The Fifteenth of September Legion (Legión Quince de Septiembre) was an anti-communist guerrilla group founded in Guatemala by exiled former junior officers of the defeated Nicaraguan National Guard, which was committed to overthrowing the Sandinista National Liberation Front government.
Eduardo Román, manager of boxer Alexis Argüello, also convinced Argüello to fund a radio station, Radio 15th of September.
To finance itself, the Legion also staged kidnappings for ransom and bank robberies, called "special operations", in Guatemala and El Salvador.
In August 1981, at the behest of the Argentine junta and the Reagan administration, it merged with the Nicaraguan Democratic Union (UDN) to form the Nicaraguan Democratic Force (FDN).
The FDN would eventually grow to become the dominant Contra rebels' faction in the 1980s.