Since about 1943, US troops have come to expect Close Air Support on call, often virtually around the clock.
All close air support has to be controlled by an observer on the ground, a Joint Terminal Attack Controller (JTAC), what used to be known as a Forward Air Controller.
In the old days (that is, back when I was in the service) the artillery provided Forward Observers and Fire Support Teams to maneuver battalions, and the Air Force provided Tactical Air Control Parties to brigades and battalions. The Army guys would control artillery, and the Air Force guys would control Close Air Support. To some extent, that’s still true. But increasingly, the division of labor is being broken down so Army troops can be qualified as JTACs and serve as the controller for air strikes.