Fairchild AC-119K (S/N 53-7839) of the 4413th Combat Crew Training Squadron, 4410th Combat Crew Training Wing, Lockbourne Air Force Base, Ohio. Photo taken at Hurlburt Field, Fla., in 1970. (U.S. Air Force photo)
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 AC-119K had several major improvements incorporated into its design. Armament included the four 7.62mm miniguns of the "Shadow" but added two 20mm cannons. Two pods housed General Electric J85 jet engines with 2,850 pounds thrust each. The J85s allowed the aircraft to takeoff at a much larger gross weight of 80,400 pounds -- more than 15,000 pounds higher than the AC-119G. The Stinger also had significantly upgraded avionics capability. A forward looking, terrain avoidance radar and a Forward Looking Infrared Radar (FLIR) system were installed. The Night Observation Device, automatic flare launcher and 1.5 million candlepower illuminator of the AC-119G were retained. A beacon tracking radar system was initially installed but removed in December 1970.
The first of 26 AC-119K gunships arrived in Vietnam at the end of 1969. By February 1970, 18 gunships were available for combat. The Stingers formed the 18th Special Operations Squadron of the 14th Special Operations Group and were initially home-based at Phan Rang Air Base with two detachments operated at Da Nang Air Base and Phu Cat Air Base. Because of the AC-119s' advanced sensors and increased armament, the aircraft's mission was oriented more toward armed reconnaissance and "truck killing" than the AC-119G.
By April 1971, the aircraft were distributed at Da Nang AB and Nakhon Phanom (NKP) Air Base, Thailand. The flight at Da Nang was primarily concerned with armed reconnaissance in the Steel Tiger region of Laos with a secondary mission of providing close air support for troops in contact in the northern region of South Vietnam. The flight at NKP was primarily oriented toward close air support for troops in contact in the Barrel Roll region of Laos with a secondary mission of armed reconnaissance in the "Plain of Jars" (central Laos).
The AC-119K was extremely effective as a truck killer, but had to be careful to avoid areas of heavy antiaircraft artillery (AAA) concentrations. The AC-119K's relatively slow speed and predictable attack pattern made it vulnerable to AAA. In areas where there was no enemy AAA, the Stinger used 5,500 feet above ground level (AGL) as a working altitude and in areas with AAA present, 7,000 AGL was used (truck killer missions). Normal working altitude for close air support of troops in contact (with the enemy) was 3,500 AGL. This enabled the AC-119K to shoot accurately with both the 20mm cannon and 7.62 miniguns and be relatively safe from small arms fire.
Combat Tactics In an effort to improve the mission capabilities of the AC-119K, the USAF and U.S. Army tried several techniques. Some techniques involved ground based marker beacons and others involved secondary aircraft flying "seek" or "hunter" patrols.
Among the most primitive ground techniques used to direct the fire of the gunship was the "fire arrow." This simple technique required the friendly ground troops to make an arrow out of flare pots to literally point to the enemy. The arrow head was used to designate the direction of the enemy and the arrow shaft was used to indicate distance (one flare pot for every hundred feet for example). The fire arrow worked reasonably well, but only in clear weather when the ground troops were out in the open. In order to provide an effective target designation system useable under the jungle canopy or in marginal weather, a ground beacon system was developed. The ground beacon provided a fixed reference point for the gunship regardless of weather. Range and bearing to the target could then be passed to the gunship and set into the fire control computer which would determine an offset aiming point for the pilot. By using this technique, the gunship could remain above the clouds and still direct its fire on the enemy position.
The AC-119K was equipped with an AN/APQ-133 Beacon Tracking Radar (BTR) that could receive signals from the X-band ground beacon. This system was designated Combat Rendezvous. The BTR was capable of search, acquisition and angular tracking of the ground beacon. The angular tracking function was critical since the gunship had to be in a 30 degree left bank during attack. The predictable attack pattern (left turning circle) required the area to be free of heavy antiaircraft artillery (AAA); however, the AC-119K could attack when light or moderate AAA was present.
Another method tested to attempt to improve the lethality of the AC-119K was the use of a Grumman OV-1 "Mohawk" (or more commonly "Spud") as a target seeker. Once a target was identified, the gunship would be called in for the attack. Two versions of the OV-1 were used, the OV-1B carrying a Side Looking Airborne Radar (SLAR) and the OV-1C with an InfraRed detector. The Army OV-1s flew out of Udorn Royal Thai Air Base and conducted nightly reconnaissance patrols of the "Plain of Jars" (or Barrel Roll) area of Laos. The IR equipped OV-1Cs could detect heat from the engines of trucks and even camp fires. The SLAR equipped OV-1Bs were used to detect moving objects. In many cases, the targets identified by the OV-1s were gone by the time the recorded reconnaissance data was gathered, interpreted and analyzed. The idea was to relay the near real time target data appearing on the OV-1 monitors to AC-119K gunships operating in the area.
The first test period of the OV-1 Seeker and AC-119K Destroyer (or Hunter Killer) teams was done between April 27 and May 23, 1970. Intelligence data indicated most enemy troop movements were conducted in the late evening, so the evaluation missions were flown between 8 and 11 p.m. When the OV-1 detected a target, the information was passed the Airborne Battlefield Command and Control Center. The ABCCC or "Alleycat" was a Lockheed HC-130 flying over Laos used to coordinate aircraft flying within its zone. If a gunship was available (support of troops in contact took precedence over all other missions), and target validation could be obtained, the ABCCC relayed the information to the gunship. The AC-119K then flew to the target area and attempted to identify the target using its Forward Looking Infrared or Night Observation Device. The test was relatively successful when all the equipment worked properly; however, this was rare. The SLAR system on the OV-1B was prone to failure and there was only one aircraft assigned to the Army detachment at Udorn. The AC-119K systems were also prone to failure. There were only three Stinger assigned at Udorn and each was scheduled (fragged) for a mission every night. The season was changing from "dry season" to "wet season" and some missions were canceled due to bad weather. Furthermore, the IR detection capability of the OV-1C was reduced with increased moisture. Wet weather virtually eliminated the IR detection capability of the AC-119K.
The most serious problem was the OV-1 / AC-119K seek and destroy team was the rules of engagement. Because of several friendly fire incidents, nearly all targets identified by the OV-1 were reported to the ABCCC which in turn relayed the information to the U.S. embassy in Laos for validation. Once validated, the target information was relayed back to the ABCCC which would then call for the gunship. The gunship would then be cleared to attack to coordinates of the original sighting, but if the target had moved, the entire validation process had to begin again.
The second test period for the OV-1 / AC-119K teams was between Sept. 19 and Nov. 19, 1971 -- 16 months after the initial test. The second test was formed in an ad hoc manner at the start of the fall dry season. A large column of enemy trucks was detected on the morning of Sept. 19 and the Army urgently requested gunship support. The OV-1s were still based at Udorn, but the AC-119 had moved to Nakhon Phanom (NKP) Air Base, Thailand. Although the tactics were essentially the same during the second test period, the results were not. The OV-1 advisories amounted to a very small number of successful attacks. The AC-130 Spectre gunships were in use by this time and were very effective at finding their own targets and destroying them without the cumbersome relay and validation scheme used for OV-1 identified contacts. With the failure of the second Hunter Killer test, the concept was dropped.
TECHNICAL NOTES: Armament: Four SUU-11A 7.62mm miniguns with 21,500 rounds of ammunition, two M61A1 20mm cannons with 3,000 rounds of ammunition, 24 MK 24 flares and LAU-74/A flare launcher. Later, the SUU-11A's were replaced by General Electric MXU-470/A gun modules. The AC-119K was equipped with a computerized fire control system with fully auto, semi-auto, manual and offset firing capabilities. The Stinger also had a 1.5 million candlepower illuminator with a variable beam, APQ-136 forward looking radar, AAD-4 forward looking infrared radar, APQ-25/26 electronic countermeasures warning device, and AN/APQ-133 Beacon Tracking Radar (removed in December 1970) Engines: Two Wright R-3350s of 3,500 hp each and two General Electric J85-GE-17 turbojets of 2,850 lbs. thrust each Combat speed: 180 knots Duration: Approx. 5 hours (plus 30 minutes reserve) Attack altitude: Approx. 3,500 ft. AGL for close air support; 5,500 feet AGL for ground attack in areas without AAA and 7,000 AGL in areas with AAA Span: 109 ft. 3 1/4 in. Length: 86 ft. 5 3/4 in.
Height: 26 ft. 7 3/4 in. Weight: 80,400 lbs. maximum
Crew: 10 (pilot, copilot, navigator, night observation sight operator, radar/FLIR operator, flight engineer, illuminator operator, three gunners) Serial numbers: 52-5864, 52-5889, 52-5910, 52-5911, 52-55926, 52-5935, 52-5940, 52-5945, 52-9982, 53-3154, 53-3156, 53-3187, 53-3197, 53-3211, 53-7826, 53-7830, 53-7831, 53-7839, 53-7850, 53-7854, 53-7877, 53-7879, 53-7883, 53-8121, 53-8145, 53-8148