Tuesday's hearing before a US House Intelligence subcommittee comes 11 months after a report documenting more than 140 cases of what the government officially calls "unidentified aerial phenomena," or UAPs, that US military pilots have reported observing since 2004.
The more popular term UFO, for unidentified flying object, has long been widely associated with the notion of alien spacecraft, which received no mention in last June's UAP presentation.
The focus, instead, was on possible implications for US national security and aviation safety.
The report did, however, include some UAPs previously revealed in Pentagon-released video footage of enigmatic airborne objects exhibiting speed and manoeuvrability exceeding known aviation technology and lacking any visible means of propulsion or flight-control surfaces.
The hearing was expected to re-examine the findings of that report, a nine-page "preliminary assessment" compiled by the Office of the Director of National Intelligence and a Navy-led task force the Pentagon formed in 2020.
"The American people deserve full transparency," Intelligence Committee Chairman Adam Schiff said in a statement last week announcing the hearings.
Defence and intelligence analysts who prepared the assessment offered no findings about the origins of any of the 144 sightings included in it, except for one attributed to a large deflating balloon.
The Navy task force behind the paper was replaced in November by a new Defence Department agency named the Airborne Object Identification and Management Synchronisation Group.
Ronald Moultrie, who oversees the new group as US defence undersecretary for intelligence and security, is one of the two officials called to testify during Tuesday's hearing. The other is Scott Bray, deputy director of naval intelligence.
Both of them were scheduled to testify behind closed doors following the public hearing.
While reaching no conclusions, last year's report said the UAP sightings probably lack a single explanation.
Further data and analysis were needed to determine whether they represent some exotic aerial system developed by a secret US government or commercial entity, or by a foreign power such as China or Russia, according to the report.
Defence and intelligence analysts have likewise yet to rule out an extraterrestrial origin for any UAP case, senior US officials told reporters ahead of the report's release last year, though the paper itself avoided any explicit reference to such possibilities.
Still, the report marked a turning point for the US government after decades spent deflecting, debunking and discrediting observations of unidentified flying objects and "flying saucers" dating back to the 1940s.
The session will mark the first open congressional hearing on the subject since the US Air Force terminated an inconclusive UFO program code-named Project Blue Book in 1969.
During its 17 years in existence, Blue Book compiled a list of 12,618 UFO sightings, 701 of which involved objects that officially remained unidentified.
But the Air Force later said it found no indication of a national security threat or evidence of extraterrestrial vehicles.
In 1966, nearly a decade before he became president, then-US Representative Gerald Ford of Michigan, who was House Republican leader at the time, organised a hearing in response to scores of witness accounts of strange glowing lights and large football shapes at low altitude around Dexter, Michigan, which an Air Force official had famously explained away as "swamp gas".
