When a commando team of U.S. Navy Seals breached a fortified compound in Pakistan and dispatched Osama bin Laden, the world's attention focused on America's special forces. Yet it is the nature of their form of war that the names of these heroes may never be known. Now TIME shines a spotlight on the secret world of military special operations units, from the Green Berets of the Vietnam War to the Navy Seals of Pakistan. Join TIME to trace their history, their training, and the missions they have fought, from World War II to Iraq and Afghanistan and more.