One of the vehicles I observed did a similar maneuver...but only after it had spent a good 15 minutes hovering in one spot, and moving around some at lower speeds, and making sudden leaps across large areas of sky to new positions. It then went from directly overhead to over the far horizon in about a second and a half. Our vehicles are simply not capable of such speeds, nor are they capable of instant acceleration and deceleration in the air at enormously high speeds. It was also silent, and had no wings, and left no contrails or anything like that. It was round, disc-shaped, with a protuberance above and below, much like some of the photos on the site that Amos provided the link to. It could vary its illumination from a dull glow to a very bright light, and it had secondary smaller lights that moved around the rim of the disc-shaped hull.

- LH