CIA Behind UFO Sightings in 1950s and 1960s

The agency finally takes credit for mysterious flying objects spotted more than half a century ago. Reuters

As 2014 comes to a close, even the CIA is pushing out "best of the year" lists.

Starting on December 22, the agency began sharing links to the ten most-popular articles they've posted on Twitter this year. Number one, which was tweeted on Monday, directs readers to a 272-page document from 1998 entitled "The CIA and the U-2 Program, 1954-1974."

The document, which the CIA originally tweeted in July, details how its U-2 spy plane program worked and how the program was responsible for the majority of UFO sightings during the time it was active.

Through the program, the CIA secretly flew U-2 spy planes at altitudes of 60,000 feet above target countries, like the Soviet Union. At the time, most commercial flights flew between 10,000 and 20,000 feet, and military aircrafts flew below 40,000 feet. Most people thought man couldn't reach such heights and assumed alien life was behind the mysterious objects in the sky.

"Consequently, once U-2s started flying at altitudes above 60,000 feet, air-traffic controllers began receiving increasing numbers of UFO reports," the document reads.

The CIA cross-referenced UFO sightings and U-2 flight logs, which "enabled the investigators to eliminate the majority of the UFO reports" the document reads. But the agency never revealed to the terrified people the truth behind the mysterious flying objects, until this year. Instead, investigators from Project BLUE BOOK, the Air Force program tasked with investigating UFO reports, attempted to attribute the sightings to natural phenomena.

The report was part of a series of documents that were declassified in 2013, along with those that detailed the existence of Area 51 in Nevada.

Other popular articles the agency shared this year on Twitter that made their top 10 list include:

#4 most read on our #Bestof2014 list: #pigeon missions are still classified.

— CIA (@CIA) December 26, 2014

#3 most read on our #Bestof2014 list: Happy 90th to our former boss @GeorgeHWBush!

— CIA (@CIA) December 26, 2014

#2 most read on our #Bestof2014 list: A Day in the Life of a CIA Operations Center Officer

— CIA (@CIA) December 29, 2014