ByANNA AHRONHEIM 
Updated: 
Amid high tensions between the US and Iran, the US Air Force has awarded Boeing a sole-source contract to replenish its arsenal of GBU-57 Massive Ordnance Penetrator (MOP) bunker buster bombs, which the US dropped over a dozen on Iranian nuclear facilities in June during Operation Midnight Hammer.

According to a partially redacted justification notice posted online last week, the US Air Force said that it was awarding Boeing the sole-source contract because “this procurement and sustainment activity is critically needed to replenish the inventory of GBU-57’s, ended during Operation Midnight Hammer (21 June 25).”

Boeing is the only company that makes the GBU-57 Massive Ordnance Penetrator, and the justification notice is intended to explain why the Pentagon did not carry out a fully competitive tender for the specially designed munition.

“No delay in award is acceptable for this effort. Delaying this requirement would undermine force readiness and efficient acquisitions for this key weapons program. A delay undermines Combatant Commanders’ capabilities, jeopardizes force readiness and strategic deterrence, hinders nuclear proliferation prevention efforts, and could result in loss of life,” the document read.

A US Air Force B-2 Spirit stealth bomber is prepared for operations before Operation Midnight Hammer, at Whiteman Air Force Base, Missouri, US, June 2025
A US Air Force B-2 Spirit stealth bomber is prepared for operations before Operation Midnight Hammer, at Whiteman Air Force Base, Missouri, US, June 2025 (credit: US AIR FORCE/HANDOUT VIA REUTERS)

The exact number of BGU-57s being purchased and the cost of the contract, along with delivery dates, were not published.

What is the MOP?

Developed in the early 2000s by Boeing and the Defense Threat Reduction Agency (DTRA), the GBU-57 MOP was designed to neutralize Hard and Deeply Buried Targets (HDBTs) – including underground labs, command centers, and chemical, biological, and nuclear facilities.

An Air Force fact sheet described 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 30,000 pounds (13,600 kilograms), with the warhead alone weighing 5,740 pounds (2,600 kg) and measuring over 20 feet (6 meters) in length, the MOP can penetrate up to 200 feet  (60 m.) of earth or 60 feet (18 m.) of reinforced concrete, making it the most powerful non-nuclear bomb in the US arsenal.

According to a report in Scientific American, the kinetic strike “delivers 800 to 900 megajoules (about 758,000 to 853,000 British thermal units) of kinetic energy – comparable to a 285-ton (285,000 kg.) Boeing 747-400 touching down at 170 mph (274 kph) or a 565-ton (565,000 kg.) Amtrak Acela train moving at 120 mph (193 kph).”

First operational use-Iran

Operation Midnight Hammer, which targeted Iran’s deeply buried nuclear facilities in June 2025, was the first-ever combat use of the MOP. During the operation, seven B-2 Spirit bombers dropped 14 GBU-57s on sites in Fordow, Natanz, and Isfahan – locations long suspected of housing critical components of Iran’s nuclear program.

While US officials hailed the mission as a success, independent assessments suggested mixed results. Fordow reportedly suffered severe damage, but Natanz and Isfahan may recover faster than anticipated.

The operation highlighted both the strengths and limitations of the MOP, particularly its massive size as well as its limited aircraft compatibility, the challenge of penetrating ultra-hardened targets, and Iran’s continued development of sophisticated defenses.