“Black Crow” sensor on Thor, an AC-130A. This sensor detected and tracked vehicles by the electrical impulses of their spark plugs. Thor was shot down by antiaircraft fire in December 1972, with the loss of 14 members of its 16 crew. (U.S. Air Force photo)
Originally, eight C-130As were scheduled for conversion to the same configuration as the prototype AC-130A with four 20mm cannons and four 7.62mm miniguns. However, in August 1969 when the modifications were about to begin on the last aircraft, the Aeronautical Systems Division at Wright-Patterson Air Force Base, Ohio, proposed the aircraft be used as a flying test bed for new equipment, weapons and tactics. The proposal was approved and modifications began on the aircraft that would be known informally as "Surprise Package" and formally as "Coronet Surprise."
Combat testing of the prototype AC-130A demonstrated the need for many improved systems. A more accurate and efficient fire control system would generate higher kill rates and minimize the time the aircraft was exposed to enemy antiaircraft fire. An improved targeting system capable of detecting through smoke, rain, fog and the jungle would improve the utility of the gunship in less than ideal conditions. A greater target detection and attack range was needed to give the aircraft improved attack capability in high threat areas. Finally, larger caliber guns were needed to effectively attack antiaircraft artillery (AAA) sites when necessary and put the aircraft out of range of the smaller caliber enemy AAA (below 37mm).
"Surprise Package" carried four weapons: two 20mm Vulcan cannons and two 40mm "Bofors" cannons. The 40mm cannon was a U.S. Navy antiaircraft gun left over from World War II selected to eliminate the time required to design a new gun. The 40mm cannon allowed the aircraft to attack from higher altitudes (5,500 to 10,500 feet above ground level) and offered a greater survival portability in AAA environments with 37mm or 57mm guns. The Bofors cannon also packed a larger punch and was much more effective in destroying lightly armored vehicles.
A significant equipment upgrade was the addition of the "Black Crow" detection system. Black Crow was used to "identify and acquire target signals by means of electrical impulses from vehicles operating with an ignition system and to provide azimuth and elevation information regarding these targets to the fire control computer." Black Crow was a good system, but it only worked if the vehicle engine was running and was only marginally effective at detecting diesel power vehicles.
The aircraft had a digital fire control computer (FCC) rather than the analog device used on the "Plain Jane" AC-130A. The digital FCC was capable of accurately firing the aircraft's guns from any altitude, bank angle or airspeed within the basic attack profile of a left banking turn. The aircraft also had a Moving Target Indicator system capable of detecting vehicles moving at least three miles per hour. It was designed to work through light to moderate jungle canopies but was largely ineffective during actual combat use. An inertial navigation system (INS) was also installed. The INS provided very precise aircraft position data to the FCC for use in computing direct fire and offset firing solutions. Besides the standard Night Observation Device, Surprise Package had a Low Light Level Television system installed. A laser target designator was installed and it allowed the AC-130A to "illuminate" ground targets for attack by F-4s carrying laser guided bombs. Like the standard AC-130A, the "Surprise Package" AC-130A was escorted by an F-4 Phantom II. The F-4 was for flak suppression and the addition of the laser target designator made the combination significantly more effective in attacking AAA sites.
The modification program was endorsed by Gen. Momyer, 7th Air Force Commander, on Aug. 12, 1969, with several conditions. First, the aircraft would have to be in Southeast Asia by Nov. 15 and operational by Dec. 1. Next, the aircraft would have to be convertible to standard AC-130A configuration in four days if the tests were unsuccessful. Finally, all spare parts and technicians required to maintain the specialized equipment would be available at Ubon Royal Thai Air Force Base where the aircraft was to be based. The actual modifications started on Sept. 2 and were completed in late October. Initial testing was done at Eglin Air Force Base, Fla., between Oct. 28 and Nov. 15, 1969. The aircraft departed for Ubon RTAFB on Nov. 25 -- 10 days behind schedule. The combat evaluation of the "Surprise Package" AC-130A was done between Dec. 12, 1969, and April 30, 1970.
During the evaluation period, the aircraft flew 112 sorties, sighted 1,261 enemy vehicles, destroyed 614 of them and damaged 218 more -- achieving better than seven trucks destroyed per sortie. The Black Crow system was extremely effective and accounted for 65 percent of all vehicles detected during the evaluation period.
The National Museum of the United States Air Force has an AC-130A (S/N 54-1630) on display in its Cold War Gallery.
Prototype AC-130 gunship
"Plain Jane" initial conversion
"Surprise Package" test aircraft
TECHNICAL NOTES: Armament: Two 20mm M61A1 Vulcan cannons firing at 2,500 rpm (3,000 rounds typically carried onboard) and two 40mm M1 "Bofors" cannons with a selectable firing rate of single shot or 120 rpm (352 rounds typically carried onboard) Engines: Four Allison T-56-A-15 turboprops of 4,050 hp Attack speed: 145 knots Cruising speed: 180 knots Duration: 3-5 hours for a typical combat mission (6 hours maximum with 30 minutes reserve fuel); most missions were about 5 hours in duration Attack altitude: Between 5,500 and 10,500 ft. above ground level depending on the threat environment Span: 132 ft. 7 in. Length: 97 ft. 10 in. Height: 38 ft. 6 in. Weight: 124,200 lbs. maximum Crew: 14 (pilot, copilot, navigator, fire control officer, low light level television operator, forward looking infrared operator, illuminator operator, electronic warfare officer, flight engineer, loadmaster, master armorer, and four gunners/armorers) Serial numbers: (Prototype) 54-1626; (Initial conversions [from JC-130A]): 53-3129, 54-1623, 54-1625, 54-1627 to 54-1630; ("Surprise Package") 56-0490 (S/N 54-1629 crashed on May 24, 1969)