For nearly a year, U.S. Navy pilots flying high over the East Coast reported that they repeatedly saw aircraft with no visible engine reaching hypersonic speeds—a type of flying object they could not readily identify, the New York Times reports. The pilots began noticing the objects—which appeared like white ovals—after their 1980s-era radar was upgraded to a more advanced system. Some of the sightings were videotaped. What stands out most to the pilots is that the video shows objects accelerating to hypersonic speed, making sudden stops and instantaneous turns—a jolting flight path that would be impossible for a human crew to achieve. “Speed doesn’t kill you. Stopping does. Or acceleration,” said Lt. Ryan Graves, a pilot who reported his sightings to the Pentagon and Congress. 

There are earthly explanations for the footage, including “bugs in the code for the imaging and display systems, atmospheric effects and reflections, neurological overload from multiple inputs during high-speed flight” according to Leon Golub, a senior astrophysicist at Harvard. But the aircraft did get the attention of the Navy, which earlier this year sent out new classified guidance for how to report what the military calls “unexplained aerial phenomena,” or, the objects formerly known as UFOs. The sightings were also reported to the Pentagon’s shadowy Advanced Aerospace Threat Identification Program. Luis Elizondo, a military intelligence official who ran the program until he resigned in 2017, called the sightings “a striking series of incidents.”