Inside the US strike on Iran’s deep nuclear bunkers: The GBU-57 ‘Midnight Hammer’ mission

The US military has deployed its most powerful non-nuclear weapon, the 30,000-pound (about 14,000 kg) GBU-57 Massive Ordnance Penetrator (MOP), in airstrikes against Iran’s fortified nuclear sites.

It marks the first combat use of these bunker-busting bombs.

A US general confirmed 14 GBU-57 MOPs were used in its strikes on three of Iran's known nuclear facilities.

Though the full impact of what the US dubbed as "Operation Midnight Hammer" remains unclear, the attack did hit Iran's most secure nuclear sites, as Iran itself had confirmed.

What can the GBU-57 do?

According to the Pentagon, GBU-57 MOP is "designed to penetrate up to 200 feet underground before exploding," cutting through layers of rock and reinforced concrete.

Unlike conventional bombs that detonate on or near impact, the GBU-57 is engineered for deep penetration.

"To defeat these deeply buried targets, these weapons need to be designed with rather thick casings of steel, hardened steel, to sort of punch through these layers of rock," said Masao Dahlgren, a missile defense expert at the Center for Strategic and International Studies (CSIS).

At 6.6 metres long, the bomb also features a specially designed fuse. "You need an explosive that's not going to immediately explode under that much shock and pressure," Dahlgren explained.

The GBU-57’s development began in the early 2000s, and Boeing received a contract in 2009 to produce 20 units.

'Midnight Hammer'

The MOP was designed for specific missions: striking hardened underground facilities such as Fordow, Iran’s uranium enrichment site buried 80 metres (262 feet) under rock near the holy city of Qom, about 150 kilometers (95 miles) southwest of Tehran. 

The facility reportedly stores key centrifuges used for uranium enrichment.

While Israel's earlier strikes damaged facilities like Natanz, Israeli aircraft lack the heavy munitions necessary to destroy Fordow. 

That task fell to the United States, whose B-2 Spirit stealth bombers — the only aircraft capable of delivering MOPs — carried out the strike under Operation “Midnight Hammer,” according to US Air Force General Dan Caine.

He confirmed that there were 75 precision-guided munitions dropped, including 14 GBU-57s, and that Iran’s 3 known nuclear facilities had been heavily damaged.

“This is a plan that took months and weeks of positioning and preparation,” said US Defense Secretary Pete Hegseth. “It involved misdirection and the highest of operational security.”

The weapons: Deepest punch

• The GBU-57 MOP can penetrate up to 61 meters (200 feet) of reinforced concrete. Multiple hits are believed to drill even deeper.

• Each B-2 can carry two MOPs.

• 75 precision-guided munitions and 125 aircraft were involved in the mission.

• B-2s flew over 37 hours round-trip from Whiteman Air Force Base, Missouri, with mid-air refuelling.

• Decoy flights were sent west to maintain tactical surprise, said General Dan Caine.

The Pentagon said Fordow was protected by both Iranian and Russian surface-to-air missile systems, but Israeli air operations had already neutralised much of Iran’s air defense capabilities.

US Air Force General Dan Caine, said: “We’re unaware of any shots fired at the package (US Air Force mission to Iran). Iran’s fighters did not fly. And it appears that Iran’s surface-to-air missile systems did not see us.”

The USS Vincennes is currently deployed in the Arabian Sea, and the USS Nimitz carrier group is en route — bolstering American firepower in the region. 

How is it delivered?

Only one aircraft can carry and deploy the GBU-57: the American B-2 stealth bomber.

Each B-2 can carry two GBU-57s.

In early May, B-2s were spotted at Diego Garcia, a joint UK-US military base in the Indian Ocean.

By mid-June, they were no longer visible, according to review of satellite images from Planet Labs.

Thanks to their long-range capabilities, B-2 bombers are able to fly all the way to the Middle East to do bombing runs. That's been done before.

But one strike may not be enough.

Iran’s reaction

Iran confirmed the attacks but claimed it had preemptively evacuated personnel and equipment from Fordow.

Foreign Minister Abbas Araghchi condemned the airstrikes as:

“Lawless aggression… The warmongering, lawless administration in Washington is solely and fully responsible for the dangerous consequences and far-reaching implications of its act of aggression.”

He warned that diplomacy was now off the table, saying:

“The door to diplomacy should always be open, but this is not the case right now.”

Retaliation imminent?

Iran is widely expected to retaliate. 

One likely flashpoint: the Strait of Hormuz, a key chokepoint for global oil flows. Iran could deploy fast-attack boats, naval mines, or missile strikes, potentially disrupting global oil supply and triggering a US naval response.

Iran’s Supreme Leader Ayatollah Ali Khamenei warned:

“Strikes on the Islamic Republic will result in irreparable damage for them.”

Foreign Ministry spokesman Esmail Baghaei added:

“Any American intervention would be a recipe for an all-out war in the region.”

Meanwhile, Israel’s military says it is preparing for a long-term conflict.

IAEA response

The Atomic Energy Organisation of Iran reported no radiation leakage and vowed to continue its nuclear program.

The International Atomic Energy Agency (IAEA) confirmed there has been no increase in off-site radiation and called an emergency meeting to assess the situation’s impact on nuclear monitoring.

IAEA Director General Rafael Grossi said they are reviewing damage to facilities and how it affects safeguards.