As Israel's confrontation with Iran escalates, the American-made GBU-57 'bunker buster' bomb has drawn renewed attention as the only weapon capable of striking Iran's deeply buried nuclear sites, raising questions over whether US President Donald Trump will authorise its use as he mulls over military intervention.
While Israel has already targeted multiple nuclear-related sites and struck key military positions, Fordo — Iran’s heavily fortified underground uranium enrichment plant — remains untouched.
Its depth and construction make it nearly impossible to destroy without outside help, raising questions about whether the United States might intervene more directly by deploying its bunker-busting bomb.
What is the ‘bunker buster’?
The “bunker buster” broadly refers to bombs designed to penetrate deep underground before detonating.
In this case, it specifically refers to the GBU-57A/B Massive Ordnance Penetrator, a 30,000-pound (13,600 kg) precision-guided bomb designed to destroy deeply buried bunkers and tunnels, according to the US Air Force.
Measuring 6.6 metres in length and equipped with a hardened steel casing and specialised delayed-fuse system, the GBU-57 is capable of penetrating up to 200 feet (61 meters) through rock or concrete before exploding — much deeper than standard munitions.
“It’s not going to immediately explode under that much shock and pressure,” said Masao Dahlgren, a missile defense fellow at the Center for Strategic and International Studies (CSIS). “These weapons need to be designed with thick, hardened casings to punch through layers of rock.”
The US began designing the bomb in the early 2000s, and Boeing was awarded an order for 20 units in 2009.
How is the bomb deployed?
The only aircraft capable of deploying the GBU-57 is the US B-2 Spirit stealth bomber, produced by Northrop Grumman.
While theoretically any aircraft with sufficient capacity could deliver it, only the B-2 has been configured and tested for the task. With a range of 7,000 miles (11,000 km) without refueling — and over 11,500 miles (18,500 km) with aerial refueling — the B-2 can reach targets worldwide.
The B-2 can carry two GBU-57 bombs, and according to Former US Army Lt. Gen. and RAND researcher Mark Schwartz, multiple strikes would likely be required. “They’re not going to just be one and done,” he said.
Earlier in May, B-2 bombers were spotted at Diego Garcia, a strategic UK-US military base in the Indian Ocean, though they had reportedly left the area by mid-June, according to AFP analysis of satellite imagery.
Why Fordo is so hard to strike?
Unlike Natanz or Isfahan, which have already seen damage from Israeli strikes, Fordo lies buried beneath some 80 to 300 feet of rock near the city of Qom, roughly 95 kilometers southwest of Tehran.
Built into the side of a mountain and protected by surface-to-air missile systems — some of which may already have been hit — Fordo was designed to withstand aerial bombardment.
While Israel has struck nuclear sites before, the International Atomic Energy Agency (IAEA) has reported no damage at Fordo so far.
“All eyes will be on Fordo, which is buried under about 300 feet of rock,” said Behnam Ben Taleblu, director of the Iran program at the Foundation for Defense of Democracies (FDD).
“There are still outsized questions as to how efficacious of a strike Israel had against the beating hearts of Iran’s nuclear program.”
According to the IAEA, Fordo continues to produce highly enriched uranium, raising concerns that an attack using the GBU-57 could risk releasing radioactive material. However, past strikes — such as at Natanz — have only resulted in contamination at the site itself, the agency says.
Could Israel strike Fordo alone?
Israel lacks the GBU-57 and the aircraft needed to deploy it. Short of a nuclear option or a high-risk ground commando raid, the bunker buster remains the most viable way to damage Fordo — but it would require American involvement. Schwartz said, “Only the United States has the conventional capacity to destroy such a site.”
Israeli Ambassador to the US Yechiel Leiter acknowledged the challenge: “This entire operation... really has to be completed with the elimination of Fordo,” he said in a Fox News interview.
Still, Israel has publicly only asked for defensive help, emphasizing that it has “a number of contingencies” to deal with Fordo.
“Not everything is a matter of, you know, taking to the skies and bombing from afar,” Leiter told ABC News.
What are the consequences?
Such a US intervention would come with "a lot of political baggage for America," Taleblu said, emphasizing that the bunker-buster bomb is not the only way to address Iran's nuclear program.
Without the GBU-57 bombs, and short of a diplomatic solution, Taleblu said Israelis could attack access to underground complexes like Fordo by "trying to hit entrances, collapse what they can, cut electricity" and take other measures that have already been taken at Natanz. But if the goal is to truly disable Fordo, the decision over whether to unleash the US’ most powerful non-nuclear bomb may soon take center stage.