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Design and Development
In 1967, JC-130A USAF 54-1626 was selected for conversion into the prototype AC-130A gunship. The modifications were done that year at Wright-Patterson Air Force Base, by the Aeronautical Systems Division. A direct view night vision telescope was installed in the forward door, an early forward looking infrared (FLIR) in the forward part of the left wheel well, and Gatling guns fixed mounted facing down and aft along the left side. The analog fire control computer prototype was handcrafted by RAF Wing Commander Tom Pinkerton at the USAF Avionics Laboratory. Then flight testing of the prototype was performed primarily at Eglin Air Force Base, followed by further testing and modifications. By September 1967, the aircraft was certified ready for combat testing and was flown to Nha Trang Air Base, South Vietnam for a 90 day test program. Following these successes, a few more AC-130As were constructed using similar equipment and manufactured versions of the analog computer. The original 54-1626 Gunship is displayed at the USAF Museum.
The AC-130 was supplemented by the AC-119 Shadow Gunship III during this time, which would prove underpowered with warload. In 1970, an additional dozen AC-130As were acquired under the "Pave Pronto" project. Regardless of their project names, the aircraft were more commonly referred to by the Squadron's call sign of Spectre.
Design
These heavily-armed aircraft incorporate side-firing weapons integrated with sophisticated sensors, navigation and fire control systems to provide precision firepower or area-saturation fire with its varied armament. The AC-130 can spend long periods flying over their target area at night and in adverse weather. The sensor suite consists of a television sensor, infrared sensor, and radar. These sensors allow the gunship to visually or electronically identify friendly ground forces and targets in most weather conditions.
The AC-130U is equipped with the AN/APQ-180, a synthetic aperture radar for long-range target detection and identification. The gunship's navigational devices include the inertial navigation systems and Global Positioning System. The AC-130U employs technologies developed in the 1990s and can attack two targets simultaneously. It also has twice the munitions capacity of the AC-130H.
During the Vietnam era the various AC-130 versions following the Pave Pronto modifications were equipped with a Magnetic Anomaly Detector (MAD) system called the Black Crow (AN/ASD-5), a highly sensitive passive device with a phased-array antenna located in the left-front nose radome that could pick up localized deviations in earth's magnetic field and is normally used to detect submerged submarines. The Black Crow system on the AC-130A/E/H could accurately detect the unshielded ignition coils of Russian trucks driven by the North Vietnamese that were hidden under the dense foliage of the jungle canopy along the Ho Chi Minh trail. It could also detect the signal from a hand-held transmitter that was used by air controllers on the ground to identify and locate specific target types. The system was slaved into the targeting computer.
Upgrades
A new program has been initiated to upgrade the armament of existing AC-130s still in service. The 25 mm GAU-12/U and 40 mm Bofors are to be replaced with two Mk 44 Bushmaster II 30 mm cannons. The first aircraft is completed, with three more to join the fleet by December 2007, and fleetwide modifications complete by 2010. There are also plans to look into replacing the M102 howitzer with a breech-loading 120 mm mortar, and to give the AC-130 a standoff capability using either the AGM-114 Hellfire missile, the Advanced Precision Kill Weapon System (based on the Hydra 70 rocket), or the Viper Strike glide bomb.
The Air Force has decided to use the Bushmaster for two reasons. First, the 40 mm Bofors gun is becoming progressively more difficult to maintain, with spare parts becoming more difficult to locate. Second, the 25 mm cannon, while a useful weapon, lacks ammunition with an air-burst capability and suffers from too much scatter; procuring the most desirable types of ammunition for the 30 mm Bushmaster is much easier.
PGM-38/U 25 mm ammunition for AC-130U
The PGM-38/U Enhanced 25 mm High Explosive Incendiary (HEI) round was created to expand the AC-130U gunships' mission in standoff range and survivability for its GAU-12/U 25 mm gun system. This round a combination of the existing PGU-25 HEI and a M758 fuse designated as FMU-151/B to meet the MIL-STD-1316. The FMU-151 has an improved arming delay with multi-sensitive range.
Production - 15 million 25mm rounds; 6 million M758 fuzes
Construction - thin walled steel
Type - composite explosive incendiary charge
Fuse armed - pre-armed 162.5 ft from muzzle, fully armed 656 ft from muzzle
Cartridge:
– Weight - 492 g
– Center of gravity - 135 mm
– Propellant wt - 92 g
Projectile:
–Weight - 184 g
–Fuse - 19 g
–Explosive - 330.2 g
–Center of gravity - 50.1 mm
Variants:
–M793 25 mm companion training round/target practice cartridge
Sources:
Wikipedia
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