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 face with thousands of unidentified objects. Yet ... (more)the details of these encounters remain classified. But some of these armed showdowns have proven too big or too explosive to contain. Join us as we count down the Top Ten military encounters between Earth's armed forces and UFOs—on UNSEALED:Alien Files.