The success of the AC-130A, especially in operations over the Ho Chi Minh trail, led to a decision to increase the number of aircraft in the AC-130 gunship fleet and update the subsystems of those already in active service. Six additional aircraft were programmed for addition to the force. These new AC-130E aircraft were codenamed Pave Spectre and were programmed for delivery to Southeast Asia not later than 1 January 1972. Thus, the 16th Special Operations Squadron was scheduled to possess 12 updated AC-130s, including new AC-130E Pave Spectre aircraft, by 1 November 1971. The addition of the AC-130E Pave Spectre aircraft to the existing AC-130 fleet, was to provide the 16th Special Operations Squadron with a total fleet strength of 18 aircraft, including AC-130As, by 1 January 1972. The initial plan called for converting eight aircraft, 2 prototypes (S/N 69-6567 and 69-6568) and 6 operational planes (69-6569 to 69-6574). Six additional aircraft were eventually reserved for Pave Spectre conversion, but only 3 were modified (S/N 69-6575 to 69-6577). A number of AC-130A aircraft, including the original AC-130A prototype, were converted to AC-130Es.
The AC-130E had an improved digital fire control system based on the LTV A-7 Corsair II system. In using an existing FCS, the program managers expected to take advantage of the training, maintenance, supply and logistics already in place to minimize the chances of a deployment delay for the operational aircraft. The FCS also featured a head up display gunsight for the pilot and a moving map display for the navigator. T he AC-130E retained the low light level television, forward looking infrared, Black Crow ignition sensor, moving target indicator and beacon tracking system successfully used on the Pave Pronto AC-130A.
The new AC-130E aircraft also became the testbed for another armament improvement program, codenamed Pave Aegis. Conceived in 1970, the Pave Aegis system went from concept to combat in little more than a year. In early 1971, Headquarters, USAF had officially approved the Pave Aegis development program to determine the feasibility of firing a large-caliber weapon from the AC-130A gunship. As a result, the USAF tested weapons ranging from 75mm to 105mm as suitable additions to the AC-130 arsenal.
A modified M102 105mm howitzer, utilizing the M137 cannon, was selected for test because of its longer range, greater explosive power, and the variety of ammunition available. From 11 through 17 September 1971, crews from the 4950 Test Wing (Tech) flew 6 test sorties to obtain data for evaluation. Initial results were favorable. As part of the program plan, it was noted that the AC-130E would be used instead of the AC-130A in the final configuration due to its greater gross weight capability and the better accuracy of its digital fire control system.
Concerns about diverting energy from converting C-130s to a proven configuration (the AC-130E Pave Spectre configuration) led to a number of delays in the program. However, after being briefed, on 19 November 1971 the USAF's Chief of Staff approved the program, directing that testing be expedited with subsequent deployment to Southeast Asia by February 1972 if further tests proved satisfactory. The Seventh Air Force in Southeast Asia remained concerned about the diversion of energy from existing AC-130E conversion.
In spite of these and other concerns, the modification of the sixth and last AC-130E to be converted as part of Pave Spectre, began at Hurlburt Field on 17 January 1972 with Ithe installation of the 105mm gun. The results of the earlier AC-130A tests were used to improve the design and installation. The tests were considered successful and plans began for the conversion of aircraft deployed in Southeast Asia for a field test of the new system.
The final configuration of the weapon component included the modified M102 weapon, blast diffuser, recoil assembly and snubber assembly, mount, adapter base plate, ammunition storage and handling system, safety cage, and a modified 40mm ammunition rack. Ballistics data for the new weapon was added to the on board fire control computer. The weapon replaced the rearmost Bofors 40mm and the beacon tracking radar, which was to be relocated on modified aircraft. It was estimated that in-theater installation could be accomplished in 12-15 hours.
The Pave Aegis AC-130E was assigned to the 16th Special Operations Squadron, 8th Tactical Fighter Wing at Ubon Royal Thai Air Force Base, Thailand for the evaluation. On 18 February 1972, the first 105mm gun was installed and 2 training missions were conducted on 22 and 23 February 1972. On the first of these training missions, flown over Cambodia, the aircraft experienced numerous equipment malfunctions and misfires. The second was more successful. The first combat mission was flown on 24 February 1972 in support of Operation Commando Hunt VII. On 4 March 1972, a single 105mm shell destroyed 3 collocated trucks, emphasizing the effectiveness of the new system.
By April 1972, ground forces in communication with AC-130 gunships often asked immediately whether or not the aircraft carried "the big gun." The weapon also proved highly accurate, with aircraft being able to target individual buildings to attack concealed vehicles or troops. This capability was utilized to a great degree during the 1972 Nyugen Hue Offensive (also known as the Easter Invasion) in South Vietnam, especially during the Seige of An Loc.
The AC-130E aircraft were later upgraded to AC-130H standards as part of Project Pave Spectre II. The original AC-130A prototype, converted to an AC-130E, was among these aircraft, as were other aircraft that had started as AC-130As.
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