He and other officials spoke on the condition of anonymity because they were not authorized to speak publicly about the classified findings in the report.

Russia has been investing heavily in hypersonics, believing the technology offers it the ability to evade American missile-defense technology. China has also developed hypersonic weaponry, and included it in military parades. If the phenomena were Chinese or Russian aircraft, officials said, that would suggest the two powers’ hypersonic research had far outpaced American military development.

Navy pilots were often unsettled by the sightings. In one encounter, strange objects — one of them like a spinning top moving against the wind — appeared almost daily from the summer of 2014 to March 2015, high in the skies over the East Coast. Navy pilots reported to their superiors that the objects had no visible engine or infrared exhaust plumes, but that they could reach 30,000 feet and hypersonic speeds.

Lt. Ryan Graves, an F/A-18 Super Hornet pilot who was with the Navy for 10 years, told The New York Times in an interview, “These things would be out there all day.” With the speeds he and other pilots observed, he said, “12 hours in the air is 11 hours longer than we’d expect.”

In late 2014, a Super Hornet pilot had a near collision with one of the objects, and an official mishap report was filed. Some of the incidents were recorded on video, including one taken by a plane’s camera in early 2015 that shows an object zooming over the ocean waves as pilots question what they are watching.

The Defense Department has been collecting such reports for more than 13 years as part of a shadowy, little-known Advanced Aerospace Threat Identification Program within the Pentagon. The program analyzed radar data, video footage and accounts provided by the Navy pilots and senior officers.

The program began in 2007 and was largely funded at the request of Harry Reid, the Nevada Democrat who was the Senate majority leader at the time. It was officially shut down in 2012, when the money dried up, according to the Pentagon. But Luis Elizondo, who ran the program at the time, said that he continued it until 2017. After the publication of a New York Times article later that year about the program and criticism from program officials that the government was not forthcoming about reports on aerial phenomena, the Pentagon restarted the program last summer as the Unidentified Aerial Phenomena Task Force.