I was communicating with a British Airways flight from Sydney to Nadi in the early 70's who reported a UFO at his level, same speed and formatting with him. The captain was dead set crapping himself. He asked if we had any traffic in the area and I knew that there was not. I had other aircraft especially when I was stationed in Darwin reporting "very strange aircraft in their vicinity" and all of a sudden flying away at incredible speeds.
Another case happened one night when I was on the doggo, and the military guy called me up to see if there was any traffic south of Darwin, being around 3am, absolutely nothing was flying, or at least that was what was supposed to be happening, he advised me he had a paint that had showed up around Port Keats, and disappeared off radar approx. 200nm nw of Darwin. He calculated the ground speed of this paint as being around 2,400kts. The blackbird immediately came to mind but was dismissed by the RAAF ATC as they would have known about it.
