Military personnel place a flag on a submarine during the Velayat-90 war games by the Iranian navy in the Strait of Hormuz in southern Iran December 27, 2011. Iran is rapidly gaining new capabilities to strike at U.S. warships in the Persian Gulf, amassing an arsenal of sophisticated anti-ship missiles while expanding its fleet of fast-attack boats and submarines. (Stringer/Iran/Reuters)

Iran is rapidly gaining new capabilities to strike at U.S. warships in the Persian Gulf, amassing an arsenal of sophisticated anti-ship missiles while expanding its fleet of fast-attack boats and submarines, U.S. and Middle Eastern analysts say.

The new systems, many of them developed with foreign assistance, are giving Iran’s commanders new confidence that they could quickly damage or destroy U.S. ships if hostilities erupt, the officials say.

Although U.S. Navy officials are convinced that they would prevail in a fight, Iran’s advances have fueled concerns about U.S. vulnerabilities during the opening hours of a conflict in the gulf.

Increasingly accurate short-range missiles — combined with Iran’s use of “swarm” tactics involving hundreds of heavily armed patrol boats — could strain the defensive capabilities of even the most modern U.S. ships, current and former military analysts say.

In recent weeks, as nuclear talks with world powers have faltered and tensions have risen, Iran has repeated threats to shut down shipping in the oil-rich gulf region. Its leaders also have warned of massive retaliation for any attacks on its nuclear facilities, which the United States believes are civilian covers for an Iranian drive to acquire a nuclear-weapons capability.

Last week, Iran’s Foreign Ministry declared that the presence of U.S. warships in the gulf constituted a “real threat” to the region’s security.

Pentagon officials have responded by sending more ships, urged on by Congress as well as U.S. allies in the region. This month, the Navy announced that it would deploy the aircraft carrier USS John C. Stennis to the Middle East four months ahead of schedule. The shift will keep two carriers in the gulf region.

The United States also has announced new military exercises in the region, including a mine-sweeping drill in the gulf, and has moved to add new radar stations and land-based missile-defense batteries in Qatar.

Assessing the risks

The likelihood that Iran would risk an all-out attack on a vastly superior U.S. fleet is judged to be small. But Iranian leaders could decide to launch a limited strike if Israel or the United States bombed the country’s nuclear facilities. Analysts also cautioned that a conflict could be sparked by an Iranian attempt to close the Strait of Hormuz — the narrow passage through which about 20 percent of the world’s oil passes from the Persian Gulf into open seas — in retaliation for international economic sanctions.

In either scenario, Iran’s ability to inflict significant damage is substantially greater than it was a decade ago. A Pentagon study in April warned that Iran had made gains in the “lethality and effectiveness” of its arsenal. The Pentagon declined to comment for this article.

Iran’s increased power to retaliate has led some military experts to question the wisdom of deploying aircraft carriers and other expensive warships to the gulf if a conflict appears imminent.

A 2009 study prepared for the Naval War College warns of Iran’s increasing ability to “execute a massive naval ambush” in the Strait of Hormuz, a narrow waterway dotted with small islands and inlets and perfectly suited for the kind of asymmetric warfare preferred by Iran’s commanders.

“If the U.S. chooses to station warships in the Strait of Hormuz during the buildup to conflict, it cedes the decision of when to fight and allows the fight to begin in the most advantageous place for Iran,” wrote the study’s author, Navy Lt. Cmdr. Colin Boynton. “This could lead to a devastating first salvo on U.S. Navy warships, which would most likely be operating under restrictive rules of engagement.”

Since 2009, analysts say, Iran has added defensive and offensive capabilities. Some of them have been on display in recent months in a succession of military drills, including a missile exercise in early July dubbed Great Prophet 7. The exercise included a demonstration of Iran’s newly deployed Khalid Farzh anti-ship missile, which has an internal guidance system, a powerful 1,400-pound warhead and a range of 180 miles.

Iran’s arsenal already included a variety of anti-ship missiles such as the Chinese-made Silkworm. More recently, Iran has boasted of progress in developing high-speed torpedoes based on Russian designs. Such claims are often exaggerated, but the April Pentagon assessment noted that Iran’s arsenal now includes ballistic missiles with “seekers” that enable them to maneuver toward ships during flight.

Modern U.S. warships are equipped with multiple defense systems, such as the ship-based Aegis missile shield. But Iran has sought to neutralize the U.S. technological advantage by honing an ability to strike from multiple directions at once. The emerging strategy relies not only on mobile missile launchers but also on new mini-submarines, helicopters and hundreds of heavily armed small boats known as fast-attack craft.

These highly maneuverable small boats, some barely as long as a subway car, have become a cornerstone of Iran’s strategy for defending the gulf against a much larger adversary. The vessels can rapidly deploy Iran’s estimated 2,000 anti-ship mines or mass in groups to strike large warships from multiple sides at once, like a cloud of wasps attacking much larger prey.

A Middle Eastern intelligence official who helps coordinate strategy for the gulf with U.S. counterparts said some Navy ships could find themselves in a “360-degree threat environment,” simultaneously in the cross hairs of adversaries on land, in the air, at sea and even underwater.

“This is the scenario that is giving people nightmares,” said the official, who spoke on the condition of anonymity in discussing strategy for defending against a possible Iranian attack.

The Navy has ordered new systems for defending against small-boat “swarms,” including ship-launched unmanned aerial vehicles and special missiles and artillery rounds for use against fast-attack craft. But many of the new defenses will not be deployed for several months, said Michael Eisenstadt, a former military adviser to the Pentagon and the State Department.

“We’re behind and we’re catching up,” Eisenstadt said. “But if there’s a conflict in the near term, we may not be completely ready.”

U.S. forces would probably recover quickly from any early losses, but Iranian leaders could claim a psychological victory if the world’s media carried images of burning U.S. warships in the gulf, Eisenstadt said. Al-Qaeda landed a similar blow in 2000 when suicide bombers on a small boat heavily damaged the destroyer USS Cole in the Yemeni port of Aden, an attack that killed 17 sailors and wounded nearly 40 others.

“A lot of Iranian ships would be at the bottom of the gulf, but [Iran] would be able to point to a victory,” Eisenstadt said. “The outcome would never be in doubt when you’re dealing with the most powerful military in the world. But in their minds they would have shown the world that if you mess with us, you’ll pay a heavy price.”

A push for credibility

The Iranian naval buildup is described by U.S. officials as part of an effort by the Islamic Republic to bolster its military credibility in the region.

The Pentagon’s April assessment said Iran was making steady progress in developing ballistic missiles capable of striking targets in Israel and beyond. It also said Tehran was enhancing its well-established capacity to launch terrorist attacks using surrogates such as Hezbollah, the Lebanon-based militia movement that operates a network of cells around the world.

U.S. and Israeli intelligence officials have linked Iran and Hezbollah to a string of assassination attempts and terrorist attacks on three continents in the past six months — from the foiled plot to kill a Saudi diplomat in Washington last fall to the deadly bombing of a tour bus filled with Israelis last week in Bulgaria. Current and former U.S. officials say more attacks are likely if Israel launches a preemptive strike on Iran’s uranium-enrichment plants.

“Iran has the capacity to attack, from Argentina to Venezuela, in Asia, in Europe and throughout the Middle East,” Danielle Pletka, a defense expert at the American Enterprise Institute, said Wednesday in testimony before the Senate Foreign Relations Committee. “It seems naïve to believe it does not have the capacity to launch attacks in the United States.”

The arms buildup in the gulf comes as Israeli officials continue to weigh an airstrike that many experts believe would ignite a larger conflict. A stream of Obama administration officials, including Secretary of State Hillary Rodham Clinton and Defense Secretary Leon E. Panetta, have visited Israel in recent weeks to lobby against a unilateral attack. Middle East experts say that Israel has not decided to attack but that the risk of an Israeli strike is rising as hopes of a diplomatic settlement to the nuclear crisis evaporate.

David Makovsky, a Middle East expert with the Washington Institute for Near East Policy, said after discussions with top Israeli officials that he assessed the chances of a strike at “50-50 . . . before the U.S. elections” in November. “There’s this feeling that Israel’s window is closing.”

U.S. ships, meanwhile, continue steaming toward the gulf as the Obama administration seeks to reassure allies in the region and discourage Iran from moving to block the flow of oil through the Strait of Hormuz. U.S. and Middle Eastern officials acknowledge that deployments carry inherent risk, but they say there are no good alternatives.

“It is a dilemma,” the Middle East intelligence official said. “When the Navy ships are in the strait, they are vulnerable to attack. But if you were to take them away, the gulf countries would feel more vulnerable. And already they feel very, very vulnerable.”