Why is the Strait of Hormuz so important?

A narrow strip of water separating Iran from Oman, the strait is the major maritime link between the oil-rich Persian Gulf region and the rest of the world. Tankers carry 17 million barrels of oil, about a fifth of the world's supply, through the channel every day. Five of the planet's biggest oil producers — Saudi Arabia, Kuwait, Iran, Iraq, and the United Arab Emirates — rely on the waterway to ship almost all of their energy exports. The waterway is now at the center of the West's increasingly tense standoff with Iran, which in recent weeks has warned that it would shut the shipping artery if the U.S. or Europe tightened economic sanctions in response to its nuclear program. Iran's top naval commander, Habibollah Sayyari, said closing the strait would be "easier than drinking a glass of water." The Obama administration has publicly dismissed the threat as "saber rattling," but sent word to Tehran through back channels that closing the strait would cross "a red line" and provoke an American military response.

Could Iran actually shut down the strait?

"The simple answer is yes, they can block it," said Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff. Over the past two decades, Iran's elite Revolutionary Guard has stockpiled at least 2,000 naval mines. Those garbage-can-size explosives could be slipped into the water by midget submarines and civilian dhows (a kind of sailboat) and other fishing vessels. Although the waterway is 21 miles wide, Iran could make the strait a no-go zone for big vessels by laying mines across the deep, central passage that holds the inbound and outbound shipping lanes, which are each only two miles wide. That operation could be completed in a matter of hours. "All the Iranians have to do is say they mined the strait and all tanker traffic would cease immediately," said Jon Rosamond, editor of the journal Jane's Navy International.

Has Iran ever acted on its threats?

Iran last tried to sabotage shipping during its decade-long conflict with Saddam Hussein's Iraq. When Iraq began attacking Iranian tankers in 1984, Iran responded by targeting vessels headed to and from Gulf ports, and laying mines in shipping lanes. The frigate USS Samuel B. Roberts almost sank after it hit an Iranian mine in 1988, leading President Reagan to order retaliatory strikes. In a single day, the U.S. Navy destroyed two Iranian oil platforms, a frigate, a gunboat, and three speedboats. Today, Iran's navy is a more formidable enemy. Not only does it have an arsenal of mines 10 times more powerful than those used in the 1980s, but it now boasts "hundreds of advanced cruise missiles and possibly more than 1,000 small, fast attack craft," U.S. Navy Cmdr. Daniel Dolan wrote in a 2010 report.

How would oil prices react?

They'd skyrocket. Energy analysts warn that even a partial blockage of the strait could send the price of a barrel of oil soaring to $150, up from about $100 today. Gas prices in the U.S. would quickly rise above $4.50 a gallon, and imperil the global economic recovery. But the Islamic Republic itself would likely pay the highest price for closing the strait. The Iranian government generates 65 percent of its revenues from oil exports, almost all of which pass through the waterway. Shutting off that cash stream would devastate Iran's economy, which is already reeling from international sanctions and mismanagement. By delivering on their threat, said Dennis Ross, a former White House adviser on the Mideast, the Iranians "would basically be taking a vow of poverty."

What could the U.S. do to reopen the strait?

It can't just send in minesweepers. Any warship entering the narrow waterway could be easily surrounded by swarms of missile-armed Iranian speedboats, and targeted by anti-ship cruise missiles hidden on Iran's coastline, islands, and oil platforms. So the U.S. would likely begin any mine-clearing mission by launching aerial attacks on Iran's naval bases and missile silos. Since that would essentially put the two nations in a state of war, the U.S. would probably go further and embark on a broader offensive against the Islamic Republic. "You'd almost certainly also see serious strikes on their nuclear facilities," said Anthony Cordesman, a defense expert at Washington's Center for Strategic and International Studies. "Once the Iranians have initiated hostilities, there is no set level at which you have to stop escalation."

So will Iran really close the strait?

Probably not. Most analysts think Iran will find less dangerous ways to dissuade the West from approving new sanctions. If they wanted to disrupt shipping, they could temporarily shut part of the strait for military exercises, or launch one-off hit-and-run attacks they could then blame on pirates. But Iran's calculation would change if the U.S. or Israel launched a bombing attack on its nuclear facilities. Then a Hormuz shutdown "would happen pretty much automatically," said Henry Smith of London-based security consultancy Control Risks. "The Iranians have been saying for a long time that is an option, and they would have little choice but to stick to that."

Sending in the dolphins

If Iran shuts the Strait of Hormuz, the U.S. will likely deploy its best mine detector: Flipper. The Navy has an 80-strong squad of bottle-nosed dolphins, some of which have been trained to find mines and mark their location by dropping an acoustic transponder. Navy divers are then sent in to destroy the explosives. The dolphins' incredible natural sonar makes them perfect minesweepers: They can distinguish between a nickel and a dime at 100 yards, and among brass, aluminum, and stainless steel — even when the metal is buried under two feet of mud. "They are astounding in their ability to detect underwater objects," said retired Adm. Tim Keating. Those skills have undoubtedly saved the lives of U.S. military personnel. During the 2003 invasion of Iraq, nine Navy dolphins helped clear more than 100 mines and underwater booby traps placed by Saddam Hussein's forces.