Fordow: What we know about Iran's secretive 'nuclear mountain' - and why it was so well protected

Deep beneath a mountain, hundreds of centrifuges were kept safe, used for enriching Iran's uranium that Israel suspects is destined for a nuclear weapon.

The Fordow plant was protected by tonnes upon tonnes of dirt and rock, far away from prying eyes - and foreign missiles.

But in the early hours of Sunday, its status was thrown into question after President Donald Trump said it had been "obliterated" along with sites at Natanz and Isfahan.

It was thought that only the American B-2 stealth bomber and its massive payload could breach the so-called "nuclear mountain", and it is this plane that was involved in the recent strikes.

Iran has repeatedly denied that it is seeking a nuclear weapon and the head of the UN's nuclear watchdog said in June that it has no proof of a "systematic effort to move into a nuclear weapon".

What is the Fordow facility?

The Fordow enrichment plant is one of three key pieces of nuclear infrastructure in Iran - the others being the Natanz enrichment plant and research facilities in Isfahan.

It is thought to be buried around 80m deep into the side of the mountain. It was previously protected by Iranian and Russian surface-to-air missile systems, but these may have wholly or partially knocked out during Israel's recent attacks.

Construction is believed to have started in around 2006 and it first became operational in 2009 - the same year Tehran publicly acknowledged its existence.

In November 2020, it was believed there were 1,057 centrifuges at Fordow. These are used to separate isotopes and increase the concentration of uranium-235, needed for nuclear fuel and weapons.

In 2023, the International Atomic Energy Agency (IAEA) - the nuclear watchdog - found uranium particles enriched to 83.7% purity - near the 90% needed for a bomb - at Fordow, the only Iranian facility where this has been found.

In June 2024, the Washington Post reported on a major expansion at Fordow, with nearly 1,400 new centrifuges earmarked for the subterranean facility.

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A key target for Israel

Israel has made no secret of its desire to cripple or remove Iran's nuclear programme, describing it as an existential threat.

It's not the only site in Iran capable of producing and using nuclear material, however.

"But of course the real big piece remains at Fordow still and this has been in the headlines quite a bit," says Dr Alexander Bollfrass, an expert on nuclear weapons from the International Institute for Strategic Studies (IISS) thinktank.

Bunker buster bombs

There has been a lot of talk about bunker buster bombs. These are munitions that explode twice - once to breach the ground surface and again once the bomb has burrowed down to a certain depth.

The Israelis used 60 to 80 of them in the strike that killed Hezbollah leader Hassan Nasrallah in September last year, according to Martin "Sammy" Sampson, a former air marshal and executive director at the IISS.

But Nasrallah was only 10-15m underground, Mr Sampson said, while Fordow is believed to be 80m beneath the surface.

"An awful lot of planes would be in the same place for an awful long time" to drop enough bombs to have a chance of getting to the buried facility, he added.

It's perhaps this that prompted the US, which operates the much more powerful GBU-57 bomb, to intervene directly in the conflict and strike Fordow.

"My sense is that it would still take multiple strikes," Mr Sampson said, putting it in "more and more unknown territory".

"It would be pretty disastrous... if you put 400 planes over the top of Fordow, or you put the might of the US over Fordow, and it survived."

According to Mr Trump, Fordow was "obliterated" in the attack.

Israel's 'contingencies' for dealing with Fordow

Israel had suggested that it could destroy or cripple Fordow without using bombs dropped from the air.

Speaking to Sky's Yalda Hakim earlier this week, former Mossad director of intelligence Zohar Palti said it was "much easier for the Americans to do it", possibly referring to the GBU-57.

"But as you see, we know how to run things alone," he added. "And if we need to do some other stuff alone, we will do it."

Israel's ambassador to the US, Yechiel Leiter, said last weekend that Israel has "a number of contingencies... which will enable us to deal with Fordow".

"Not everything is a matter of, you know, taking to the skies and bombing from afar," he told ABC News.

There has been talk of using special forces to raid the facility on the ground, but that has its downsides as well.

"This would be an incredibly high-risk mission if you were to do something on the ground," said Mr Sampson.

There was also the possibility Israel could replicate what happened at the Natanz enrichment plant, where the IAEA said 15,000 centrifuges were likely destroyed in the IDF bombardment of Iran.

This was possibly due to an Israeli airstrike disrupting the power supply to the centrifuges, rather than actual physical damage to the centrifuge hall, according to the nuclear watchdog.

(c) Sky News 2025: Fordow: What we know about Iran's secretive 'nuclear mountain' - and why it was so well prot