In
military tactics,
close air support (CAS) is defined as air action such as
air strikes by fixed or rotary-winged aircraft against hostile targets that are
in proximity to friendly forces and which requires
detailed integration of each air mission with fire and movement of these forces and attacks with
aerial bombs,
glide bombs,
missiles,
rockets,
aircraft cannons,
machine guns, and even
directed-energy weapons such as
lasers.
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 (JFOs),
Joint Terminal Attack Controllers (JTACs), and
forward air controllers (FACs).
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 (AI),
battlefield air interdiction, 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.
The use of aircraft in the close air support of ground forces dates back to
WW1, 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 caliber
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
recognized the need for close air support.
Most
theorists advocated the adaptation of
fighters or
light bombers into the role. During this period,
airpower advocates crystallized their views on the role of air-power in warfare.
Aviators and ground officers developed largely
opposing views on the importance of CAS, views that would frame institutional battles for CAS in the 20th century.
World War II marked the
universal acceptance of the integration of air power into combined arms warfare as close air support. Although the German
Luftwaffe was the only force to use CAS at the
start of the war, all the major combatants had developed effective air-ground coordination techniques by the war's end.
The
Royal Air Force (RAF) entered the war
woefully unprepared to provide CAS. In 1940 during the
Battle of France, the Royal Air Force and Army headquarters in France were located at separate positions, resulting in
unreliable communications. After the RAF was withdrawn in May,
Army officers had to
telephone the War Office in London to arrange for air support.
The
stunning effectiveness of German air-ground coordination spurred change. On the basis of tests in
Northern Ireland in August 1940,
Group Captain A. H. Wann RAF and Colonel J.D. Woodall (British Army) issued the
Wann-Woodall Report, recommending the creation of a
distinct tactical air force liaison officer (known colloquially as
"tentacles") to accompany Army divisions and brigades. Their report spurred the RAF to create an
RAF Army Cooperation Command and to develop tentacle equipment and procedures placing an Air Liaison Officer with each brigade.
In World War II,
dive bombers and fighters were used in close air support.
Dive bombing permitted greater accuracy than level bombing runs, while the rapid altitude change made it more
difficult for antiaircraft gunners to track. The
Junkers Ju 87 Stuka is a well known example of a
dive bomber built for precision bombing but which was
successfully utilised for CAS. It was fitted with wind-blown whistles on its landing gear to enhance its psychological effect. Some variants of the Stuka were equipped with 37 mm anti-tank cannon.
Other than the
A-36, a
P-51 modified with dive brakes, the
Americans and British used
no dedicated CAS aircraft in World War II,
preferring fighters or fighter-bombers that could be pressed into CAS service. While some such as the
Hawker Typhoon and the
P-47 Thunderbolt, performed admirably in that role, there were a number of
compromises that
prevented most fighters from making effective CAS platforms. Fighters were usually optimized for
high-altitude operations without bombs or other external ordnance – flying at low level with bombs quickly expended fuel.
Cannons had to be mounted differently for strafing – strafing required a
farther and lower convergence point than aerial combat did.
Of the World War II allies, the
Soviet Union used specifically designed ground attack aircraft more than the UK and US. Such aircraft included the
Ilyushin Il-2, the single most produced military aircraft design in all of aviation history. The Soviets also used the
Polikarpov Po-2, a biplane, as a ground attack aircraft.
