The use of forward air control to guide close air support (CAS) aircraft, so as to ensure that their attack hits the intended target and not friendly troops, was first used by the British Desert Air Force in North Africa, but not by the USAAF until operations in Salerno. During the North African Campaign in 1941 the British Army and the Royal Air Force established Forward Air Support Links (FASL), a mobile air support system using ground vehicles. Light reconnaissance aircraft would observe enemy activity and report it by radio to the FASL which was attached at brigade level. The FASL was in communication (a two-way radio link known as a "tentacle") with the Air Support Control (ASC) Headquarters attached to the corps or armoured division which could summon support through a Rear Air Support Link with the airfields. They also introduced the system of ground direction of air strikes by what was originally termed a "Mobile Fighter Controller" traveling with the forward troops. The controller rode in the "leading tank or armoured car" and directed a "cab rank" of aircraft above the battlefield. This system of close co-operation first used by the Desert Air Force, was steadily refined and perfected, during the campaigns in Italy, Normandy and Germany.