This 1952 comic shows how the local population sensationalized the blips spotted on the National Airport radar.

Air Staff / National Archives, Records of Headquarters U.S. Air Force

On Saturday, July 19, 1952, the crew at Washington National Airport saw something unusual, according to the next day’s national headlines. “Saucers Swarm Over Capitol,” read the front page of the Cedar Rapids Gazette. That headline, among many others that day, expressed an anxious curiosity as to why a group of unidentified flying objects spent their Saturday night hovering over D.C. just five years after the now-legendary incident in Roswell, New Mexico.

While other sightings may have eyewitness testimony or indirect evidence of the objects moving through our world, these UFOs spotted at National Airport were undeniably present on a radar.

It’s the reaction to the blips on the radar screen that really sets D.C.’s alleged alien incident apart, says Dr. Kevin Randle, a prominent ufologist and author of Invasion Washington: UFOs Over the Capitol. At one point, Randle says, fighter planes tried to head out to the UFOs’ locations.

“There was an attempted intercept,” he says. “But the planes got there and everything was gone.”

One week later, on Saturday, July 26, the same crew was working at the radar facility, Randle says. This time around, though, they were prepared for the potential of seeing UFOs. Sure enough, the blips reappeared on the radar screen, and the crew called for another interception.

“It seemed that every time the fighters showed up, all the uncorrelated blips disappeared from the radar. In other words, all the UFOs went away,” Randle says. “When the fighters returned to base, the blips came back.”

The incidents over D.C. was one of a number of UFO sightings across the country that the Air Force investigated via Project Blue Book, a study that began five years prior in Wright-Patterson Air Force Base in Dayton, Ohio. A code name for the country’s most well-known investigation into UFOs, it eventually became a household name for alien enthusiasts.

The investigation staff tracked sightings and wrote summaries of reports from around the country, according to the National Archives. In commemoration of the 50th anniversary of the investigation’s end, declassified documents from Project Blue Book are now on display in the East Rotunda Gallery of the National Archives.

Project Blue Book was a systematic attempt to follow up on UFO sightings, says Rebecca Charbonneau, a Ph.D. candidate and Gates Cambridge scholar at the Department of History and Philosophy of Science at the University of Cambridge. She is an expert on the search for extraterrestrial intelligence, also known as SETI.

With the Cold War looming, the 1950s was a fascinating time for these sightings to have taken place, she says.

While the Space Race did not officially begin until the launch of Sputnik in 1957, tensions with the Soviet Union were increasing in the early 1950s, when American surveillance technology was nowhere near as effective as it is now. From a national security standpoint, Charbonneau says, Project Blue Book was more than just a perfect future X-Files fodder: it was a way to see if these UFOs could actually be technologically advanced Soviet aircraft.

“If you are, say, in a remote outpost in Alaska, and you’re seeing something funky in the sky, the U.S. Air Force wants to know about that,” Charbonneau says.

Statistics supplied by the Archives show that 12,618 UFO sightings were reported to Project Blue Book between the launch of the program in 1947 and its end in 1969. Of those, just over 700 of the flying objects they investigated could not be identified.

In the end, according the Archives, Project Blue Book had three major conclusions: none of the UFO sightings seemed to pose a threat to United States national security; the technology present in all UFO sightings did not suggest otherworldly advancements to aircraft technology of the day; and there was no evidence suggesting that the UFOs were from outer space.

The D.C. sightings in July of 1952 were no exception. A few months after those reports, the Central Intelligence Agency was ready to explain what had happened. In January 1953, the agency sponsored a panel to announce their findings.

The official explanation? Temperature inversions, which occur when a layer of hot air moves over a layer of cool air and bends radar beams.

Randle’s book highlights the relationship between the crewmen who witnessed the UFOs and prominent UFO debunker Dr. Donald Menzel, a Harvard University astronomer. As one of the major skeptics of the D.C. case, he communicated regularly with the witnesses to better understand what they had seen in the sky and determine just what those radar blips were.

“These are the guys who are there watching the stuff,” Randle says, in reference to the National Airport crewmen. “Then you have the so-called experts come in and say, ‘Well, this is what you really saw.’”

In the end, Menzel concluded that the radar had been detecting changes in the weather, not extraterrestrials: “A thorough study of the situation showed that inversions of both temperature and humidity must have been present.”

Mere radar mistakes or actual little green men, D.C. was in the throes of UFO excitement. The Washington Post regularly reported on the sightings. “All’s Quiet Along the Potomac On the Flying Saucer Front,” read one late July 1952 headline. Another reported on a later sighting in Northwest D.C. from August: “D.C. Girl Sees Saucer Float Under Clouds.” The American University student paper The Eagle also reported sightings over the campus in mid-October.

But UFO fever didn’t strike everyone in the region.

“Why all the whoop-de-doo about flying saucers?” wrote Vienna resident D.V. Gallory in a letter to the editor published in the Washington Post on August 15, 1952. “I don’t see anything astounding about them at all. The air and the sky around us are full of wonders much more spectacular than saucers.”