In arguing their case, U.S. officials acknowledged some uncertainty over whether even the Pentagon’s newest “bunker-buster” weapon — called the Massive Ordnance Penetrator, or MOP — could pierce in a single blow the subterranean chambers where Iran is making enriched uranium. But they said a sustained U.S. attack over multiple days would probably render the plant unusable by collapsing tunnels and irreparably damaging both its highly sensitive centrifuge equipment and the miles of pipes, tubes and wires required to operate it.
“Hardened facilities require multiple sorties,” said a former senior intelligence official who has studied the formerly secret Fordow site and agreed to discuss sensitive details of U.S. strike capabilities on the condition of anonymity. “The question is, how many turns do you get at the apple?”
U.S. confidence has been reinforced by training exercises in which bombers assaulted similar targets in deeply buried bunkers and mountain tunnels, the officials and experts said.
U.S. officials have raised the necessity of multiple strikes as they warn Israel against a unilateral strike against Iran’s nuclear installations, the officials said. While Israel is capable of launching its own bunker-buster bombs against Fordow, it lacks both the United States’ more advanced munitions and the capability of waging a sustained bombing campaign over days and weeks, U.S. officials and analysts said.
All they are really claiming is that they can "shake things up" a bit by repeated sorties. This is roughly what they tried in Tora Bora. The problem is of course is that Iran has a greater ability to "fight back". i.e. they could get some anti-aircraft missiles and start shooting at the incoming bombers. This is what they guy is talking about when he mentions "the bite of the apple". It's not an impossible strategy by any means, but probably one that Israel can't pursue. And to some extent, you won't know when you're "done". The part that would scare you is that someone might get desperate at some point and decide to try to put a penetrating nuke into there, after softening up the ground a bit.
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