When it comes to dealing with Iran's nuclear program, Pentagon planners and outside experts say there are no attractive options, but there are options.
"There is a broad and widely dispersed program infrastructure that could be targeted," said National Defense University professor Richard Russell, a former CIA analyst. "It's not an easy target package to target but you could do it in a sustained aerial bombardment campaign."
With U.S. forces tied down in Iraq and Afghanistan, U.S. officials are reluctant to even speculate about military action against Iran.
The current U.S. strategy is to apply diplomatic pressure on Iran through the U.S. Security Council, which is expected to take up the Iranian issue next week. But the question is: What if diplomacy fails?
"I think there is a very real probability the first choice of diplomacy is going to be shown to be a dead end," said John Pike of GlobalSecurity.org. "And then everybody is going to have to confront what your second choice is -- is it atomic ayatollahs or is it the military option?"
There are significant obstacles to military action. For one, not all the targets are known. U.S. officials believe there are secret Iranian nuclear facilities that are not known by U.S. intelligence.
"Our experience from Iraq, for example, showed substantial intelligence shortcomings," said Russell. "You'd have to assume we too suffer from enormous intelligence shortcoming vis a vis Iran. That would be a problem."
And even the known sites are well-fortified and spread out across the country, making them difficult to destroy with air power alone.
But privately, senior Pentagon planners believe U.S. airstrikes could significantly disrupt and delay the Iranian nuclear program, setting it back years.
It's a view shared by many military analysts.
"You can delay, disrupt and kick the can down the road," Russell said. "You are not going to solve it. Ultimately you need to have a political resolution in some shape or form, but the military instrument can help you achieve that diplomatic resolution and it can also buy you time."
There are about a dozen known high-value targets, including uranium mines, research and development facilities and, most importantly, the Natanz uranium enrichment plant. Natanz is considered the crown jewel of the Iranian nuclear program. Experts believe it is big enough to produce enough weapons-grade uranium to fuel 20 nuclear bombs a year.
But Natanz is also heavily fortified. It's buried at least 30 feet underground and perhaps much deeper. Natanz is also believed to be protected by concrete walls that are nearly 10 feet thick.
It's unclear whether it can be penetrated by even the biggest "bunker-buster" bombs in the U.S. arsenal. If airstrikes can't destroy Natanz, however, they could severely damage it.
"You might not be able to get the deep bunker if it's sufficiently deep but you can certainly create a lot of rubble on top of it," said Russell. "And make it very difficult to dig out the material underneath it.
"You can delay, disrupt and kick the can down the road," he said. "You are not going to solve it. Ultimately, you need to have a political resolution in some shape or form, but the military instrument can help you achieve that diplomatic resolution and it can also buy you time."