The U.S. military is moving to restock its supply of the GBU-57 Massive Ordnance Penetrator bunker-busting bombs it used against Iran’s underground nuclear facilities last June, according to Air Force documents.
The Air Force is finalizing a deal with Boeing worth over $100 million to replace the bombs it used to pummel Iran’s Fordow and Natanz nuclear sites.
In partially redacted documents released on a government website Feb. 12, the service said the acquisition is “critically needed to replenish the inventory of GBU-57s expended during Operation Midnight Hammer.”
The service is also continuing its competition for the next-generation weapons to take out deeply buried targets.
U.S. Air Force B-2 Spirit stealth bombers dropped 14 weapons on the sites in the operation on June 22, 2025. Each of the B-2s carried two MOPs. Six of the bombs were dropped on Fordow, and two were dropped on Natanz. Operation Midnight Hammer was the first time the 30,000-pound bunker-busting bombs were used operationally.
The redacted documents are intended to provide a justification for not awarding a fully competitive contract for the specially designed munition.
“This action is essential to restore operational readiness … and ensure Air Force Global Strike Command (AFGSC) possesses the necessary assets to support strategic contingency war plans for all Combatant Commands (COCOMs),” according to the document.
The documents do not say how many MOPs the U.S. government is purchasing in the forthcoming deal, which is set to be the last lot of GBU-57s purchased by the U.S. military before moving on to its new Next-Generation Penetrator, or NGP.
Even before the release of the documents, there were signs that the Pentagon was repurposing funds so it could buy more of the bombs. A reprogramming request in August of last year for $123 million stated that funds were needed to replace the MOPs used in Operation Midnight Hammer.
The newly released documents indicate that the Air Force is seeking full MOP weapon systems. The document states that the weapon’s tailkits are projected to be delivered starting on Jan. 10, 2028, to “replace expended units.” Components for all-up rounds—the bombs themselves—are also being purchased.
The exact number of MOPs being purchased, along with other delivery dates appear to be part of the redacted portions of the document.
Operation Midnight Hammer involved 125 aircraft, including F-35s, F-22s, F-16s, refueling aircraft, and the bomb-dropping B-2s. The U.S. also struck a third facility at Isfahan with more than two dozen Tomahawk land-attack cruise missiles.
The MOP has a hardened casing that can slice through layers of rock, concrete, and steel. Inside the bomb, sensors are designed to detect the area the bomb is passing through before detonating at a chosen depth.
“The weapons functioned as designed, meaning they exploded,” Chairman of the Joint Chiefs of Staff Gen. Dan Caine told reporters after the strikes.
The weapons traveled down ventilation shafts at the facilities at over 1,000 feet per second, according to Caine.
“A bomb has three effects that causes damage: blast, fragmentation, and overpressure,” he said. “In this case, the primary kill mechanism in the mission space was a mix of overpressure and blast ripping through the open tunnels and destroying critical hardware.”
It is unclear how many MOPs have been built in previous years and precisely how many remain.
The MOP was initially tested from a B-52. But it was always intended to be dropped by the B-2, since the heavily protected targets the bomb was designed to hit were expected to be defended by top-tier air defense systems that the stealth bomber could penetrate. The weapon achieved initial operational capability in 2011.
The Air Force performed test drops from B-2s from 2014 to 2016 followed by further tests in 2017 to validate enhancements. The most recent upgrade to the bomb is the Large Penetrator Smart Fuse modification, which was tested in 2020 against a tunnel target. Three more tests were conducted between 2021 and 2022. Two full-scale tests were performed in 2024 to verify its integration on the B-2.
The military appears set to move on to MOP’s successor after this new buy.
“The MOP program production is concluding after these procurement efforts conclude,” the document states.
Last September, the Air Force issued a prototype contract for NGP development. That followed a March 2024 request for information from industry for the weapon, seeking concepts for “a prototype penetrator warhead design capable of defeating Hard and Deeply Buried Targets.”
The 2024 document said the design should not exceed 22,000 pounds, roughly two-thirds the size of the MOP.
The new B-21 Raider bomber is known to be smaller than the B-2, at roughly two-thirds the size, with a smaller payload capacity. It is unclear if the MOP could fit in a B-21, which is expected to enter service within the next couple of years.
The Air Force document refers to the Next-Generation Penetrator as “a similar MOP-like capability” that will have “superior technology.”
The government appears to be pursuing a more competitive approach to the NGP than the GBU-57, as Boeing holds much of the weapon’s intellectual property and software.
For NGP, the Pentagon is seeking contracts that allow “independent development, modification, and improvement of all hardware, software algorithms, and logical interfaces related to NGP and subsequent MOP weapon systems,” according to the recently released documents. “This approach will empower a diverse supplier base to compete on innovation, performance, and cost, driving technological advancements.”
