The Fifteenth of September Legion (Legión Quince de Septiembre) was founded by former junior officers of the defeated Nicaraguan National Guard to overthrow the Sandinista National Liberation Front government.
Based in Guatemala City, it received some support from Guatemala's National Liberation Movement. Eduardo Román, manager of boxer Alexis Argüello, also convinced Argüello to fund a radio station, Radio 15th of September. The Legion also staged kidnappings and bank robberies, called "special operations", in Guatemala and El Salvador. Local leftist guerrillas were already financing themselves through these acts, and the Legion rightly figured that leftists would be blamed. Argentina also began providing assistance.
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 grow into the dominant Contra army.
Legion head Enrique Bermúdez became the military commander of the FDN. At the time of the merger, the Legion's strength has been estimated at sixty men. The Legion also brought to the new FDN their shortwave radio station, Radio Fifteen.