The United States Army Special Forces, colloquially known as the "Green Berets" due to their distinctive service headgear, are a special operations force of the United States Army that are designed to deploy and execute nine doctrinal missions: unconventional warfare, foreign internal defense, direct action, counter-insurgency, special reconnaissance, counter-terrorism, information operations, counterproliferation of weapons of mass destruction, and security force assistance. The first two missions, unconventional warfare and foreign internal defenses, emphasize language, cultural, and training skills in working with foreign troops. Other Special Forces missions, known as secondary missions, include: combat search and rescue (CSAR), counter-narcotics, hostage rescue, humanitarian assistanc