AC-119K Stinger
In 1967, Fairchild converted 52 C-119G aircraft into gunships for use in South Vietnam with one-half being AC-119G Shadows and the other 26 AC-119K Stingers. Because the G-model C-119’s twin piston engined performance was so marginal at combat gross weight, the Air Force intended from the beginning to upgrade selected Gs to a newly designated K-model configuration. The K bolstered the piston engines with two wing-mounted J-85 jet engines. The difference was no small thing. While the rate of climb with one engine out was 500 feet per minute for the K, the G model’s performance under the same conditions was listed “unsatisfactory at combat gross weight.” Perhaps to spare squeamish pilots, no performance numbers of any kind were included to describe just how “unsatisfactory” the situation was!
The two AC-119 models had two completely different missions. The Shadows provided troops in contact and airbase defense. The Stingers were devoted to the truck hunting mission especially on the Ho Chi Minh Trail. With their 20mm weapons in addition to their 7.62mm guns, they could very effectively destroy most trucks used by the North Vietnamese. Success with the G-model led directly and quickly to the AC-119K with its two auxiliary jet engines. Armed also with 20mm Gatling guns with more than 4,200 rounds of ammunition and advanced avionics, the K-model proved to be even more effective. The AC-119K had upgraded radar, communications and navigation systems and two J85 engines for jet-assisted takeoff.
Intended for interdiction, though with a secondary mission of supporting ground troops, the Stinger carried heavier armament than the Shadow, a pair of multibarrel 20-mm guns and four multibarrel 7.62-mm machine guns, whereas the AC–119G mounted only the machine guns. Both aircraft used the standard night observation device, but the K model could also search out targets with infrared equipment. A beacon-tracking radar helped the AC–119K pinpoint friendly troops, who had the necessary transponder; this feature helped the Stinger interpose a curtain of fire to protect besieged outposts, for example, but served no purpose on interdiction missions.
In their fire control systems, both the AC–119G and the K version used the same kind of analog computer as had been tested in Gunship II. Basically, the computer lacked flexibility, since it could be programmed for only a limited range of airspeeds, bank angles, and altitudes. If a shift from one sensor to another, or enemy fire, dictated a marked change in altitude, the crew might have to reprogram the computer to continue the mission. The inability of the automatic pilot to hold the gunship in a steeply banked turn further complicated the task of fire control with the Shadow and Stinger.
The 4413th Combat Crew Training Squadron received its first AC-119K gunship Nov. 8, 1968. This squadron had been organized at Lockbourne Air Force Base, Ohio, March 1, 1968, and assigned to the 1st Air Commando Wing with a mission to train gunship crews. The 71st Air Commando Squadron (Reserve) was called to active duty at Lockbourne May 12. Although assigned to the 1st ACW at Hurlburt Field, they received their gunship training at Lockbourne in the AC-119 and deployed to Southeast Asia in late December for assignment to the 14th Special Operations Wing. Four gunships, two AC-119s and two AC-130s, of the 4413th CCTS at Lockbourne deployed to Hurlburt Field for COMBAT RENDEZVOUS. That exercise evaluated the ability of these gunships to strike targets close to friendly forces. The tests validated their offset mode of fire control. Training during the first half of 1969 qualified 341 aircrew members in the AC-119G/K gunships. The 18th SOS although assigned to the 1st SOW activated at Lockbourne Jan. 25, 1969, to fly the AC-119. They received their first gunship March 5 and transferred to Southeast Asia and assignment to Pacific Air Forces Oct. 1, 1969.
The first K-model gunships (call sign “Stinger”) began arriving in Vietnam in October 1969, and by the following January, the second C-119 gunship squadron, the 18th SOS, was also combat ready. In addition to the two J-85 jet engines, the K model bolstered the four-minigun armament of the G with two 20 mm multibarrel cannon and 4,500 rounds of 20 mm ammunition. In addition to carrying the G-model NOD, the K models were also equipped with a state-of-the-art forward looking infrared (FLIR) system. This was a noticeable improvement over the seldom used NOD on the 17th SOS gunships because the FLIR did not require starlight or moonlight. In addition to the previously described flare equipment, both models were also equipped with a door-mounted, 20-watt “white light” illuminator. Its 1.5-million candle power variable beam could light up a football stadium with superb clarity on the darkest nights. Of course, it also told the bad guys below exactly where to point their weapons, a drawback that discouraged the gunship crews from using the illuminator whenever possible.
Although the AC–119K Stinger performed adequately during a combat evaluation lasting from November 1969 through February 1970, the sixteen aircraft of this type assigned to Southeast Asia soon revealed other weaknesses, as well as certain strengths, in missions against the trail. Experience in combat demonstrated that the 20-mm shell was too light to destroy trucks, and the rapid-fire weapon often jammed. Although the two auxiliary jet engines improved performance, they increased the operating ceiling to only about fifty-five hundred feet above ground level, beyond reach of machine guns, but well within range of the 23-mm, 37-mm, and 57-mm antiaircraft guns that were becoming more numerous along the trail. On the other hand, the auxiliary jets also enabled the flight engineer to reduce the power setting and richness of the fuel mixture for the piston engines, adjustments that curtailed the exhaust plumes and made optical tracking difficult for the gunners below. Moreover, if the gun crews should knock out an engine or inflict other severe damage, the auxiliary powerplants gave the Stinger a chance to survive, provided the crew reacted promptly and skillfully.
Enemy antiaircraft fire became deadlier as the enemy deployed an increasing number of weapons that could reach the Stinger’s normal operating altitude. Unable to climb out of range of the antiaircraft guns, the AC–119K also lacked the maneuverability to avoid the strings of tracers rising from the ground, for the added thrust of the jet engines could not fully compensate for the additional weight of guns, fire control system, and sensors, leaving the aircraft likely to stall if the pilot banked too steeply or pulled up too sharply. Because of this vulnerability, pilots tried to avoid any AAA [antiaircraft artillery] environment of larger than 57-mm weapons, although even the 57-mm weapon could be effective, without radar control, at altitudes of nine thousand to eleven thousand feet. By February 1971, the AC–119K gunships no longer attacked traffic in the vicinity of Mu Gia, Ban Karai, and Ban Raving Passes; Tchepone; and Ban Laboy Ford, though the planes continued to serve elsewhere in Laos.
As General Momyer had feared, maintenance problems dogged the Fairchild gunships throughout their service in Southeast Asia. The G models in particular proved to be a mechanic’s nightmare, though the Ks had troubles enough. Beginning in December 1971, 20-mm fire from the Stingers unaccountably kept missing targets. The problem appeared to lie in the computerized fire control system, which somehow misinterpreted the sensor data it was translating into instructions for the pilot. Accuracy had not improved by the end of March 1972, when North Vietnam invaded the South, and emphasis shifted from interdiction of the Ho Chi Minh Trail to the support of South Vietnamese troops.
ENHANCE PLUS directed by the Air Force Chief of Staff, Oct. 1, 1972, transferred 16 AC-119Ks assigned to PACAF and the six assigned to the 1st SOW to the Air Force of South Vietnam. This decision wiped out the entire 1st SOW AC-119K force. Therefore, on Oct. 20, with no available aircraft, the AC-119K class at Hurlburt was advised that their training had been cancelled. Since they require auxiliary fuel tanks in order to fly across the Pacific Ocean, the Hurlburt aircraft deployed Oct. 22 to Robins Air Force Base, Ga., for that modification. However, when ENHANCE PLUS was cancelled, three of the six 1st SOW aircraft redeployed home. Hardly had they returned when the program was revived and all six aircraft departed for SEA Oct. 29.
Title to the aircraft didn't automatically provide the needed aircraft capability. Besides lacking electronics technicians to repair and fine tune certain of the AC–119K’s sensors, the South Vietnamese Air Force faced a shortage of crews able to fly the aircraft. In December 1972, six AC-119K crewmembers from the 415th Special Operations Training Squadron deployed to SEA to train the South Vietnamese. This training team consisted of one pilot, two navigators, one flight engineer, one gunner and one illuminator operator. It completed its mission and returned home March 5, 1973. The 415th SOTS earned the Air Force Outstanding Unit Award for the period between Sept. 15, 1970 and July 25, 1971, when it had been located at Lockbourne and had flown the gunships.
South Vietnam received the first of a projected eighteen AC–119Ks, a gunship that outperformed either the AC–47 or AC–119G. The March 1972 invasion delayed the beginning of an AC–119K crew training program until December of that year, and the Air Force did not complete the transfer of ten of the gunships until March 1973. The Air Force phased out its last AC-119 in 1973. By the time the South Vietnamese began flying the AC–119K, its time had passed as a weapon of interdiction; not even the AC–130 could roam at will over an expanded and better defended Ho Chi Minh Trail.
