When I was a kid, I had a family friend who had been a radio operator on a B-17, and he had a very detailed story of seeing a flight of Foo fighters one afternoon coming back from a mission over Germany. He said his plane was tailed for half an hour by four (4) of them at a range of three hundred yards. The bombardier came back with a pair of field glasses and studied them quite carefully. Here were his impressions: (1) They seemed small: larger than basketballs, perhaps the diameter of inflatable beach balls. (2) They were bright and luminous: white to a pale blueish white. (3) They were indistinct: even with the aid of field glasses no hard surface or edge could be detected. (4) They flew and maintained a set formation, there was nothing random about the way they acted. (5) They were under intelligent control. The B-17 changed altitude and direction several times and the corresponding maneuvers of the Foo fighters left little doubt. He was quite clear about this, "under intelligent control." The vet said they were a top-secret German weapon.
When I got to college two things happened: I read about Foo fighters, and I took a 'methods of historical research' class. The first time I went home for a school break I went to interview and record his voice because I knew how important getting that history was. He had passed away.