GBU-28

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 US Air Force Air Armament Division at Eglin Air Force Base, Florida, was asked to create a weapon that could, and engineer Al Weimorts sketched improved BLU-109 variants. By January 1991, as the Persian 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.^[7]

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^[8] with the BLU-113 bomb body made by National Forge of Irvine, Pennsylvania.^[6] They weigh 5,000 pounds (2,268 kg) and contain 630 pounds (286 kg) of tritonal explosive.^[9]

The GBU-28 C/B version uses the 5,000-pound BLU-122 bomb body, which contains AFX-757 explosive in a 4,000-pound (1,800 kg) casing machined from a single piece of ES-1 Eglin steel alloy.^[10][11]

The operator illuminates a target with a laser designator and the munition guides itself to the spot of laser light reflected from the target. When the GBU-28 hits the ground, a short-delay time fuze is activated which triggers detonation when it has penetrated deeply enough to completely destroy the target.

The bomb underwent testing at the Tonopah Test Range, Nevada, a test facility for United States Department of Energy funded weapon programs. An F-111F of the 431st Test and Evaluation Squadron based at McClellan AFB in California dropped the first GBU-28 at Tonopah on February 24, 1991.^[9] It proved capable of penetrating over 160 feet (50 m) of earth or 16 feet (5 m) of solid concrete; this was demonstrated when a test bomb, bolted to a missile sled, smashed through 22 feet (6.7 m) of reinforced concrete and still retained enough kinetic energy to travel a half-mile (800 m) downrange.^[12][13] The GBU-28 went from finalized design to first use in combat in only two weeks between 13 and 27 February 1991.^[9]

On the night of 27/28 February 1991, just hours before 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 miles (24 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".^{[14][clarification needed]} 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.^{[citation needed]}

The bomb was used during the NATO bombing of Yugoslavia in 1999 by USAF F-15Es, notably against Straževica Command Center but without success.

The bomb was used during Operations Enduring Freedom in 2002 and Invasion of Iraq in 2003 by USAF F-15Es.

The first foreign sale of the GBU-28 was the acquisition of 100 units by Israel, authorized in April 2005.^[15] 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.^[16] Fifty-five GBU-28s were delivered to Israel in 2009.^[17] There were unconfirmed reports that Israel used the GBU-28 during the 2008–2009 Gaza War.^[18]

In June 2009 United States agreed to sell the GBU-28s to South Korea, following the nuclear test conducted on 25 May 2009 by North Korea. The bombs were to be delivered between 2010 and 2014.^[19]

According to the Jerusalem Post on 23 December 2011 the US Justice Department announced that it had reached a settlement with Kaman Corp. which allegedly substituted a fuze in four lots of fuzes made for the bombs. Under the settlement, Kaman Corp. will pay the government $4.75 million. Israel raised concerns, it had also received GBU-28 bombs fuzed to prematurely detonate before penetration or at other times.^[20] In bombardment of Gaza in May 2021, referred to by the Israeli military as the Guardian of the Walls operation, the GBU-28 was used extensively.^[21]

In October 2021, the USAF completed assessments of the GBU-72 Advanced 5K Penetrator (A5K), a 5,000 lb (2,300 kg) penetrator bomb consisting of a BLU-138 penetrator warhead combined with a JDAM GPS guidance kit. In development since 2017, the GBU-72 is expected to cause significantly more damage against hardened, buried targets and is fitted with a more durable and efficient smart electronic fuse that can activate at a preprogrammed location. The Air Force plans to begin buying the weapon in 2022 to replace the GBU-28.^[22] Israel is also reportedly interested.^[23]

• GBU-72

• Raas, Whitney; Long, Austin (April 2006), Osirak Redux? Assessing Israeli Capabilities to Destroy Iranian Nuclear Facilities, Security Studies Program Working Paper (PDF), MIT