Between 1947 and 1969, the US Air Force meticulously recorded over 10,000 incidents involving Unidentified Flying Objects. Inside the Project Blue Book archive, which has recently been put online, witnesses described objects as “concave as a soup bowl”, “onion-shaped” and resembling “a frosty silvery football” shooting across the sky.

Here are four of the most extraordinary accounts: …

In 1948, the US government launched several inquiries into UFO sightings, which many believed were sparked by Cold War paranoia.

In what became known as ‘Project Blue Book,’

more than 12,000 encounters with UFOs were looked into by the Air Force.

Now, decades after the files were closed, the microfilms have been made available online for free – allowing anyone to re-examine the evidence.