The United States Army Special Forces, known as the Green Berets because of their distinctive service headgear, are a special operations force tasked with five primary missions: unconventional warfare (the original and most important mission of Special Forces), foreign internal defense, special reconnaissance, direct action, and counter-terrorism. The first two emphasize language, cultural, and training skills in working with foreign troops. Other duties include combat search and rescue (CSAR), counter-narcotics, counter-proliferation, hostage rescue, humanitarian assistance, humanitarian demining, information operations, peacekeeping, psychological operations, security assistance, and manhunts; other components of the United States Special Operations Command (USSOCOM) or other U.S. government activities may also specialize in these secondary areas. Many of their operational techniques are classified, but some nonfiction works and doctrinal manuals are available.