Why only US bunker-buster bombs can strike Iran's Fordow nuclear facility

As Israel intensifies its military campaign against Iran, the fortified Fordow nuclear facility has emerged as one of its highest-priority targets – but also one of the most inaccessible.

Buried beneath 80 to 90 metres of rock inside a mountain near the city of Qom, the site is effectively shielded from any known Israeli air-launched munitions.

The Fordow Fuel Enrichment Plant first came to international attention in 2009, when US President Barack Obama, alongside French President Nicolas Sarkozy and UK Prime Minister Gordon Brown, publicly revealed its existence.

At the time, Obama said the facility's size and configuration were "inconsistent with a peaceful programme". Iran, which had already informed the International Atomic Energy Agency (IAEA) about the site days earlier, claimed the facility was a contingency location to protect against military threats.

Since then, Fordow has become central to concerns over Iran's nuclear ambitions. Satellite imagery shows five tunnel entrances burrowed into the mountain, along with a wide security perimeter and a concealed ventilation shaft. The main enrichment halls are believed to lie nearly 300 feet underground, making a successful aerial strike almost impossible without advanced bunker-penetrating weapons.

Israel has reportedly targeted the facility during its latest military operation, but according to the IAEA, it has so far been unable to inflict any real damage. While some analysts warn Iran could convert its enriched uranium stockpile into weapons-grade material at Fordow, the facility remains operational.

Now, attention has turned to the US, which alone possesses the Massive Ordnance Penetrator (MOP), or GBU-57 – a 30,000-pound bomb capable of reaching facilities like Fordow. It can only be deployed from a US B-2 stealth bomber, a capability Israel lacks.

A senior unnamed US official told Axios that President Donald Trump had viewed the MOP as a critical pressure point to push Iran back to negotiations. "Trump thinks in terms of deals and leverage," the official said. "This is leverage." The official added that the potential use of bunker-busting bombs could mark a "turning point" in the confrontation.

The New York Times reported that while Trump sometimes implies he developed the GBU-57, the weapon was actually conceived during the George W. Bush administration in 2004 and tested under Trump’s first term.

Israeli Prime Minister Benjamin Netanyahu has long urged the US to provide bunker-busting capabilities, but Washington has resisted. Sources say the topic has come up repeatedly in recent private talks between Netanyahu and Trump.

Experts believe even one GBU-57 would not be enough to neutralise Fordow. Pentagon assessments reportedly conclude that a successful strike would require multiple B-2 bombers dropping MOPs in succession at the same impact point to breach the depth of the facility. Only US personnel and equipment could conduct such an operation.

Bunker-busting bombs were first developed during the 1991 Gulf War, when US forces struggled to reach buried bunkers in Iraq. Using repurposed artillery barrels, engineers designed steel-cased bombs filled with high explosives like Tritonal, a TNT-aluminium mix offering 18 percent more explosive power than TNT alone.

While some bunker busters contain depleted uranium, raising environmental and health concerns, others, like the nuclear-capable B61-11, present major diplomatic and ethical risks.

Recent US drills over the Mojave Desert showed a B-1 bomber carrying what appeared to be a large bunker-buster, believed to be a GBU-57. The weapon is reportedly capable of penetrating more than 200 feet of reinforced concrete.

Although Trump continues to oscillate between escalation and calls for diplomacy, it remains unclear whether the White House is prepared to greenlight the use of its most powerful bunker-busting arsenal in a direct strike on Iran.