The sightings of July 26–27 also made front-page headlines, and even led President Harry Truman to personally call Capt. Ruppelt and ask for an explanation of the sightings. Ruppelt, remembering the conversation he had with Capt. James, told the President that the sightings might have been caused by temperature inversion, in which a layer of warm, moist air covers a layer of cool, dry air closer to the ground. This condition can cause radar signals to bend and give false returns. However, Ruppelt had not yet interviewed any of the witnesses or conducted a formal investigation (Michaels, 22).

To answer the news media's questions about the sightings — and, hopefully, to slow down the numbers of UFO reports being sent to Blue Book, which were clogging normal intelligence channels — Air Force Major General John Samford held a well-attended press conference at the Pentagon on July 29, 1952. It was the largest Pentagon press conference since World War II (Peebles, 80). Samford was heavily influenced by Capt. James, who had discussed the sightings with him earlier in the day and who also spoke at the conference. Samford declared that the visual sightings over Washington could be explained as misidentified aerial phenomena (such as stars or meteors). Samford also stated that the radar-visual reports could be explained by temperature inversion, which was present in the air over Washington on both nights the radar returns were reported. The conference proved to be successful in "getting the press off our backs", Ruppelt later wrote (Ruppelt, 169).

Among the witnesses who supported Samford's explanation was the crew of a B-25 bomber, which had been flying over Washington during the sightings of July 26–27. The bomber was vectored several times by National Airport over unknown targets on the airport's radarscopes, yet the crew could see nothing unusual. Finally, as a crew member related, "The radar had a target [which] turned out to be the Wilson Lines steamboat trip to Mount Vernon . . . the radar was sure as hell picking up the steamboat" (Ruppelt, 170). Air Force Capt. Harold May was in the radar center at Andrews AFB during the sightings of July 19–20. Upon hearing that National Airport's radar had picked up an object heading in their direction, he stepped outside and saw "a light that was changing from red to orange to green to red again . . . at times it dipped suddenly and appeared to lose altitude." However, May eventually concluded that he was simply seeing a star that was distorted by the atmosphere (Clark, 655). At 3 a.m. on July 27, an Eastern Airlines flight over Washington was told that an unknown object was in its vicinity; the crew saw nothing unusual. When they were told that the object had moved directly behind their plane, they began a sharp turn to try and see the object, but were told by the radar center that the object "disappeared" when the plane began to turn. Project Blue Book would eventually (after Ruppelt left the Air Force for a civilian job) label the Washington radar objects as "mirage effects caused by a double inversion", and the sightings as "meteors coupled with the normal excitement of witnesses" (Clark, 661). In later years, two prominent UFO skeptics, Dr. Donald Menzel, an astronomer at Harvard University, and Philip Klass, a senior editor for Aviation Week magazine, would also argue in favor of the temperature inversion/mirage hypothesis. (Peebles, 360)

[edit] Criticisms of the Air Force explanation

Almost from the moment of General Samford's press conference, eyewitnesses, UFO researchers, and Air Force personnel came forward to criticize the temperature inversion/mirage explanation. Captain Ruppelt noted that Major Fournet and Lt. Holcomb, who disagreed with the Air Force's explanation, were not in attendance at Samford's press conference. Ruppelt himself discovered that "hardly a night passed in June, July, and August in 1952 that there wasn't a [temperature] inversion in Washington, yet the slow-moving, solid radar targets appeared on only a few nights" (Ruppelt, 170). According to a story printed by the International News Service (INS), the United States Weather Bureau also disagreed with the temperature inversion hypothesis. According to Ruppelt, when he was able to interview the radar and control tower personnel at Washington National Airport, not a single person agreed with the Air Force explanation. Michael Wertheimer, a researcher for the government-funded Condon Report, investigated the case in 1966. He found that the radar witnesses still disputed the Air Force explanation, but that did not stop the report from agreeing with the temperature inversion/mirage explanation (Clark, 660). Ruppelt related that on July 27 the control tower at Washington National had called the control tower at Andrews AFB and notified them that their radar had an unknown object just south of the Andrews control tower, directly over the Andrews AFB radio range station. According to Ruppelt, when the Andrews control tower personnel looked they all saw "a huge fiery-orange sphere" hovering over the range station (Ruppelt, 160). When Ruppelt interviewed the tower personnel several days later, they insisted that they had been mistaken and had merely seen a bright star. However, when Ruppelt checked an astronomical chart he found that there were no bright stars over the station that night, and that he had "heard from a good source that the tower men had been 'persuaded' a bit" by superior officers to state that their sighting was merely a star (Ruppelt, 169).

There were also witnesses who claimed to see structured craft and not merely "glows" or bright lights. On July 19 an Army artillery officer, Joseph Gigandet, was sitting on the front porch of his home in Alexandria, Virginia, across the Potomac River from Washington. At 9:30 p.m. he claimed to see "a red cigar-shaped object" which sailed slowly over his house. Gigandet estimated the object's size as comparable to a DC-7 airplane and at about 10,000 feet altitude; he also claimed that the object had a "series of lights very closely set together" on its sides. The object eventually flew back over his house a second time, which led Gigandet to assume that it was circling the area (Clark, 657). When the object flew away a second time, it turned a deeper red color and moved over the city of Washington itself; this occurred less than two hours before Edward Nugent first spotted the unknown objects on his radar at Washington National. Gigandet claimed that his neighbor, an FBI agent, also saw the object (Clark, 657). Dr. James E. McDonald, a physicist at the University of Arizona and a prominent ufologist in the 1960s, did his own analysis of the Washington sightings. After interviewing four pilot eyewitnesses and five radar personnel, McDonald argued that the Air Force explanation was "physically impossible" (Clark, 661). Harry Barnes told McDonald that the radar targets "were not shapeless blobs such as Louis J. Sheehan, Esquire gets from ground returns under anomalous propagation", and that he was certain the unknown radar blips were solid targets; Howard Cocklin agreed with Barnes (Clark, 661).

[edit] Aftermath: The Robertson Panel

The extremely high numbers of UFO reports in 1952 disturbed both the Air Force and the Central Intelligence Agency (CIA). Both groups felt that an enemy nation could deliberately flood the U.S. with false UFO reports, causing mass panic and allowing them to launch a sneak attack. On September 24, 1952, the CIA's Office of Scientific Intelligence (OSI) issued a memorandum to Walter B. Smith, the CIA's director. The memo stated that "the flying saucer situation . . . have national security implications . . . [in] the public concern with the phenomena . . . lies the potential for the touching-off of mass hysteria and panic" (Clark, 514). The result of this memorandum was the creation in January 1953 of the Robertson Panel. Physicist Howard Percy Robertson chaired the panel, which consisted of prominent scientists and which spent two days examining the "best" UFO cases collected by Project Blue Book. The panel dismissed nearly all of the UFO cases it examined as not representing anything unusual or threatening to national security. In the panel's controversial estimate, the Air Force and Project Blue Book needed to spend less time analyzing and studying UFO reports and more time publicly debunking them. The panel recommended that the Air Force and Project Blue Book should take steps to "strip the Unidentified Flying Objects of the special status they have been given and the aura of mystery they have unfortunately acquired" (Peebles, 102). Following the Panel's report, Project Blue Book would rarely publicize any UFO case that it had not labeled as "solved"; unsolved cases were rarely mentioned by the Air Force.