Special Reconnaissance (SR) is conducted by small units of highly trained military personnel, usually from Special Operations Forces (SOF) who avoid combat with, and detection by, the enemy. In the United States SR is recognized as a key Special Operations capability at the level of the US Secretary of Defense: "Special Reconnaissance is the conduct of environmental reconnaissance, target acquisition, area assessment, post-strike assessment, emplacement and recovery of sensors, or support of Human Intelligence (HUMINT) and Signals Intelligence (SIGINT) operations."