By 1948, UFO fever was sweeping the nation and sightings multiplied. The U.S. Air Force began an investigation. The conclusion: At least some UFOs were probably sophisticated spy aircraft. At the time, the U.S. and the Soviet Union were engaged in the Cold War (1947-1991), a period of tension and hostility between the two superpowers. So it made sense to U.S. officials that the Soviets were spying by air.
Still, the number of UFO reports kept climbing. In 2007, the U.S. government secretly started a special program, led by Elizondo, to investigate the sightings. Sometimes, what people thought were UFOs turned out to be optical illusions—tricks of the eye—caused by sunlight or clouds (see photo above). Other times, they were drones or special military planes.
But some UFOs cannot easily be explained away, says Elizondo. For example, U.S. Navy and Air Force pilots have described seeing odd-shaped objects without visible wings or engines that move at sharp angles and seem to defy gravity.
“Whatever they are,” says Elizondo, “they do not fit our current understanding of aircraft technology.”