Operation Gladio was a clandestine "stay-behind" operation sponsored by the CIA and NATO to counter communist influence after World War II in Italy, as well as in other European countries, which has been involved in various terrorist acts. While Gladio is usually used to refer to only the Italian "stay-behind", the term has also been applied to all other "stay-behind" operations. NATO stay-behind armies existed in all countries of Western Europe during the Cold War, including Turkey. Suspected at least since the 1984 revelations of Avanguardia Nazionale member Vincenzo Vinciguerra during his trial, Gladio’s existence was acknowledged by head of Italian government Giulio Andreotti on October 24, 1990, who spoke of a "structure of information, response and safeguard", with arms caches and reserve officers. Further investigations revealed links to neofascists, the mafia, Propaganda Due masonic lodge (aka P2), and the "strategia della tensione" followed in Italy during the 1970s–80s to block the electoral success of the Italian Communist Party (PCI).
Further reading: NATO's Secret Army (Contemporary Security Studies (Paperback))