US moves to replenish “mother of all bombs” after strikes on Iran

The U.S. Air Force is preparing to restock its supply of GBU-57 Massive Ordnance Penetrator (MOP) bunker-busting bombs used in strikes on Iran’s nuclear facilities last June, according to recently released Air Force documents.

The service is finalising a deal with Boeing worth over $100 million to replace the bombs expended during Operation Midnight Hammer, when B-2 Spirit stealth bombers targeted Iran’s Fordow and Natanz nuclear sites. The documents describe the acquisition as “critically needed to replenish the inventory of GBU-57s expended” during the operation.

In the June 22, 2025, mission, 14 MOPs were dropped — six on Fordow and two on Natanz — marking the first operational use of the 30,000-pound weapons. Operation Midnight Hammer involved 125 aircraft, including F-35s, F-22s, F-16s, refuelling aircraft, and the bomb-dropping B-2s. A third facility at Isfahan was struck with more than two dozen Tomahawk cruise missiles.

“The weapons functioned as designed, meaning they exploded,” said Chairman of the Joint Chiefs of Staff Gen. Dan Caine. He explained that the bombs travelled down ventilation shafts at over 1,000 feet per second, with blast and overpressure effects destroying critical underground infrastructure.

The documents do not specify the number of MOPs being purchased. They indicate, however, that this will be the last U.S. MOP procurement before the Air Force transitions to the Next-Generation Penetrator (NGP), designed to defeat hard and deeply buried targets with “superior technology.”

The MOP, initially tested from a B-52 but intended for the B-2, achieved initial operational capability in 2011. It has undergone multiple upgrades, including the Large Penetrator Smart Fuse modification, with full-scale tests conducted as recently as 2024.

The NGP, weighing roughly 22,000 pounds, is intended to be compatible with the upcoming B-21 Raider bomber, which has a smaller payload capacity than the B-2. Pentagon documents suggest a more competitive approach for NGP production, aiming to allow multiple suppliers to innovate and drive performance and cost improvements.

According to the Air Force, the MOP program will conclude after the final procurement, with NGP expected to take over its role in penetrating heavily fortified underground targets.

By Tamilla Hasanova