The United States military is moving to replenish its stockpile of the GBU-57 Massive Ordnance Penetrator (MOP) bunker-buster bombs, following their high-profile use against Iran’s nuclear facilities during “Operation Midnight Hammer” in June 2025.
Recently published, partially redacted US Air Force (USAF) acquisition documents dated February 12, 2026, reveal that the service is finalising a sole-source contract worth approximately $100 million with Boeing to supplement its inventory of the GBU-57 MOP. The disclosure confirms what defence analysts had widely anticipated: that the expenditure of the weapon during last year’s strike has compelled the Pentagon to restock one of its most specialised and powerful conventional munitions.
The GBU-57 MOP was used operationally for the first time on June 22, 2025, when the United States launched Operation Midnight Hammer against Iran’s hardened nuclear facilities at Fordow and Natanz. The strikes followed Israel’s 12-Day War with Iran and marked a dramatic escalation in the shadow conflict surrounding Tehran’s nuclear programme.
According to defence officials, approximately seven B-2 Spirit bombers were deployed in the operation, each carrying two MOPs. In total, 14 of the 30,000-pound bunker-busters were dropped on deeply buried targets. The operation represented the first combat use of the weapon more than 15 years after it was declared operational in 2010.
Air Force procurement documents state that the new contract is “critically needed to replenish the inventory of GBU-57s expended during Operation Midnight Hammer.” Deliveries under the new agreement are projected to begin in January 2028.
The documents justify the sole-source award to Boeing by noting that the company is the only manufacturer currently capable of producing the highly specialised munition. Awarding the contract to another bidder, the Air Force states, “would result in unacceptable delays” and jeopardise operational preparedness.
The redacted filing emphasises Boeing’s “uniquely acquired expertise over a period of 18 years of adapting this specialised weapon to meet evolving mission needs as MOP transitioned from proof-of-concept to Full Operational Capability.” It further notes that the action is essential to ensure that Air Force Global Strike Command (AFGSC) maintains sufficient assets to support contingency war plans across all Combatant Commands.
The GBU-57 was conceived in the early 2000s amid growing concern over adversaries placing critical weapons-of-mass-destruction infrastructure deep underground. Developed by Boeing in cooperation with the Defence Threat Reduction Agency (DTRA), the MOP was specifically designed to destroy Hard and Deeply Buried Targets (HDBTs), including reinforced command centres, subterranean laboratories, and nuclear facilities.
An official Air Force data sheet describes the MOP as “a weapon system designed to accomplish a difficult, complicated mission of reaching and destroying our adversaries’ weapons of mass destruction located in well-protected facilities.”
Weighing approximately 30,000 pounds (13,600 kilograms), the MOP is the most powerful non-nuclear bomb in the US arsenal. Its warhead alone weighs around 5,740 pounds (2,600 kilograms). At over 20 feet in length, the munition delivers an immense kinetic impact, generating between 800 and 900 megajoules of energy upon penetration.
The bomb is capable of penetrating up to 200 feet of earth or approximately 60 feet of reinforced concrete before detonation, making it uniquely suited to engage targets such as Iran’s Fordow facility, which is buried deep within a mountain near Qom.
Independent assessments suggest that Fordow sustained significant structural damage from the strikes. However, reports indicate that Natanz and Isfahan were less severely affected than anticipated and may recover more quickly than US officials had expected.
The operation demonstrated both the potency and the limitations of the GBU-57. While the bomb succeeded in breaching heavily fortified structures, analysts noted that ultra-hardened and deeply buried targets remain extraordinarily challenging to neutralise fully. The weapon’s enormous size and weight restrict its compatibility to only a handful of aircraft—primarily the B-2 Spirit stealth bomber—limiting operational flexibility.
The exact number of MOPs currently in the US inventory remains classified. Open-source reporting suggested that at least 20 GBU-57s were in service as of 2015. Production continued in subsequent years, but there was little indication of significant procurement in the period leading up to 2025. The combat expenditure of 14 units during Operation Midnight Hammer likely represented a substantial portion of the available stock.
Although the Air Force is now replenishing its MOP inventory, the weapon is already slated for eventual replacement by the Next Generation Penetrator (NGP). The NGP is envisioned as a more advanced “MOP-like” capability incorporating superior technology, improved guidance, and potentially standoff strike features through an attached rocket booster.
The NGP is expected to be compatible with the B-21 Raider, the Air Force’s next-generation stealth bomber designed to replace the B-2. Unlike the MOP, which was tailored primarily for the B-2, the NGP aims to integrate seamlessly into future long-range strike architectures.
In September 2025, the Air Force awarded the NGP development contract to Applied Research Associates (ARA), with Boeing serving as a partner and system design agent. The contract calls for rapid prototyping, including approximately 10 sub-scale test articles and three to five full-scale warhead models.
The timeline is aggressive: prototypes are expected within 18 to 24 months of the award, meaning between March and September 2027. However, the NGP remains in the early stages of development, with no publicly disclosed date for Initial Operational Capability (IOC) or full operational deployment.
Given this gap, the current MOP replenishment is widely seen as a stopgap measure to maintain strategic readiness until the NGP becomes available.
The Air Force is not relying solely on the NGP to modernise its penetrating munitions. It is also considering the Global Precision Attack Weapon (GPAW), a smaller bunker-buster concept designed to fit within the internal weapons bay of the F-35 stealth fighter.
Meanwhile, the USAF has begun inducting the precision-guided GBU-72/B, a 5,000-pound-class bunker buster first employed in combat against Houthi militia targets in Yemen in 2024. Unlike the MOP, which is optimised for extreme penetration, the GBU-72 offers greater flexibility and compatibility across a broader range of aircraft.
This layered approach reflects the Pentagon’s recognition that future conflicts may demand a spectrum of penetrating capabilities—from massive bunker-busters aimed at strategic facilities to smaller precision weapons suited for tactical targets.
The timing of the replenishment contract is significant. It comes amid renewed tensions between Washington and Tehran and mounting speculation about the possibility of another confrontation.
US President Donald Trump recently stated that nuclear talks with Iran must continue, following a meeting with Israeli Prime Minister Benjamin Netanyahu. However, he warned that action would be taken if a satisfactory agreement is not reached.
In parallel, the Pentagon has ordered the USS Gerald R. Ford to deploy from the Caribbean to the Middle East area of responsibility, reinforcing US naval presence in the region.
Speaking in Jerusalem on February 15, 2026, Netanyahu outlined strict conditions for any future nuclear agreement with Tehran. He insisted that all enriched uranium must be removed from Iran and that enrichment infrastructure must be dismantled entirely.
“The first is that all enriched material has to leave Iran,” Netanyahu said. “The second is that there should be no enrichment capability – not stopping the enrichment process, but dismantling the equipment and the infrastructure that allows you to enrich in the first place.”
He also demanded rigorous inspection mechanisms, calling for “real inspection, substantive inspections, no lead-time inspections, but effective inspections for all of the above.”
Iran, for its part, has signalled a willingness to scale back aspects of its nuclear programme in exchange for sanctions relief. However, President Masoud Pezeshkian has warned that Tehran will “not yield to their excessive demands,” particularly regarding zero enrichment, which Iranian leaders consider a red line under the Nuclear Non-Proliferation Treaty framework.
US Secretary of State Marco Rubio recently stated that President Trump “prefers diplomacy and an outcome of negotiated settlement” over direct attacks. Nonetheless, the military build-up in the region and the decision to restock the MOP underscore that Washington is maintaining credible strike options should negotiations fail.
White House spokesperson Anna Kelly reiterated that “President Trump has all options on the table with regard to Iran,” emphasising that the president listens to diverse perspectives but ultimately makes decisions based on national security considerations.
The replenishment of the GBU-57 inventory serves not only a logistical function but also a strategic signalling role. By restoring its capacity to conduct deep-penetration strikes against hardened nuclear facilities, the United States reinforces deterrence against adversaries who may seek sanctuary underground.
At the same time, the evolution toward the NGP reflects the Pentagon’s broader shift toward next-generation systems tailored for contested, GPS-denied environments and integration with platforms like the B-21 Raider.
Operation Midnight Hammer demonstrated that even the most formidable conventional bunker-buster has operational constraints. But it also underscored the enduring importance of maintaining credible options to strike deeply buried strategic targets.
For now, the MOP remains a critical—if interim—component of America’s strategic toolkit, bridging the gap until its successor arrives. As diplomacy and deterrence continue to shape US-Iran relations, the replenishment of these massive bunker-busters highlights a familiar reality: even in an era of negotiations, the shadow of military power looms large.
