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The Air Force’s New 5,000-Pound Bunker Buster Bomb Breaks Cover

The U.S. Air Force has successfully completed a series of tests of a new 5,000-pound-class bunker-buster bomb, the GBU-72/B. This included the release of a prototype of the weapon from an F-15E Strike Eagle combat jet over a range associated with Eglin Air Force Base in Florida.

The testing of this weapon, developed under a program variously referred to the Advanced 5,000 Pound Warhead or Advanced 5,000 Pound Penetrator, and abbreviated A5K, took place earlier this year, but the Air Force only announced the results today. The flight tests followed an earlier round of ground testing, including an arena test, where the bomb’s warhead was detonated inside an array of barriers to gather data about its blast and other effects. The 96th Test Wing at Eglin said that this was the largest such explosive test event in the base’s history but did not identify what weapon previously held that record.

Outwardly, the GBU-72/B itself looks essentially like an enlarged 2,000-pound class GBU-31/B Joint Direct Attack Munition (JDAM) precision-guided bomb configured with a bunker-buster warhead, such as the BLU-109/B or the improved BLU-137/B. The latter of these was originally known as the Advanced 2000 Pound Warhead, or A2K, and you can read more about that bomb here. This 5,000-pound-class weapon uses a modified version of the GBU-31/B’s tail kit, which contains a GPS-assisted Inertial Navigation System (INS) guidance package. 

This new bomb differs most visibly from the GBU-31/B series in that it has a pair of long fins or strakes, one attached to each side of the bottom of the bomb’s body. GBU-31/B-series JDAMs have a set of strakes that attach to the center of the weapon.

The Air Force also touted the heavy use of modeling and simulation in the development of the GBU-72, as well as to explore its projected lethality. “An advantage to the modeling and simulation to design approach used is early prototypes are production representative,” James Culliton, the GBU-72 Program Manager, said in a statement. “This helps us bring our operational test partners in sooner with eyes-on, hands-on participation, validating our design and procedures sooner while including input that improves the weapon.”

“The GBU-72 was developed to overcome hardened deeply buried target challenges and designed for both fighter and bomber aircraft,” according to an official Air Force press release. “Lethality is expected to be substantially higher compared to similar legacy weapons like the GBU-28.”

The GBU-28/B is a 5,000-pound-class precision-guided bunker-buster that uses a Paveway-series laser guidance system and that first entered Air Force service in 1991. These weapons were originally developed due to concerns about the ability of the BLU-109/B to reach certain deeply-buried targets in Iraq in the lead up to the first Gulf War. To help rush these weapons into service, the BLU-113/B warheads used in the first batch of GBU-28/Bs had cases that had been fashioned from the barrels of retired U.S. Army 203mm howitzers. 

The Air Force subsequently employed GBU-28/Bs during the NATO-led bombing campaign over Serbia in 1999, and during the early stages of the interventions in Afghanistan and Iraq in 2002 and 2003, respectively. The U.S. government has since exported examples of these weapons to Israel and South Korea.

The exact capabilities of the Air Force’s current GBU-28/Bs, which now use improved BLU-122/B warheads, are classified, but the original design reportedly had the ability to penetrate through more than 150 feet of earth and at least 15 feet of reinforced concrete. As already noted, the service expects the GBU-72/B to have much better performance. 

At present, the GBU-28/Bs offer the Air Force the only intermediate conventional bunker-busting capability between the aforementioned variants of the GBU-31/B and the 30,000-pound-class GBU-57/B Massive Ordnance Penetrator (MOP). The Air Force is understood to only have a relatively small number of MOPs and the B-2 Spirit stealth bomber is the only aircraft certified to employ them operationally. The service does have nuclear gravity bombs with bunker-busting capabilities, the B61-11 and the B83-1, but those weapons are not in any way available for any kind of routine operational use and are not precision-guided.

As such, the GBU-72/B looks set to offer an improved bunker-busting capability for use against targets that are out of reach of GBU-31/B-series bombs, but that do not warrant the employment of a MOP. There is certainly no shortage of potential deeply buried, hardened facilities that the Air Force could be called upon to try to destroy in a future conflict, especially one against Iran or North Korea, where this additional flexibility in weapon options could be extremely valuable. 

In addition, the GBU-72/B’s use of the JDAM GPS/INS guidance package rather than the GBU-28/B’s laser guidance will give the Air Force the ability to conduct these types of strikes in any weather. Dense cloud cover, smoke, and other obscurants can impede the use of laser-guided weapons. The GBU-72/B would allow the launching platform to stay further away from the target, providing an added margin of survivability, too. GPS/INS guidance does mean that the GBU-72/B can only be used against fixed points, but deeply buried, hardened facilities are also not generally, in any way, a mobile target set.

In addition, in recent years, particularly during U.S. operations against ISIS in Iraq, 2,000-pound bunker-buster bombs have been routinely employed against less traditional hardened target sets. This has included tunnel networks and above-ground buildings. In the latter instances, bunker-busters, with their delayed blast effects, have offered a way to try to limit collateral damage to adjacent structures and their occupants.


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