Pilot Francis Gary Powers (R) speaks with U-2 designer Kelly Johnson in this 1966 U.S. Air Force handout photo. Powers was a USAF fighter pilot recruited by the CIA in 1956 to fly civilian U-2 missions deep into Russia. Powers and other USAF Reserve pilot
Pilot Francis Gary Powers (R) speaks with U-2 designer Kelly Johnson in this 1966 U.S. Air Force handout photo. Powers was a USAF fighter pilot recruited by the CIA in 1956 to fly civilian U-2 missions deep into Russia. Powers and other USAF Reserve pilots resigned their commissions to become civilians. REUTERS/U.S. Air Force/Handout

There were no flying aliens, according to the U.S. Central Intelligence Agency. The CIA is claiming responsibility on at least half of the UFO sightings reported in the ‘50s.

The CIA explained on Monday the connection between the agency’s testing of planes and the increased reported sightings of unidentified flying objects around the late 1950s until the ‘60s. As it reported, the flying things in the sky weren’t aliens, but its U-2 spy plane that was flying at 60,000 feet altitude and higher.

#1 most read on our #Bestof2014 list: Reports of unusual activity in the skies in the '50s? It was us. http://t.co/BKr81M5OUN (PDF 9.26MB)

— CIA (@CIA) December 29, 2014

Back then, people didn’t believe planes could fly at such high altitude. Most commercial airlines only flew between 10,000 and 20,000 feet, while military aircraft could fly below 40,000 feet. So when the CIA started flying U-2 planes above 60,000 feet, UFO sightings reports increased.

“High-altitude testing of the U-2 soon led to an unexpected side effect – a tremendous increase in reports of unidentified flying objects (UFOs),” the CIA wrote in the report, adding that when the plane flew from an altitude of 60,000 feet when the sun dropped below the horizon of an airliner, its silver wings would catch and reflect the rays of the sun, which would perhaps looked like fiery objects to others.

“Even during daylight hours, the silver bodies of the high-flying U-2s could catch the sun and cause reflections or glints that could be seen at lower altitudes and even on the ground. At this time, no one believed manned flight was possible above 60,000 feet, so no one expected to see an object so high in the sky.”

The CIA knew that the people assumed its flying spy planes were aliens, but it couldn’t inform the public of the truth. After cross-referencing the purported UFO sightings with the schedule of the U-2 flights, investigators eliminated the majority of the UFO reports.

U-2 planes were developed to capture photos of the country’s enemy targets from secret bases in California and Nevada. They flew across and country and even outside in other countries’ bases, including in Britain, West Germany and Taiwan. Today, U-2 planes are flown by the United States Air Force.