With missile batteries, fleets of attack boats and stocks of naval mines, Iran can disrupt traffic through the Strait of Hormuz but probably cannot completely shut down the world's most important oil route, military analysts say.
The question for Iran's leadership is whether it is worth the heavy price.
Trying to close the strait would bring down a powerful military response on Iran's head from U.S. forces in the Gulf and turn its few remaining international allies against it.
That Iran is making such dire threats at all illustrates its alarm over new sanctions planned by the U.S. that will target oil exports -- the most vital source of revenue for its economy. Iran's leaders shrugged off years of past sanctions by the U.S. and United Nations, mocking them as ineffective. But if it cannot sell its oil, its already-suffering economy will be sent into a tailspin.
"It would be very, very difficult for Iran even to impede traffic for a significant period of time," said Jonathan Rue, a senior research analyst at the Washington-based Institute for the Study of War. "They don't have the ability to effectively block the strait."
What the Iranians can do, Rue and other analysts say, is harass traffic through the Gulf -- anything from stopping tankers to outright attacks. The goal would be to panic markets, drive up shipping insurance rates and spark a big enough rise in world oil prices to pressure the United States to back down on sanctions.
The strait would seem to be an easy target, a bottleneck only about 30 miles across at its narrowest point between Iran and Oman.
Tankers carrying one-sixth of the world's oil supply pass through it, from the oil fields of Iran and its Gulf Arab neighbors, exiting the Persian Gulf into the Arabian Sea and on to market. They move through 2 1/2 -mile-wide shipping lanes, one entering the Gulf, one exiting.
In recent years, Iran has dramatically ramped up its navy, increasing its arsenal of fast-attack ships, anti-ship missiles and mine-laying vessels.
Its elite Revolutionary Guards boasts the most powerful naval forces, with approximately 20,000 men, with at least 10 missile patrol boats boasting C-802 missiles with a range of 70 miles and a large number of smaller patrol boats with rocket launchers and heavy machine guns, according to a recent report by Anthony Cordesman at the Center for Strategic and International Studies.
The navy has three submarines and an unknown number of midget subs, capable of firing "smart" torpedoes. It also has a large scale capability for laying mines, according to the report.
The Revolutionary Guard has also deployed a heavy array of anti-ship Seersucker missiles with a range of up to 60 miles along its coast overlooking the strait, on mobile platforms that make them harder to hit.
Still, those forces would not likely be enough to seal the strait, given the presence of the U.S. 5th Fleet based in the Gulf nation of Bahrain. Wednesday, Pentagon spokesman George Little warned that any "interference with the transit or passage of vessels through the Strait of Hormuz will not be tolerated."
Hormuz is in the territorial waters of Iran and Oman, but it is considered an international strait where free passage is guaranteed, meaning that under international law, closing it by any nation would be considered an act of war.
Russia and China, Iran's main allies that have protected it from stronger U.N. sanctions, would have little choice but to respond. Russia, which now has oil production contracts in Iraq, and China, which relies on the region for its supplies, also have no interest in seeing traffic stop, said Olivier Jakob of the Switzerland-based oil monitor Petromatrix.
Hormuz's closure would also be a heavier blow to Iran than any sanctions hitting the approximately 2.5 billion barrels a day of oil it exports, which provide 80 percent of its revenue. Not only do all of its oil exports go through the strait, but also most of its imports, including vital gasoline supplies.