Israel's best chance at destroying the facility at Fordo could lie with a U.S.-produced bomb that's so heavy that it can only be dropped by a U.S. plane.

The U.S.B-2 stealth bomber is the only aircraft capable of carrying and dropping 'bunker busters," the world's most powerful nonnuclear bomb. Here's what we know about the 30,000-pound weapons and why the US is using them to strike nuclear sites in Iran.