Only once: While on an Army training exercise at Fort Irwin California, through the IR scope of a Bradley Fighting Vehicle, at night (~ 9:45 PM) in the summer of 2009. I was gazing at the exhaust of a hovering black hawk when a perfectly spherical, very hot, object moved into my field of view. It was behind the helicopter, and as I followed it I realized It was rotating 360 degrees -- at an unknown distance -- around our position. I attempted to range the object with my gun, but once I did, it immediately froze in its position, went from white hot to cold black and back again, and then shot up (very quickly) and out of my view where I lost sight of it. I shared this with the rest of my platoon afterwords, after which we all took to our scopes, ... and it came back, but six spheres this time and in a diamond shaped formation. After one full rotation, the objects slowly broke formation and disappeared into the sky. I never knew what to make of it, but like Mulder, I want to believe.