Military historian and best-selling author Patrick K. O'Donnell discusses his latest book "First SEALs: The Untold Story of the Forging of America's Most Elite Unit." The book tells the story of four extraordinary men who in 1942 united to form the Navy's Sea, Air, and Land (SEAL) teams that would led to the establishment of one of the military's most esteemed units. O'Donnell discusses the sources he used for the book, which for a long time were unavailable, as well as the in-depth research required to tell the story.