As early as 1911, Germany was conducting laboratory experiments with closed-cycle propulsion systems that did not breathe air, hoping that it would be possible to build a true submarine, one that was designed to stay submerged, as opposed to a submersible boat. By the start of the Second World War, research had gathered momentum and, in 1940, following the trials of a prototype hydrogen peroxide-driven submarine - the little V80 - a number of experimental boats were built.
In 1946, one such experimental boat, the U-Boat 1407, which has been scuttled at the German collapse, was salvaged and, after a long delay, commissioned into the Royal Navy as HMS Meteorite. Her recovery led to a British development programme which resulted in two 1120-ton submarines, Explorer and Excalibur, being constructed at Barrow. Built for speed trials only, they were purely experimental, unarmed submarines. Their high-test hydrogen peroxide engines were basically steam turbines, with steam being supplied from the heat generated by the interaction of high-test hydrogen peroxide (HTP), a catalyst and diesel oil.
