Spain
Spain's Ejército del Aire (EA) ran a continuous classified UAP intake from 1962 through 1992, when most of the corpus was declassified under Orden 13/1992 of the Ministerio de Defensa. Some 1,900 pages, covering ~80 case files, were transferred to public access through the Air Force Historical Archive in Villaviciosa de Odón. Spain was the first European NATO state to declassify the bulk of its UAP corpus to civilian researchers.
Verbatim — Orden 13/1992, Ministerio de Defensa
"Se desclasifica con carácter general la totalidad de la documentación relativa a observaciones de objetos volantes no identificados que obran en poder de los Servicios de Información del Ejército del Aire, declarándola accesible al público en general."
Notable files
Caso Manises, 11 Nov 1979 — TAE Supercaravelle JK297 forced to divert and land at Manises (Valencia) after two luminous objects paced the aircraft. Mirage F1 fighters scrambled. Full file released 1994.
Caso Talavera la Real, 12 Nov 1976 — Badajoz air base, multiple ground witnesses, photographic stills.
Caso Canarias, 22 Jun 1976 — Y-shaped object reported by multiple ships and aircraft over the Atlantic west of Gran Canaria.
Why this matters historically
The 1992 declassification programme was led, internally, by Capt. Juan Antonio Fernández Peris at SIDA (Servicio de Información de la Defensa Aérea). Its comprehensiveness — declassifying essentially the entire corpus — set the model that France's GEIPAN and Italy's AM later adapted.