Top security officials in the U.S. remain stumped after an unknown fleet of drones breached restricted military airspace for 17 straight days last December.

A new report, first detailed by the Wall Street Journal, says military personnel reported witnessing the mysterious fleet over a stretch of land at Langley Air Force Base along Virginia’s shore. The drones would appear in the sky about 45 minutes to an hour after sunset each night.

Former air force general Mark Kelly was first made aware of the drone sightings in December 2023, the outlet reports. They showed up for 17 consecutive days, with officials at the Pentagon suspecting they might have been deployed by Chinese or Russian agents to spy on the American military.

But because the drones did not pose an imminent threat, and officials at the time weren’t certain if they were being used for nefarious purposes or perhaps it was just wayward hobbyists, the military was prohibited from shooting them down, citing potential risks to troops and civilians.

The White House met with the Defense Department, the FBI and the Pentagon’s UFO office, as well as outside experts, to discuss what to do about the mystery formations, but several solutions, including shooting nets to catch the drones and using electronic signals to jam their navigation systems, also did not make the cut.

According to the Wall Street Journal, the phalanx of drones flew in a precise pattern along the same route each night.

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Kelly described the first drone he saw as roughly 20 feet long and flying at more than 100 kilometres an hour, at an altitude of roughly 3,000 to 4,000 feet. Kelly said as many as a dozen more drones followed behind and said the drones looked like constellations in the night sky.

It was such an alarming breach that Langley officials cancelled their nighttime training missions and moved their F-22 fighter jets to another base.

A US Air Force Lockheed Martin F-22 Raptor stealth fighter aircraft performs a demonstration flight during the inaugural Trilateral Exercise between the US Air Force, United Kingdom's Royal Air Force and the French Air Force at Joint Base Langley-Eustis in Hampton, Virginia, December 15, 2015.

FILE – A U.S. Air Force Lockheed Martin F-22 Raptor stealth fighter aircraft performs a demonstration flight during the inaugural Trilateral Exercise between the U.S. Air Force, the United Kingdom’s Royal Air Force and the French Air Force at Joint Base Langley-Eustis in Hampton, Va., Dec. 15, 2015.

Saul Loeb / AFP via Getty Images

According to Fox News, two months before the fleet emerged over Langley, five mysterious drones reportedly breached restricted airspace over a government nuclear weapons experiment site in Nevada.

The outlet reports that four of the drones were detected by the Energy Department’s Nevada National Security Site outside Las Vegas, while the fifth was spotted by employees. The Defense Department has yet to publicly state who is behind these drones.

According to the Federal Aviation Administration (FAA) website, “reports of unmanned aircraft (UAS) sightings from pilots, citizens and law enforcement remain high.”

The FAA says it receives more than 100 UAS reports a month.

“The agency wants to send out a clear message that operating drones around airplanes, helicopters and airports is dangerous and illegal. Unauthorized operators may be subject to stiff fines and criminal charges, including possible jail time,” the website states, reminding drone operators to review the rules about where and when a drone is safe to fly.

From July to September of this year, the FAA recorded more than 400 UAS sightings.