The Fuerza Especial de Reacción (Special Reaction Force) or FER, previously known as GAFES del Alto Mando or Fuerza Especial del Alto Mando (High Command Special Force) is one of Mexican Army's most elite special forces units. Their status comes mostly from their higher level training pedigree in black operations, clandestine operation, counterinsurgency, counter-narcotics, counterproliferation, counterterrorism, covert operation, direct action, executive protection, forward observer, hostage rescue, irregular warfare, long-range penetration, operation behind enemy lines, special operations, special reconnaissance, unconventional warfare, among other courses Details of FER size, composition and operations are classified, though observers claim that in the current time Mexico's War on Drugs is their main operational focus. Members are recruited from the "regular" Mexican Army Special Forces Corps battalions. Prospective members must be experienced officers or non-commissioned officers and complete a rigorous selection process, and they can only get recruited through special invitation. The FER is one of four highly specialized elite groups within SEDENA's Special Forces Corps, as well as the only one of these four units whose existence is officially known to the public. Known operations Their first major engagements took place during the Zapatista uprising in the well known "Operación Arcoiris" (Operation Rainbow), where they employed counter insurgency tactics against the EZLN socialist guerrilla group, infiltrating and eliminating enemy targets in the jungle terrain of the southern state of Chiapas. One of the very first times its operators were seen in public was hours after the successful capture of Osiel Cárdenas Guillén as they arrived in Mexico City in 2003, during which they killed some of the elite personal security team of the drug lord; as the top leader of the Gulf Cartel at the time, Osiel was one of the most wanted men in Mexico and the United States They were also responsible for hunting down almost all of the first generation of "Los Zetas”, (ex-GAFEs that deserted from the Mexican army to become security for the Gulf Cartel until they splintered to form their own organization) since they knew how they operated and how to counter them, it is mentioned that they located and then gunned down the first leader and co-founder of Los Zetas, Arturo Guzman Decena in the border city of Matamoros in 2002. These operations at the time, allowed the FER to enter into a very small list of special forces that had fought against other special forces (since the