The Advanced Aerospace Threat Identification Program (AATIP) was a Pentagon program to study unidentified flying objects. It officially ran from 2007 until 2012. The program was secret, but not classified. Its existence was first made public on December 16, 2017, at a press conference (where it was initially introduced as the Advanced Aviation Threat Identification Program). The press conference was co-organized by Luis Elizondo, who had overseen the program, and a related group of interested professionals from a nonprofit organization called, 'To the Stars Academy of Arts & Science.'
Note that in an interview in July 2018, Luis Elizondo said the name of the program has been misreported, and that its actual name was the Advanced Aerospace Threat Identification Program, and not Advanced Aviation Threat Identification Program.
But then in October 2021, a book - Skinwalker at the Pentagon - was published in which it was claimed that the information that was released in December 2017 confused and combined elements of two separate programs. The cause of the confusion was that the AATIP name had been used in one letter by Senator Reid to refer to a different program in which he was involved, and that was called the Advanced Aerospace Weapons Systems Application Program (AAWSAP), which was run by Bigelow's BICS. It only would have lasted for two years.
The AAWSAP program was initiated by then U.S. Senator Harry Reid (D-Nevada) at the urging of Reid's friend, Nevada businessman and governmental contractor Robert Bigelow, and with support from the late Senators Ted Stevens (R-Alaska) and Daniel Inouye (D-Hawaii). This is the program that had a budget of 22 million USD.
AAWSAP was never a DIA program, but they did have an AATIP program, which they first denied, but then later acknowledged.
AATIP allegedly ran for five years.
The Advanced Aviation Threat Identification Program has generated a 490-page report that documents alleged worldwide UFO sightings over several decades. At present, that report has not been made public.
Given the few resources it had, it is likely that AATIP, like its predecessors - Sign, Blue Book, and Grudge - was more of a PR exercise than a genuine investigation. Like Col. Garret before him, back in the 40s, Luis Elizondo has gone on the record expressing his surprise at the complete lack of interest by his superiors with regard to his investigation.
NOTE: much of the information about AAWSAP and AATIP does not match, and their actual relationship is unclear.
- Skinwalker at the Pentagon