The US Navy has for the first time confirmed that a set of eerie, grainy videos that appear to show UFOs flying through the sky are indeed real – and contain phenomena the military still cannot identify.

The sensational footage in question – which began appearing in media outlets including The New York Times from December 2017 onward – was captured by US Navy pilots, and sourced by a private research group, To The Stars Academy of Arts & Science (TTSA), founded by rock musician Tom DeLonge.

While this footage was at the time reportedly declassified, that appears to now not be the case, at least according to intelligence website The Black Vault.

A spokesperson for the US Navy has allegedly told the site that the videos are authentic – the first official confirmation by the military that the footage depicts flying phenomena that can't be identified, although the abbreviation UFO (unidentified flying object) is no longer in official use.

"The Navy designates the objects contained in these videos as unidentified aerial phenomena," Joseph Gradisher, the official spokesperson for the Deputy Chief of Naval Operations for Information Warfare, reportedly told John Greenewald at The Black Vault.

"The 'Unidentified Aerial Phenomena' terminology is used because it provides the basic descriptor for the sightings / observations of unauthorised / unidentified aircraft / objects that have been observed entering / operating in the airspace of various military-controlled training ranges."

To be clear, this doesn't mean the videos show aliens, or that the US Navy is suggesting that's what they are. It only means the unidentified aerial phenomena (UAPs) are objects that cannot be identified.

The US Navy has previously used another descriptor for these strange objects: Anomalous Aerial Vehicles (AAVs), and leaked Pentagon documentation shows the US military has studied the mysterious phenomena for several years, although they don't exactly broadcast it.

"The Navy has not released the videos to the general public," Gradisher said, suggesting the torrent of media coverage surrounding the eerie videos was never part of the Pentagon's plan.

We're still no closer to knowing what these things really are, but even the change in military terminology – and the public confirmation of the unidentified phenomena – has surprised some.

"That the Navy is using the term 'Unidentified Aerial Phenomena' shows that they have broadened what is expected to be reported by US fighter pilots to investigate anything unknown in their airspace that in the past has been connected with a stigma," UFO expert and researcher Roger Glassel told Motherboard.

"If these investigations are due to an interest in finding the cause of the UFO phenomenon - in a ufology sense - or due to reducing flight hazards or to counter unidentified intrusions by known adversaries, and readiness for technological surprise, remains to be seen."