NASA
NASA frequently fields questions in regard to the ETH and UFOs. As of 2006, its official standpoint was that ETH has a lack of empirical evidence.
“no one has ever found a single artifact, or any other convincing evidence for such alien visits”. David Morrison.
“As far as I know, no claims of UFOs as being alien craft have any validity — the claims are without substance, and certainly not proved”. David Morrison
Despite public interest, NASA considers the study of ETH to be irrelevant to its work because of the number of false leads that a study would provide, and the limited amount of usable scientific data that it would yield.
Conspiracy
A frequent concept in ufology and popular culture is that the true extent of information about UFOs is being suppressed by some form of conspiracy of silence, or by an official cover-up that is acting to conceal information.
In 1968, American engineer James Harder argued that significant evidence existed to prove UFOs “beyond reasonable doubt,” but that the evidence had been suppressed and largely neglected by scientists and the general public, thus preventing sound conclusions from being reached on the ETH.
“Over the past 20 years a vast amount of evidence has been accumulating that bears on the existence of UFOs. Most of this is little known to the general public or to most scientists. But on the basis of the data and ordinary rules of evidence, as would be applied in civil or criminal courts, the physical reality of UFOs has been proved beyond a reasonable doubt.” J A Harder
A survey carried out by Industrial Research magazine in 1971 showed that more Americans believed the government was concealing information about UFOs (76%) than believed in the existence of UFOs (54%), or in ETH itself (32%).
Documents and investigations regarding ETH

Other private or governmental studies, some secret, have concluded in favor of the ETH, or have had members who disagreed with official conclusions against the conclusion by committees and agencies to which they belonged. The following are examples of sources that have focused specifically on the topic:
In 1967, Greek physicist Paul Santorini, a Manhattan Project scientist, publicly stated that a 1947 Greek government investigation into the European Ghost rockets of 1946 under his lead quickly concluded that they were not missiles. Santorini claimed the investigation was then quashed by military officials from the U.S., who knew them to be extraterrestrial, because there was no defense against the advanced technology and they feared widespread panic should the results become public.
A 1948 Top Secret USAF Europe document states that Swedish air intelligence informed them that at least some of their investigators into the ghost rockets and flying saucers concluded they had extraterrestrial origins: “…Flying saucers have been reported by so many sources and from such a variety of places that we are convinced that they cannot be disregarded and must be explained on some basis which is perhaps slightly beyond the scope of our present intelligence thinking. When officers of this Directorate recently visited the Swedish Air Intelligence Service… their answer was that some reliable and fully technically qualified people have reached the conclusion that ‘these phenomena are obviously the result of a high technical skill which cannot be credited to any presently known culture on earth.’ They are therefore assuming that these objects originate from some previously unknown or unidentified technology, possibly outside the earth.”
In 1948, the USAF Project Sign produced a Top Secret Estimate of the Situation, concluding that the ETH was the most likely explanation for the most perplexing unexplained cases. The study was ordered destroyed by USAF chief of staff General Hoyt Vandenberg, citing lack of proof. Knowledge of the existence of the Estimate has come from insiders who said they read a surviving copy, including later USAF Project Blue Book head Edward J. Ruppelt and astronomer and USAF consultant J. Allen Hynek.
West Germany, in conjunction with other European countries, conducted a secret study from 1951 to 1954, also concluding that UFOs were extraterrestrial. This study was revealed by German rocketry pioneer Hermann Oberth, who headed the study and who also made many public statements supporting the ETH in succeeding years. At the study’s conclusion in 1954, Oberth declared, “These objects (UFOs) are conceived and directed by intelligent beings of a very high order. They do not originate in our solar system, perhaps not in our galaxy.” Soon afterwards, in an article in The American Weekly, October 24, 1954, Oberth wrote “It is my thesis that flying saucers are real and that they are space ships from another solar system. I think that they possibly are manned by intelligent observers who are members of a race that may have been investigating our earth for centuries…”
The CIA started their own internal scientific review the following day. Some CIA scientists were also seriously considering the ETH. An early memo from August was very skeptical, but also added, “…as long as a series of reports remains ‘unexplainable’ (interplanetary aspects and alien origin not being thoroughly excluded from consideration) caution requires that intelligence continue coverage of the subject.” A report from later that month was similarly skeptical but nevertheless concluded “…sightings of UFOs reported at Los Alamos and Oak Ridge, at a time when the background radiation count had risen inexplicably. Here we run out of even ‘blue yonder’ explanations that might be tenable, and we still are left with numbers of incredible reports from credible observers.” A December 1952 memo from the Assistant CIA Director of Scientific Intelligence (O/SI) was much more urgent: “…the reports of incidents convince us that there is something going on that must have immediate attention. Sightings of unexplained objects at great altitudes and traveling at high speeds in the vicinity of U.S. defense installation are of such nature that they are not attributable to natural phenomena or known types of aerial vehicles.” Some of the memos also made it clear that CIA interest in the subject was not to be made public, partly in fear of possible public panic. (Good, 331–335)
The CIA organized the January 1953 Robertson Panel of scientists to debunk the data collected by the Air Force’s Project Blue Book. This included an engineering analysis of UFO maneuvers by Blue Book (including a motion picture film analysis by Naval scientists) that had concluded UFOs were under intelligent control and likely extraterrestrial.
Extraterrestrial “believers” within Project Blue Book included Major Dewey Fournet, in charge of the engineering analysis of UFO motion, who later became a board member on the civilian UFO organization NICAP. Blue Book director Edward J. Ruppelt privately commented on other firm “pro-UFO” members in the USAF investigations, including some Pentagon generals, such as Charles P. Cabell, USAF Chief of Air Intelligence who, angry at the inaction and debunkery of Project Grudge, dissolved it in 1951, established Project Blue Book in its place, and made Ruppelt director. In 1953, Cabell became deputy director of the CIA. Another defector from the official Air Force party line was consultant J. Allen Hynek, who started out as a staunch skeptic. After 20 years of investigation, he changed positions and generally supported the ETH. He became the most publicly known UFO advocate scientist in the 1970s and 1980s.
The first CIA Director, Vice Admiral Roscoe H. Hillenkoetter, stated in a signed statement to Congress, also reported in The New York Times, February 28, 1960, “It is time for the truth to be brought out… Behind the scenes high-ranking Air Force officers are soberly concerned about the UFOs. However, through official secrecy and ridicule, many citizens are led to believe the unknown flying objects are nonsense… I urge immediate Congressional action to reduce the dangers from secrecy about unidentified flying objects.” In 1962, in his letter of resignation from NICAP, he told director Donald Keyhoe, “I know the UFOs are not U.S. or Soviet devices. All we can do now is wait for some actions by the UFOs.”
Although the 1968 Condon Report came to a negative conclusion (written by Condon), it is known that many members of the study strongly disagreed with Condon’s methods and biases. Most quit the project in disgust or were fired for insubordination. A few became ETH supporters. Perhaps the best known example is David Saunders, who in his 1968 book UFOs? Yes lambasted Condon for extreme bias and ignoring or misrepresenting critical evidence. Saunders wrote, “It is clear… that the sightings have been going on for too long to explain in terms of straightforward terrestrial intelligence. It’s in this sense that ETI (Extra Terrestrial Intelligence) stands as the ‘least implausible’ explanation of ‘real UFOs’.”
In 1999, the private French COMETA report (written primarily by military defense analysts) stated the conclusion regarding UFO phenomena, that a “single hypothesis sufficiently takes into account the facts and, for the most part, only calls for present-day science. It is the hypothesis of extraterrestrial visitors.” The report noted issues with formulating the extraterrestrial hypothesis, likening its study to the study of meteorites, but concluded that although it was far from the best scientific hypothesis, “strong presumptions exist in its favour”. The report also concludes that the studies it presents “demonstrate the almost certain physical reality of completely unknown flying objects with remarkable flight performances and noiselessness, apparently operated by intelligent [beings] … Secret craft definitely of early origins (drones, stealth aircraft, etc.) can only explain a minority of cases. If we go back far enough in time, we clearly perceive the limits of this explanation.”
Jean-Jacques Velasco, the head of the official French UFO investigation SEPRA, wrote a book in 2005 saying that 14% of the 5800 cases studied by SEPRA were utterly inexplicable and extraterrestrial in origin. Yves Sillard, the head of the new official French UFO investigation GEIPAN and former head of the French space agency CNES, echoes Velasco’s comments and adds the U.S. is guilty of covering up this information. However this is not the official public posture of SEPRA, CNES, or the French government. (The CNES placed their 5,800 case files on the Internet starting March 2007.)
Official White House position
In November 2011, the White House released an official response to two petitions asking the U.S. government to acknowledge formally that aliens have visited Earth and to disclose any intentional withholding of government interactions with extraterrestrial beings. According to the response, “The U.S. government has no evidence that any life exists outside our planet, or that an extraterrestrial presence has contacted or engaged any member of the human race.”[46][47] Also, according to the response, there is “no credible information to suggest that any evidence is being hidden from the public’s eye.”[46][47] The response further noted that efforts, like SETI, the Kepler space telescope and the NASA Mars rover, continue looking for signs of life. The response noted “odds are pretty high” that there may be life on other planets but “the odds of us making contact with any of them—especially any intelligent ones—are extremely small, given the distances involved.”