The Pentagon did not change it. It was changed by the people who wrote the language in the 2023 NDAA. My previous email:
The A stood for "Aerial" originally, which was used for the first task force in 2020-2021. See:
https://www.intelligence.gov/index....phenomena-preliminary-intelligence-assessment
It was changed to "Anomalous" in late 2022 with the James M. Inhofe National Defense Authorization Act
for Fiscal Year 2023, signed into law on December 23, 2022 (Public Law 117-263, Section 1673).
You can see the name change in the title of the NASA panel, for example:
https://en.wikipedia.org/wiki/NASA_...Team#:~:text=renaming it by changing "Aerial"
The change was largely to include underwater objects, which some UFO proponents were interested in, despite vastly less evidence than for flying objects.
This legislation was written with a lot of input from a small group of UFO enthusiasts, including Chris Mellon, Luis Elizondo, David Grusch, Tim Gallaudet, and Karl Nell - along with SASC staffers like Kirk McConnell (a Skinwalker ranch fan). Previously, they had pushed to include underwater objects (sometimes called USO Unidentified Submersible Objects) or "Transmedium" objects in the legislation. That led to confusion as UAP still meant Aerial, but they also included underwater in the previous year's (2022) NDAA, which led to the establishment of AARO - with "All-domain Anomaly" deliberately in the title but with the old UAP definition in the establishing documents in July 2022.
https://media.defense.gov/2022/Jul/...-THE-ALL-DOMAIN-ANOMALY-RESOLUTION-OFFICE.PDF
"The AARO will serve as the authoritative office of the Unidentified
Aerial Phenomena (UAP) and UAP-related activities for the DoD."
So in NDAA 2022, you had:
https://www.govinfo.gov/content/pkg/PLAW-117publ81/html/PLAW-117publ81.htm
(5) The term ``unidentified aerial phenomena'' means--
(A) airborne objects that are not immediately
identifiable;
(B) transmedium objects or devices; and
(C) submerged objects or devices that are not
immediately identifiable and that display behavior or
performance characteristics suggesting that the objects
or devices may be related to the objects or devices
described in subparagraph (A) or (B).
Obviously, this is a little confusing, as submerged objects are not aerial
Then in NDAA 2023 it was changed to "anomalous" - basically to fix that confusion.
https://www.govinfo.gov/content/pkg/PLAW-117publ263/html/PLAW-117publ263.htm
So, short story, it was the tacking on of "transmedium" and "submerged" objects to "aerial" that made the change necessary. That tacking on was done by a small group of lobbyists who thought there was something to the underwater stuff.
But there isn't. You can't see very far underwater, so there's no video or photos. There are only stories about anomalous sonar returns and occasional sightings that might as well be of sea monsters. The "transmedium" claim largely hinges on one video, "Aguadilla", which has a perfectly reasonable explanation of two wedding lanterns and parallax illusions.