Close air support

In military tactics, close air support (CAS) is defined as air action by fixed or rotary-winged aircraft against hostile targets, that are in close proximity to friendly forces, and which requires detailed integration of each air mission with fire and movement of these forces.

The requirement for detailed integration because of proximity, fires or movement is the determining factor. CAS may need to be conducted during shaping operations with Special Operations Forces (SOF), if the mission requires detailed integration with the fire and movement of these forces. A closely related subset of air interdiction, battlefield air interdiction (AI) denotes interdiction against units with near-term effects on friendly units, but which does not require integration with friendly troop movements. The term "battlefield air interdiction" is not currently used in U.S. joint doctrine.

Close air support requires excellent coordination with ground forces. In advanced modern militaries, this coordination is typically handled by specialists such as Joint Fires Observers (JFO)s, Joint Terminal Attack Controllers (JTAC)s, and Forward Air Controllers (FAC)s.

The use of aircraft in the close air support of ground forces dates back to World War I, the first significant use of aerial units in warfare. Air warfare, and indeed aviation itself, was still in its infancy—and the direct effect of rifle calibre machine guns and light bombs of World War I aircraft was very limited compared with the power of (for instance) a World War II fighter bomber, but close support aircraft still had a powerful psychological impact. The aircraft was a visible and personal enemy—unlike artillery—presenting a personal threat to enemy troops, while providing friendly forces assurance that their superiors were concerned about their situation.

Most successful attacks of 1917–1918 included planning for co-ordination between aerial and ground units, although it was very hard at this early date to co-ordinate these attacks due to the primitive nature of air-to-ground radio communication. Though most air-power proponents sought independence from ground commanders and hence pushed the importance of interdiction and strategic bombing, they nonetheless recognised the need for close air support.

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