A military artillery observer or spotter is responsible for directing artillery and mortar fire onto a target, and may be a Forward Air Controller (FAC) for close air support and spotter for naval gunfire support. Also known as "Forward Observer", "Fire Support Specialist", or "FISTer". Most commonly observers accompany a tank or infantry manoeuvre unit. More recently a mission controller for an Army Unmanned Air System (UAS) may also act as an artillery observer and some armies use special artillery patrols behind the enemy's forward elements.