|Guided Bomb Unit 28|
|Type||Hard target laser-guided weapon|
|Place of origin||United States|
|In service||1991 to present|
|Used by||United States, Israel|
|Designer||Defense Systems and Electronics Group (Texas Instruments)|
|Length||7.6 metres (25 ft)|
|Diameter||35.6 centimetres (14.0 in)|
|Wingspan||1.7 metres (5.6 ft)|
|More than 9 kilometres (4.9 nmi)|
The Guided Bomb Unit 28 (GBU-28) is a 5,000-pound (2,268 kg) laser-guided "bunker busting" bomb nicknamed "Deep Throat" produced originally by the Watervliet Arsenal, Watervliet, New York. It was designed, manufactured, and deployed in less than three weeks due to an urgent need during Operation Desert Storm to penetrate hardened Iraqi command centers located deep underground. Only two of the weapons were dropped in Desert Storm, both by F-111Fs.
Design and development 
In August 1990, the U.S. military began planning an air offensive campaign against Iraq. Planners noticed that a few command and control bunkers in Baghdad were located deep underground to withstand heavy fire. Doubts were raised about the ability of the BLU-109/B to penetrate such fortified structures, so the USAF Air Armament Division at Eglin AFB, Florida, was asked to create a weapon that could. An engineer who was part of the study group named Al Weimorts, made sketches of improved BLU-109 variants. By January 1991, as the Gulf War was well underway, it was determined that the BLU-109/B-equipped laser-guided bombs (LGB) would be unable to penetrate fortified bunkers deep underground.
The initial batch of GBU-28s was built from modified 8 inch/203 mm artillery barrels (principally from deactivated M110 howitzers), but later examples are purpose-built with the BLU-113 bomb body made by National Forge of Irvine, Pennsylvania. They weigh 4,700 pounds (2132 kg) and contain 630 pounds (286 kg) of high explosive. The operator illuminates a target with a laser designator and the munition guides itself to the spot of laser light reflected from the target.
The bomb underwent testing at the Tonopah Test Range, Nevada, a test facility for United States Department of Energy funded weapon programs. It proved capable of penetrating over 30 meters (100 ft) of earth or 6 meters (20 ft) of solid concrete; this was demonstrated when a test bomb, bolted to a rocket sled, smashed through 22 ft (6.7 m) of reinforced concrete and still retained enough kinetic energy to travel a mile downrange. The GBU-28 is unique in that the total development time from conception to the first drop test took only two weeks, and the weapon went into active service after only one test drop, at Eglin AFB, Florida on 19 February 1991.
Operational history 
On the night of 27/28 February 1991, within hours of the ceasefire, two General Dynamics F-111Fs, loaded with one GBU-28 each, headed towards a target on the outskirts of Baghdad. The al-Taji Airbase, located 15 mi (27.4 km) northwest of the Iraqi capital, had been hit at least three times by GBU-27/Bs from F-117 Nighthawks, "digging up the rose garden". The first GBU-28 was dropped off-target due to target misidentification. The second GBU-28 was a direct hit and penetrated the thick reinforced concrete before detonating, killing everyone inside.
The first foreign sale of the GBU-28 was the acquisition of 100 units by Israel, authorized in April 2005. Delivery of the weapons was accelerated at the request of Israel in July 2006. Delivery was described as "upcoming" in a cable dated November 2009 which suggested that the weapon could be used against Iran's nuclear facilities. Fifty-five GBU-28's were delivered to Israel in 2009.
According to the Jerusalem Post on December 23, 2011 the US Justice Department announced that it had reached a settlement with Kaman Corp. which allegedly substituted a fuse in four lots of fuses made for the bombs. Under the settlement, Kaman Corp. will pay the government $4.75 million. Israel is concerned it had also received GBU-28 bombs fused to prematurely detonate before penetration or at other times.
See also 
- Report to Congress on the Conduct of the Persian Gulf War, Es.rice.edu, retrieved 14 July 2011
- "PROCUREMENT OF AMMUNITION". USAF. Retrieved 29 January 2012.
- Clancy 1995, p. 154.
- Raytheon (Texas Instruments) Paveway III, Designation-systems.net, 21 August 2008 (last updated), retrieved 14 July 2011
- Guided Bomb Unit-28 (GBU-28) Bunker Buster — Smart Weapons, FAS.org, retrieved 14 July 2011
- Clancy 1995, p. 155.
- Raytheon GBU-28 Bunker Buster, A US Air Power, retrieved 14 July 2011
- "History Eglin Heritage Briefing" (PDF). Nwfdailynews.com. Retrieved 16 July 2011.
- Clancy 1995, p. 157.
- US Wants to Sell Israel 'Bunker-Buster' Bombs, Commondreams.org, retrieved 14 July 2011
- "US embassy cables: Israel seeks to block US planes for SaudiUS embassy cables: Israel seeks to block US planes for Saudi". The Guardian. 28 November 2010.
- "US to sell 'bunker-buster' bombs to SKorea: official". AFP. 2009-06-02. Retrieved 2011-12-22.
- Raas, Whitney; Long, Austin (April 2006), Osirak Redux? Assessing Israeli Capabilities to Destroy Iranian Nuclear Facilities, Security Studies Program Working Paper (PDF), MIT