Bob Ballard: He discovered the Titanic, the Bismarck, and dozens of other lost wrecks like the Lusitania and JFK’s PT-109. He helped prove the theory of plate tectonics, unearthed newfound forms of life at hydrothermal vents, pioneered the use of deep-diving submersibles, and remotely operated vehicles for undersea exploration. Now, National Geographic’s Bob Ballard reveals the inside stories behind his most exciting discoveries while sharing the personal triumphs, challenges and tragedies that led him to them.