HMS Explorer was an experimental British submarine based on the captured German high test peroxide (HTP) powered U-boat U-1407. U-1407 had been scuttled following the German collapse at the end of the Second World War, was salvaged and eventually commissioned into the Royal Navy as HMS Meteorite. Her recovery was the impetus for a British research programme which resulted in the construction of two experimental submarines, HMS/m Explorer and HMS Excalibur. Built for speed trials, they were unarmed. Their HTP engines were essentially steam turbines, with the steam being generated by the interaction of HTP with diesel oil and a catalyst.