United States Army Special Forces
The United States Army Special Forces (SF), colloquially known as the "Green Berets" due to their distinctive service headgear, is a branch of the United States Army Special Operations Command (USASOC). The core missionset of Special Forces contains five doctrinal missions: unconventional warfare, foreign internal defense, direct action, counterterrorism, and special reconnaissance.
Source: Wikipedia — United States Army Special Forces (CC BY-SA 4.0)