Iran’s secretive nuclear site that only a US bomb could hit

23rd Jun 2025 | Source: BBC

Hidden away in a mountainside south of Tehran is an enrichment plant that is vital to Iran’s nuclear ambitions - and Israel’s attempts to dismantle them.

Israel may have achieved dominance over Iran’s skies but the Fordo nuclear facility - believed to be deeper underground than the Channel Tunnel connecting the UK and France - has remained out of reach of Israel’s weaponry.

Only the US is considered to have a bomb that might be large enough to destroy Fordo, a move that could dramatically widen a Middle East war.

We take a look at the secretive site, which Iran insists is for civilian purposes only but Israel says threatens its survival.

What is the Fordo enrichment site?

Situated about 60 miles (96km) south of the capital Tehran, the uranium enrichment site at Fordo is located in a mountainous region close to the city of Qom.

Fordo is built deep within northern Iran’s rugged, remote mountains

Designed to withstand air strikes, its underground location shields it from conventional bombs

The complex at Fordo was originally a series of tunnels used by the country’s elite Islamic Revolutionary Guard Corps, but Iran acknowledged the existence of the enrichment plant in 2009 after it was revealed by Western intelligence agencies.

Reuters

Iranian officials with members of the International Atomic Energy Agency during a visit to the facility in November last year

The underground facility is thought to consist of two main tunnels that house centrifuges used to enrich uranium, as well as a network of smaller tunnels.

Planet Labs

It is secured by a ring of fencing with access through one checkpoint

There are thought to be six entrance tunnels that lead through to the underground complex

Above ground, there is one large support building and a road to a nearby support site

Is Fordo indestructible?

The Fordo plant presents a unique challenge to the Israeli military because of the depth of its underground facilities.

To cause any meaningful damage to the site would need to be targeted by "bunker buster" munitions that are able to penetrate deep below the surface.

Israel is thought to have such weapons but they can only operate to a depth of less than 10m (33ft). The US, however, does have a bomb that might be able to do the job: the 13,000kg (30,000lb) GBU-57 Massive Ordnance Penetrator (MOP).

The MOP’s heavy casing and weight allows it to penetrate about 18m of concrete or 61m of earth before exploding, according to analysts at Janes, a defence intelligence company.

But even a strike with an MOP is not guaranteed to destroy the Fordo site as the tunnels are thought to be 80-90m (262-295ft) below the surface. It is thought that repeated strikes would be needed to cause significant damage.

Fordo is much deeper than Iran’s other underground uranium enrichment site at Natanz, which analysts believe is about 20m (65ft) below the surface. Israel has already targeted the Natanz facility and experts believe it is now "severely damaged if not destroyed altogether".

Vice-Admiral Mark Mellett, the former head of the Irish Defence Forces, told BBC Verify that the likelihood of these “bunker busters” being able to destroy a site like Fordo would depend on how heavily reinforced the underground tunnels are.

"[Iran] would know the specification of this type of ordnance. They'd know what they need to try and withstand from this ordnance. So the question is, are [the Fordo facilities] beyond the reach of that ordnance?"

US Air Force via AP

USAF airmen alongside a GBU-57 bomb at Whiteman Air Base in Missouri

One sign that the US might be preparing to use the MOP on targets in Iran would be the deployment of its B-2 stealth bombers to Diego Garcia, an air base 2,300 miles (3,700km) from Iran but within the B-2 range.

The B-2 is the only US bomber capable of carrying the 6.2m-long (20.5ft) MOP bombs.

Six B-2 bombers were pictured at the base in Diego Garcia in early April, but it is unclear if any remain stationed there as they have not been seen in more recent satellite imagery of the site.

Air Marshal Greg Bagwell - a former RAF deputy operations chief - told BBC Verify that the US would be able to sustain rolling B-2 missions from Diego Garcia far more efficiently than having the planes operate from bases in the US.

But he added: "What we're talking here is not a sustained operation against the bunkers. It may only take one or two of these specialist weapons to create the breach that you're looking for."

Will the US get involved?

While the US is already helping shoot down Iranian missiles that have been sent towards Israel in retaliation, it has not been directly involved in any of the attacks on Iran.

But analysis by BBC Verify suggests the US could be preparing for a wider role in the conflict. In the past few days, 30 US military planes have been moved from bases in the US to Europe. Many of them are KC-135 aerial refuelling tankers that are used to refuel fighter jets and bombers.

g.lockaviation

A photograph showing four US fighter jets flying alongside a KC-135 refuelling tanker aircraft in the skies over Suffolk, England, on Tuesday

Justin Bronk, a senior analyst with the Royal United Services Institute think tank, said that the deployments were "highly suggestive" that the US was putting in place contingency plans to "support intensive combat operations" in the region in the coming weeks.

US President Donald Trump said he was still considering whether the US would join Israeli strikes on Iran, adding that his patience "had already run out" with Tehran.

"I will make my decision whether or not to go within the next two weeks," he said in a statement on Thursday.