For Israeli military planners, it is something like “Mount Ham”: a heavily guarded nuclear enrichment facility, buried half a kilometer under a mountain, surrounded by air defenses and symbolically located near the ancient religious city of Qom.
For Tehran, the Fordow facility symbolizes its desire to protect its nuclear program — designed to survive even an all-out attack, with enough centrifuges and sufficient quantities of highly enriched uranium for the possible construction of a nuclear weapon, or for a so-called “break out.”
Buried under hard rock and enclosed by reinforced concrete that makes it impervious to any publicly known Israeli weapon, Fordow is also a symbol of Iran’s strategic insecurity.
“Fordow is the alpha and omega of Iran’s nuclear activity.”
Was he attacked?
On Saturday, June 14, 2025, Iran announced that Fordow had been attacked, according to the semi-official ISNA news agency, citing the country’s Atomic Energy Organization, although the damage was limited.
In contrast, Israel managed to destroy the above-ground experimental enrichment facility at Natanz, the head of the International Atomic Energy Agency (IAEA), Rafael Grossi, told the Security Council on Friday. According to an analysis of open-source satellite imagery by the Institute for Science and International Security (ISIS), the underground centrifuge halls at Natanz are likely rendered unusable due to extensive damage to the power grid.
Fordow will be a challenge without US involvement It is heavily fortified and deep in a mountain. Iran is not yet at ground zero, that is, the complete destruction of its nuclear program… It still has significant capabilities. Fordow is the most difficult—and likely the last—target in Israel’s air campaign.
It’s not the only one…
Fordow is not unique in the world as a protected facility. Every major military power with a nuclear program has similar underground military bunkers, which have inspired a host of spy thrillers and conspiracy theories.
- Raven Rock in the US, the so-called “Underground Pentagon,” is built into a mountain in Pennsylvania.
- The secretive Mount Yamantau in Russia is believed to house a large nuclear weapons facility.
- The same goes for North Korea’s underground missile bases, built into mountains, while China’s Longpo naval base includes an underground facility for nuclear submarines accessed via tunnels.
- Fordow, however, is the only major underground military base to have been directly attacked — a precedent that shows the extraordinary risk taken by Israeli Prime Minister Benjamin Netanyahu in authorizing the Israeli strikes this week.
Tehran’s stance
Iranian officials have denied for years that they are seeking a nuclear bomb, and the most recent U.S. intelligence assessment concluded that Iran has not restarted its nuclear weapons program, which it suspended in 2003 under international pressure. But if Tehran chooses to do so, ISIS estimates that Fordow could convert Iran’s entire stockpile of highly enriched uranium—estimated at 408 kilograms by the IAEA in May—and produce enough uranium to make nine nuclear weapons in just three weeks.
“Iran could produce the first 25 kilograms of weapons-grade uranium at Fordow in just two to three days,” ISIS has warned.
The differences between Fordow and Natanz encapsulate much of Tehran’s nuclear history — as well as multilateral efforts to limit enrichment and deter attacks like the one by Israel.
After public revelations of a secret facility, Natanz was finally declared by Iran to the UN in 2003. Although it is a sprawling industrial complex with up to 16,000 centrifuges, it was designed for mass-scale enrichment of uranium to lower levels. This, combined with regular inspections by the UN, made it more suitable for peaceful nuclear use.
Natanz’s underground enrichment plant is also only about 20 meters underground. In contrast, Fordow stands out for its geological resilience, which makes the centrifuge rooms virtually immune to conventional aerial bombs. This could even include the US’s giant Massive Ordnance Penetrator bomb, capable of penetrating up to 60 metres of concrete.
The revelations
Built in secret, Fordow’s existence was publicly revealed in September 2009, in a dramatic moment when US, British and French officials declassified information indicating that Iran had secretly built an underground factory — incompatible with a peaceful nuclear programme.
The discovery, which British Prime Minister Gordon Brown said demonstrated Iran’s “serial deception,” was so significant that it even prompted a rare rebuke from Russia and a warning from China. Iran insisted at the time. “What we did was perfectly legal,” said then-President Mahmoud Ahmadi-Nejad, adding: “It’s not your job to tell us what to do.”
Nevertheless, Fordow has been at the center of international efforts to curb Iran’s nuclear program. It led to tougher UN sanctions and was at the heart of the 2015 multilateral deal, known as the Joint Comprehensive Plan of Action (JCPOA), between Iran and the United States, the United Kingdom, France, Russia, China, and Germany.
In exchange for the lifting of sanctions, Iran agreed, among other things, to convert the facility into a research center, limit the number of centrifuges there, freeze uranium enrichment for 15 years and allow enhanced oversight by international inspectors. The US withdrew from the JCPOA in 2018 during Donald Trump’s first presidency, and Iran has since begun enriching more uranium.
Tensions
Following an explosion at Natanz in 2021—which Iran blamed on Israel and which damaged its enrichment capacity—Tehran activated the Fordow centrifuges. They began converting low-enriched uranium to 60% purity, from which weapons-grade uranium could be produced within days.
Unless destroyed by Israeli attacks, Fordow could be the centerpiece of an Iranian “breakout” effort. The country could withdraw from the Nuclear Non-Proliferation Treaty, stop cooperating with the IAEA, and quickly build a nuclear bomb.
Iran has previously threatened such a response if its nuclear facilities are targeted—which could also implicate the U.S. military in the Israeli campaign. Adding to the risks is the fact that Fordow is not the only heavily protected facility that Iran can rely on.
Tehran has recently been building an even deeper and better shielded facility at Kūh-e Kolang Gaz Lā, also known as “Pickaxe mountain,” a few kilometers south of Natanz.
While Fordow is believed to have two tunnel entrances, Pickaxe has at least four, making it more difficult to block the entrances with bombing.
The underground chambers also have a larger surface area. Some fear that the facility, which Iran has so far refused to allow to be inspected by the IAEA, could even be used to assemble a nuclear bomb while Iran is under attack.
A key question is whether Iran has already placed fissile material at Pickaxe or at some other unknown facility.
