UFO and UAP

Flying saucer, the 1947 press coinage that preceded both, survives as a popular label. The succession from saucer to UFO to UAP tracks the official investigations, which have run in two phases: the US Air Force projects of 1947 to 1969, and the Pentagon, intelligence community, and NASA programs active since 2007.

What the two terms mean

UFO: unidentified flying object

The Air Force introduced unidentified flying object as a working replacement for flying saucer and flying disc. Edward J. Ruppelt, the Air Force captain who directed Project Blue Book from March 1952 to late 1953, is generally credited with establishing the term, on the grounds that the saucer labels were misleading when applied to objects of every conceivable shape and performance.¹ In official usage a UFO was any aerial object that trained analysts could not identify, a definition that made no reference to spacecraft. In popular usage the acronym drifted toward meaning alien craft specifically, and the label came to carry a stigma that discouraged pilots from reporting what they saw.²

UAP: from aerial to anomalous

US agencies adopted unidentified aerial phenomena as the Navy built reporting procedures in 2019 and the Pentagon established the UAP Task Force in 2020.² The stated logic was stigma reduction: a neutral term was expected to let military and commercial aircrews file reports without fearing ridicule or professional damage.² In December 2022 the Pentagon announced that UAP would stand for unidentified anomalous phenomena, a change codified in the fiscal year 2023 National Defense Authorization Act, so that the category covers objects observed in the air, in space, underwater, and moving between domains. Undersecretary of Defense for Intelligence and Security Ronald Moultrie stated: "This new terminology expands the scope of UAP to include submerged and trans-medium objects."³

Historical development

Kenneth Arnold and the flying saucer, 1947

On June 24, 1947, private pilot Kenneth Arnold reported nine shiny objects flying in formation near Mount Rainier, Washington, and estimated their speed at roughly 1,200 miles per hour, far beyond any aircraft of the day.⁴ The saucer language came from the press, not from Arnold's description of shape. Bill Bequette's Associated Press wire story described "nine bright saucer-like objects," and within days flying saucer headlines were running nationwide.⁵ Arnold maintained that he had been misquoted, saying "I said that they flew in a saucer-like fashion," a reference to motion rather than form.⁴ Several hundred similar reports followed in the United States and abroad within weeks.⁴

Projects Sign, Grudge, and Blue Book, 1947 to 1969

The Air Force opened its first formal investigation, Project Sign, in late 1947.⁶ According to Ruppelt's later account, Sign's analysts produced a 1948 intelligence estimate concluding that the objects were real craft of likely extraterrestrial origin, and Chief of Staff Hoyt Vandenberg rejected it for lack of physical proof.⁶ Project Grudge replaced Sign at the end of 1948 and took a posture Ruppelt described as debunking.⁶ Project Blue Book followed in March 1952, based at Wright-Patterson Air Force Base with Ruppelt as its first director, and the term unidentified flying object entered service use during his tenure.^6,1 In 1953 an advisory panel led by physicist H. P. Robertson recommended campaigns to lessen public interest in the subject.⁶ By its termination Blue Book had collected 12,618 reports, of which 701 remained unidentified after analysis.⁶

The Condon Report and the end of Blue Book

In 1966 the Air Force contracted the University of Colorado to run an independent review under physicist Edward Condon, formally titled the Scientific Study of Unidentified Flying Objects.⁷ The committee delivered its 1,485-page report in November 1968, and it was released publicly in January 1969. Condon wrote that "further extensive study of UFOs probably cannot be justified in the expectation that science will be advanced thereby," and a National Academy of Sciences panel endorsed the conclusion.⁷ The Air Force closed Project Blue Book on December 17, 1969, ending the sequence of official projects begun in 1947, and no comparable public US program followed for almost four decades.^6,7

Hynek's classification system

Astronomer J. Allen Hynek served as scientific consultant to Sign, Grudge, and Blue Book from 1948, beginning with the expectation that conventional explanations would cover the reports and concluding over time that they deserved serious study.⁸ His 1972 book The UFO Experience introduced the classification still in general use. Distant sightings divide into nocturnal lights, daylight discs, and radar-visual cases.⁹ Close encounters divide into three kinds: a first kind, with an object within roughly 500 feet of the witness, a second kind, with physical effects on the environment or the witness, and a third kind, in which witnesses report occupants in or near the object.^8,9 Hynek founded the Center for UFO Studies in 1973 to continue civilian casework after Blue Book closed.⁸

The return of official investigation

AATIP and the December 2017 disclosure

Between 2007 and 2012 the Department of Defense funded the Advanced Aerospace Threat Identification Program, an unpublicized effort of roughly 22 million dollars initiated by Senator Harry Reid.¹⁰ It stayed out of public view until December 16, 2017, when the New York Times published an account by Ralph Blumenthal, Helene Cooper, and Leslie Kean, accompanied by cockpit video recorded by Navy aircrews.¹⁰ Luis Elizondo, a former director of the effort, had left government service and helped bring the material forward.¹⁰ The Navy later confirmed the videos were authentic and referred to the objects in them as unidentified aerial phenomena.¹⁰

The UAP Task Force and the 2021 ODNI assessment

The Navy created the first standardized UAP reporting mechanism in March 2019, and the Air Force adopted it in November 2020.¹¹ In August 2020 the Deputy Secretary of Defense approved the Unidentified Aerial Phenomena Task Force to detect, analyze, and catalog UAP that could pose a national security threat.¹² The Office of the Director of National Intelligence published an unclassified preliminary assessment on June 25, 2021.¹¹ It covered 144 reports from US government sources between 2004 and 2021 and identified exactly one with high confidence, a large deflating balloon.¹¹ It sorted potential explanations into five categories: airborne clutter, natural atmospheric phenomena, US government or industry developmental programs, foreign adversary systems, and a residual category labeled other.¹¹ In 18 incidents, observers reported unusual movement patterns or flight characteristics.¹¹

AARO and the change to anomalous, 2022 to present

The Pentagon replaced the task force with the All-domain Anomaly Resolution Office on July 20, 2022, first directed by Sean Kirkpatrick, with a mandate spanning air, sea, space, and land.¹² The fiscal year 2023 National Defense Authorization Act, passed that December, codified the office and the anomalous redefinition and ordered a review of US government records dating back to January 1, 1945.³ The resulting Historical Record Report, released March 6, 2024, stated that AARO found no empirical evidence that any investigated sighting represented off-world technology, no reverse-engineering program withheld from Congress, and that most sightings involved misidentification of ordinary objects.¹² Jon Kosloski was named director in August 2024.¹²

NASA's study and the 2023 congressional hearing

NASA convened a 16-member independent study team chaired by David Spergel, president of the Simons Foundation, and released its report on September 14, 2023. The team found the existing observations too limited in quality to "draw firm scientific conclusions about their nature" and recommended that the agency apply its satellite assets and machine learning tools to the problem. NASA simultaneously named Mark McInerney as Director of UAP Research.¹³

On July 26, 2023, a national security subcommittee of the House Oversight Committee heard testimony from retired Navy commander David Fravor, former Navy pilot Ryan Graves, and retired Air Force intelligence officer David Grusch.¹⁴ Fravor recounted a 2004 encounter off San Diego, and Graves described a 2014 incident off Virginia Beach and told the panel that "the stigma attached to UAP is real and powerful."^14,2 Grusch testified that the United States has operated a multi-decade program to retrieve and reverse engineer crashed craft and that non-human "biologics" had been recovered, noting that his testimony rested on interviews with other officials rather than direct observation.¹⁴ The Defense Department responded that it had found no "verifiable information to substantiate claims that any programs regarding the possession or reverse-engineering of extraterrestrial materials have existed."¹⁴

Documentation and research record

The modern record is built from standardized aircrew reporting channels, military sensor data, congressional testimony, and a series of published annual assessments, layered on the Blue Book case files of the earlier era. The 2021 preliminary assessment covered 144 reports from US government sources and resolved one case with high confidence.¹¹ ODNI's 2022 annual report catalogued 510 reports in total, and of 366 newly received reports it initially characterized 163 as balloon or balloon-like entities, 26 as unmanned aircraft systems, and 6 as clutter, leaving 171 uncharacterized.¹⁵

AARO's fiscal year 2024 consolidated report, covering May 1, 2023 to June 1, 2024, recorded 757 new reports and a cumulative total of 1,652 as of October 2024.¹⁶ During the period 49 cases were resolved and a further 243 were recommended for closure, all as balloons, birds, unmanned aircraft, satellites, or ordinary aircraft. Twenty-one cases were judged to merit further analysis, and 444 were placed in an active archive for lack of usable data.¹⁶ The report states: "To date, AARO has discovered no evidence of extraterrestrial beings, activity, or technology."¹⁶ AARO director Jon Kosloski said at its release that "interesting cases" remain that he does "not understand."¹⁷

The limits of the record recur across every official review. Observations are brief and rarely instrumented for the purpose, military sensors are built for other tasks, no standardized reporting existed before 2019, and stigma suppressed aircrew reports for decades.^11,13 No official body has attributed any case, resolved or unresolved, to a non-human source, and what the unresolved cases represent is a question active programs are still working to resolve.^12,16

Research perspectives

Researchers and official assessments bring several perspectives to the unresolved cases. The perspectives are not mutually exclusive, and official reviews invoke more than one of them at once.

The record and open questions

Documented: Flying saucer entered the language through press coverage of Kenneth Arnold's June 1947 report. UFO was adopted inside the Air Force in the early 1950s, and UAP entered official use in 2019 and 2020, redefined in December 2022 as unidentified anomalous phenomena. The institutional history is documented from Projects Sign, Grudge, and Blue Book through the Condon Report to AATIP, the UAP Task Force, and AARO, and every published official review to date states that it has found no verified evidence of extraterrestrial technology.

Reported: Witnesses, including trained military aircrews, describe objects with shapes and flight behavior they could not identify, and a minority of official cases record movement the observers considered unusual, 18 incidents in the 2021 assessment. A witness before Congress in July 2023 testified, on the basis of interviews with other officials, that the government holds recovered non-human material. The Pentagon states it has found no verifiable information supporting that testimony.

Open questions: The central question is what the unresolved cases consist of. Official reports assign most incidents to conventional categories when the data is sufficient, and they continue to test whether the remainder reflects those same categories seen through sparser data, undisclosed human technology, or something genuinely anomalous. That residue is what the current programs were built to resolve, and the cases AARO's director has called interesting remain under study.

Frequently asked questions

What is the difference between UFO and UAP?

The two terms cover the same core idea, an observed object or phenomenon that remains unidentified after analysis. UFO is the older Air Force term and refers to flying objects. UAP is the current official term, expanded in December 2022 to unidentified anomalous phenomena, covering unexplained observations in air, space, and water.³ Officials also adopted UAP because UFO had accumulated decades of cultural association with alien spacecraft.²

Why was the term UFO changed to UAP?

Two documented reasons. The first is stigma: officials and pilots stated that the UFO label discouraged aircrews from filing reports.² The second is scope, since the December 2022 change to unidentified anomalous phenomena extended the category beyond the air to submerged and transmedium objects, matching AARO's all-domain mandate.³

Where did the term flying saucer come from?

From press coverage of Kenneth Arnold's sighting of June 24, 1947. The Associated Press story described "nine bright saucer-like objects," and newspapers turned the phrase into flying saucer within days.⁵ Arnold maintained he had described how the objects flew, not their shape.⁴

When did Project Blue Book end and why?

The Air Force closed Project Blue Book on December 17, 1969, following the University of Colorado's Condon Report, which concluded that further extensive study of UFOs could not be justified by the expectation of scientific advance, and a National Academy of Sciences review that endorsed it.⁷ Blue Book had logged 12,618 reports, of which 701 remained unidentified.⁶

Has the US government said UAP are alien?

No. AARO's March 2024 historical review found no empirical evidence of off-world technology, and its fiscal year 2024 report states that AARO has discovered no evidence of extraterrestrial beings, activity, or technology.^12,16 Testimony describing secret retrieval programs was presented to Congress in 2023, based on the witness's interviews with other officials, and the Pentagon states it has found no verifiable information to substantiate it.¹⁴

What percentage of UFO sightings are explained?

In the historical record, 701 of Project Blue Book's 12,618 cases, about 5.5 percent, stayed unidentified.⁶ In current data the resolved share depends on data quality. ODNI's 2022 report initially characterized 195 of 366 new reports as balloons, drones, or clutter, and AARO's fiscal year 2024 report resolved or recommended closure of nearly 300 cases as balloons, birds, drones, satellites, or aircraft, while 444 lacked the data for analysis and 21 merited further study.^15,16

Sources and further reading

1. Wikipedia. "Edward J. Ruppelt." https://en.wikipedia.org/wiki/Edward_J._Ruppelt
2. CBS News. "What are UAPs, and why do UFOs have a new name?" https://www.cbsnews.com/news/what-are-uaps-unexplained-aerial-phenomenon-ufos-new-name/
3. DefenseScoop. "Pentagon changes 'UAP' terminology as it looks to investigate unexplainable sightings across all domains." December 19, 2022. https://defensescoop.com/2022/12/19/pentagon-changes-uap-terminology-as-it-looks-to-investigate-unexplainable-sightings-across-all-domains/
4. Wikipedia. "Kenneth Arnold UFO sighting." https://en.wikipedia.org/wiki/Kenneth_Arnold_UFO_sighting
5. Smithsonian National Air and Space Museum. "1947: Year of the Flying Saucer." https://airandspace.si.edu/stories/editorial/1947-year-flying-saucer
6. Wikipedia. "Project Blue Book." https://en.wikipedia.org/wiki/Project_Blue_Book
7. Wikipedia. "Condon Committee." https://en.wikipedia.org/wiki/Condon_Committee
8. History.com. "Meet J. Allen Hynek, the Astronomer Who First Classified UFO 'Close Encounters.'" https://www.history.com/articles/j-allen-hynek-ufos-project-blue-book
9. Center for UFO Studies. "Classification Systems." https://cufos.org/types-of-ufos/classification-systems/
10. Wikipedia. "Advanced Aerospace Threat Identification Program." https://en.wikipedia.org/wiki/Advanced_Aerospace_Threat_Identification_Program
11. Office of the Director of National Intelligence. "Preliminary Assessment: Unidentified Aerial Phenomena." June 25, 2021. https://www.dni.gov/files/ODNI/documents/assessments/Prelimary-Assessment-UAP-20210625.pdf
12. Wikipedia. "All-domain Anomaly Resolution Office." https://en.wikipedia.org/wiki/All-domain_Anomaly_Resolution_Office
13. NASA. "NASA Shares UAP Independent Study Report; Names Director." September 14, 2023. https://www.nasa.gov/news-release/update-nasa-shares-uap-independent-study-report-names-director/
14. NPR. "Whistleblower testifies U.S. salvaged 'non-human biologics' from UFO crash sites." July 27, 2023. https://www.npr.org/2023/07/27/1190390376/ufo-hearing-non-human-biologics-uaps
15. Office of the Director of National Intelligence. "2022 Annual Report on Unidentified Aerial Phenomena." https://www.dni.gov/files/ODNI/documents/assessments/Unclassified-2022-Annual-Report-UAP.pdf
16. US Department of Defense, All-domain Anomaly Resolution Office. "Fiscal Year 2024 Consolidated Annual Report on Unidentified Anomalous Phenomena." November 2024. https://media.defense.gov/2024/Nov/14/2003583603/-1/-1/0/FY24-CONSOLIDATED-ANNUAL-REPORT-ON-UAP-508.PDF
17. DefenseScoop. "'The truly anomalous': New AARO chief unveils Pentagon's annual UAP caseload analysis, new efforts." November 14, 2024. https://defensescoop.com/2024/11/14/uap-aaro-chief-unveils-pentagon-annual-caseload-analysis-new-efforts/