HORMUZ STRAIT

Iran's bellicose rhetoric and recent Gulf wargames have given rise to the question of whether Tehran could close the Strait of Hormuz. As many analysts have observed, the answer is no -- not for a meaningful period of time. Less frequently addressed, however, is whether Iran would even try. The answer to that question is also "no" -- even the attempt would have devastating strategic consequences for Iran.

The presumable target of an Iranian effort to close the Strait would be the United States. The U.S., however, gets little of our petroleum from the Gulf. The U.S. imports only about 49 percent of the petroleum we consume, and over half of those imports come from the Western Hemisphere. Less than 25 percent of U.S. imports came from all the Gulf countries combined in October 2011 -- far less than is available in the U.S. Strategic Petroleum Reserve, were Gulf supplies to be interrupted.

China, on the other hand, would find its oil supplies significantly threatened by an Iranian move against the Strait. China's most significant oil supplier is Saudi Arabia. China also happens, however, to be Iran's primary oil customer and perhaps its most important ally: Beijing provides Iran with its most sophisticated weaponry and with diplomatic cover at the United Nations. Thus a move to close the Strait would backfire strategically by harming the interests of -- and likely alienating -- Iran's most important patron and cutting off Iran's own economic lifeline, while doing little to imperil U.S. supplies of crude.

It is perhaps no coincidence, then, that China quickly dispatched Vice Foreign Minister Zhai Jun to Tehran in the wake of Iran's bellicose statements. In typically opaque fashion, the Chinese Foreign Ministry said only that "China hopes that peace and stability can be maintained in the Strait"; this is essentially diplo-speak for "Cool it."

Even if Iran ignored these considerations and proceeded with an effort to close the Strait, the U.S. and others would move to keep it open, and would be unlikely to stop there. As Iran has crept closer to a nuclear weapons capability, the possibility of military action against Iran has also become more imminent. President Obama has been reluctant to threaten Iran militarily, and any U.S. president would think long and hard before engaging in another armed conflict in the Middle East.

An effort by Iran to shut down the oil trade in the Gulf, however, would make such a decision straightforward. The U.S. would react with force, and once engaged in hostilities with Iran, would likely take the opportunity to target Iran's nuclear facilities and other military targets. It is difficult to envision any scenario beginning with an Iranian effort to close the Strait of Hormuz that does not end in a serious strategic setback for the Iranian regime.

Recognizing that Iran is neither able nor likely to try to close the Strait, the U.S. could simply sit back, confident in our superior firepower. This would be a mistake. The real danger in the Gulf is lower-level activity by Iran to harass shipping and confront the U.S. Navy. Iranian commanders in the area are increasingly brazen. If not deterred, Iran's sense of impunity -- rather than its nuclear progress -- may be the spark that ignites a conflict in the region.

Iran's navy -- especially the naval arm of Iran's Revolutionary Guards -- has invested in vessels and armaments that are well-suited to asymmetric warfare, rather than the sort of ship-to-ship conflict that Iran would surely lose. Thus, they have purchased, with Chinese and Russian help, increasingly sophisticated mines, midget submarines, mobile anti-ship cruise missiles, and a fleet of small, fast boats. In addition, they have reportedly sought to develop a naval special warfare, or frogman, capability.

Iran has also demonstrated a growing willingness to confront U.S. and allied forces in the area. The best known of these incidents occurred in March 2007, when fifteen British marines and sailors were taken captive by an entrepreneurial Revolutionary Guard commander. But other incidents abound. On many occasions, including at least one reported case this year, Iranian small boats have conducted mock "swarming" attacks on US carriers and warships. In each case, U.S. or allied commanders have shown restraint, which is inevitably interpreted as passivity by Iranian leaders, who then proceed to push the envelope further.

Rather than waiting for one of these gambits to succeed and force our hand in response, the U.S. should actively seek to discourage Iran from further testing of U.S. limits through a stronger deterrence effort.

First, the U.S. should resume a more active program of military exercises and signaling activities in the Gulf, in order to demonstrate U.S. capabilities and make Iran reconsider its actions in the area.

Second, the U.S. should signal our enduring commitment to the Gulf after our withdrawal from Iraq and continue to bolster the littoral, air, and missile defense capacity of our GCC allies and integrate their forces into the aforementioned exercises.

Finally, the U.S. should indicate clearly to Iran that we are prepared to use selective military force in response to further provocations such as those discussed above. Such limited force -- whether against Iran's navy in the late 1980s, or against the Revolutionary Guards' Qods Force in Iraq in recent years -- has proven effective in compelling Iran to draw back.

It is frequently observed that the consequences of military action are unpredictable, and rightly so; it should only ever be used with caution and deliberation. However, excessive risk aversion that results in a failure of deterrence and feeds Iran's sense of impunity may, paradoxically, be just as risky. The most prudent course is neither belligerence nor passivity, but a robust posture that makes Tehran think twice.