UFO sightings in the 1960s were probably top-secret flight tests of advanced American spy planes and spacecraft, a Pentagon report has found.

The highly anticipated report, which was submitted to Congress on Friday, found no evidence that the US government had covered up the existence of aliens.

Most sightings of UFOs, described in the report as “unidentified anomalous phenomena” (UAPs), were actually ordinary objects, the report said.

“However, we ᴀssess that some portion of these misidentifications almost certainly were a result of the surge in new technologies that observers would have understandably reported as UFOs,” it said.

The landmark report is seen as the Pentagon’s most definitive response to decades-old questions and conspiracy theories claiming that it has information on extraterrestrial life or technology.

“All investigative efforts, at all levels of classification, concluded that most sightings were ordinary objects and phenomena and the result of misidentification,” Maj Gen Pat Ryder told reporters.

Maj Gen Ryder said that the Pentagon had approached the report with an open mind.

The Pentagon’s All-domain Anomaly Resolution Office (AARO) concluded that even the sightings it was not able to solve could be identified if better data were available.

“Most of these cases also could be identified and resolved as ordinary objects or phenomena,” it said.

Roughly two out of five Americans believe in aliens, according to a 2023 Ipsos poll, while one in 10 claim to have seen one.

A Gallup poll in 2019 found that 68 per cent of Americans believe the US government knows “more about UFOs than it is telling us”.

The AARO concluded that the report was unlikely to dispel the widespread belief that the government is hiding the truth about the existence of aliens.

“The proliferation of television programmes, books, movies, and the vast amount of internet and social media content centred on UAP-related topics most likely has influenced the public conversation on this topic, and reinforced these beliefs within some sections of the population,” the report said.

“Aside from hoaxes and forgeries, misinformation and disinformation is more prevalent and easier to disseminate now than ever before, especially with today’s advanced pH๏τo, video and computer-generated imagery tools.”

To produce the report, the AARO examined classified and unclassified files and reviewed all official government investigations into UFOs dating back to the end of the Second World War.

Researchers identified a “spike” in UFO sightings between 1952 and 1957, then again in 1960.

These spikes, the report concluded, “most likely are attributed to observers unknowingly having witnessed new technological advancements and testing and reporting them as UFOs”.

The report also includes a list of declassified aerospace programmes that it said “probably were ᴀssociated with erroneous UAP reporting”.

Among them were several experimental aircraft including the U-2 spy plane and its successor, the SR-71 Blackbird, as well as the Mercury, Gemini and Apollo space programmes. It also mentioned later programmes for stealth aircraft and drones.

Investigators also examined a sample from an alleged extraterrestrial crash that was acquired from a private UFO investigating organisation.

Testing revealed that the sample to be “a manufactured, terrestrial alloy” of magnesium, zinc and bismuth that “does not represent off-world technology or possess any exceptional qualities”.

The report also directly challenges whistleblowers who have claimed that the government is concealing evidence of aliens or extraterrestrial material from the public.

In July, David Grusch, a former US intelligence official, told Congress that he was “absolutely certain” that the government had recovered crashed alien spacecraft and claimed that “non-human biologics” had also been found.

Those comments came at a hearing in which a former US Navy pilot claimed he had seen a UFO and accused the government of downplaying the threat they posed.

The Pentagon said that it found no evidence to back up any of the claims made by former officials.

The AARO plans to release a second report examining more recent sightings.

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