As the conflict with Iran intensifies, military analysts believe that the United States' use of one of the most powerful conventional weapons in its arsenal: the GBU-57 Massive Ordnance Penetrator (MOP) was the gam-changer in Iran. This 30,000-pound bomb is engineered to pierce hundreds of feet of earth and reinforced concrete, making it the only non-nuclear weapon capable of striking Iran’s deeply buried Fordow nuclear enrichment facility, the Wall Street Journal reported.
Designed to destroy hardened underground bunkers, the MOP had never before been used in combat prior to the Iranian strike. But it was used as its specifications are tailor-made for targets like Fordow, which is built under a mountain near the holy city of Qom. While Israel has targeted above-ground nuclear infrastructure in recent days, Fordow remained untouched as it required a weapon that only the US possessed.
Why Fordow matters
Fordow long represented one of Iran’s most secure nuclear sites. Unlike Natanz, which has been hit multiple times over the years by cyberattacks and aerial strikes, Fordow had been protected by the natural shield of rock and a maze of tunnel entrances. Inside, Iran housed advanced centrifuges that could enrich uranium close to weapons-grade levels. Its depth and design made it resistant to standard airstrikes. But that was before Sunday. Also Read - Decoded: What pushed Trump to pull the trigger on Iran N-site attack?
Israel has launched an extensive campaign to degrade Iran’s nuclear capabilities and military leadership. Experts had said that even multiple Israeli bombs would have struggled to reach the centrifuge halls at the heart of the complex.
“The approach with the highest confidence of success would be a US strike,” said William Wechsler, former deputy assistant defence secretary for special operations.
Inside the MOP’s capabilities
The MOP is over 20 feet long and contains a steel casing capable of penetrating up to 200 feet of reinforced concrete or mountain rock before detonating. The US Air Force developed it as a conventional alternative to nuclear weapons for hardened targets. Each bomb costs millions and is carried exclusively by the stealthy B-2 Spirit bomber.
The GBU-57 was used for the first time during this week’s coordinated strike on Fordow, as part of a surprise US operation. The Pentagon has confirmed that a dozen MOPs were dropped on Fordow during the night-time raid, while others targeted Natanz and Isfahan with Tomahawk missiles launched from submarines.
“It's a really specialized weapon for a very specialized set of targets that don’t come up very often,” said Mark Cancian of the Center for Strategic and International Studies, who previously worked on military weapons procurement at the Pentagon.
Low radiation risk, high strategic value
Despite fears over hitting nuclear infrastructure, analysts believe the risk of radiological fallout from Fordow is low. The International Atomic Energy Agency (IAEA) reported only internal contamination after the Natanz strike and said there was no radiation hazard to the public. Nuclear security expert Scott Roecker of the Nuclear Threat Initiative added that even a successful strike on Fordow would not pose an external radiation threat.
Why now?
Until recently, President Trump had resisted military escalation, pressing for a diplomatic solution with Iran. But following recent Israeli strikes and the failure of renewed nuclear talks, Trump appears to have pivoted. Iran’s Supreme Leader Ayatollah Ali Khamenei has vowed to continue enrichment and resist international pressure, heightening the sense that time is running out.
Israeli officials reportedly urged the US to join the fight and help neutralize sites that only American assets could reach. “This is what the MOP was built for,” said Mick Mulroy, a former Pentagon official. “If you want to hit Fordow, there is no other way to do it.”
What comes next
With Israel dominating Iranian airspace and the US now using the most advanced tools in its arsenal, attention shifts to how Tehran will respond. Iran has warned of severe consequences, and US military bases across the Middle East remain on high alert.
But in terms of military capability, the deployment of the MOP may mark a turning point. If it successfully destroyed the centrifuge halls at Fordow, Iran's ability to enrich uranium could be set back by years—perhaps without the need for a broader war.
The question now is whether the bomb that’s been sitting quietly in America’s arsenal for over a decade has changed the trajectory of a decades-long nuclear standoff.
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