy to test a propulsion system based on the use of highly concentrated Hydrogen peroxide (HTP) and diesel fuel to achieve high underwater endurance and speeds. Germany had started experimenting with this technology early in the Second World War and developed it into the Walter cycle. They had built some experimental boats. One of these, the U-Boat 1407, which had been scuttled at the end of the war was salvaged and eventually recommissioned into the Royal Navy as HMS Meteorite.