On the night of June 22, 2025, seven Northrop B-2 Spirit heavy strategic stealth bombers dropped 14 GBU-57A/B MOP bombs on Iran's nuclear facilities at Fordow and Natanz. This was the first combat use of the United States' most powerful non-nuclear weapon. What is the GBU-57AB MOP and what can this bomb "do"?
Bunker-busting bombs and the development of the GBU-57A/B MOP
The GBU-57A/B MOP is the latest, as of now, version of the so-called "bunker destroyers", bombs for destroying underground infrastructure, command posts, protected submarine bases, missile silos, and other underground enemy facilities.
Similar bombs were manufactured during World War II by Germany (PC 500 Rs, PC 1000 Rs, and PC 1800 Rs rocket bombs, the latter weighing over 2 tons), Great Britain (Disney – 2 tons, Tallboy – 5.4 tons, Grand Slam – 10 tons) and the USA (ASM-A-1 Tarzon – 5.9 tons).
The heaviest modern standard conventional bomb of the 80 series in the arsenal of the US Air Force is the Mark 84 or BLU-117 weighing 900 kg, which has been produced since the 1950s. This is followed only by custom-made products for specific tasks, such as the BLU-82B/C-130 (6.8 tons) for clearing helicopter landing pads in the jungle, which was used during the Vietnam War (only 225 pieces were produced). Or the M118 bombs (1.4 tons), which were converted into high-precision bombs GBU-9/B.
Since 1991, the US Air Force has used high-precision laser-guided GBU-28 aircraft bombs (1.8–2.3 tons, depending on the modification) as anti-bunker bombs. Interestingly, the GBU-28 body was initially made from the barrels of decommissioned M110 howitzers (the same ones that could fire nuclear shells), and then from BLU-113 or BLU-122 bombs. After the invasion of Iraq in 2003, it became clear that the GBU-28 had insufficient penetration and destructive capacity, so in 2004, the US Air Force ordered the development of a new anti-bunker weapon weighing 13 tons.
As a result, the Air Force received two bombs - the "mother of all bombs" GBU-43/B MOAB (9.8 tons), which was used in 2017 in Afghanistan (this is a conventional bomb without anti-bunker capabilities), and the GBU-57A/B MOP (Massive Ordnance Penetrator), which was tested in Iran.
The GBU-57A/B MOP was developed by the U.S. Air Force Research Laboratory and Boeing for use exclusively on the Northrop B-2 Spirit heavy strategic bomber and its future B-21 Raider successor. Each aircraft can carry two GBU-57A/B MOPs. Testing was conducted in 2007–2008, and in 2009, Boeing began work on integrating the bombs onto the aircraft.
Specifications of the GBU-57A/B MOP
The GBU-57A/B MOP uses the BLU-127 modular bomb as its warhead, the body of which is made of high-strength ES-1 steel to withstand the stress during "diving" into the surface. The strength of ES-1 at room temperature is 1,336 MPa, while the strength of the steel used to make gun barrels is only 517 MPa.
The bomb's filling is 2,082 kg of AFX-757. This is a low-sensitivity explosive, a mixture of hexogen, aluminum powder, ammonium perchlorate and a polybutadiene hydroxyl plasticizer, developed by the same US Air Force Research Laboratory. Plus 341 kg of polymer-bound explosive PBXN-114. PBXN is optimized for controlled detonation, AFX-757 must withstand the "dive" of the bomb without detonation.
The GBU-57A/B MOP is equipped with an inertial guidance system and a GPS module and does not require an additional JDAM module. After release, the bomb releases lattice control surfaces, almost the same as those of the SpaceX Falcon launch vehicle (but the GBU-57A/B MOP appeared earlier). The guidance accuracy is several meters. The detonation is controlled by the Large Penetrator Smart Fuze (LPSF), which selects the moment of detonation according to the depth of penetration and the characteristics of underground structures.
Regarding the penetration depth of the GBU-57A/B MOP. Unfortunately, it is still impossible to assess the results of a strike on Iran's nuclear facilities on site, so this data is purely theoretical. The US Air Force says that the GBU-57A/B MOP can penetrate 60 m, but does not specify what surface it is talking about. Specialists from the Janes Information Services agency believe that this is about 60 m of soil, or 18 m of concrete. Other sources write about 18 m of reinforced concrete with a strength of 34 MPa, or 2.4 m of reinforced concrete with a strength of 69 MPa.
| Name | GBU-57A/B MOP |
| Length | 6.2 m |
| Diameter | 0.8 m |
| Weight | 12,304 kg |
| Warhead weight | 2,423 kg (AFX-757 – 2,082 kg, PBXN-114 – 341 kg) |
Operation Midnight Hammer
The US bombing of Iran's nuclear facilities was called Operation Midnight Hammer.
The fact that the US was going to join Israel's confrontation with Iran and use GBU-57A/B MOP bunker-busting bombs became clear almost immediately after the attacks by the Israeli Air Force, when information appeared that the Israeli air force had not achieved the desired result, they did not have conventional weapons of greater power, so the option of a ground operation was being discussed. And when on June 16, 2025, the US Air Force began to send tanker aircraft to Europe, 31 aircraft, an incredible number, everything became more than obvious.
On June 21, 2025, seven Northrop B-2 Spirit strategic bombers took off from Whiteman Air Force Base in Missouri. Each aircraft carried two GBU-57A/B MOP bombs. During the 17-hour flight over the Atlantic and Mediterranean, several mid-air refuelings were carried out. Somewhere over Israel, the bombers were joined by an escort of fighters and decoys. After 18 hours of flight, the B-2 Spirits entered Iranian airspace, dropped bombs for another 40-60 minutes, and crossed the Iranian border in the opposite direction after another 40 minutes.
The strike on the targets in Fordow and Natanz took place at 2:30 local time. In addition, 30 BGM-109 Tomahawk missiles were launched from a submarine, most likely from the USS Georgia (SSGN-729), at the same targets. The Northrop B-2 Spirits turned back and after additional refueling and 36 hours in the air returned to Whiteman Air Force Base. The total range of the B-2 Spirit non-stop flight was about 25 thousand km. The total number of aircraft involved in the operation was 125 units.
Satellite images of Iranian nuclear facilities show the GBU-57A/B MOP bombs hitting their targets precisely. For example, at Fordow, 12 bombs were dropped in succession on two ventilation shafts to hit structures 79 meters deep in the bedrock. Iran claims that all important materials and equipment from the facilities were removed a few days ago. It is currently impossible to verify the extent of the damage and the effectiveness of the GBU-57A/B MOP "on the ground".
Number of GBU-57A/B MOPs and their carriers
It is important to understand that the Northrop B-2 Spirit bomber is a man-made product. Only 21 of these aircraft were built, and 18 remain in service, all of them with the 509th Bomb Wing, based in the heart of America, at Whiteman Air Force Base in Missouri. Another aircraft is at the disposal of the 412th Test Wing at Edwards Air Force Base in California.
Similarly, the GBU-57A/B MOP is an artificial and expensive product for a specific use. It is known that in 2009 Boeing received a contract to integrate the GBU-57AB MOP into the B-2 Spirit. In 2013, the integration was completed, and by 2015 Boeing had supplied the Air Force with all the bombs ordered – 20 units. The cost of one GBU-57A/B MOP with associated equipment was $3.5 million in 2011 prices. Taking into account inflation, it is now over $5 million per bomb.
In 2021, Boeing received an additional contract to produce an unknown number of BLU-127C/B warheads and a modification of the GBU-57A/B MOP. The contract is worth $111 million, so it could be another 20-30 bombs. In 2023, a photo on the Whiteman Air Force Base Facebook page (the page and photo have since been deleted) revealed that the 509th Bomb Wing had received at least two more GBU-57A/B MOP bombs.
Defense Express believes that after the modernization of the ammunition plant in Oklahoma, the production of GBU-57A/B MOP should increase to 6-8 bombs per month, that is, 72-96 bombs per year. We consider this assumption to be too optimistic. First, nothing is known about additional bomb integration contracts for Boeing, and second, such a number of bombs is simply not needed, the tasks of destroying underground infrastructure are isolated and very rare.
Whether the US will order additional GBU-57A/B MOPs after a significant portion of the arsenal has been used is currently unknown.