The story of Roswell, New Mexico looms large in any discussion of UFOs.
In 1947, an unknown craft crashed in a desert in the American southwest, spurring all sorts of theories about secret government sites, stashed extraterrestrial bodies, live alien prisoners, and more.
But the truth is most likely mundane.
In the late 1940s, as the Cold War ramped up, the United States was looking for ways to monitor the Soviet Union. The US had dropped the first two atomic bombs on Japan in 1945, and was wary about the USSR's dedication to developing their own atomic weapons (they would succeed in 1949). One attempt to monitor the Soviets was the US Air Force's Project Mogul, which involved launching weather balloons that were affixed with microphones and radio transmitters to listen for potential nuclear tests.
The project was eventually scrapped, but not before one such weather balloon crashed near Roswell, New Mexico.
In 1997, around the 50th anniversary of the Roswell Incident, the Air Force publicly offered this explanation of the incident.
The Air Force also had an explanation for the claim that alien bodies had been recovered from the crash site. Around the same time as Project Mogul, the US military was developing specialized parachutes and ejection seats for its high-speed, high-altitude aircraft. Early tests of these seats involved pushing dummies out of planes to see how much a human body would spin during the descent. Hence, mangled, hairless humanoid "remains" in the desert.
However, even after the information about these tests came out, UFO enthusiasts were not convinced, as the Washington Post reported.