With the success of the AC-47D "Spooky" gunships in Vietnam, the USAF created two modification programs for improved and larger gunships. The Fairchild AC-119G and AC-119Ks were developed under the Gunship III program, and the Lockheed AC-130A was developed under the Gunship II program.
Compared to the AC-47D, the AC-130A "Spectre" gunship was equipped with more and bigger guns -- four MXU-470 7.62mm miniguns and four M61A1 20mm cannons. Gunship II was also equipped with a more sophisticated avionics suite including the Night Observation Device, Forward Looking InfraRed, side looking radar, beacon tracking radar and a fire control computer system. The AC-130A was also equipped with a 20 kilowatt (1.5 million candlepower) illuminator and a flare launcher.
On Feb. 26, 1967, the first aircraft (JC-130A S/N 54-1626) was selected for conversion into the prototype AC-130 gunship. The modifications were done in April and May 1967 at Wright-Patterson Air Force Base, Ohio, by the Aeronautical Systems Division. Flight testing of the prototype was done primarily at Eglin Air Force Base, Fla., and began on June 6, 1967. Testing and additional modifications were done throughout the summer of 1967. By early September, the aircraft was certified ready for combat testing. The prototype was flown to Nha Trang Air Base, South Vietnam arriving on Sept. 21, 1967, for a 90-day test program.
Combat Tests and Evaluation The prototype AC-130A Gunship II (initially designated Gunboat) was modified at Wright-Patterson Air Force Base, Ohio, in the spring of 1967. Initial flight testing was done during the summer of 1967, primarily at Eglin Air Force Base, Fla. The aircraft was flown to South Vietnam for follow-on flight testing under combat conditions.
The AC-130A arrived at Nha Trang AB on Sept. 21, 1967. The initial tests of the Gunship II involved Close Air Support in the southern region of South Vietnam in the Mekong river delta area. Close Air Support was a critical mission since support of Troops In Contact always took precedence over other gunship missions. The next series of tests evaluated the aircraft's interdiction capabilities primarily against enemy supply trucks operating on the Ho Chi Minh trail in the Tiger Hound (southeast quadrant of the panhandle) area of Laos. The final phase of the test program involved flying armed reconnaissance missions in the central highlands of South Vietnam (2nd Corps area). Actual combat sorties were flown between Sept. 24 and Dec. 1, 1967.
The results of the combat test program were very encouraging. The Gunship II was particularly good at interdiction of enemy supply vehicles. Of the 94 vehicles sighted, 38 were destroyed (verified direct hits and secondary explosions or sustained fire). During the combat evaluation, the AC-130A fired more than 85,000 rounds of 20mm ammunition and more than 220,000 rounds of 7.62mm ammunition. While the combat test program was successful, there were some serious problems identified which would require fixing before the "production" AC-130A modification program could begin.
After the prototype AC-130A completed its initial combat evaluation in early December 1967, problems identified during the test program were evaluated and integrated into an upgrade and overhaul plan expected to take until midsummer 1968. However, because of the success of the first combat test, Gen. Westmoreland, Commander of the United States Military Assistance Command, Vietnam, requested the AC-130A be returned to Vietnam as soon as possible, so it could be used before the start of the "wet" season in late spring 1968. Gen. Momyer, Commander of the 7th Air Force, directed the AC-130A overhaul include only essential fixes and the gunship be returned to Vietnam by the beginning of spring 1968. The overhaul was completed in early February and the aircraft arrived back in Southeast Asia on Feb. 12, 1968. During the second combat test, the Gunship II was based at Ubon Royal Thai Air Force Base, a forward operating location of the 14th Air Commando Wing based at Nha Trang Air Base, South Vietnam (location of the first combat test).
The AC-130A prototype conducted the second combat evaluation between Feb. 27 and May 14, 1968. Forty-three combat missions were flown over Laos, primarily in the "Steel Tiger" area of the panhandle. Eight hundred 74 enemy vehicles were sighted -- 212 were destroyed and 107 damaged. The gunship also destroyed one 37mm antiaircraft artillery (AAA) site and damaged four more 37mm AAA sites.
Because of some early problems with the gunship's fire control system and often heavy AAA, the AC-130A teamed up with Cessna O-2 "Covey" forward air controllers and Lockheed C-130 "Blindbat" flare ships. The Blindbat was very effective at detecting targets using its star light scope; however, it flew a predictable search pattern at predictable attitudes (right hand circular or race track at 8000-11000 feet altitude). Enemy gunners were quick to realize if they heard or saw the unarmed Blindbat orbiting their position, an attack strike was imminent and to hold fire waiting on the strike aircraft. The AC-130A was highly vulnerable in this situation, so if a Blindbat spotted a target, it would relay the information to the gunship and clear the area. This allowed the gunship to achieve some amount of surprise when attacking defended ground targets, although in most cases, the AC-130A simply avoided areas known to contain heavy enemy AAA.
The AC-130A worked well using the O-2 "Covey" as a seeker aircraft. In general, the O-2 would fly slightly higher and inside the gunship's orbit. When an enemy AAA position was spotted, the O-2 marked the gun and called for a "fast mover" to attack it while the AC-130A moved off to search for truck traffic in areas with little or no AAA gun positions.
The overall conclusion of the second test program was the AC-130A would be extremely effective in interdicting supply lines if the AAA defenses were first neutralized. Note: Because of the bombing halt in place during the spring of 1968, three O-2 "Coveys", one C-130 "Blindbat" and three F-4s based at Ubon RTAFB were shot down over Laos (May 1968) -- the enemy used the time to set-up many AAA sites along the Ho Chi Minh trail routes through southern Laos.
Following the second combat evaluation, all major aircraft systems and components were critiqued based on combat performance, ease of maintenance and reliability. The illuminator system was broken throughout the test period and was eventually removed from the aircraft. Problems with the system included lack of spare parts, poor repair manuals and contamination of the water cooling system. The LAU-74 semiautomatic flare launcher installed beside the illuminator on the aft ramp worked well throughout the tests. When the fire control computer was "down," the pilot sometimes resorted to AC-47D-style attack tactics -- drop flares to light the target and manually site the gun and "walk" the tracer path to the target. The fire control radar (DPN-34) was broken much of the time and required extensive maintenance between flights. The evaluation team recommended an entirely new system be used on all further gunship conversions. The infrared tracking system was useable, but required a very experienced operator to continuously track a ground target with the aircraft in attack mode (30 degree left bank). The guns all performed well and only minor jamming problems (fixable in flight by the gunners) were reported. The fire control system performed well in direct fire operation (no offset computations) but was prone to problems otherwise. The fire control computer was subject to in-flight failure but worked well when it was functional. The Night Observation Device worked well and was among the most reliable pieces of equipment on the Gunship II prototype. The navigation equipment worked well and most problems were associated with the AC-130A attack tactics. For example, the search radar had a limited range of just 30 miles and tended to have roll stabilization problems during sustained banked flight.
The typical AC-130A attack profile was flown at 5,000 feet above ground level (AGL) for armed reconnaissance and interdiction missions. If moderate or heavy AAA fire was encountered the aircraft would attack from 6,500 or 8,000 feet AGL (in most cases, the Gunship II would depart areas with heavy AAA without attacking). For close air support of Troops In Contact (TIC) the aircraft would fly as low as 3,500 feet AGL to improve gun accuracy. The standard attack speed was 145 knots. The aircraft attacked while in a 30 degree left bank and the guns were depressed 20 degrees (down). This combined with an approximate 10 degree ballistic arc caused the rounds to impact the target area at approximately 60 degrees (from horizontal). This high angle of incidence produced good results even when penetrating the jungle canopy. The 20mm "Vulcan" cannons were the primary weapons used and a 2-second burst (75-100 rounds) from a single 20mm cannon was usually sufficient to destroy an enemy truck. When firing on a group of vehicles located close to one another, two 20mm cannons were fired simultaneously. The only time all eight guns (four 20mm and four 7.62mm) were fired together was when attacking an enemy antiaircraft artillery (AAA) site. When the Gunship II encountered an AAA site and didn't attack it (this was usually the case), a flare, timed to ignite when it hit the ground, was sometimes dropped on the site to mark it (and be avoided by the Gunship and any FAC aircraft in the area).
The final recommendations of the evaluation team included the need for an upgraded fire control system which could minimize the time over target, reliably maintain target lock, and store multiple target locations. The need for larger caliber guns to deal with AAA sites and armored vehicles was also included in the report. The evaluation team suggested a 25mm cannon; however, follow-on gunships included 40mm cannons and some were equipped with a 105mm howitzer!
TECHNICAL NOTES: Armament: Four 7.62mm miniguns and four 20mm cannons Engines: Four Allison T-56-A-11 turboprops of 4,050 hp Maximum speed: 380 mph Cruising speed: 335 mph Range: 2,500 miles Service ceiling: 33,000 ft. Span: 132 ft. 7 in. Length: 97 ft. 10 in. Height: 38 ft. 6 in. Weight: 124,200 lbs. maximum Crew: 11 (pilot, co-pilot, navigator, fire direction officer, night observation device operator, radar sensor operator, flight engineer, loadmaster, master armorer, 7.62mm minigun gunner/armorer and 20mm cannon gunner/armorer) Serial number: 54-1626