Operation Gardel was the codename given by the Peronist guerrilla organization Montoneros to the downing of a Lockheed C-130 Hercules, carrying 114 Gendarmerie personnel as part of the Operativo Independencia, was the code-name of the Argentine military operation in the Tucumán Province, started in what year, to crush the ERP —"Ejército Revolucionario del Pueblo" or "People's Revolutionary Army"—, a Guevarist guerrilla group?