Operation Gladio is the codename for clandestine "stay-behind" operations of armed resistance that was planned by the Western Union (WU), and subsequently by NATO, for a potential Warsaw Pact invasion and conquest in Europe. Although Gladio specifically refers to the Italian branch of the NATO stay-behind organizations, "Operation Gladio" is used as an informal name for all of them. Stay-behind operations were prepared in many NATO member countries, and some neutral countries.

https://en.wikipedia.org/wiki/Operation_Gladio