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GBU-15

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Gross mass: 1,134 kg (2,500 lb). Height: 3.93 m (12.90 ft). Diameter: 0.46 m (1.50 ft). Span: 1.49 m (4.90 ft).

Historical Essay © Andreas Parsch

Rockwell GBU-15(V)/B

The GBU-15(V)/B is a family of electro-optically guided glide bombs (EOGB) developed and used by the U.S. Air Force. These bombs are included in this missile directory, because the missile designator AGM-112 was at one time requested for them.

Development of the GBU-15 EOGB family was begun in 1974 by the Air Force Systems Command's Armament Division at Eglin AFB as an improved version of the Vietnam era GBU-8/B and -9/B HOBOS (Homing Bomb System) EOGBs. The design by Rockwell was also known as the MGWS (Modular Guided Weapon System), because different warheads, guidance units, and control airfoils could be combined to create numerous configurations. The USAF originally requested to use the guided missile designations AGM-112A and AGM-112B for two MGWS configurations (presumably for the initial TV and imaging infrared (IIR) versions, respectively). However, because the weapon was an unpowered glide bomb, these designators were not approved, and the basic guided bomb designation of GBU-15(V)/B was allocated instead. The M-112 slot in the guided missile series therefore remained effectively unassigned.

Flight tests of the GBU-15 started in 1975, in a general configuration known as CWW (Cruciform Wing Weapon), because of the arrangement of the control surfaces. There was also a version called the PWW (Planar Wing Weapon, GBU-20/B), with flip-out wings for longer glide range, but this was not developed into a production variant. Two basic MGWS models were developed initially, the GBU-15(V)1/B using a daylight-only DSU-27A/B TV image-contrast seeker, and the GBU-15(V)2/B with a WGU-10/B IIR guidance unit (the same as in the AGM-65D Maverick) for limited night/all-weather capability. Other components were identical for both versions, e.g. the 900 kg (2000 lb)-class MK 84 warhead, the WCU-6A/B integrated control module, the MXU-723/B airfoil group (wings and fins), the FMU-124/B fuzes, and the OA-8921/AXQ-14 data-link transceiver group. The first fully operational version was the GBU-15(V)1/B in 1983, followed by the (V)2/B in 1985.

The basic guidance principle for all GBU-15 configurations is the same. The glide bomb is equipped with an optical seeker (TV or IIR), which transmits a picture to a screen in the attack aircraft's cockpit. When the pilot or weapon operator identifies a target on the screen, he "locks" the image and releases the weapon. The guidance system then continually matches the current image with the locked one, and corrects the course of the missile to compensate any deviations. Alternatively, he can pre-release the bomb and guide it manually via an AN/AXQ-14 two-way data-link to the general target area, while already leaving the area in his aircraft. He can then either lock the missile's guidance unit onto a target, or manually guide it all the way to impact. This guidance principle is essentially the same as the one used in the U.S. Navy's AGM-62 Walleye guided bomb. Just as Walleye, the USAF EOGBs are very accurate against high-contrast targets, but always have lock-on problems in low or varying lighting conditions.

Originally it was intended to also create an MGWS configuration with a CBU-75/B cluster bomb (1800 BLU-63/B or BLU-86/B anti-personnel/anti-materiel bomblets in an SUU-54A/B dispenser) as warhead, but this variant (provisionally designated GBU-15(V)N/B) was not developed.

The are alternate options for both the original warhead and control surfaces. The MK 84 can be replaced by a BLU-109/B 900 kg (2000 lb) penetrating warhead, and the original "long-chord" delta wings and fins can be replaced by "short-chord" rectangular surfaces (with smaller wing area but bigger canards). The variants with MK 84 warhead and "short-chord" wings are designated GBU-15(V)21/B (TV) and GBU-15(V)22/B (IIR), respectively. The BLU-109/B variants always use the "short-chord" wings, and are designated as GBU-15(V)31/B (TV) and GBU-15(V)32/B (IIR). The (V)21/22 (MK 84/short-chord) versions are currently not procured, reportedly not for technical but for budgeting reasons only. The latest subvariants are known as GBU-15(V)1C/B, GBU-15(V)2C/B, GBU-15(V)31A/B, and GBU-15(V)32A/B. For all these weapons there are specific inert training versions, designated as GBU-15(V)1C(T-1)/B, GBU-15(V)2C(T-1)/B, GBU-15(V)31A(T-1)/B, and GBU-15(V)32A(T-1)/B, respectively. The latest version of the data-link system is the AN/ZSW-1, an improved AN/AXQ-14.

In the late 1990s, an enhanced guidance unit for the GBU-15 was developed which added a GPS navigation system. This significantly increases the versatility and accuracy of the weapon in night and/or bad weather, because it can now find its way to the vicinity of the expected target after release without manual guidance by the pilot. In addition to the manual and electro-optical homing, there is now also the option to use no explicit terminal guidance at all, and letting the glide bomb continue to the selected target coordinates. The GPS-equipped GBU-15s are known as EGBU-15 (Enhanced GBU), a non-standard, but apparently at least semi-official designation. An initial batch of 100 GBU-15s were converted to EGBU-15 standard in 1999, and a further 1200 are planned to follow. EGBU-15s apparently always use the "short-chord" wings, regardless of warhead.

A powered version of the GBU-15 family with a strap-on solid-propellant rocket motor for longer range is known as the AGM-130 guided missile.

Note: Data given by several sources show slight variations. Figures given below may therefore be inaccurate! Range of a glide bomb of depends of course heavily on altitude, and is quoted for high-altitude drops.

Data for GBU-15(V)1/B, (V)2/B, (V)31/B, (V)32/B:

[1] Christopher Chant: "World Encyclopaedia of Modern Air Weapons", Patrick Stephens Ltd., 1988
[2] Bill Gunston: "The Illustrated Encyclopedia of Rockets and Missiles", Salamander Books Ltd, 1979