In the spring of 1952, UFO sightings go off the charts. For years, the U.S. government has told the postwar public that UFOs do not exist, but behind the scenes, U.S. Air Force officials are divided.

They're our first line of defense in the darkest of times. And they're often the first responders to threats from another world. Over the past 70 years the world's military forces have come face to ...