The US Air Force has quietly initiated work on a new version of its Massive Ordnance Penetrator (MOP), the 13.6-ton bunker-buster bomb designed to destroy deeply buried and fortified targets. The upgrade follows reports that the weapon was used in a covert strike against an Iranian nuclear facility earlier this year. As adversaries invest in increasingly hardened underground infrastructure, the MOP remains central to US strategic deterrence and strike capabilities.
The GBU-57 MOP: Origins and Capabilities
The GBU-57A/B Massive Ordnance Penetrator was developed by Boeing for the US Air Force as a response to emerging threats from deeply buried facilities—particularly those related to weapons of mass destruction (WMDs). Weighing approximately 30,000 pounds (13.6 metric tons), the MOP is currently the largest non-nuclear conventional bomb in the US inventory. It is designed to penetrate up to 60 meters of reinforced concrete or 40 meters of hard rock before detonation.
Unlike earlier penetrators such as the BLU-109 or BLU-113 series, which weigh between 900–2,000 kg and are carried by fighter aircraft like the F-15E or F-35A (with modifications), the MOP requires a strategic bomber platform due to its size. Currently, only the B-2 Spirit stealth bomber is certified to carry and deploy it.
The weapon uses GPS-aided inertial navigation for precision guidance and features multiple delay fuzes that allow detonation at specific depths. It is not equipped with rocket propulsion; instead, it relies on kinetic energy from high-altitude release to achieve penetration velocity.
Reported Strike on Iranian Facility Raises Strategic Questions
In early 2024, reports emerged—initially via Middle Eastern intelligence leaks and later echoed by Western defense sources—that two MOPs were used in a clandestine operation targeting Iran’s Fordow Fuel Enrichment Plant (FFEP). The site is located deep within a mountain near Qom and has long been considered one of Iran’s most heavily fortified nuclear facilities.
While neither Washington nor Tehran officially confirmed the strike, satellite imagery reviewed by open-source analysts showed signs consistent with deep-earth impact near Fordow’s perimeter in late January 2024. Israeli media outlets speculated that either Israel or the United States—or both acting jointly—executed the operation using B-2 bombers launched from Diego Garcia or another forward base.
If confirmed, this would mark one of only two known operational uses of the GBU-57 since its fielding in 2011—the other being test drops at White Sands Missile Range and Tonopah Test Range. The alleged use underscores both its strategic value and limitations amid evolving adversary countermeasures such as deeper burial and electromagnetic shielding.
Next Generation MOP Development Underway
According to recent budget documents reviewed by Air & Space Forces Magazine, Northrop Grumman has received funding under classified line items for “advanced penetrator capability upgrades.” These likely pertain to enhancements for both kinetic performance (e.g., improved casing metallurgy or aerodynamics) and survivability against countermeasures such as GPS jamming or decoy tunnels.
The Air Force Research Laboratory (AFRL) has also been exploring technologies for variable-yield warheads and adaptive fuzing mechanisms that can adjust penetration depth dynamically based on sensed material resistance—a feature that could be incorporated into future MOP variants.
- MOP-X: A rumored designation for an extended-range variant with improved standoff capability via glide-kit attachment or powered booster stage.
- Smart Fuzing: Integration of AI-driven target recognition algorithms to optimize detonation timing based on real-time feedback during penetration.
- Hardening Counter-Countermeasures: Radiation-hardened electronics and enhanced GNSS receivers resistant to spoofing/jamming environments typical around high-value underground sites.
No public timeline exists for fielding these upgrades; however, industry insiders suggest prototype testing could begin as early as FY2025 under classified programs managed by Air Force Global Strike Command (AFGSC).
Basing Constraints Limit Deployment Options
A key limitation of current MOP capability lies in its delivery platform dependency. Only 20 B-2 Spirits exist in USAF inventory—of which fewer than half are mission-ready at any given time due to maintenance cycles under Northrop Grumman’s PDM program at Whiteman AFB. The upcoming B-21 Raider may eventually assume this role but is not expected to reach IOC before mid-to-late 2020s.
This constraint complicates rapid global deployment scenarios where time-sensitive strikes against mobile or quickly hardened targets are required. While forward basing options like Diego Garcia offer some flexibility, they also carry geopolitical risks—especially if operations must be conducted without host-nation disclosure or approval.
A potential solution involves modularizing future penetrators for compatibility with additional platforms such as B-52H Stratofortress (with rotary launcher modifications) or even unmanned combat air systems (UCAS) capable of carrying heavy ordnance internally over intercontinental ranges.
Strategic Implications Amid Global Underground Arms Race
The renewed focus on ultra-deep penetrators reflects broader shifts in military engineering worldwide. China continues expanding its underground tunnel networks—known collectively as “the Underground Great Wall”—for command bunkers and missile silos. Russia maintains legacy Soviet-era subterranean complexes beneath Moscow believed capable of withstanding nuclear attack.
This arms race below ground has prompted NATO allies including France and Germany to revisit their own hardened facility vulnerabilities while seeking joint solutions through NATO Support & Procurement Agency (NSPA) working groups focused on counter-WMD strike capabilities.
The US Department of Defense views deep-strike options like MOP not merely as tactical tools but strategic levers within escalation management frameworks—particularly when confronting adversaries who believe their critical assets are invulnerable due to depth alone.
Conclusion: Maintaining Credible Deep Strike Deterrence
The reported use of GBU-57 against Iran’s Fordow site highlights both current capabilities and looming gaps in America’s ability to hold deeply buried targets at risk. As adversaries continue investing in subterranean resilience—from centrifuge halls under mountains to command bunkers beneath cities—the need for advanced penetrators remains urgent but complex.
The USAF’s move toward upgrading the Massive Ordnance Penetrator signals recognition that brute force alone may no longer suffice; precision guidance resilience, adaptive fuzing logic, platform flexibility—and above all credible readiness—will define next-generation bunker-busting effectiveness in contested environments where denial is measured not just by distance but depth itself.
