Iran’s most heavily fortified nuclear site, Fordo, was built deep inside a mountain to protect it from an attack. Only the U.S. military has the 30,000-pound (roughly 14-ton) bomb capable of even reaching it.

The bomb is commonly known as a "bunker buster” because it is designed to destroy deep underground bunkers, or well-buried weapons in highly protected facilities. It is believed to be the only air-delivered weapon that would have a chance of destroying the site.

The bomb has a much thicker steel case and contains a smaller amount of explosives than similarly sized general-purpose bombs. The heavy casings allow the munition to stay intact as it punches through soil, rock or concrete before detonating.