Explainer: US bunker-buster bombs and Iran’s underground nuclear facilities
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Diverging Reports Breakdown
Could US attack Iran’s Fordow nuclear site? Military movements offer a clue
The US has stepped up its military presence in the Middle East since the weekend but has left certain details vague to preserve operational ambiguity. There has been no new information about the deployment of B-2 bombers that would be used to attack Iran’s deep-lying nuclear enrichment site at Fordow. The planes, mostly KC-135 Stratotankers and KC-46s, were tracked by AirNav Systems, a flight-tracking website, as they headed east towards Europe on Sunday. There were further reports of some planes flying further east on Tuesday. Only the US is considered to have a bomb large enough – the GBU 57/B Ordnance Penetrator – to possibly destroy Fordow, 80-90 metres below a mountain. The IAEA nuclear watchdog said on Monday that no damage to the enrichment plant had been seen. Several companies supplying commercial satellite imaging also work for the US government. The US may also consider attacking other nuclear enrichment sites, such as Natanz, in the north of the country.
Critically, there has been no new information about the deployment of B-2 bombers that would be used to attack Iran’s deep-lying nuclear enrichment site at Fordow with 13.6-tonne (30,000lb) bunker-buster bombs, designed to penetrate 60 metres of rock.
On Monday night, the US defence secretary, Pete Hegseth, said he had “directed the deployment of additional capabilities” to US Central Command in the Middle East, an exercise he said was “to enhance our defensive posture in the region”.
Donald Trump, meanwhile, told reporters he was looking for “a real end” to the conflict as the US president returned to Washington having cut short his trip to the G7 summit in Canada. “I’m not looking for a ceasefire, we’re looking at better than a ceasefire,” he said, without being more specific.
However, clues that the Pentagon is considering a long-range air raid came from the movement of more than 31 US Air Force refuelling aircraft. The planes, mostly KC-135 Stratotankers and KC-46 Pegasuses, were tracked by AirNav Systems, a flight-tracking website, as they headed east towards Europe on Sunday. There were further reports of some planes flying further east on Tuesday.
US Air Force B-2 bombers have a long range, of about 6,000 miles without refuelling, but they usually operate from a limited number of bases: Whiteman in Missouri, Fairford in Oxfordshire and most notably the isolated base of Diego Garcia in the south Indian Ocean, now leased from Mauritius by the UK for the US.
B-2 bombers attacked five underground Houthi weapon facilities from Whiteman, 8,000 miles away, last October. Diego Garcia is far closer to Fordow, a 3,200-mile trip each way, which would require refuelling on the return leg once a bombing run on Iran’s nuclear sites had been completed.
Only the US is considered to have a bomb large enough – the GBU 57/B Massive Ordnance Penetrator – to possibly destroy Fordow, one of Iran’s two main uranium enrichment sites, estimated to be 80-90 metres below a mountain. The only plane certified to carry the 6-metre weapon is the B-2.
At one point in the middle of the last decade, the US was thought to have only 20 of the bombs, its largest non-nuclear weapon, but more recent estimates are higher.
Though Israel appears to have achieved dominance over Iran’s skies since it launched its attack on the country on Friday, it attacked Fordow on only the first day of the operation. The IAEA nuclear watchdog said on Monday that no damage to the enrichment plant had been seen.
View image in fullscreen A satellite image provided by Maxar Technologies of the Fordow fuel enrichment plant in central Iran on 14 June. Photograph: Maxar Technologies/AFP/Getty Images
Justin Bronk, an aviation expert with the Royal United Services Institute thinktank, said “multiple impacts” would almost certainly be required to destroy Fordow, “with the second bomb impacting inside the hole made by the first”.
Though a B-2 can carry two bunker-busting bombs, a serious assault by the US designed to eliminate the facility would probably require the deployment of more than one bomber. Bronk said: “An attack would require redundancy since the weapons have to function and be delivered perfectly to get down into the facility and explode at the right depth to cause critical damage.”
Satellite imagery in May showed the presence of six B-2 bombers at Diego Garcia, about half the total number considered operational at any one time – the US has a total of 19 – but there has not been any more recent reporting. Several companies supplying commercial satellite imaging also work for the US government.
According to a 2019 article in the New York Times, at some point a decade before, the US Pentagon constructed a replica of Fordow and test-bombed it with a 30,000lb device. A highly classified video of the attack was later shown by Leon Panetta, a defence secretary under Barack Obama’s presidency, to the Israeli politician Ehud Barak. “The bomb destroyed the mock-up in the desert,” the newspaper reported.
The US may also consider attacking Iran’s other nuclear enrichment site, at Natanz. Though a smaller overground site was destroyed by bombing on Friday, a facility somewhere between 8 and 12 metres underground is said by the IAEA to be relatively undamaged, though the Israeli military has disputed this.
An important question for the White House and the Pentagon is whether they believe, after five days of airstrikes by Israel, that there is any threat to US jets operating over Iran. But there is no shortage of military assets available if the US wants to mount an expanded attack targeting any remaining air defence and missile launch sites.
A second aircraft carrier strike group, led by the USS Nimitz was sent from east Asia towards the Middle East earlier this week, where it will join the USS Carl Vinson carrier, which is already operating relatively close to Iran, around the Arabian Sea. At least three US destroyers are now also in the eastern Mediterranean.
What is a bunker buster bomb? US weapon could be key to destroying Iran’s nuclear sites
Israel has struck near multiple nuclear facilities, including at Natanz and Isfahan, while assassinating a host of Iran’s top military commanders and nuclear scientists. But despite Israel now commanding swathes of Iranian airspace, analysts say that only the US has the conventional aerial weapons capable of successfully penetrating Fordow. The weapon is the Massive Ordnance Penetrator (MOP), a bomb six metres in length and weighing 13.6 tonnes. It is reportedly capable of reaching up to 61 metres underground before exploding – around 10 times further than the GBU-28 bunker busters owned by Israel. But with Iranian nuclear facilities at Fordow believed to be as deep as 80 or 90 metres underground, even the US weapons – of which Washington reportedly has around 20 in its stockpile – would potentially struggle to destroy the facility. Despite these risks, however, Donald Trump fuelled speculation of potential US involvement in the war on Monday night as he left the G7 summit in Canada early. He said his reason for leaving early “certainly has nothing to do with a ceasefire”, adding: “Much bigger than that … Stay tuned!”
As Israel launches its unprecedented military effort to eradicate Tehran’s nuclear programme by force, experts suggest only the US has the weapons capable of doing so.
Since prime minister Benjamin Netanyahu announced “Operation Rising Lion” last Friday, Israel has struck near multiple nuclear facilities, including at Natanz and Isfahan, while assassinating a host of Iran’s top military commanders and nuclear scientists.
But while the UN’s nuclear watchdog assessed on Monday that Israel has damaged sites above ground at Natanz and Isfahan, and potentially underground centrifuges at the former site, Iran’s underground facilities at Isfahan and – crucially – the Fordow enrichment plant are believed to remain unaffected.
What are bunker buster bombs?
Fordow, Iran’s most fortified nuclear site, was clandestinely built deep inside a mountain to protect it from attack. In March 2023, the UN’s International Atomic Energy Agency (IAEA) warned that it had discovered uranium enriched to 83.7 per cent purity at Fordow – close to the 90 per cent level needed to create nuclear weapons.
But despite Israel now commanding swathes of Iranian airspace, analysts say that only Washington’s arsenal contains the conventional aerial weapons capable of successfully penetrating Fordow’s mountainous shell.
That weapon is the Massive Ordnance Penetrator (MOP), a bomb six metres in length and weighing 13.6 tonnes, whose dense casings enable it to remain intact while it punches through rock and concrete before detonating deep underground.
open image in gallery A satellite image shows the Natanz nuclear facility in Iran after an airstrike ( Maxar Technologies )
Technically known as the GBU-57F/B, the “bunker busting” bomb is reportedly capable of reaching up to 61 metres underground before exploding – around 10 times further than the GBU-28 bunker busters owned by Israel.
However, with Iranian nuclear facilities at Fordow believed to be as deep as 80 or 90 metres underground, even the US weapons – of which Washington reportedly has around 20 in its stockpile – would potentially struggle to destroy the facility.
And it remains unlikely that the US would enter the fray directly in such a way, as doing so would significantly raise the risk to Washington’s military assets in the region and spark a destabilising conflict impacting Iran’s neighbours.
open image in gallery The Fordow enrichment facility is situated near the Shia holy city of Qom ( Planet Labs PBC )
Will the US get involved in Iran?
Despite these risks, however, Donald Trump fuelled speculation of potential US involvement in the war on Monday night as he left the G7 summit in Canada early.
Contradicting claims by France’s President Emmanuel Macron, Mr Trump – who has praised Israel’s attacks on Iran as “excellent” – said his reason for leaving early “certainly has nothing to do with a ceasefire”, adding: “Much bigger than that … Stay tuned!”
The clearest sign that the US was planning to deploy its bunker busters would be if Washington opted to move its B-2 bomber jets – the only aircraft approved to carry GBU-57F/Bs – to the UK-US military base in the Chagos Islands, The Times suggested.
US General Joseph Votel, formerly chief of the Pentagon’s Central Command during Mr Trump’s first presidential term, told the New York Times: “We’ve had a policy for a long time of not providing those to the Israelis because we didn’t want them to use them.”
open image in gallery A GBU-57, also known as a Massive Ordnance Penetrator bomb, pictured in 2023 at Whiteman Air Base in Missouri ( US Air Force )
Would attacks on nuclear sites endanger civilians?
Alongside the geopolitical and military risks of joining Israel in attacking a sovereign nation, the nuclear contamination from such an attack could pose a danger to civilians, warned Mr Votel.
The IAEA chief, Rafael Grossi, has issued similar warnings in recent days, stressing that “any military action jeopardising the safety and security of nuclear facilities risks grave consequences for the people of Iran, the region, and beyond”.
Urging “all parties to exercise maximum restraint to avoid further escalation”, Mr Grossi warned that nuclear facilities must never be attacked under any circumstances.
However, Israel’s ambassador to Washington, Yechiel Leiter claimed on Sunday that Israel has “a number of contingencies which will enable us to deal with Fordow”, telling ABC News: “Not everything is a matter of taking to the skies and bombing from afar.”
open image in gallery Smoke rises after an Israel airstrike in central Tehran ( EPA )
What other options does Israel have besides bombing?
Former US officials told the New York Times that one plan previously floated by Israel to the Obama administration suggested Israeli commandos could fight their way into the facility and blow it up from the inside – in a similar but far more dangerous operation to one successfully carried out at a Hezbollah missile production factory last year.
“The Israelis have sprung a lot of clandestine operations lately, but the physics of the problem remain the same,” US General Kenneth McKenzie Jr told the outlet, adding: “It remains a very difficult target.”
open image in gallery Rescue teams searching the debris inside a buidling in Tehran, targeted by Israeli strikes ( Iranian Red Crescent )
Iran has denied allegations that it is secretly developing nuclear weapons, the pretext upon which Israel began striking Iran on Friday morning. More than 200 people have been killed in Iran and more than 20 in Israel, their respective authorities have reported.
Claiming to have struck dozens of targets linked to Iran’s nuclear and ballistic missile programmes overnight, an Israeli military official told Reuters on Tuesday that the Israeli airforce had yet to target Fordow – but that this could still happen.
With the anonymous official insisting that Israel was taking precautions to avoid triggering a nuclear disaster, defence minister Israel Katz told reporters that the facility at Fordow is “an issue that will certainly be addressed”.
The one ‘bunker buster’ bomb that could be used to hit Iran’s secretive Fordow enrichment plant
Israel has made no secret of its wish to destroy Iran’s nuclear programme. The only bomb believed to be powerful enough to penetrate the Fordow facility is an American “bunker buster” bomb. The Israeli military has a number of bunker buster bombs but does not have the vaunted GBU-57, a 14-ton bomb that is so heavy it can only be launched from America’s fleet of heavy bomber aircraft. Its 30,000lb (13,600kg) weight means that its sheer kinetic force enables it to reach deeply buried targets. It’s understood that it can penetrate about 200ft (61m) below the surface before exploding. The three sites they really want are Natanz, Isfahan and Fordow, says military analyst Michael Clarke. The Natanz enrichment plant has been struck by Israel in the last few days, with its subterranean centrifuge hall believed damaged but not destroyed. The IAEA says the Natanz plant sustained extensive damage, likely destroying 15,000 centrifuges, possibly due to an Israeli airstrike disrupting the power supply.
Israel has made no secret of its wish to destroy Iran’s nuclear programme, but the only bomb believed to be powerful enough to penetrate the Fordow facility is an American “bunker buster” bomb that the Israelis do not have – yet.
As President Donald Trump appears to switch between calling on Iran to negotiate and threatening retaliation “at levels never seen before”, discussion is now turning to whether the US will be inexorably drawn into another Middle East conflict – something the president has repeatedly said he does not want.
What are bunker buster bombs?
Simply put, bunker buster bombs are designed to explode twice. Once to breach the ground surface and again once the bomb has burrowed down to a certain depth.
They’re used to reach military headquarters, bunkers and other facilities buried deep underground – hence their name.
Image: File picture of a GBU-28 bunker buster bomb being released by an American warplane. Pic: Reuters
“They are big, very heavy. There’s a lot of explosives in them,” military analyst Michael Clarke says.
The Israeli military has a number of bunker buster bombs but does not have the vaunted GBU-57, a 14-ton bomb that is so heavy it can only be launched from America’s fleet of heavy bomber aircraft.
Image: A GBU-57, or the Massive Ordnance Penetrator bomb, at Whiteman Air Base in Missouri. in 2023. File pic: US Air Force via AP
It’s that GBU-57 which is believed to be the only one capable of destroying the highly protected Fordow plant.
Analysts say it can only be delivered from a US B-2 stealth bomber. Its 30,000lb (13,600kg) weight means that its sheer kinetic force enables it to reach deeply buried targets.
It’s understood that it can penetrate about 200ft (61m) below the surface before exploding.
Image: A B-2 stealth bomber flies over Washington DC during a 4 July celebration. File pic: AP
What are Iran’s key nuclear facilities?
Prime Minister Benjamin Netanyahu has made clear his desire to destroy Iran’s nuclear programme and any hint of a threat of nuclear weapons – something Iran has long denied seeking.
In the several days since Israel launched its surprise attack on Iran there has been a lot of attention paid to how well they would be able to disrupt Iran’s nuclear programme, much of which is buried deep underground.
“The three sites they really want are Natanz, Isfahan and Fordow,” says Prof Clarke.
Natanz and Fordow are uranium enrichment sites and Isfahan is one of the largest nuclear research centres in Iran.
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What damage has Israel done to Iran’s nuclear programme?
The Natanz enrichment plant has been struck by Israel in the last few days, with its subterranean centrifuge hall believed damaged but not destroyed.
Rafael Grossi, head of the International Atomic Energy Agency, told the BBC that the Natanz plant sustained extensive damage, likely destroying 15,000 centrifuges.
This was possibly due to an Israeli airstrike disrupting the power supply to the centrifuges, rather than actual physical damage to the centrifuge hall, he said.
Image: Centrifuge machines at the Natanz uranium enrichment facility seen in 2019. Pic: AP
At Fordow, however, no damage was seen. Mr Grossi added: “There is very limited if any damage registered (there).”
At Isfahan, Iran’s third key nuclear location, there was damage to buildings including the central chemical laboratory and a uranium conversion plant.
Mr Grossi said: “In Isfahan you have underground spaces as well, which do not seem to have been affected.”
Read more:
‘They are lying’: Israeli president hits out at Iran
Iran’s ambassador to UK speaks to Sky News
Image: A satellite image shows the Natanz nuclear facility in Iran after airstrikes. Pic: Maxar Technologies/Reuters
What will Israel do now?
Prof Clarke says Israel is likely to continue its bombing campaign against Iran’s nuclear facilities.
“I think they will keep on revisiting Natanz,” he said. “They will want to keep targeting down with more bunker busters until they actually hit the centrifuge hall itself.”
Fordow, on the other hand, appears too deep for even Israel’s bunker buster bombs.
“It’s the most important because it’s the one the Iranians think they can protect,” he adds. “You have to blast the mountain to get to it.”
Please use Chrome browser for a more accessible video player 2:12 Israeli president: ‘No choice’ but to attack Iran
It’s possible, prof Clarke says, that Israel could try damaging it in a similar way to what happened to Natanz – disrupting the power supply – which could have the cumulative effect of rendering the centrifuges inoperable.
“What Netanyahu wants is to say: look at the destruction we have wrought on Iran. Their weapons programme is destroyed it would take them 30 years to rebuild… we have taken them off the table as a threat to us for a generation.”
But it remains to be seen if this is possible without direct American intervention – something President Trump may want to avoid at all costs.
German Chancellor says Israel is ‘doing the dirty work for the rest of us’ with Iran strikes
German Chancellor says Israel is ‘doing the dirty work for the rest of us’ with Iran strikes. Merz: “We are also victims of this regime. This mullah regime has brought death and destruction to the world.” “Large parts of the military leadership and the so-called Revolutionary Guards are no longer alive, so things will not be the same as they were,” Merz told Welt TV. An Israeli military official disclosed Tuesday that recent airstrikes had inflicted significant damage on Iran’s nuclear weapons infrastructure.
Merz: “We are also victims of this regime. This mullah regime has brought death and destruction to the world.”
By Vered Weiss, World Israel News
German Chancellor Friedrich Merz spoke in support of Israel’s Operation Rising Lion against Iran.
Addressing German ZDF television journalists at the G7 conference in Canada on Tuesday, Merz said, “This is the dirty work Israel is doing for all of us.”
“We are also victims of this regime,” he said, referring to Iran. “This mullah regime has brought death and destruction to the world.”
In another interview, the chancellor told Welt TV that he believed the Iranians could bring down the regime.
“I assume that the attacks of the last few days have already weakened the mullah regime considerably and that it is unlikely to return to its former strength, making the future of the country uncertain,” Merz said. “To be honest, I can hardly imagine the mullah regime returning to its old functions.
“Large parts of the military leadership and the so-called Revolutionary Guards are no longer alive, so things will not be the same as they were.”
When asked if he believed that the US would get involved in the conflict, Merz answered, “No decision yet from the American government.”
“It now depends very much on how far the mullah regime is prepared to return to the negotiating table,” he added. “If not, there could be further developments of this kind.”
An Israeli military official disclosed Tuesday that recent airstrikes had inflicted significant damage on Iran’s nuclear weapons infrastructure. He described a coordinated, multi-front operation that successfully targeted several critical sites across the country.
The official reported that Operation Rising Lion dealt a major blow to Iran’s nuclear weapons capabilities by striking not only uranium enrichment facilities but also key infrastructure and personnel vital to the program.
According to the source, the operation has secured Israeli air superiority over Tehran, allowing for real-time precision strikes guided by live intelligence.
This operational advantage also enabled the IDF to identify and eliminate Iran’s recently appointed wartime chief of staff, Maj. Gen. Ali Shadmani, in a targeted strike on a central Tehran command center Monday night.
Explainer: US bunker-buster bombs and Iran’s underground nuclear facilities
The B-2 is only flown by the Air Force, and is produced by Northrop Grumman. Such a bomb would have to be dropped from an American aircraft, which could have wide-ranging ramifications. Israeli officials have also suggested that there are other options for it to attack Fordo as it seeks to destroy Iran’s nuclear capabilities. But aside from a commando attack on the ground or a nuclear strike, the bunker buster bomb seems the most likely option.
If the US chooses to offer more direct support to Israel in its offensive against Iran, one possibility for Washington would be to supply the “bunker-buster” bombs thought necessary to severely damage the country’s Fordo nuclear fuel enrichment facility, which is deeply embedded within a mountain.
If the US decides to support Israel more directly in its attack on Iran, one option for Washington would be to provide the “bunker-buster” bombs believed necessary to significantly damage the Fordo nuclear fuel enrichment plant, built deeply into a mountain.
Such a bomb would have to be dropped from an American aircraft, which could have wide-ranging ramifications, including jeopardizing any chance of Iran engaging in Trump’s desired talks on its nuclear program. Israeli officials have also suggested that there are other options for it to attack Fordo as it seeks to destroy Iran’s nuclear capabilities.
But aside from a commando attack on the ground or a nuclear strike, the bunker buster bomb seems the most likely option.
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The B-2 is only flown by the Air Force, and is produced by Northrop Grumman.
(FRANCE 24 with AP)
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