Tension between Iran and the United States flared on December 28, 2011, when Habibollah Sayyari, commander of Iran’s navy, threatened to close the Strait of Hormuz, the 34-mile-wide passage through which more than one-third of the world’s oil tanker traffic travels. His televised statement that “closing the Strait of Hormuz is very easy for Iranian naval forces .  .  . easier than drinking a glass of water” came against the backdrop of naval war games, the third major Iranian naval demonstration in recent years. The Iranian military ended its exercise five days later with a barrage of missile tests signaling the peril facing warships and tankers alike.

War games may propel the Iranian Navy into the headlines, but the challenge the Islamic Republic poses to international shipping is broader and growing; indeed, it has been building for a quarter of a century. During the Iran-Iraq war (1980-88), Tehran and Baghdad each sought to target the other’s business partners. Between 1984 and 1988, in the so-called Tanker War, Iran’s navy and its parallel Islamic Revolutionary Guard Corps-Navy (IRGC-N) developed a doctrine of maritime guerrilla warfare using speedboats, mines, antiship cruise missiles, and, on occasion, aircraft to target neutral or enemy shipping.

Revolutionary leader Ayatollah Khomeini learned quickly, however, that it was one thing to target Kuwaiti or Saudi ships, and quite another to attack American vessels. Four days after the guided missile frigate USS Samuel B. Roberts struck an Iranian mine in international waters on April 14, 1988, President Ronald Reagan launched Operation Praying Mantis. After warning the crews of two Iranian oil platforms to evacuate, Reagan ordered the Navy to attack them. The Iranian Navy scrambled and confronted U.S. forces head on. For Tehran, it was a fateful mistake. By the end of the day, Iran had lost a frigate, a gunboat, and three speedboats, on top of the two oil platforms, in what had become the largest U.S. surface engagement since World War II.

The lopsided U.S. victory convinced Iranian leaders of the need to avoid sustained conflict at sea. Rather than seek bigger and better ships, Iranian strategists prioritized surprise and ambush. Their goal became not victory, but the ability to create enough casualties to make victory unpalatable for both the Pentagon and the American public. In short, they sought the maritime equivalent of the low-grade insurgency they subsequently perfected on land in Afghanistan and Iraq.

As the Islamic Republic pursues this asymmetric naval strategy, geography works to its advantage. The Persian Gulf is both narrow and shallow—its average depth is only 160 feet—so American warships and submarines have reduced maneuverability. Not only can Iranian speedboats idle in Iranian waters just minutes from international shipping lanes, but both IRGC-N small boats and unmarked smuggling dhows—the traditional wooden boats that ply the Persian Gulf—can shelter in rocky coves along Iran’s 1,000-mile coastline.

It is these Iranian speedboats, and perhaps Iranians undercover in civilian boats, that pose the gravest threat to U.S. ships, not the Iranian drones, which most recently made headlines when they claimed to have photographed the aircraft carrier USS John C. Stennis transiting the strait. In the last few months, the frequency and aggressiveness of Iranian speedboat probing of American ships has increased dramatically according to sailors in the Persian Gulf.

Iranian small boats’ growing aggressiveness is in line with the Islamic Republic’s new military doctrine. In September 2007, the new IRGC commander, Mohammad Ali Jafari, reorganized his land forces to focus inward. He argued, presciently as the June 2009 election protests demonstrated, that the Iranian people posed a greater threat to Iran’s theocracy than did external armies.

Because the army was required to keep the lid on at home, the Islamic Republic would have to rely far more on its navy to meet external challenges. During a visit to a Bandar Abbas naval base in July, Supreme Leader Khamenei blessed the Iranian Navy and its IRGC counterpart as “symbols of the might of the Iranian nation” and promised their expansion.

Three months later, IRGC-N commander Ali Fadavi elaborated upon Iranian thinking. “The military power of the United States is maritime,” he explained. “Naturally, the main battlefield is the sea, .  .  . and the Revolutionary Guards Navy will be the center of resisting and defending and safeguarding the Islamic Revolution.”

President Barack Obama may have asked Iran to unclench its fist, but Fadavi dismissed the olive branch. “We are not in peacetime,” he declared. He subsequently announced the expansion of operations into the Sea of Oman, once the domain of the more conventional ordinary navy, and the establishment of separate IRGC naval bases in Jask and Chahbahar, both outside the Strait of Hormuz. It was against this backdrop that the Islamic Republic sent two naval vessels through the Suez Canal to the Mediterranean Sea last February. More recently, Iran has announced deployments into the Gulf of Aden, and Sayyari has said Iran will send a ship into the Atlantic Ocean, perhaps bluster but nonetheless worth watching as Iran cultivates ties with Venezuela and littoral African states.

Iranian tactics should also be cause for concern. In recent years, the IRGC-N has drilled swarming larger ships with increasing numbers of speedboats, and has probed U.S. vessels with increasing frequency. In the last few months, Iranian boats have retreated only when U.S. vessels have fired warning shots. While the Pentagon does not publicize such incidents, sailors say there are now near daily occurrences. The proximity of the Iranian boats means that, should any be intent on a suicide plot, American sailors would likely lose their lives.

Smugglers add another layer of danger. Prior to entering or exiting the strait, ships—be they warships or tankers—line up and proceed in queue to avoid the risk of collision. Smugglers traversing the strait from the Iranian shore to the rocky outcrops on the Arabian side of the waterway regularly cut across the path of even America’s largest carriers, sometimes disappearing into the 300-meter blind spot beneath the carrier’s bow.

It would be a fatal mistake for the U.S. Navy to assume these smugglers are harmless. Even if they are not Revolutionary Guards, they depend on the IRGC for access to what Iranians call “invisible jetties,” the network of IRGC-run smuggling ports. Certainly, the IRGC could also use a dhow for surveillance, if not to attack U.S. ships or helicopters, the maritime equivalent of Iranian-backed militiamen dressing in civilian clothes and taking up positions in mosques and schools.

The Iranian leadership regularly seeks plausible deniability for its actions in order to diminish the likelihood of retaliation. The supreme leader may be a dictator, but he is not crafted in the mold of the late Saddam Hussein or Kim Jong Il. Rather, he operates by veto, eliminating policies of which he disapproves but allowing his subordinates to pursue any plan he does not explicitly reject. In practice, this means the U.S. intelligence community will never find a smoking gun—an intercept in which the supreme leader orders an attack on American forces— allowing dovish diplomats to dismiss most Iranian aggression as rogue activity.

When it comes to the IRGC-N, however, operational proximity to U.S. warships might lead to real rogue action. Robert Rook, a military historian at Towson University who regularly teaches on deploying carrier strike groups and marine expeditionary units, notes that the U.S. intelligence community has apparently never cross-referenced the passenger manifest of Iran Air Flight 655, mistakenly downed by the USS Vincennes on July 3, 1988, with currently serving IRGC-N officers. Should any speedboat pilot have had family members killed in the incident, his motive to go rogue might be high. Fadavi himself was reportedly a junior officer at the time of the Vincennes tragedy.

With tensions running so high, it would be a no-brainer for officials in both Tehran and Washington to establish communication to mitigate the risk of conflict. That assumes, however, that the Iranian leadership wants to avoid a confrontation. Contrary to the statements of advocacy groups like the National Iranian American Council, which seeks both to exculpate the Islamic Republic and to fundraise over false claims of American aggressiveness, both the Bush and Obama administrations have sought consistently to establish communications to avoid any accidental conflict. In both cases, the Iranian government rejected such overtures. In September 2011, for example, Fadavi responded to a White House suggestion to establish a hotline with Tehran by declaring, “The only way to end American concerns is [for the United States] to leave the region.”

Herein lies the danger of Obama’s conciliatory approach: When in 1998 al Qaeda leader Osama bin Laden called the United States a “paper tiger,” the Clinton administration ignored him. This emboldened him to strike at America in East Africa, Yemen, and eventually in New York and Washington.

With regard to Iran, the same dynamic is in play. On almost every deployment over the last decade, American sailors have photographed Revolutionary Guardsmen on speedboats unfurling banners with slogans such as “America can’t do a damned thing” (the same slogan with which the IRGC presented the captured American drone in early December) as they buzz American ships. One intelligence officer said that on her previous deployment, an Iranian boat had gotten so close that an Iranian crewman had used a cell phone to photograph her.

Rather than compel Iran to negotiate, Obama has convinced the Iranian leadership that the United States is on the ropes and that their defiance rather than compromise will win the day. Obama may see the withdrawal from Iraq as a campaign promise kept, but Iranian authorities label it a historic defeat for the United States.

Iranian authorities seek to transform the Persian Gulf into a Persian lake. It is in this context that Hossein Shariat-madari, who as editor of the Islamic Republic’s flagship Kayhan newspaper serves as the supreme leader’s voice, has referred to the island nation of Bahrain, home to the U.S. Fifth Fleet headquarters, as a renegade Iranian province. As the West learned when Saddam made similar references to Kuwait, sometimes dictators mean what they say.

As the Iranian naval challenge grows, what should Obama do? The United States will soon have three aircraft carriers in the Fifth Fleet area of operation, but absent the willingness to lay down red lines, a show of force will not be enough. Constant Iranian probing with minimal response has convinced the IRGC that American ships are vulnerable. Iranian authorities do not believe they must defeat the U.S. Navy head-on; causing casualties while crippling a ship might be enough to achieve their goals. After all, if the IRGC believe that they not only served America a catastrophic defeat in Iraq, but are on the verge of doing so again in Afghanistan, then they will conclude that the quickest way to force a U.S. withdrawal from the Persian Gulf is not to close the Strait of Hormuz, but rather to kill American sailors, directly or by proxy.

On board American vessels, there is general consensus that American restraint will end up costing lives. When an IRGC speedboat rams a U.S. vessel or smugglers on board a dhow down an American helicopter with a surface-to-air missile, Congress will hold hearings as in the aftermath of the 2000 USS Cole bombing, and the Pentagon will revise its rules of engagement in order to ensure that hostile vessels can no longer get within striking distance of American warships. The question is, why wait to act until American sailors come home in body bags?

Should Obama—or any successor—wish to protect American lives and preserve peace, the best policy may be to communicate a no-nonsense red line and then use deadly force to impose it. The U.S. Navy, for example, might declare a one-mile exclusion zone around every American vessel. Smugglers would learn the lesson quickly. After all, they seek worldly profit, not premature entry to paradise. As for the Revolutionary Guards, if they have forgotten the lesson of Operation Praying Mantis, a refresher course may be in order.

Michael Rubin, a resident scholar at the American Enterprise Institute, lectures on board aircraft carriers for the Naval Postgraduate School.

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