The most important special operations development which came out of the Vietnam War was the gunship - the AC-47, the AC-119, and at its best, the AC-130. The AC-130 performed its interdiction and close air support missions in an outstanding manner and proved to be the most effective "truck killer" in the war. This radical concept, calling for a transport with side firing guns, met considerable initial opposition within the Air Force. However, once a C-47 was equipped and tested in Vietnam, the results were convincing. Although the gunship was vulnerable to enemy ground fire, it had the advantage of being able to keep a target under constant fire by executing its signature orbit overhead.
In the face of heavier ground fire, the Air Force responded by improving avionics and increasing gunship firepower to permit it to operate at higher and safer altitudes. Gunship development progressed from the AC-47 through the AC-119G/K models, to the AC-130A during the Vietnam era. The AC-130H, and the newest gunship, the AC-130U, continues this legacy by providing greater capabilities and larger, more accurate weapons. The initial armament of 7.62mm miniguns on the AC-47, while devastating to enemy ground troops, could not compare with the power of the 25mm, 40mm, and 105mm weapons of the AC-130U. Due to continuing technology improvements, day or night precision strikes came to be a gunship hallmark.
The gunship concept was controversial, and its advocates need evidence it would work. They began flight tests from WPAFB with Capt. John C. Simmon flying T-28 and C-131 aircraft to demonstrate the feasibility of holding a target in sight during a pylon turn. In spite of promising results, the project struggled until the arrival of Capt. Ronald W. Terry in the summer of 1964. Capt. Terry was returning to Wright Field from duty in South Vietnam, and, from his experience with Air Force operations in support of SVN troops, he recognized the potential of the gunship concept. It was Capt. Terry's persistent advocacy, piloting skills, leadership and enthusiasm that revitalized Project Tailchaser and that ultimately led to combat success.
Capt Ronald W. Terry from the Aeronautical Systems Division at Wright-Patterson AFB, Ohio, revolutionized the Air Force concept for close air support. Returning from field observations made during a 1963 trip to Vietnam, Captain Terry wondered why a C-47 couldn't help village defenders with very accurate gunfire of its own. Back at Wright-Patterson AFB, Terry's inquisitive mind led to the discovery of the semi-dormant experimental effort to provide close air support from a single aircraft orbiting a specific spot on the ground, while its side-firing guns struck the spot. Appropriately, the effort was designated Project Tailchaser. By August-September 1964, Terry and a small team had advanced Tailchaser to field testing the General Electric SUU-11A, a 7.62 mm minigun mounted on a C-131, over Eglin AFB's test ranges. Capt. Terry had a C-131 modified to an experimental gunship configuration and was ready for flight testing at Eglin AFB. A 7.62 minigun was bolted to the floor of the fuselage, with the gun barrel pointing out the left-side cargo door. In subsequent live-fire tests, the crew of the C-131 demonstrated the ability to bring continuous, accurate firing on ground targets measuring as small as a ten-foot square.
Continuing success with the concept resulted in an opportunity for combat trials in Vietnam with a C-47 modified to a gunship configuration. In December 1964 Capt. Terry and his team arrived in South Vietnam for a series of combat missions, which began on December 15th. They modified two Farm Gate C-47s with the minigun and briefed crews from the 1st Air Commando Squadron on their employment. The C-47 gunship flew against several target types under varying conditions, but it was the success with night attacks that defined the future. Prior to these missions, the enemy had moved with relative impunity during the night.
In late 1964, the biggest threat to Tailchaser came from the corporate fighter pilot community in USAF's Tactical Air Command. When the fighter community learned the aircraft were to be designated FC-47 ("F" for fighter), the Pentagon didn't need telephones to hear the howls from Headquarters TAC several hundred miles away. The following year, the designation finally settled upon was AC-47 ("A" for attack).
The Air Force created the 4th Air Commando Squadron in August 1965 and equipped it with C-47 gunships, now known as AC-47D 'Spooky.' As later models developed, it also became designated Gunship I. For all its success, the AC-47D was a rather primitive weapon system, and proponents of the gunship concept pushed for a more sophisticated, more capable system. The escalation of the war in Southeast Asia caused the establishment of the Limited War Office at Wright Field, and this office initiated planning in September 1966 for Gunship II. It would utilize a C-130 as the platform, and it would be equipped with a larger armament package, a multi-spectral sensor package, and a computerized fire control system that linked guns and sensors. The fire control computer was the product of engineers in the Avionics Laboratory.
The prototype Gunship II, the AC-130, would be produced by the Aircraft Modification Division of the 4950th Test Wing at Wright Field. Starting with aircraft SN54-1626, the shops had the modifications completed and the prototype ready for flight tests in June 1967. Through the summer of 1967 the AC-130 was evaluated at Eglin AFB, and then in September was flown to South Vietnam for combat trials. The new equipment provided a significant increase in effectiveness over the AC-47, and the Secretary of the Air Force authorized additional modifications of C-130As to the Gunship II configuration.
Development work for gunship systems improvements continued at Wright Field under the direction of (now) Major Terry, chief of the Gunship Program Office. His team designed a prototype of an advanced gunship, with modification authorized in September 1969. This version would be known by the designation 'Surprise Package.' Deployed to Southeast Asia with the designation Coronet Surprise, this advanced gunship proved twice as effective as the standard AC-130A. Beginning in January 1970 the earlier AC-130A models were modified to the 'Surprise Package' configuration.
With the success of the AC-47D "Spooky" gunships in Vietnam, the USAF created modification programs for improved and larger gunships. The Fairchild AC-119G and Ks were developed under the Gunship III program. The AC-119K "Stinger" was an improved version of the AC-119G "Shadow" and was built as the second phase of the Gunship III program.
The Credible Chase program began in May 1971, and was designed to add firepower and mobility to the South Vietnamese Air Force in a relatively short time. The combat evaluation, Project PAVE COIN, of the Fairchild AU-23A and Helio AU-24A was done in June and July of 1971. These aircraft were evaluated for potential use in Southeast Asia as an armed light utility short take off and landing gunship. The AU-24A, like the AU-23A, was found to be unsuitable for combat operations. Major problems identified included a low attack speed of about 135 knots, a low operating altitude below 5,000 feet, no "zoom" escape capability after an attack run, and an extreme vulnerability to antiaircraft fire. Further testing was recommended after the aircraft were updated to combat standards.
The location of the side-firing gun in relation to the center of gravity made both aircraft tail heavy. In the Peacemaker, the condition proved so dangerous that forty pounds of lead had to be inserted under the engine cowling to restore some semblance of equilibrium. To overcome the lack of balance required a heavy hand on the controls and forced the small-framed South Vietnamese to wrestle the stick with both hands in performing basic maneuvers. As if this were not enough, neither range nor payload lived up to expectations; a minigunship carrying one thousand pounds and flying a distance of one hundred nautical miles could remain on station just thirty minutes before turning back to refuel.
The XM197 Armament System evaluated in this test is similar to the M61 Vulcan 20mm rapid fire cannon. The XM197 consists of three rotating barrels instead of six and has a rate of fire of approximately 400 rounds per minute (rdpm) slow rate, and 700 rdpm fast rate. For the test reported here, the gun was pedestal mounted just behind the pilot's seat in the Fairchild-Hiller Peacemaker Aircraft. The M61 and XM197 20mm guns are automatic aircraft cannons for use against aircraft and ground or seaborne targets. These guns are electrically or hydraulically powered, belt fed or linkless feed, and electrically fired. A round of ammunition is fired through one barrel at a time, as the barrels and rotor assembly rotate once around the rotor housing.
In January 1972, the second test phase for the AU-24A began at Eglin Air Force Base, Fla. The initial aircraft used (S/N 72-1319) was leased from Helio and retained its civilian configuration, but it allowed basic flight testing to begin. The combat evaluation of the Credible Chase program was canceled in February 1972, but the initial (stateside) evaluation was kept on the program schedule. The Credible Chase program failed to provide South Vietnam with a weapon of aerial interdiction. Both Thailand and Cambodia, however, seemed to need a light aircraft capable of operating from primitive airfields to conduct general counterinsurgency missions. As a result, Cambodia received fourteen Stallions and Thailand thirteen Peacemakers, with one of each type going into storage at Davis-Monthan Air Force Base, Arizona.
The development history of the gunship describes a cycle of improvement, testing, combat operations, and requests for more improvements. In 1971 the Gunship Program Office proposed project Pave Aegis, which featured the installation of a very large gun, an Army 105mm howitzer, in addition to two 20mm cannon and one 40mm cannon in a C-130E. Once again the Wright Field shops prepared the prototype, whose success led to the conversion of ten more aircraft. Subsequently, these 'E' models were upgraded to 'H' model standards, and they remained with Air Force Special Operations units into the 1990s. With the acquisition of the AC-130U version, the older gunships have been retired.
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