During the Fascism, Gelli volunteered for the "Black Shirt" expeditionary forces sent by Mussolini to Spain in support to Francisco Franco, and subsequently became a liaison officer between the Italian blackshirt government and the Third Reich, with contacts including Hermann Göring.
Gelli has been accused of having assumed an influential role in Operation Gladio, a clandestine "stay-behind" operation sponsored by the CIA and NATO to counter communist influence in Italy, as well as in other European countries. However, in the interested country, the Gladio affair has been treated (judicially too) with no sensible connection with the P2 affair.
Gelli repeatedly publicly declared to be a close friend of Argentina's leader Juan Peron (but no confirmations ever came from South America), and often affirmed, in strange forms, that this friendship was really important for Italy, but he never explicitly explained why.
In 1981, a police raid on his villa in Arezzo, led to the discovery of a famous list of Italian military officers and civil servants involved in P2. The list included also industrials, journalists and wealthy people like the current premier Silvio Berlusconi (at the time not yet in politics) and Victor Emanuel of Savoy.
The following national scandal was quite thrilling, given that most of the most delicate charges of the Republic were ruled by Gelli's affiliates. A Pariamentar Commission, directed by On. Tina Anselmi (from Democrazia Cristiana), found no evidence of crimes, but the Parliament soon issued a law to ban secret associations in Italy.
A certain power the P2 lodge undoubtedly had in italy, given the "weight" of its adherents. And many observators still now consider it is in an extremely strong position. Many people today famous in Italy (starting from the top TV "anchor-man" Maurizio Costanzo) come from P2. One of associates was presumed to be Michele Sindona, a banker with quite clear connections to the Mafia.
A few years after the scandal, many suspects were pointed toward Gelli with reference to his eventual involvement in the murder of the Milanese banker Roberto Calvi (also known as "God's banker"), who had been jailed in the wake of the collapse of Banco Ambrosiano.