The Obama administration reportedly has little desire to launch a preemptive strike on Iran's nuclear facilities, but just in case it ever did, US weaponry is capable of destroying even Iran's most protected site, experts tell the Washington Post. Iran's Fordow facility—which, until recently, the country had been keeping secret—was specifically built underneath the northwestern mountain ranges to protect it from aerial assault. Iran's civil defense chief once boasted that it was "impregnable."
US officials admit that they can't destroy the facility in one shot. But after recent training exercises on similar targets, they're confident that given several days of sustained attacks, the Pentagon's latest bunker-buster, the Massive Ordnance Penetrator, could collapse the tunnels around the facility and destroy the centrifuges buried there. Israel has less advanced bunker busters, and that's part of the reason it's more eager to attack; it believes its window of opportunity is closing as Iran moves operations underground.