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Why US bunker-busting bombs are key to Israel's Iran goals
Smoke rises following an Israeli attack in Tehran, Iran, on June 18, 2025. PHOTO: WANA VIA REUTERS
Why US bunker-busting bombs are key to Israel's Iran goals
In launching their military offensive against Iran, Israeli officials have said their goal is to neutralise the country's ability to develop nuclear weapons.
It's widely thought that to truly cripple Iran's capacity to produce fuel for such weapons, Israel would require the help of its chief ally, the US.
That's because the US has something Israel does not: A so-called bunker-busting bomb potentially powerful enough to destroy Iran's most fortified uranium enrichment facility, the Fordow plant.
What's the Fordow plant?
At the heart of Iran's nuclear programme are two main facilities for producing enriched uranium, which can be used to fuel a nuclear bomb when processed to contain a high percentage of uranium-235 isotopes to support a fission chain reaction.
Both facilities, Natanz and Fordow, were designed to have at least some resilience to military attacks.
The biggest site, Natanz, located in the centre of the country, is a mix of assets above and below ground. The subterranean portion was constructed more than 40m beneath the surface with a steel and concrete shell that researchers estimated is 8m thick.
Following Israeli strikes, the International Atomic Energy Agency said that the enrichment hall above ground at Natanz had been destroyed, and that satellite imagery indicated the plant underground had suffered 'direct impacts'.
But Fordow – which lies outside the city of Qom, south of Tehran – hadn't seen significant damage as of June 18, according to IAEA Director General Rafael Mariano Grossi.
Fordow is a more heavily fortified site, built into the side of a mountain and believed to be buried about 60m to 90m below the surface. That puts it beyond the reach of Israel's known airborne munitions.
Iran has been enriching uranium to 60 per cent at both Fordow and Natanz, a level of purity the IAEA says is technically indistinguishable from weapons-grade fuel.
What's special about the US bunker-bursting bomb?
The term 'bunker buster' refers to a bomb that's able to penetrate deep into the ground or through heavy fortifications before exploding.
Israel has smaller bunker-busting bombs but not the GBU-57 Massive Ordnance Penetrator, or MOP, developed by the Americans.
Weighing 30,000 pounds and measuring 6m long, the MOP is the world's largest precision-guided weapon and is explicitly designed to destroy 'weapons of mass destruction located in well protected facilities,' according to a US Air Force fact sheet.
The MOP has never been used in combat before.
It's capable of penetrating as deep as 61m before exploding, according to the Air Force. Parts of Fordow are buried further underground. However, MOPs can be delivered one on top of another, meaning they could drill down even more with each successive blast.
How could the bunker busters be delivered?
Israel would have to rely on the US not just for the bombs but for their delivery. MOPs can only be deployed on the US Air Force's B-2 stealth bomber, which can carry two of them.
The aircraft has a range of 11,000km, which can be extended to 19,000km with a mid-air refueling, according to its manufacturer, Northrop Grumman.
That means one of the planes could be flown all the way from the B-2 operational base, Whiteman Air Force Base in Missouri, to deliver the MOPs.
Could Israel destroy Fordow without US assistance?
Israeli forces could bomb the entry and exit tunnels to seal off Fordow.
But unless they're willing to maintain a longer-term campaign that includes follow-up strikes, 'efforts to dig down to the facilities to re-establish access and supplies would likely begin almost immediately', Ms Darya Dolzikova and Professor Justin Bronk, senior research fellows at the UK-based Royal United Services Institute, wrote in a commentary.
A riskier approach would be to deploy Israeli forces on the ground with a mission to breach the facility and destroy it from within.
Such an operation would pose significant logistical challenges and would raise the possibility of engagement with well-armed Iranian forces.
Israel, which is widely believed to possess nuclear weapons, could potentially use them to destroy Fordow. However, the use of such arms would be an extraordinary escalation. BLOOMBERG
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