If the tense confrontation with Iran ignites into war, strategists say they expect Iran will strike with thousands of deadly sea mines to try to halt oil tanker traffic and take out American warships.
In the shallow, crowded waters of the Persian Gulf, mines pose a sobering challenge. When the U.S. Navy has faced a massive mine threat there in the past, it has failed to protect even its own ships.
Now, both Iran and the United States seem poised to fight it out again. Iran has acquired a stockpile of 2,000 to 3,000 mines, including "smart'' Chinese-built mines that could track and target U.S. warships, according to a report by Anthony Cordesman of the Center for Strategic and International Studies, a nonpartisan think tank in Washington.The 660-pound warhead carried by one such mine could puncture the hull of a U.S. aircraft carrier, the report says.
But the Navy says this time it's prepared for a mine war, with a four-ship fleet of high-tech counter-mine vessels patrolling the Gulf, along with airborne sensors, robot submarines, a squadron of mine-hunting dolphins and sea lions on standby -- and two decades worth of operational experience off the coast of Iran.
The United States holds air and naval superiority across the region. Nevertheless, mine warfare in the Persian Gulf could be a lengthy, nerve-wracking conflict, putting at risk the steady flow of oil tankers and the ships and sailors of the U.S. Fifth Fleet.
Just as cheap, makeshift bombs, or IEDs, have exacted a bloody toll on Americans in Iraq and Afghanistan -- killing more than 3,000 and wounding more than 31,000, according to the Defense Department -- mines are an indirect but effective tactic for Iran to use against a more powerful opponent.
"No nation from this region wants to take the U.S. on with conventional munitions," said a senior Navy official, who agreed to discuss the issue anonymously because of continuing international diplomacy relating to Iran. "The asymmetric weapon is the way to go, and mines are cheap, easily manufactured and, not unlike an IED, are tripped by an unsuspecting victim," he said.
Iran has threatened to flood the Gulf with thousands of mines, which Navy officials say could take a year or more to clear, hampering oil shipping and exposing ships to mine blasts in the meantime.
"It's a volume issue more than a technical challenge," Navy Lt. Cmdr. Wayne Liebold, the skipper of the mine-hunter USS Gladiator, told The Huffington Post in a phone interview from the Persian Gulf.
The Gladiator is one of four U.S. mine warfare ships, built in Wisconsin of spruce, cedar and fir, that are permanently stationed in the Persian Gulf. Their wooden construction gives them a low magnetic signature to avoid detonating mines that sense magnetic fields, a benefit appreciated by their crews who rotate from the United States every six months.
"My concern is going out there and having to search a large volume of water with large quantities of mines," said Liebold, who has done three mine-hunting deployments in the Gulf.
And until the Gulf is cleared of mines, danger lurks.
In 1991, as U.S. forces gathered against Saddam Hussein's army, Iraq floated more than 1,000 mines out into the Gulf. Despite an intense international mine-clearing effort, two massive warships -- the amphibious assault carrier USS Tripoli and the USS Princeton, a high-tech guided missile cruiser -- were rocked by explosions that set off fires and flooding below decks.
Both ships were saved, but a planned amphibious landing of 30,000 Marines was canceled because of the mine threat, according to a Navy account.
Three years earlier, Iranian mines blew up and almost sank the USS Samuel B. Roberts, an American frigate, during the so-called Tanker War. After the U.S. agreed to provide protection for convoys of oil tankers, the first convoy ran into trouble when the U.S.-flagged supertanker Bridgeton struck a mine that blew a large hole in its hull.
Today, as the United States and others press economic sanctions against Iran's nuclear weapons program, the USS Gladiator and the three other U.S. Avenger-class mine warfare ships are out patrolling the Gulf daily.
No mines have been found. But the threat is there, said the senior U.S. Navy official.
Navy mine-hunting ships and crews, stationed in the Gulf continually since the 1990s, have more mine-hunting familiarity with its waters and undersea terrain than anywhere else on Earth. "We don't really need to train for the threat here,'' he said.
But mine-hunting is a difficult, dangerous and time-consuming task. "Handling the mine threat is easier said than done," the Navy official said. "We are certainly ready, confident and prepared." But he recalled that in 1991, it took almost a year for 32 mine-hunting ships to eliminate the Iranian mines. "But during that time, oil kept flowing, global commerce remained stable; it just took some working around," he said.
The proliferation of mines -- there are more than 250,000 in the global inventory, according to Navy officials -- and accelerating pace of technology has led the Pentagon's counter-IED agency, the Joint IED Defeat Organization, to list surface and submersible mines as a global IED threat.
Mines are no longer the simple spiked iron sphere that floats unseen in the path of an oncoming warship -- although it was just such a World War I-era mine that blew up the USS Samuel Roberts.
One Iranian mine, the Chinese-built EM-52, is designed to wait on the bottom, listening for the distinctive magnetic or acoustic signature of a particular ship -- say, an aircraft carrier -- before launching a propelled 660-pound warhead at the target.
In other Iranian mines, microcomputers can sense a target approaching, identify the type of target, take countermeasures to avoid being detected -- by going "dark," for example -- and then calculate the best moment to attack.
As some mines have gotten more high-tech, other mine designers have followed the IED model by going more low-tech. Some are built into discarded refrigerators or 50-gallon drums. Responding to new U.S. mine-hunting techniques, some mines are disguised as irregular sea-bottom objects among the other junk that clutters the Persian Gulf seabed. Others are wrapped in plastic or fiberglass to avoid detection by the Gladiator's sensors.
Even "relatively unsophisticated 'dumb' mines, however, present a threat to US forces and Gulf shipping, as they are not easily detected or removed, and can be laid in large numbers by almost any ship that has the capacity to physically carry them,'' Cordesman wrote in his report.
Iran also is said to have acquired as many as a dozen midget submarines from North Korea that could lay mines or fire torpedoes. It was with just such a weapon that North Korea sank the South Korean corvette Cheonan in 2010.
Al Qaeda operatives have planned to use swimmers to attach mines to moored ships, or to launch manned or unmanned underwater vehicles as self-propelled suicide attack mines.
Detecting these weapons in the shallow, brackish and cluttered waters of the Gulf can be difficult. In winter, high winds chop the water into an opaque froth; summertime drives the temperatures above 120 degrees, hammering crews and delicate electronics. The USS Gladiator hunts for mines with sonar and video, often stopping dead in the water while its sailors pore over video screens, trying to identify a suspicious blur on the seabed.
When a mine is identified, it is not blown up in place -- that's too dangerous. Instead, a robot or swimmer attaches a small charge to it to crack its shell; sea water pours in to destroy the electronics and render the mine harmless.
The Navy has long trained dolphins and sea lions to hunt for and detonate mines. Just like missiles or other weapons, the mammals carry technical designations: Mark 4 Mod 0 (dolphins that work in shallow water), Mark 4 Mod 1 (sea lions that work below 500 feet) and Mark 6 Mod 1 (dolphins trained to detect and attack underwater swimmers). They are the only Navy asset that can detect mines buried in the seabed, but they can only search small areas at a time.
At present, the Navy has not deployed dolphins to the Persian Gulf. But it could get them there in a hurry from their base in San Diego if they were needed, Navy officials said.
Meantime, it is the sailors aboard the Gladiator and her three sister ships who are ultimately responsible for fighting a mine war, should it come to that. "Mine warfare doesn't get a lot of high-profile 'Top Gun'-type attention,'' skipper Liebold said. "When it's needed, people ask for it right away."
"I have 80 sailors working for me, average age 21, and they work extremely hard in extremely difficult circumstances,'' he said. "I'm very fortunate to have the highly trained crew that I do. They come to work every day and do a great job for the American people.''
CORRECTION: An earlier version of this article identified the USS Samuel B. Roberts as a destroyer. The ship was a frigate.