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 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 assistance, humanitarian demining, information operations, peacekeeping, and manhunts. Other components of the United States Special Operations Command (USSOCOM) or other U.S. government activities may also specialize in these secondary missions. The Special Forces conduct these missions via seven geographically focused groups. Many of their operational techniques are classified, but some nonfiction works and doctrinal manuals are available.