As tensions escalate in the Middle East over Iran’s nuclear program, a rare but formidable weapon has entered public discourse—the GBU-57A/B Massive Ordnance Penetrator (MOP). Weighing 30,000 pounds (13,600 kg), this U.S.-made bunker-buster bomb is designed to destroy deeply buried and fortified structures, such as underground nuclear facilities. Unlike the commonly known “Mother of All Bombs” (MOAB), the MOP is far more penetrative and lethal against hardened underground targets.
As tensions over Iran’s underground nuclear facilities once again make global headlines, understanding the technical prowess, operational limits, and geopolitical significance of the MOP has never been more relevant.
What Is the GBU-57 Massive Ordnance Penetrator (MOP)?
The GBU-57A/B MOP is a next-generation bunker-busting bomb developed by Boeing for the United States Air Force. Weighing a staggering 30,000 pounds (13,600 kg), the MOP is designed to penetrate up to 200 feet (60 meters) of earth or 60 feet (18 meters) of reinforced concrete before detonating its high-explosive payload.
- Weight: 30,000 lbs (13,600 kg)
- Length: Approx. 20.5 feet (6.2 meters)
- Diameter: 31.5 inches (0.8 meters)
- Explosive Fill: High-explosive within a hardened steel casing
- Penetration: Up to 200 ft (60 m) of earth or 60 ft (18 m) of concrete
- Delivery Platform: Only the US Air Force’s B-2 Spirit stealth bomber is currently certified to carry and deploy the MOP.
How Powerful is the MOP?
Compared to the MOAB, which weighs 9,800 kg, the MOP is heavier, more targeted, and designed specifically for hard-to-reach bunkers. While MOAB causes widespread surface-level destruction, the MOP focuses its energy to breach solid layers of rock and concrete.
Key differences include:
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MOP contains explosives encased in a hardened metal shell for deep penetration.
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It can be dropped in multiple succession to increase underground damage.
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Has been tested at White Sands Missile Range, New Mexico, but never used in combat.
Unlike conventional bombs, the MOP is designed for maximum penetration. Its extremely dense, hardened steel casing allows it to burrow deep into the earth or through reinforced concrete before detonation. This makes it particularly effective against underground bunkers and nuclear facilities built under mountains or deep below the surface.
Why is the MOP Making Headlines Now?
Amid reports of increased uranium enrichment at Iran’s Fordow nuclear facility, military analysts and global powers are revisiting the MOP’s relevance. The Fordow plant is built deep within a mountain, surrounded by up to 80 meters (260 feet) of rock and reinforced earth. Israeli and U.S. officials believe it may be used to develop weapons-grade material.
However, even Israel—despite its advanced military capabilities—does not have access to the MOP. The U.S. has not shared this technology with any ally, including Israel, making it a uniquely American strategic tool.
How Many MOPs Does the U.S. Have?
According to military analysts, the U.S. possesses only 10–20 operational MOPs, highlighting their role as rare strategic assets rather than commonly deployed weapons.
Expert Analysis
Professor Paul Rogers of the University of Bradford remarks that MOP represents “the best option the U.S. has for destroying deeply buried nuclear sites.” Yet, he cautions, no one can guarantee its effectiveness against facilities like Fordow, given the unknown depth and fortification measures employed.
Kelsey Davenport of the Arms Control Association adds, “As long as Fordow remains operational, the risk of nuclear proliferation from Iran remains high.”
The proliferation of underground facilities—especially for nuclear programs in countries like Iran and North Korea—challenged the effectiveness of traditional munitions. The MOP was developed as a direct response to these “hardened and deeply buried targets” that were beyond the reach of earlier “bunker buster” bombs like the GBU-28.
- 2000s: Intelligence agencies identified a new generation of potential adversary bunkers, especially in Iran (Fordow, Natanz) and North Korea.
- 2007: Boeing awarded contract to build the MOP.
- 2011: Declared operational by the US Air Force, with subsequent upgrades to improve guidance, penetration, and detonation reliability.
| Bomb Name | Weight (lbs) | Penetration Capacity | Deployment Aircraft |
|---|---|---|---|
| GBU-28 (US) | 5,000 | ~20 ft concrete, ~100 ft earth | F-15E, F-111 |
| BLU-109 (US) | 2,000 | ~4–6 ft reinforced concrete | Multiple |
| GBU-43 MOAB (“Mother of All Bombs”) | 21,600 | Surface/area targets (not penetration) | MC-130 |
| GBU-57 MOP | 30,000 | 200 ft earth, 60 ft concrete | B-2 Spirit Only |
The MOP is by far the heaviest and most powerful non-nuclear bomb in US inventory, designed specifically to address targets that even the GBU-28 cannot destroy.
The existence of the MOP is itself a deterrent, signaling to adversaries that no underground facility is beyond US reach. It complicates the strategic calculations of any nation building secret underground nuclear or military complexes.
The MOP is intended as a “last resort” weapon for situations where all other means of neutralizing a target have failed. Its use would likely signal a major escalation in any conflict.
Despite requests from allies, most notably Israel, the US has never exported the MOP. Israel has only received smaller, less-capable bunker busters (like the GBU-28). The MOP’s extreme weight and size also mean only the B-2 Spirit stealth bomber can deliver it—a platform the US has never exported.
One of Iran’s most heavily fortified nuclear sites is the Fordow Fuel Enrichment Plant, built into a mountain near Qom and protected by roughly 80 meters (260 feet) of rock and soil. The site was designed to withstand airstrikes and, possibly, bunker busters.
- Depth: The MOP is theoretically capable of penetrating up to 200 feet of earth. However, rock hardness, facility design, and unknown countermeasures could limit its effectiveness.
- Multiple Strikes: Experts suggest that repeated strikes, possibly with multiple MOPs “in tandem,” might be needed to guarantee destruction of such a target.
- Operational Challenges: Only B-2 bombers can carry the MOP, and a strike would require complex support—including stealth operations, suppression of enemy air defenses (possibly with F-22s), and post-strike assessment via drones.
- The actual effectiveness of the MOP against Fordow or similar facilities remains untested in combat.
- The US is believed to have only a limited number of operational MOPs (estimated 10–20).
- The US has never used this weapon in war, only in test detonations at White Sands Missile Range, New Mexico.
Despite possessing advanced airpower, Israel does not have the GBU-57 MOP. The US has so far declined to provide it, likely due to concerns over escalation and control. Only the US Air Force’s B-2 bombers can carry the bomb, and Israel has no such aircraft.
If Israel were to target Fordow or similar sites, it would have to rely on smaller bunker busters, cruise missiles, or (potentially) direct US military support.
A strike against a target like Fordow would be highly complex:
- Stealth Insertion: B-2 bombers would have to evade advanced air defenses.
- Suppression of Enemy Air Defenses: Support from F-22 Raptors or other assets would likely be needed.
- Multiple MOP Drops: To maximize penetration and destruction, several bombs might be used in sequence.
- Post-Strike Assessment: Drones or satellites would assess the damage and determine if further strikes are necessary.
Such an operation would require direct US involvement and a high degree of strategic risk.
The MOP in International Security and Nonproliferation
Arms control experts describe the MOP as a “game changer” in terms of conventional strike capability. However, because the depth and fortification of some facilities (like Fordow) are not fully known, there is no guarantee that even the MOP could destroy them completely.
As long as deep underground facilities remain operational, the risk of future nuclear proliferation persists. The MOP’s existence may deter some, but cannot guarantee permanent compliance or destruction of clandestine programs.
The use of the MOP would have major political ramifications, signaling a dramatic escalation. US presidents—including Donald Trump—have so far kept this weapon as a deterrent rather than an active option.
The GBU-57 Massive Ordnance Penetrator (MOP) stands as the world’s most powerful non-nuclear bunker-buster bomb—a weapon designed for the most challenging, deeply buried targets. Its purpose is both practical and psychological: to deny adversaries any sanctuary underground and to provide the US with a unique strategic capability.
Yet, the MOP’s actual effectiveness against modern underground nuclear facilities like Iran’s Fordow remains unproven. Its use would represent a major escalation in any conflict, requiring not just advanced technology but also significant political will and international coordination.
For now, the MOP remains an exclusive, formidable tool in America’s arsenal—one that embodies both the promise and peril of modern military technology.
