Close Air Support (CAS)

Close air support is airpower applied against enemy forces in close proximity to friendly troops, which makes it the most demanding and dangerous form of air-to-ground attack. The defining word is close. When the target is a hundred meters from your own infantry, a targeting error is not a miss, it is friendly fire, so CAS requires a coordination discipline that ordinary bombing does not, and the person who provides it, the Joint Terminal Attack Controller, is one of the more specialized jobs in any military.

The JTAC and the kill chain

A JTAC (or FAC in some services) is a qualified controller on the ground with the friendly unit, who sees both the enemy and the friendlies and talks the aircraft onto the target. The nine-line brief, a standardized script passing target location, marking, friendly positions, and attack heading, is the CAS ritual, and the controller's final clearance, cleared hot, is what authorizes the pilot to release. This human-in-the-loop rigor exists precisely because the margin for error is measured in meters, and CAS friendly-fire tragedies, when they happen, usually trace to a break in this chain, a misidentified position, a wrong grid, a marking seen by the wrong aircraft.

Almost any strike aircraft can do CAS, fighters, bombers, gunships, attack helicopters, drones, and the two-decade counterinsurgency era made it routine, with orbiting aircraft on call to troops in contact. The AC-130 gunship and the AH-64 Apache are CAS-optimized, and armed drones added persistence the fast jets could not match.

The A-10 argument and the peer problem

No aircraft debate in US defense runs hotter than the A-10 Warthog. Built around a 30mm cannon, heavily armored, able to loiter low and slow over a fight, it is beloved by ground troops and repeatedly targeted for retirement by an Air Force that would rather buy multirole jets. The dispute is really about a deeper question: the slow, low CAS that worked over Afghanistan is close to suicidal against a peer enemy's air defenses, where survivable support means standoff weapons launched from distance, drones, and loitering munitions rather than a gun run. Ukraine confirmed it, manned CAS over contested lines is rare, and the job has largely shifted to drones and artillery. So the CAS mission endures while its classic form fades, and militaries are still working out what replaces the gun run.

Why does CAS need such tight coordination when other strikes don't?

Proximity. A strike on a target far from friendly forces tolerates ordinary targeting error. CAS does not, because the same error that would be a harmless miss in open country is a friendly casualty when your own troops are within the weapon's effects radius. Everything distinctive about CAS, the JTAC, the nine-line, the cleared-hot discipline, exists to manage that single unforgiving fact.