Close air support

The use of aircraft in the close air support of ground forces dates back to the First World War, the first conflict to make significant military use of aerial forces.[2] Air warfare, and indeed aviation itself, was still in its infancy—and the direct effect of rifle caliber machine guns and light bombs of the First World War aircraft was very limited compared with the power of (for instance) an average fighter bomber of the Second World War, but CAS aircraft were still able to achieve 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.

The most successful attacks of 1917–1918 had included planning for co-ordination between aerial and ground units, although it was relatively difficult 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.[3]

The F.E 2d was one of the first aircraft to be used for close air support in 1917 (the observer is demonstrating the use of the rear-firing Lewis gun).

From the commencement of hostilities in 1914, aviators engaged in sporadic and spontaneous attacks on ground forces, but it was not until 1916 that an air support doctrine was elaborated and dedicated fighters for the job were put into service. By that point, the startling and demoralizing effect that attack from the air could have on the troops in the trenches had been made clear.

At the Battle of the Somme, 18 British armed reconnaissance planes strafed the enemy trenches after conducting surveillance operations. The success of this improvised assault spurred innovation on both sides. In 1917, following the Second Battle of the Aisne, the British debuted the first ground-attack aircraft, a modified F.E 2b fighter carrying 20 lb (9.1 kg) bombs and mounted machine-guns. After exhausting their ammunition, the planes returned to base for refueling and rearming before returned to the battle-zone. Other modified planes used in this role were the Airco DH.5 and Sopwith Camel—the latter was particularly successful in this role.[2]

Aircraft support was first integrated into a battle plan on a large scale at the 1917 Battle of Cambrai, where a significantly larger number of tanks were deployed than previously. By that time, effective anti-aircraft tactics were being used by the enemy infantry and pilot casualties were high, although air support was later judged as having been of a critical importance in places where the infantry had got pinned down.[4]

At this time, British doctrine came to recognize two forms of air support; trench strafing (the modern-day doctrine of CAS), and ground strafing (the modern-day doctrine of air interdiction)—attacking tactical ground targets away from the land battle. As well as strafing with machine-guns, planes engaged in such operations were commonly modified with bomb racks; the plane would fly in very low to the ground and release the bombs just above the trenches.

The Junkers J.I, a First World War German ground-attack aircraft

The Germans were also quick to adopt this new form of warfare and were able to deploy aircraft in a similar capacity at Cambrai. While the British used single-seater planes, the Germans preferred the use of heavier two-seaters with an additional machine gunner in the aft cockpit. The Germans adopted the powerful Hannover CL.II and built the first purpose built ground attack aircraft, the Junkers J.I. During the 1918 Spring Offensive, the Germans employed 30 squadrons, or Schlasta, of ground attack fighters and were able to achieve some initial tactical success.[3] The British later deployed the Sopwith Salamander as a specialized ground attack aircraft, although it was too late to see much action.

During the Sinai and Palestine Campaign of 1918, CAS aircraft functioned as an important factor in ultimate victory. After the British achieved air superiority over the German aircraft sent to aid the Ottoman Turks, squadrons of S.E 5a's and D.H. 4s were sent on wide-ranging attacks against German and Turkish positions near the Jordan river. Combined with a ground assault led by General Edmund Allenby, three Turkish armies soon collapsed into a full rout. In the words of the attacking squadron's official report:

No 1 Squadron made six heavy raids during the day, dropped three tons of bombs and fired nearly 24,000 machine gun rounds.[2]

The British used air power extensively during the interwar period to police areas in the Middle East.

The close air support doctrine was further developed in the interwar period. 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.

The inter-war period saw the use of CAS in a number of conflicts, including the Russo-Polish War, the Spanish Civil War, colonial wars in the Middle East and the Gran Chaco War.[2]

The British used air power to great effect in various colonial hotspots in the Middle East and North Africa during the immediate postwar period. The newly formed RAF contributed to the defeat of Afghan forces during the Third Anglo-Afghan War by harassing the enemy and breaking up their formations. Z force, an air squadron, was also used to support ground operations during the Somaliland campaign, in which the "Mad Mullah" Mohammed Abdullah Hassan's insurgency was defeated. Following from these successes, the decision was made to create a unified RAF Iraq Command to use air power as a more cost-effective way of controlling large areas than the use of conventional land forces.[5] It was effectively used to suppress the Great Iraqi Revolution of 1920 and various other tribal revolts.

The Condor Legion reduced the city of Guernica to rubble, and greatly influenced German military strategists.

During the Spanish Civil War German volunteer aviators of the Condor Legion on the Nationalist side, despite little official support from their government, developed close air support tactics that proved highly influential for subsequent Luftwaffe doctrine.

U.S. Marine Corps Aviation was used as an intervention force in support of U.S. Marine Corps ground forces during the Banana Wars, in places such as Haiti, the Dominican Republic and Nicaragua. Marine Aviators experimented with air-ground tactics and in Haiti and Nicaragua they adopted the tactic of dive bombing.[6]

The observers and participants of these wars would base their CAS strategies on their experience of the conflict. Aviators, who wanted institutional independence from the Army, pushed for a view of air-power centered around interdiction, which would relieve them of the necessity of integrating with ground forces and allow them to operate as an independent military arm. They saw close air support as both the most difficult and most inefficient use of aerial assets.

Close air support was the most difficult mission, requiring identifying and distinguishing between friendly and hostile units. At the same time, targets engaged in combat are dispersed and concealed, reducing the effectiveness of air attacks. They also argued that the CAS mission merely duplicated the abilities of artillery, whereas interdiction provided a unique capability. Ground officers contended there was rarely sufficient artillery available, and the flexibility of aircraft would be ideal for massing firepower at critical points, while producing a greater psychological effect on friendly and hostile forces alike. Moreover, unlike massive, indiscriminate artillery strikes, small aerial bombs would not render ground untrafficable, slowing attacking friendly forces.[3]

Although the prevailing view in official circles was largely indifferent to CAS during the interwar period, its importance was expounded upon by military theorists, such as J. F. C. Fuller and Basil Liddell Hart. Hart, who was an advocate of what later came to be known as 'Blitzkrieg' tactics, thought that the speed of armoured tanks would render conventional artillery incapable of providing support fire. Instead he proposed that:

actual 'offensive' support must come from an even more mobile artillery moving alongside. For this purpose the close co-operation of low-flying aircraft...is essential[7]

A flight of Ju 87 D-5s over the Eastern Front, winter 1943–44.

As a continental power intent on offensive operations, Germany could not ignore the need for aerial support of ground operations. Though the Luftwaffe, like its counterparts, tended to focus on strategic bombing, it was unique in its willingness to commit forces to CAS. Unlike the Allies, the Germans were not able to develop powerful strategic bombing capabilities, which implied industrial developments they were forbidden to take according to the Treaty of Versailles.[8] In joint exercises with Sweden in 1934, the Germans were first exposed to dive-bombing, which permitted greater accuracy while making attack aircraft more difficult to track by antiaircraft gunners. As a result, Ernst Udet, chief of the Luftwaffe's development, initiated procurement of close support dive bombers on the model of the U.S. Navy's Curtiss Helldiver, resulting in the Henschel Hs 123, which was later replaced by the famous Junkers Ju 87 Stuka. Experience in the Spanish Civil War lead to the creation of five ground-attack groups in 1938, four of which would be equipped with Stukas. The Luftwaffe matched its material acquisitions with advances in the air-ground coordination. General Wolfram von Richthofen organized a limited number of air liaison detachments that were attached to ground units of the main effort. These detachments existed to pass requests from the ground to the air, and receive reconnaissance reports, but they were not trained to guide aircraft onto targets.

These preparations did not prove fruitful in the invasion of Poland, where the Luftwaffe focused on interdiction and dedicated few assets to close air support. But the value of CAS was demonstrated at the crossing of the Meuse River during the Invasion of France in 1940. General Heinz Guderian, one of the creators of the combined-arms tactical doctrine commonly known as "blitzkrieg", believed the best way to provide cover for the crossing would be a continuous stream of ground attack aircraft on French defenders. Though few guns were hit, the attacks kept the French under cover and prevented them from manning their guns. Aided by the sirens attached to Stukas, the psychological impact was disproportional to the destructive power of close air support (although as often as not, the Stukas were used as tactical bombers instead of close air support, leaving much of the actual work to the older Hs 123 units for the first years of the war). In addition, the reliance on air support over artillery reduced the demand for logistical support through the Ardennes. Though there were difficulties in coordinating air support with the rapid advance, the Germans demonstrated consistently superior CAS tactics to those of the British and French defenders. Later, on the Eastern front, the Germans would devise visual ground signals to mark friendly units and to indicate direction and distance to enemy emplacements.

Despite these accomplishments, German CAS was not perfect and suffered from the same misunderstanding and interservice rivalry that plagued other nations' air arms, and friendly fire was not uncommon. For example, on the eve of the Meuse offensive, Guderian's superior cancelled his CAS plans and called for high-altitude strikes from medium bombers, which would have required halting the offensive until the air strikes were complete. Fortunately for the Germans, his order was issued too late to be implemented, and the Luftwaffe commander followed the schedule he had previously worked out with Guderian. As late as November 1941, the Luftwaffe refused to provide Erwin Rommel with an air liaison officer for the Afrika Korps, because it "would be against the best use of the air force as a whole."[3]

German CAS was also extensively used on the Eastern Front during the period 1941–1943. Their decline was caused by the growing strength of the Red Air Force and the redeployment of assets to defend against American and British strategic bombardment. Luftwaffe's loss of air superiority, combined with a declining supply of aircraft and fuel, crippled their ability to provide effective CAS on the western front after 1943.

US Navy SBD Dauntless dropping its bomb.

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.[9]

Although the RAF was working on its CAS doctrine in London, officers in North Africa improvised their own coordination techniques. In October 1941, Sir Arthur Tedder and Arthur Coningham, senior RAF commanders in North Africa, created joint RAF-Army Air Support Control staffs at each corps and armored division headquarters, and placed a Forward Air Support Link at each brigade to forward air support requests. When trained tentacle teams arrived in 1942, they cut response time on support requests to thirty minutes.[3] It was also in the North Africa desert that the cab rank strategy was developed.[10] It used a series of three aircraft, each in turn directed by the pertinent ground control by radio. One aircraft would be attacking, another in flight to the battle area, while a third was being refuelled and rearmed at its base. If the first attack failed to destroy the tactical target, the aircraft in flight would be directed to continue the attack. The first aircraft would land for its own refuelling and rearming once the third had taken off. The CAS tactics developed and refined by the British during the campaign in North Africa served as the basis for the Allied system used to subsequently gain victory in the air over Germany in 1944 and devastate its cities and industries.[4]

British Mobile Fighter Controllers operating during World War II

The use of forward air control to guide close air support (CAS)[11] aircraft, so as to ensure that their attack hits the intended target and not friendly troops, was first used by the British Desert Air Force in North Africa, but not by the USAAF until operations in Salerno.[12] During the North African Campaign in 1941 the British Army and the Royal Air Force established Forward Air Support Links (FASL), a mobile air support system using ground vehicles. Light reconnaissance aircraft would observe enemy activity and report it by radio to the FASL which was attached at brigade level. The FASL was in communication (a two-way radio link known as a "tentacle") with the Air Support Control (ASC) Headquarters attached to the corps or armoured division which could summon support through a Rear Air Support Link with the airfields.[13][14] They also introduced the system of ground direction of air strikes by what was originally termed a "Mobile Fighter Controller" traveling with the forward troops. The controller rode in the "leading tank or armoured car" and directed a "cab rank" of aircraft above the battlefield.[15] This system of close co-operation first used by the Desert Air Force, was steadily refined and perfected, during the campaigns in Italy, Normandy and Germany.

By the time the Italian Campaign had reached Rome, the Allies had established air superiority. They were then able to pre-schedule strikes by fighter-bomber squadrons; however, by the time the aircraft arrived in the strike area, oftentimes the targets, which were usually trucks, had fled.[16] The initial solution to fleeing targets was the British "Rover" system. These were pairings of air controllers and army liaison officers at the front but able to switch communications seamlessly from one brigade to another – hence Rover. Incoming strike aircraft arrived with pre-briefed targets, which they would strike 20 minutes after arriving on station only if the Rovers had not directed them to another more pressing target. Rovers might call on artillery to mark targets with smoke shells, or they might direct the fighters to map grid coordinates, or they might resort to a description of prominent terrain features as guidance. However, one drawback for the Rovers was the constant rotation of pilots, who were there for fortnightly stints, leading to a lack of institutional memory. US commanders, impressed by the British tactics at the Salerno landings, adapted their own doctrine to include many features of the British system.[17]

At the start of the War, the United States Army Air Forces (USAAF) had, as its principal mission, the doctrine of strategic bombing. This incorporated the unerring belief that unescorted bombers could win the war without the advent of ground troops. This doctrine proved to be fundamentally flawed. However, during the entire course of the war the USAAF top brass clung to this doctrine, and hence operated independently of the rest of the Army. Thus it was initially unprepared to provide CAS, and in fact, had to be dragged "kicking and screaming" into the CAS function with the ground troops. USAAF doctrinal priorities for tactical aviation were, in order, air superiority, isolation of the battlefield via supply interdiction, and thirdly, close air support. Hence, during the North African Campaign, CAS was poorly executed, if at all. So few aerial assets were assigned to U.S. troops that they fired on anything in the air. And in 1943, the USAAF changed their radios to a frequency incompatible with ground radios.

The situation improved during the Italian Campaign, where American and British forces, working in close cooperation, exchanged CAS techniques and ideas. There, the AAF's XII Air Support Command and the Fifth U.S. Army shared headquarters, meeting every evening to plan strikes and devising a network of liaisons and radios for communications. However, friendly fire continued to be a concern – pilots did not know recognition signals and regularly bombed friendly units, until an A-36 was shot down in self-defense by Allied tanks. The expectation of losses to friendly fire from the ground during the planned invasion of France prompted the black and white invasion stripes painted on all Allied aircraft from 1944.[18][19]

A-36A of the 86th Fighter Bomber Group (Dive) in Italy in 1944.

In 1944, USAAF commander Lt. Gen. Henry ("Hap") Arnold acquired 2 groups of A-24 dive bombers, the army version of the Navy's SBD-2, in response to the success of the Stuka and German CAS. Later, the USAAF developed a modification of the North American P-51 Mustang with dive brakes – the North American A-36 Apache. However, there was no training to match the purchases. Though Gen. Lesley McNair, commander of Army Ground Forces, pushed to change USAAF priorities, the latter failed to provide aircraft for even major training exercises. Six months before the invasion of Normandy, 33 divisions had received no joint air-ground training.

The USAAF saw the greatest innovations in 1944 under General Elwood Quesada, commander of IX Tactical Air Command, supporting the First U.S. Army. He developed the "armored column cover", where on-call fighter-bombers maintained a high-level of availability for important tank advances, allowing armor units to maintain a high tempo of exploitation even when they outran their artillery assets. He also used a modified antiaircraft radar to track friendly attack aircraft to redirect them as necessary, and experimented with assigning fighter pilots to tours as forward air controllers to familiarize them with the ground perspective. In July 1944, Quesada provided VHF aircraft radios to tank crews in Normandy. When the armored units broke out of the Normandy beachhead, tank commanders were able to communicate directly with overhead fighter-bombers. However, despite the innovation, Quesada focused his aircraft on CAS only for major offensives. Typically, both British and American attack aircraft were tasked primarily to interdiction, even though later analysis showed them to be twice as dangerous as CAS.

XIX TAC, under the command of General Otto P. Weyland used similar tactics to support the rapid armored advance of General Patton's Third Army in its drive across France. Armed reconnaissance was a major feature of XIX TAC close air support, as the rapid advance left Patton's Southern flank open. Such was the close nature of cooperation between the Third Army and XIX TAC that Patton actually counted on XIX TAC to guard his flanks. This close air support from XIX TAC was credited by Patton as having been a key factor in the rapid advance and success of his's Third Army.[20]

The American Navy and Marine Corps used CAS in conjunction with or as a substitute for the lack of available artillery or naval gunfire in the Pacific theater. Navy and Marine F6F Hellcats and F4U Corsairs used a variety of ordnance such as conventional bombs, rockets and napalm to dislodge or attack Japanese troops using cave complexes in the latter part of the Second World War.[21][22]

A Soviet Air Force Il-2M Sturmovik

The Soviet Union's Red Air Force quickly recognized the value of ground-support aircraft. As early as the Battles of Khalkhyn Gol in 1939, Soviet aircraft had the task of disrupting enemy ground operations.[23] This use increased markedly after the June 1941 Axis invasion of the Soviet Union.[24] Purpose-built aircraft such as the Ilyushin Il-2 Sturmovik proved highly effective in blunting the activity of the Panzers. Joseph Stalin paid the Il-2 a great tribute in his own inimitable manner: when a particular production factory fell behind on its deliveries, Stalin sent the following cable to the factory manager: "They are as essential to the Red Army as air and bread".[25]

From Navy experiments with the KGW-1 Loon, the Navy designation for the German V-1 flying bomb, Marine Captain Marian Cranford Dalby developed the AN/MPQ-14, a system that enabled radar-guided bomb release at night or in poor weather.[26]

F4U-5 Corsairs provide close air support to U.S. Marines fighting Chinese forces during the Korean War, December 1950.

Though the Marine Corps continued its tradition of intimate air-ground cooperation in the Korean War, the newly created United States Air Force (USAF) again moved away from CAS, now to strategic bombers and jet interceptors. Though eventually the Air Force supplied sufficient pilots and forward air controllers to provide battlefield support, coordination was still lacking. Since pilots operated under centralized control, ground controllers were never able to familiarize themselves with pilots, and requests were not processed quickly. Harold K. Johnson, then commander of the 8th Cavalry Regiment, 1st Cavalry Division (later Army Chief of Staff) commented regarding CAS: "If you want it, you can't get it. If you can get it, it can't find you. If it can find you, it can't identify the target. If it can identify the target, it can't hit it. But if it does hit the target, it doesn't do a great deal of damage anyway."[27]

It is unsurprising, then, that MacArthur excluded USAF aircraft from the airspace over the Inchon Landing in September 1950, instead relying on Marine Aircraft Group 33 for CAS. In December 1951, Lt. Gen. James Van Fleet, commander of the Eighth U.S. Army, formally requested the United Nations Commander, Gen. Mark Clark, to permanently attach an attack squadron to each of the four army corps in Korea. Though the request was denied, Clark allocated many more Navy and Air Force aircraft to CAS. Despite the rocky start, the USAF would also work to improve its coordination efforts. It eventually required pilots to serve 80 days as forward air controllers (FACs), which gave them an understanding of the difficulties from the ground perspective and helped cooperation when they returned to the cockpit. The USAF also provided airborne FACs in critical locations. The Army also learned to assist, by suppressing anti-aircraft fire prior to air strikes.

The U.S. Army wanted a dedicated USAF presence on the battlefield to reduce fratricide, or the harm of friendly forces. This preference led to the creation of the air liaison officer (ALO) position. The ALO is an aeronautically rated officer that has spent a tour away from the cockpit, serving as the primary adviser to the ground commander on the capabilities and limitations of airpower. The Korean War revealed important flaws in the application of CAS. Firstly, the USAF preferred interdiction over fire support while the Army regarded support missions as the main concern for air forces. Then, the Army advocated a degree of decentralization for good reactivity, in contrast with the USAF-favored centralization of CAS. The third point dealt with the lack of training and joint culture, which are necessary for an adequate air-ground integration. Finally, USAF aircraft were not designed for CAS: "the advent of jet fighters, too fast to adjust their targets, and strategic bombers, too big to be used on theatre, rendered CAS much harder to implement".[8]

UH-1B with rockets and a grenade launcher

During the late 1950s and early 1960s, the US Army began to identify a dedicated CAS need for itself. The Howze Board, which studied the question, published a landmark report describing the need for a helicopter-based CAS requirement.[28] However, the Army did not follow the Howze Board recommendation initially. Nevertheless, it did eventually adopt the use of helicopter gunships and attack helicopters in the CAS role.[29]

Though the Army gained more control over its own CAS due to the development of the helicopter gunship and attack helicopter, the Air Force continued to provide fixed-wing CAS for Army units. Over the course of the war, the adaptation of The Tactical Air Control System proved crucial to the improvement of Air Force CAS.[30] Jets replaced propeller-driven aircraft with minimal issues. The assumption of responsibility for the air request net by the Air Force improved communication equipment and procedures, which had long been a problem. Additionally, a major step in satisfying the Army's demands for more control over their CAS was the successful implementation of close air support control agencies at the corps level under Air Force control.[30] 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.[30]

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.[31] 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.[32] The issue would eventually be put to rest, however, as the helicopter gunship proved crucial in the combat environment of Vietnam.

AH-1 Cobra over Vietnam

Though helicopters were initially armed merely as defensive measures to support the landing and extraction of troops, their value in this role lead 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.[33]

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.