A few years ago, a friend told me an extraordinary story.Two recreational divers have discovered a World War II-era German submarine with the remains of 56 crew members on board off the coast of New Jersey.Neither the government, experts, historians nor the Navy know what happened to the submarine, its crew, or why it sank off the coast of New Jersey. My first reaction at the time was that the story was too bizarre to be true.But it still brings back memories of my childhood.Years ago when I was in elementary school, the school organized a field trip to the Chicago Museum of Science and Industry.At that time, I mainly visited two exhibitions: the coal mine working site and U505, a German submarine captured in 1944.Most children prefer to visit the coal mine because there are moving locomotives and live explosion demonstrations.And I was fascinated by submarines.Filled with pipes, wires, gauges and weapons, the eel-shaped fighting machine looked more formidable than any kind of bomber or Sherman tank.It was placed just yards from the shore of Lake Michigan.It made me fantasize that this invisible hunter might have been cruising around the shoreline where I was swimming; that this submarine might have been prowling the water a mile or two from my house.

I called two divers, John.Chatterton and Ricky.Kohler, would like to meet them and ask them to tell me about their experiences in person.We meet at Chatterton's house, his vintage Royal Enfield parked next to Kohler's new Harley.Chatterton was a commercial diver doing undersea construction work around Manhattan.Kohler ran a glass company.They spend their weekends diving in search of the wreckage of the wrecked ship.No matter how you look at it, they are ordinary people. I promise not to take too much of their time.But 14 hours later, I still can only play the role of the audience.What they have discovered is not just a submarine, but a mystery of history that they have weathered through hardships, painful disagreements and confusion.What they tell is also an intellectual adventure in which they researched like experts, consulted original documents, learned about German history, looked for clues abroad, constructed their own theories, challenged historians, and ended up in a history that has long been accepted as truth. An important page has been rewritten.

"Sounds like a novel!" Kohler told me in his thick Brooklyn accent as he started his Harley.On the way back that night, I could hardly believe my luck.In Chatterton and Koehler, I found two stories of ordinary people in dire peril trying to unravel a historical mystery that not even governments can explain.Any one thread in their story will raise eyebrows.And when all the clues are combined, it provides a creative theme that is hard to find in a lifetime.I wouldn't pass up this opportunity to write, any more than they would pass up their chance to find the mysterious submarine.In this sense, Chatterton, Kohler, and I already have something in common.

This is their story.All content is true and accurate.There is no fabrication or interpretation, nor any deliberate literary processing.This book is based on hundreds of hours of interviews with Chatterton and Kohler, as well as numerous interviews with divers, historians, experts, stakeholders, and other eyewitnesses.The dialogues in the book (even during World War II) are directly quoted from my interviews with relevant personnel and witnesses.Whenever possible, all the content was repeatedly confirmed by different sources. When examining the dangers of deep-sea wreck diving, I was stunned by divers' descriptions.They said the mysterious submarine sank in the dark depths of the ocean floor, rendering them sometimes unable to do any work other than diving in hazy shadows.Their words made me feel all kinds of shadows in the whole story-the lost sailors, the second world war, the plausible history and the questions the divers kept asking themselves.Chatterton and Koehler were shadow divers for six years.For six years, they have been on an extraordinary journey.And my purpose of writing this book is to take you to experience this strange adventure together.