CIA U-2/OXCART UFO admission (Haines 1997).
official-recordgovernment_reportMajestic 12 & Disinfo
The CIA's own history (Gerald Haines, Studies in Intelligence 1997) conceding that 'over half' of late-1950s-1960s UFO reports were misidentified U-2 and A-12/OXCART spy-plane flights - and that the Air Force gave deliberately misleading 'ice crystals / temperature inversion' explanations to protect the program.
The cleanest documented case of the intelligence community USING UFO belief as cover for classified technology. Note 'over half' is an insider estimate, not an audited count, but the deliberate misdirection is on the CIA's own record.