WASHINGTON (AP) — A former Air Force intelligence officer has testified that the U.S. is concealing a longstanding program that retrieves and reverse engineers unidentified flying objects.

Retired Maj. David Grusch’s highly anticipated testimony on Wednesday before a House Oversight subcommittee was Congress’ latest foray into the world of UAPs — or “unidentified aerial phenomena,” which is the official term the U.S. government uses instead of UFOs.

The Pentagon has rejected Grusch’s claims and denies it is concealing any such program.

While the study of UFOs often evokes talk of aliens and “little green men,” Democrats and Republicans in recent years have pushed for more research as a national security matter.