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The Guided Bomb Unit 28 (GBU-28) is a 5,000 pound (2,268 kg) laser-guided "bunker busting
Bunker buster
A bunker buster is a bomb designed to penetrate hardened targets or targets buried deep underground.-Germany:Röchling shells were bunker-busting artillery shells, developed by German engineer August Cönders, based on the theory of increasing sectional density to improve penetration.They were tested...

" bomb
A bomb is any of a range of explosive weapons that only rely on the exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy...

 nicknamed "Deep Throat" produced originally by the Watervliet Arsenal
Watervliet Arsenal
The Watervliet Arsenal is an arsenal of the United States Army located in Watervliet, New York, on the west bank of the Hudson River. It is the oldest continuously active arsenal in the United States, and today produces much of the artillery for the army, as well as gun tubes for cannons, mortars,...

, Watervliet, New York
Watervliet, New York
Watervliet is a city in Albany County in the US state of New York. The population was 10,254 as of the 2010 census. Watervliet is north of Albany, the capital of the state, and is bordered on the north, west, and south by the town of Colonie. The city is also known as "the Arsenal City".- History...

. It was designed, manufactured, and deployed in less than three weeks due to an urgent need during Operation Desert Storm to penetrate hardened Iraq
Iraq ; officially the Republic of Iraq is a country in Western Asia spanning most of the northwestern end of the Zagros mountain range, the eastern part of the Syrian Desert and the northern part of the Arabian Desert....

i command centers located deep underground. However, only two of the weapons were dropped in Desert Storm, both by F-111Fs
General Dynamics F-111
The General Dynamics F-111 "Aardvark" was a medium-range interdictor and tactical strike aircraft that also filled the roles of strategic bomber, reconnaissance, and electronic warfare in its various versions. Developed in the 1960s by General Dynamics, it first entered service in 1967 with the...


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
BLU-109 bomb
The BLU-109/B is a hardened penetration bomb used by the United States Air Force . As other "bunker busters", it is intended to smash through concrete shelters and other hardened structures before exploding...

 to penetrate such fortified structures, so the USAF Air Armament Division at Eglin AFB, Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...

, 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 bomb
Laser-guided bomb
A laser-guided bomb is a guided bomb that uses semi-active laser homing to strike a designated target with greater accuracy than an unguided bomb. LGBs are one of the most common and widespread guided bombs, used by a large number of the world's air forces.- Overview :Laser-guided munitions use a...

s (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 howitzer
M110 howitzer
The 8 inch Self-Propelled Howitzer M110 was the largest available self-propelled howitzer in the United States Army's inventory. It was deployed in division artillery in general support battalions and in separate corps- and Army-level battalions. Missions include general support, counter-battery...

s), but later examples were purpose-built. 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
Laser designator
A laser designator is a laser light source which is used to designate a target. Laser designators provide targeting for laser guided bombs, missiles, or precision artillery munitions, such as the Paveway series of bombs, Lockheed-Martin's Hellfire, or the Copperhead round, respectively.When a...

 and the munition guides itself to the spot of laser light reflected from the target.

The bomb underwent testing at the Tonopah Test Range
Tonopah Test Range
Tonopah Test Range , also known as Area 52, is a restricted military installation located about southeast of Tonopah, Nevada. It is part of the northern fringe of the Nellis Range, measuring . Tonopah Test Range is located about northwest of Groom Dry Lake, home of the Area 51 facility...

, Nevada
Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...

, a test facility for United States Department of Energy
United States Department of Energy
The United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...

 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 2 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 were loaded with two GBU-28s headed towards a target on the outskirts of Baghdad
Baghdad is the capital of Iraq, as well as the coterminous Baghdad Governorate. The population of Baghdad in 2011 is approximately 7,216,040...

. The al-Taji Airbase, located 15 nmi (27.4 km) northwest of the Iraqi capital, had been hit at least three times by GBU-27/Bs
GBU-27 Paveway III
The GBU-27 Paveway III is a laser-guided bomb with bunker buster capabilities. It is a GBU-24 Paveway III that has been redesigned to be used by the F-117A Nighthawk stealth ground attack aircraft.-Combat history:...

 from F-117 Nighthawks, "digging up the rose garden". The two GBU-28s 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
The State of Israel is a parliamentary republic located in the Middle East, along the eastern shore of the Mediterranean Sea...

, 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.