Close air support
Other notable adaptations were the usage of airborne Forward Air Controllers (FACs), a role previously dominated by FACs on the ground, and the use of B-52s for CAS.
U.S. Marine Corps Aviation was much more prepared for the application of CAS in the Vietnam War, due to CAS being its central mission. In fact, as late as 1998, Marines were still claiming in their training manuals that "Close air support (CAS) is a Marine Corps innovation." One of the main debates taking place within the Marine Corps during the war was whether to adopt the helicopter gunship as a part of CAS doctrine and what its adoption would mean for fixed-wing CAS in the Marine Corps. The issue would eventually be put to rest, however, as the helicopter gunship proved crucial in the combat environment of Vietnam.

Though helicopters were initially armed merely as defensive measures to support the landing and extraction of troops, their value in this role led to the modification of early helicopters as dedicated gunship platforms. Though not as fast as fixed-wing aircraft and consequently more vulnerable to anti-aircraft weaponry, helicopters could use terrain for cover, and more importantly, had much greater battlefield persistence owing to their low speeds. The latter made them a natural complement to ground forces in the CAS role. In addition, newly developed anti-tank guided missiles, demonstrated to great effectiveness in the 1973 Yom Kippur War, provided aircraft with an effective ranged anti-tank weapon. These considerations motivated armies to promote the helicopter from a support role to a combat arm. Though the U.S. Army controlled rotary-wing assets, coordination continued to pose a problem. During wargames, field commanders tended to hold back attack helicopters out of fear of air defenses, committing them too late to effectively support ground units. The earlier debate over control over CAS assets was reiterated between ground commanders and aviators. Nevertheless, the US Army incrementally gained increased control over its CAS role.
In the mid-1970s, after Vietnam, the USAF decided to train an enlisted force to handle many of the tasks the ALO was saturated with, to include terminal attack control. Presently, the ALO mainly serves in the liaison role, the intricate details of mission planning and attack guidance left to the enlisted members of the Tactical Air Control Party.

NATO and AirLand Battle: Since their 1977 introduction into modern military practice for close air support purposes, General Crosbie E. Saint provided the AH-64 Apache the doctrinal cover for use in AirLand Battle operations such as in the NATO European theatre.

Aircraft: Various aircraft can fill close air support roles. Military helicopters are often used for close air support and are so closely integrated with ground operations that in most countries they are operated by the army rather than the air force. Fighters and ground attack aircraft like the A-10 Thunderbolt II provide close air support using rockets, missiles, bombs, and strafing runs.
During the Second World War, a mixture of dive bombers and fighters were used for CAS missions. Dive bombing permitted greater accuracy than level bombing runs, while the rapid altitude change made it more difficult for anti aircraft 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 used for CAS. It was fitted with wind-blown sirens on its landing gear to enhance its psychological effect. Some variants of the Stuka were equipped with a pair of 37 mm (1.5 in) Bordkanone BK 3,7 cannons mounted in under-wing gun pods, each loaded with two six-round magazines of armour-piercing tungsten carbide-cored ammunition, for anti-tank operations.
Other than the North American A-36 Apache, a P-51 Mustang modified with dive brakes, the Americans and British used no dedicated CAS aircraft in the Second World War, preferring fighters or fighter-bombers that could be pressed into CAS service. While some aircraft, 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 further and lower convergence point than aerial combat did.
Of the Allied powers that fought in the Second World War, 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 at any point in world history. The Soviet military also frequently deployed the Polikarpov Po-2 biplane as a ground attack aircraft.
The Royal Navy Hawker Sea Fury fighters and the U.S. Vought F4U Corsair and Douglas A-1 Skyraider were operated in a ground attack capacity during the Korean War. Outside of the conflict, there were numerous other occasions that the Sea Fury was used as a ground attack platform. Cuban Sea Furies, operated by the Fuerza Aérea Revolucionaria ("Revolutionary Air Force"; FAR), were used to oppose the US-orchestrated Bay of Pigs Invasion to attack incoming transport ships and disembarking ground forces alike. The A-1 Skyraider also saw later use, especially throughout the Vietnam War.
In the Vietnam War, the United States introduced a number of fixed and rotary wing gunships, including several cargo aircraft that were refitted as gun platforms to serve as CAS and air interdiction aircraft. The first of these to emerge was the Douglas AC-47 Spooky, which was converted from the Douglas C-47 Skytrain/Douglas DC-3. Some commentators have remarked on the high effectiveness of the AC-47 in the CAS role. The USAF developed several other platforms following on from the AC-47, including the Fairchild AC-119 and the Lockheed AC-130. The AC-130 has had a particularly lengthy service, being used extensively during the War in Afghanistan, the Iraq War and the US military intervention in Libya during the early twenty-first century. Multiple variants of the AC-130 have been developed and it has continued to be modernised, including the adoption of various new armaments.

 
Usually close support is thought to be only carried out by fighter-bombers or dedicated ground-attack aircraft, such as the A-10 Thunderbolt II (Warthog) or Su-25 (Frogfoot) or attack helicopters such as the AH-64 Apache, but even large high-altitude bombers have successfully filled close support roles using precision-guided munitions. During Operation Enduring Freedom, the lack of fighter aircraft forced military planners to rely heavily on US bombers, particularly the B-1B Lancer, to fill the CAS role. Bomber CAS, relying mainly on GPS guided weapons and laser-guided JDAMs has evolved into a devastating tactical employment methodology and has changed US doctrinal thinking regarding CAS in general. With significantly longer loiter times, range, and weapon capacity, bombers can be deployed to bases outside of the immediate battlefield area, with 12-hour missions being commonplace since 2001. After the initial collapse of the Taliban regime in Afghanistan, airfields in Afghanistan became available for continuing operations against the Taliban and Al-Qaeda. This resulted in a great number of CAS operations being undertaken by aircraft from Belgium (F-16 Fighting Falcon), Denmark (F-16), France (Mirage 2000D), the Netherlands (F-16), Norway (F-16), the United Kingdom (Harrier GR7s, GR9s and Tornado GR4s) and the United States (A-10, F-16, AV-8B Harrier II, F-15E Strike Eagle, F/A-18 Hornet, F/A-18E/F Super Hornet, UH-1Y Venom).

The use of information technology to direct and coordinate precision air support has increased the importance of intelligence, surveillance, and reconnaissance in using CAS. Laser, GPS, and battlefield data transfer are routinely used to coordinate with a wide variety of air platforms able to provide CAS. The 2003 joint CAS doctrine reflects the increased use of electronic and optical technology to direct targeted fires for CAS. Air platforms communicating with ground forces can also provide additional aerial-to-ground visual search, ground-convoy escort, and enhancement of command and control (C2), assets which can be particularly important for low intensity conflict.

Doctrine: MCWP 3-23.1: CLOSE AIR SUPPORT (PDF). U.S. Marine Corps. 30 July 1998.
JP 3-09.3: Close Air Support (PDF). Joint Chiefs of Staff. 25 November 2014.

See also: Artillery observer
Attack aircraft
Counter-insurgency aircraft, a specific type of CAS aircraft
Flying Leathernecks
Forward air control
Light Attack/Armed Reconnaissance
Pace-Finletter MOU 1952
Tactical bombing, a general term for the type of bombing that includes CAS and air interdiction

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External links: Can Our Jets Support the Guys on the Ground? – Popular Science
The Forward Air Controller Association
The ROMAD Locator The home of the current ground FAC
Operation Anaconda: An Airpower Perspective Archived 2019-07-14 at the Wayback Machine – Close air support during Operation Anaconda, United States Airforce, 2005.