The diesel engine was invented by a brilliant German engineer, Dr Rudolf Diesel. Before World War 1, it was successfully used in German submarines. Dr Diesel crossed the North Sea on September 29, 1913, heading to the UK, apparently to discuss his new engine’s use in British Royal Navy submarines. He never made it. When the SS Dresden docked in Harwich, England, on September 30, Dr Diesel’s cabin was empty. His body was later discovered floating in the North Sea. Was he pushed by a German spy? Did he jump? Did he fall? More than 100 years later, we still don’t know.