But in the fall of 1991, not even these courageous divers were prepared for what they found 230 feet below the surface, in the frigid Atlantic waters 60 miles off the coast of New Jersey: a World War II German U-boat, its ruined interior a macabre wasteland of twisted metal, tangled wires, and human bones all buried under decades of accumulated sediment.

No identifying marks were visible on the submarine or the few artifacts that Chatterton and Kohler brought to the surface. No historian, expert, or government had a clue as to which U-boat the men had found. In fact, the official records all agreed that there simply could not be a sunken U-boat and crew at that location.

Over the next six years, an elite team of divers embarked on a quest to solve the mystery. Chatterton and Kohler, at first bitter rivals, would be drawn into a friendship that deepened to an almost mystical bond of brotherhood. As the men's marriages frayed under the pressure of a shared obsession, their dives grew more daring, and each realized that he was hunting more than the identities of a lost U-boat and its nameless crew.

Author Robert Kurson's account of this quest is at once thrilling and emotionally complex. The story of Shadow Divers often seems too amazing to be true, but it all happened, 230 feet down, in the deep blue sea.