In 1819, the 238-ton Essex set sail from Nantucket on a routine voyage for whales. Fifteen months later, the unthinkable happened: in the farthest reaches of the South Pacific, the Essex was rammed and sunk by an enraged sperm whale. Its twenty-man crew, fearing cannibals on the islands to the west, decided instead to sail their three tiny boats for the distant South American coast. They would eventually travel over 4,500 miles. The next three months...