Iran’s secretive Fordow uranium enrichment plant is buried deep beneath a mountain, its vital centrifuges protected by tons upon tons of rock.
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.
“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.
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.
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.
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.
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.”
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.”
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.
