Shadow divers : the true adventure of two Americans who risked everything to solve one of the last mysteries of World War II

Two deep sea wreck divers discover an unknown sunken German submarine from World War II and spend multiple years of diving and researching history to properly identify the U-Who as U-869.  I listened to this one twice just to absorb all of the intricate details of this narrative about John Chatterton and Richey Kohler's extraordinary efforts to identify this boat.