In event of an Iran-Israel showdown, what would US military do?

How would the US military respond if Iran attacked US interests – in retaliation for, say, an Israeli strike on its nuclear facilities? What would a US counterattack look like?

Israeli Prime Minister Benjamin Netanyahu's visit to Washington Monday to meet with President Obama – which comes in the midst of increasingly vocal warnings from Pentagon officials urging caution on any military action in the region – has brought these questions into sharp focus this week.

These questions, too, were at the heart of one of the largest US military war-game exercises in a decade, meant to mirror the conditions that US troops would face if Iran were to, say, shut down shipping through the Strait of Hormuz.

The war game, dubbed “Bold Alligator,” included some 16,000 US Navy seamen and Marines, as well as a a contingent of US allies from Europe and Australia, and took place near Norfolk, Va., last month. 

Yet Iran conducts its own war-game exercises, too, designed to practice how best to make US military operations in the region difficult, defense analysts note.

The Pentagon’s exercise, for its part, was designed to explore what might happen when US troops face threats in a populated, “built-up” area like the Persian Gulf, according to senior US military officials. 

The exercises were “certainly informed by recent history,” says Adm. John Harvey, head of the US Navy’s Fleet Forces Command.

Operating in seaway as narrow as the Strait of Hormuz – one of the most important in the world for US commercial interests – becomes “very difficult when you talk about irregular threats,” says Lt. Gen. Dennis Hejlik, commander of US Marine Corps Forces Command. Those threats include the widespread mining of the Strait, as well as small boats that could swarm US vessels.

The war games also explored the threat that Iran could pose with its shore-based cruise missiles, to which US ships might be exposed “under certain circumstances,” according to Harvey.

In any case, if the Pentagon were forced to respond to, say, the closing of the Strait of Hormuz, it would likely make extensive use of Special Operations Forces first, according to Hejlik. Such special forces “are going to condition that battle space” prior to any US Navy mission, he adds. 

US military officials have been careful to emphasize, however, that it is not their first choice to attack Iran. 

That’s because they are unsure how Iran would respond to such an attack, top Pentagon officials say. The chairman of the Joint Chiefs of Staff, Gen. Martin Dempsey, said uncertainty surrounding Iran's response to a a military strike is “the question with which we all wrestle and the reason we think that it’s not prudent at this point to decide to attack Iran.”

The problem is, too, that even a “successful” military strike on Iranian nuclear targets would likely delay Iran’s nuclear ambitions only for a limited time. 

Iran might retaliate by striking at Israel with missiles, which would force the United States to join in missile defense. 

More likely than closing down the Strait of Hormuz – which would be nearly certain to provoke a US military response – Iranian officials would choose a more subtle, complex response.

“Closing the Strait – [discussing] that is fine for talking heads on TV – but that doesn’t have anything to do with the complexity” of Iran’s potential response to a military strike, says Anthony Cordesman, a national security analyst at the Center for Strategic and International Studies.

It might use free-floating mines in the southern coast of the Persian Gulf, or conduct military exercises that wouldn’t justify a military response but that would give other nations’ commercial vessels pause before traveling in the region, thus affecting commerce. These are all scenarios that the Iranian military also war games, Dr. Cordesman notes.

Iran might also engage in covert acts that it would ensure are difficult to attribute to the regime, such as sabotaging Saudi oil fields. Iran is “very careful to test out all the ways they can apply pressure” on the interests of the United States and its allies, Mr. Cordesman adds. “And they practice all of this.”