Donald Trump is weighing whether to help Israel destroy Iran's defence capabilities as he called for the “unconditional surrender” of Ayatollah Ali Khamenei.
But if the US president chooses the path of confrontation, he has just one weapon, apart from nuclear warheads, capable of destroying the despotic regime’s buried facilities.
The GBU-57, also known as the Massive Ordnance Penetrator (MOP), was developed to destroy bunkers that other weapons could not reach.
Weighing about 30,000 pounds and carrying up to 2.5 tonnes of high explosives, the bunker-buster bomb can be launched only by the 630mph B-2 Spirit stealth bomber.
Six B-2s were deployed to the British-owned island of Diego Garcia in April as a show of force to Tehran, although in the end they were involved in missions against Houthi targets in Yemen and MOPs have never been fired in anger.
Since Operation Rising Lion was launched last Friday, the IDF has struck more than 170 targets and 700 army facilities, including the Natanz and Fordo enrichment plants, while assassinating top Iranian commanders and scientists.
While the United Nations assessed on Monday that Israel has damaged atomic bases above ground, Iran’s centrifuge at Isfahan and Fordow are believed to remain intact.
However, experts said the MOP, when dropped from high altitude, can penetrate up to 200ft underground before exploding, navigating through concrete and rock.
By comparison, the Israeli military has GBU-28 laser-guided bombs busters, which can penetrate just 20ft of concrete.
It also differs from missiles or bombs that typically detonate their payload near or upon impact, according to Masao Dahlgren, a fellow at the Washington-based Center for Strategic and International Studies.
He said the six-metre-long bomb made of high-density steel alloy has a specialised fuse because "you need an explosive that's not going to immediately explode under that much shock and pressure”.
MOPs are currently missing from Israel's arsenal despite its stated goal of preventing Iran from building nuclear weapons.
Moreover, the Pentagon is believed to have limited supplies of Boeing-made MOPs, perhaps no more than 20.
Some have also questioned the cost-effectiveness of MOPs, given its estimated price tag of around $20 million (£15 million) apiece.
Behnam Ben Taleblu, of the Foundation for Defense of Democracies, said without MOPs Israelis would have to “hit entrances, collapse what they can (and) cut electricity" in order to enter the complexes.
The UN’s International Atomic Energy Agency claims it discovered uranium enriched to 83 per cent purity at Fordow – close to the 90 per cent level needed to create nuclear weapons.
Rafael Grossi, the atomic watchdog’s head, said he fears of both radiological and chemical contamination from damaged installations.
Defence analyst Michael Clarke told Sky News: "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."
