Guided Bomb Unit-28 (GBU-28)

A pair of chartered Airbus A310 transport aicraft carrying 5,000-lb GBU-28 bunker buster bombs staged through Scotland's Prestwick International Airport outside Glasgow on 22 July 2006 to refuel and give the crew a rest before continuing to deliver the bombs to Israel. At least two more flights were anticipated before mid-August.

The GBU-28 laser guided bomb was developed, built, tested, and used in combat in a 17 day period. The deepest Iraqi bunkers were secure from the best penetrating bomb, the GBU-24A/B, with the I-2000 warhead. Coalition leaders required the capability to destroy these vital command and control facilities. Texas Instruments and Lockheed combined their efforts to build the 18 ft long bomb. TI adapted the seeker from the GBU-24 and Lockheed built the bomb body from discarded eight inch howitzer barrels. The Air Force initially contracted for 30 bombs but the cease fire started after only two were employed. Two more of the bombs were used in testing before the bombs were dropped in combat and the Air Force expended two or three more in additional tests after the war. The Air Force ordered an additional 100 GBU-28s with the BLU-113 (8 inch gun barrel) bomb body and stocks remained low due to the limited number of targets and the only fighter capable of employing it initially was the F-111F.

The Guided Bomb Unit-28 (GBU-28) bomb is designed to penetrate hardened targets before exploding, capable of penetrating 100 feet of earth or 20 feet of concrete. The GBU-28 was initially developed in 1991 for penetrating hardened Iraqi command centers located deep underground. This "bunker buster" was required for special targets during the Desert Storm conflict and was designed, fabricated and loaded in record time. The GBU-28 is a laser-guided conventional munition that uses a modified Army artillery tube as the bomb body. They are fitted with GBU-27 LGB kits, 14.5 inches in diameter and almost 19 feet long. The operator illuminates a target with a laser designator and then the munition guides to a spot of laser energy reflected from the target.

Some considerable confusion exists in the literature concerning the weight of this bomb. Although nominally a 5,000 pound bomb, it appears that the actual weight is somewhat less than this, and that the 5,000 figure is arrived at by rounding up [the 250, 500, 1000 and 2000 pound figures for the Mk80 family are also such approximations. Statements that it is a 4,000 pound bomb reflect a similar rounding, but rounding down and rounding rather further from the exact number. Reports that the bombs weigh 4,637 pounds, and contain 630 pounds of high explosives, are too precise to be in error. Reports that the bomb weighs 4,700 pounds are in close agreement with this more precise number. A report that the bomb incorporates a 4,400-pound penetrating warhead may reflect the weight of the filled bomb body, minus guidance head and tail kit.

The GBU 28 "Bunker Buster" was put together in record time to support targeting of the Iraqi hardened command bunker by adapting existing materiel. The GBU-28 was not even in the early stages of research when Kuwait was invaded. The USAF asked industry for ideas in the week after combat operations started. The bomb was fabricated starting on 01 February 1991, using surplus 8-inch artillery tubes. The official go-ahead for the project was issued on 14 February 1991, and explosives for the initial units were hand-loaded by laboratory personnel into a bomb body that was partially buried upright in the ground outside the laboratory in New York.

This new system was needed to deal with deeply buried command and control bunkers that were beyond the reach of existing systems. The need was great, the time was short, and the only solution was to innovate a solution in an unprecedented short period of time. A team of government and industry people came together sharing the common objective of solving a difficult technical challenge in a breakneck race against time.

Personal interests were set aside as were traditional approaches, with long hours being the norm. The team worked to trade time against everything (cost, risk, performance). Reuse of existing subsystems offered the only answer. However, the pieces would have to be integrated in a very innovative way to achieve the desired results. The GBU-28 Bunker Buster that was conceived, developed, tested, and deployed in approximately 28 days. This was less time than had ever been dreamed possible.

The first two units were delivered to the USAF on 16 and 17 February 1991, and the first flight to test the guidance software and fin configuration was conducted on 20 February 1991. These tests were successful and the program proceeded, with a contract let on 22 February. A sled test on 26 February 1991proved that the bomb could penetrate over 20 feet of concrete, while an earlier flight test had demonstrated the bomb's ability to penetrate more than 100 feet of earth.

The Energetic Materials Branch of Air Force Research Laboratory (AFRL/MNME) is the home of the High Explosives Research and Development (HERD) Facility. This facility was established to provide the Air Force with a modern in-house explosive research, development, test and evaluation (RDT&E) capability and quick reaction explosives loading. The HERD Facility includes the Explosives Properties Laboratory, the Explosives Processing Laboratory, and the Explosives Dynamics Laboratory,as well as other explosives storage and test buildings. The HERD responded to an immediate need for explosive loading of the GBU-28 warhead (BLU-113). The first two warheads were received at the HERD, loaded, x-rayed and delivered to the Desert Storm theater of operations within 72 hours. The first two operational bombs were delivered to the theater on 27 February 1991.

The Air Force produced a limited quantity of the GBU-28 during Operation Desert Storm to attack multi-layered, hardened underground targets. Only two of these weapons were dropped in Desert Storm, both by F-111Fs. One weapon hit its precise aimpoint, and the onboard aircraft video recorder displayed an outpouring of smoke from an entrance way approximately 6 seconds after impact. Initially it was reported that one of the GBU-28s was used to destroy a bunker in a residential neighborhood of Bagdad, that turned out to be a shelter for hundreds of key family members of the Ba'ath Party elite. Originally over 500 casualties were reported, but that was later changed to 314. After the war it was reported that an F-117 dropped a Penetrator I-2000 on this target, and that it was not one of the GBU-28's from an F-111.

After Operation Desert Storm, the Air Force incorporated some modifications, and further tested the munition. The FY1997 budget request contained $18.4 million to procure 161 GBU-28 hard target penetrator bombs.

An F-15E Strike Eagle assigned to the 494th Fighter Squadron, RAF Lakenheath, United Kingdom, conducted a GBU-28 laser guided bomb mission on Wednesday, April 28, 1999 against targets in Yugoslavia. This was the first time the F-15 had employed the GBU-28 operationally. Members of the 494th FS were deployed to Aviano AB, Italy supporting NATO Operation Allied Force.

The Hard and Deeply Buried Target Defeat System (HDBTDS) program is an effort designed to hold at risk those highest priority assets essential to the enemy's war fighting ability, which are heavily defended and protectively hardened. Hardening techniques include construction of facilities, many of which are deep underground with multiple layers of reinforced concrete, rock rubble, and/or earth overburden. Other hardened targets include operations within caves, tunnels, and mountains built using rapidly improving construction equipment exported by allies and adversaries on a large scale. (Examples include enemy command and control facilities, air defense facilities, facilities for the production, storage, and deployment of weapons including weapons of mass destruction, surface to surface missile launch sites, aircraft storage sites, artillery sites.) Potential solutions include (but are not limited to) Special Forces, conventional short or long range ballistic missiles (land or sea launched), cruise missiles, direct attack munitions, and standoff weapons.

An Analysis of Alternatives (AOA) was conducted to evaluate the weapon concepts to determine the most promising concepts to move forward into a follow-on program. The potential weapon concepts were evaluated in an air campaign analysis. The results of the AOA were presented to the Joint Requirements Oversight Council (JROC) in 4th Quarter FY 1999. The AOA is being documented into a report for future reference. The primary legacy hard target penetrator weapon, GBU-28, was tested in rock to validate computer models used in the AOA analysis and to provide test data for future use when considering weapon design alternatives for increased penetration capability. The results were presented in 1st Quarter FY 2001.

In FY2000 the Air Force's Hardened Target Munitions program conducted a GBU-28 rock test program. This included acquiring GBU-28 test assets and launching the weapons from F-15E aircraft into rock targets to validate models and provide data for potential future design of improved warhead penetration capability. Field agency activities included project office and contractor support to manage the Hardened Target Munitions program, consisting of testing GBU-28 in rock in coordination with the Defense Threat Reduction Agency (DTRA), and documentation of the AOA. System Engineering and Technical Analysis (SETA) support included evaluation of GBU-28 performance in rock and design analysis and prototype evaluation of potential future upgrades to the GBU-28 5000 lb hard target penetrator weapon and other legacy weapons.

By 2005 the Air Force was improving capability to attack hardened and/or deeply buried targets during adverse environmental conditions. The MIL-STD 1760 conduit will also be extended to connect the guidance system to the fuze to support a future in-flight fuze reprogramming capability. The existing GBU-28 B/B--B-2 interface was maintained and the GBU-28 will also be integrated onto the F-15E through the Joint Direct Attack Munition (JDAM) Smart Unknown Weapon Interface. This program was a NEW START in FY03. The program is in Budget Activity 04 (BA 04) because the program will develop and demonstrate a hard target munition capability to defeat hard and deeply buried targets not currently held at risk.

Raytheon Missile Systems, Tucson, Ariz., was awarded on February 10, 2005 a $10,490,029 firm fixed price contract to provide for Guided Bomb Unit-28C/B (BLU-122) guidance control units and tail kits, quantity of 71. The Guided Bomb Unit-28C/B, also known as BLU-122 or Enhanced Paveway III, provides the Air Force with an improved aerial delivery capability for the 5000 Pound BLU-113 P3I warhead. The Guided Bomb Unit-28C/B possesses a Global Positioning System aided laser guidance capability with improved lethality, survivability, and penetration over the Previously produced Guided Bomb Unit-28B/B weapons system. Total funds have been obligated. This work will be complete by May 2006. Solicitation began July 2004 and negotiations were completed January 2005. The Air Armament Center, Eglin Air Force Base, Fla., is the contracting activity (FA8681-05-C-0075).

Raytheon Missile Systems, Tucson, Ariz., was awarded October 19, 2005 an $18,478,880 firm fixed price contract modification for 140 production Lot 2 of the Guided Bomb Unit-28C/B guidance control units and tail kits. The Guided Bomb Unit-28C/B, or Enhanced Paveway III, provides the Air Force with an improved aerial delivery capability for the 5000-Pound class BLU-122 warhead. It possesses a global positioning system aided laser guidance capability to be compatible with F-15E and B-2A aircraft platforms. The GBU-28C/B, with BLU-122 warhead, will improve the lethality, survivability, and penetration over the previously produced GBU-28B/B weapon system. At this time, $18,478,880 has been obligated. This work will be complete May 2007. The Air Armament Center, Eglin Air Force Base, Fla., is the contracting activity (FA8681-05-C-0075/P00008).