Massive Ordnance Penetrator

The GBU-57 series MOP (Massive Ordnance Penetrator) is a class, precision-guided munition "bunker buster" bomb developed by Boeing for the United States Air Force (USAF). Composed of a BLU-127 bomb body and an integrated GPS/INS guidance package, there are seven GBU-57 variants. Due to its size and weight, the GBU-57 MOP can only be carried by the Northrop B-2 Spirit strategic bomber, although initial tests were conducted with the Boeing B-52 Stratofortress.

The first combat use of the GBU-57 MOP came on 22 June 2025, when seven Northrop B-2 Spirit stealth bombers dropped a total of fourteen GBU-57 bombs on Iran's Fordow Uranium Enrichment Plant and Natanz Nuclear Facility.

The bomb is much larger than earlier USAF bunker busters such as the GBU-28 and GBU-37.

Development and production

Bunker-busting bombs were used in the 2003 invasion of Iraq, but failed to penetrate deeply or achieve the desired destruction. This renewed interest in a larger bunker buster, so the Defense Threat Reduction Agency (DTRA) launched the MOP project.

In July 2004, USAF asked defense contractors how they might develop a 30,000-pound, precision-guided bomb that could destroy targets deep underground, in caves, or in hardened bunkers.

The USAF developed a concept for a collection of very large penetrator and blast weapons: the so-called "Big BLU" (Bomb Live Unit) collection, which includes the GBU-43/B MOAB (Massive Ordnance Air Blast) and the GBU-57 MOP. The MOP was developed by the Air Force Research Laboratory Munitions Directorate at Eglin Air Force Base, and designed by Boeing to be used with the B-2 Spirit and the B-21 Raider.

In March 2007, the MOP was tested in a DTRA tunnel at the White Sands Missile Range in New Mexico. In July 2007, Northrop Grumman received a $2.5 million contract to refit the USAF's B-2s, enabling the aircraft to carry two 14-ton MOPs. Beginning in 2008, the MOP was tested under various conditions, including on rocket sleds at Holloman High Speed Test Track and from B-52 and B-2 strategic bomber aircraft at White Sands.

In October 2009, the Pentagon had obtained permission from Congress to shift funding to accelerate the project. Funding delays and test-schedule changes meant the bomb would not be deployable until December 2010, six months later than planned.

In February 2011, Boeing received a $15 million contract for modification and increased testing. In April 2011, the USAF ordered eight MOPs plus supporting equipment for $28 million. The USAF began receiving the MOP in September 2011. In February 2012, Congress approved $81.6 million to further develop and improve the weapon. In March 2012, there was an "operational stockpile" at Whiteman Air Force Base. In 2012, the Pentagon requested $82 million to develop greater penetration power for the existing weapon. By early 2013, the MOP had been successfully integrated onto the B-2 Spirit.

At least 20 of the bombs were built and delivered to the USAF by November 2015. In April 2019, Boeing received a $21 million contract modification for production of more bombs. In October 2019, the USAF awarded $90 million in contracts for the production of an unspecified number of case assemblies for the BLU-127C/B warhead to be used in the bomb.

Key components

The GBU-57 uses a BLU-127 series bomb as the explosive component. The BLU-127 series bombs feature modular design that allows for incremental improvements and future upgrades. One variant of the BLU-127 bomb body contains of AFX-757 and of PBXN-114, a polymer-bonded explosive (PBX), for a total explosive payload of . The PBX is optimized for controlled detonation in confined spaces. The bomb's casing is made from high-density Eglin steel alloy, engineered to survive the extreme stresses of deep penetration before detonation.

The GBU-57 is a precision-guided munition equipped with an integrated GPS/INS guidance package, and therefore does not require the addition of a Joint Direct Attack Munition guidance package. This integrated system enables the bomb to strike within meters of its intended target. Detonation timing is managed by the Large Penetrator Smart Fuze (LPSF), which adjusts the moment of explosion based on impact depth and the characteristics of the underground structure.

In flight, the bomb is stabilized by grid fins, which help maintain trajectory and allow for mid-course adjustments. The GBU-57 uses grid fins as opposed to the planar fins found on most conventional bombs due to their greater control at the high mach flight regimes the bomb operates under, as well as their ability to fold for storage in a B-2's bomb bays. As grid fins have higher drag than planar fins at any given mach number, their size is usually decreased to compensate while maintaining maneuverability.

Combat use

US airstrikes on Iranian nuclear facilities

The first combat use of the GBU-57 MOP was during the United States strikes on Iranian nuclear sites on 22 June 2025, when seven Northrop B-2 Spirit stealth bombers dropped a total of fourteen GBU-57 bombs, twelve on the Fordow Uranium Enrichment Plant and two on the Natanz Nuclear Facility.

According to General Dan Caine, Chairman of the U.S Joint Chiefs of Staff, both sites sustained severe damage. Darya Dolzikova, Senior Research Fellow at RUSI, argues that the exact damage to the facilities is unclear. Rafael Grossi, director general in IAEA said “no one, including the IAEA, is in a position to have fully assessed the underground damage at Fordow”, it is expected to be “very significant”.

Specifications and capabilities

* Length:
* Diameter:
* BLU-127 bomb body weight:
* Explosive weight:
** AFX-757:
** PBXN-114:
* Penetration: (debated) There is debate regarding the penetration capabilities of the bomb. The US Air Force has said that the GBU-57 can penetrate up to of unspecified material before exploding. The BBC reports that analysts at Janes say the weapon can penetrate about of earth or of concrete. This is consistent with a separate source which suggests penetration of up to into reinforced concrete with a compressive strength of and into reinforced concrete.

The MOP does not have a void-sensing fuze and detonates only after it comes to a stop, even if it has passed the target area.

Operationally, the MOP can be dropped only by the B-2 Spirit, which can carry up to two of the bombs. The B-21 Raider is slated to carry it. The B-52 has been used during weapons testing of the MOP, but requires modifications to carry the bomb.

Users

*
** – At least 20 in service as of November 2015.

Gallery

File:Off loading of MOP cropped.jpg, MOP being offloaded in preparation for its first explosive test, 2007.
File:Inside Tunnel MOP cropped.jpg, MOP underground at White Sands Missile Range before its first explosive test, 2007.
File:MOP in the B-2 bomb bay.jpg, Mock up of MOP inside a bomb bay of a B-2 simulator, 2007.
File:B-52 releases the MOP during a weapons test.jpg, B-52 releases a MOP during a weapons test, 2009.

See also

* Earthquake bomb
* Thermobaric weapon
;Specific large bombs
* BLU-82 Daisy Cutter bomb
* Father of All Bombs
* GBU-43/B Mother of All Bombs, another very large US bomb
* Grand Slam (bomb)
* T-12 Cloudmaker
* Tallboy (bomb)
* FAB-9000

References

External links

Massive Ordnance Penetrator Fact Sheet

{{USAF equipment

Anti-fortification weapons
Boeing
Guided bombs of the United States
Military equipment introduced in the 2010s