By Peter Apps, Political Risk Correspondent
LONDON (Reuters) - Under pressure over its nuclear ambitions, Iran might never act on its threat to close the Strait of Hormuz but could retain enough tricks in its playbook to keep its enemies, shippers and global markets on edge.
As Western states tighten sanctions and its enemies wage an apparent covert war against its uranium enrichment program, Tehran has warned several times it may seal off the waterway, choking the supply of Gulf crude and gas.
Few intelligence, military and security experts contacted by Reuters either in or outside government, however, believe that is genuinely likely. Instead, they say, Iran's leaders will be looking for ways to harass enemies and cause disruption while falling short of triggering a massive U.S.-led retaliation.
Possible Iranian gambits could include harrying tanker traffic in the Gulf with fast attack boats, seizing uninhabited Gulf islands claimed by other states, grabbing hostages from passing civilian or military ships, stoking trouble in Sunni Muslim-ruled Arab states with restive Shi'ite Muslim communities and orchestrating attacks on U.S. forces in Afghanistan or elsewhere using militant "proxies" such as Hezbollah.
The risk inherent in all this, however, is that someone on either side miscalculates and triggers a full-blown conflict.
"These scenarios make sense as likely actions falling short of actively blocking the Strait -- but they will certainly raise tensions," says Nikolas Gvosdev, professor of national security studies at the U.S. Naval War College in Rhode Island.
"Iran's goal in raising tensions in the Gulf may be to get other countries to put pressure on the United States to show restraint (and) as a way to create some breathing room for Tehran to maneuver."
Iran's Revolutionary Guard plans more military exercises for February, sending more swarms of gunboats into international waters and showing off its anti-ship missile arsenal.
That in itself could close some areas of the Gulf to shipping, as well is rattling neighbors and shipping firms.
Iran's 2007 capture of 15 British naval personnel proved hugely embarrassing for London. Tehran may be looking for similar ways success in humbling Western powers without inflicting physical harm.
Already, U.S. and allied naval officers say their vessels are often shadowed by Iranian gunboats, and some worry that if matters escalate further those confrontations could intensify.
"They could easily keep it coming and make it more harassing," said one Western naval officer with considerable experience in the region, speaking on condition of anonymity because he was not authorized to speak to the press.
"But short of an Iranian small boat actually attacking one of our ships, our responses will be within the letter of the law and non-lethal in nature."
Beyond the waters of the Gulf, many analysts expect Iran to further raise its support for regional proxies, from militants attacking U.S. forces in Afghanistan to Shi'ite protesters and militants in Bahrain, Saudi Arabia and elsewhere.
It could add to the growing sense of regional confrontation arising from Iran's defiance of several U.N. resolutions demanding that it suspend its atomic energy program, seen in the West as a camouflaged bid for nuclear weapons capability, and engage in negotiations with world powers on a solution.
Washington seems keen to stress its resolve and showcase its military strength. This week, the aircraft carrier USS Abraham Lincoln passed through Hormuz flanked by British and French warships - in open defiance of Tehran's warning earlier this month that Washington should keep its carriers out of the Gulf.
In reality, naval sources say the move was likely planned months or longer in advance - every time a giant U.S. carrier docks anywhere, dozens of contracts need to be in place for it to be serviced and supplied.
But this time, given the Iranian threat and the heightened tension, the warships' entry would have been approved at the highest level and deliberately publicized to an unusual degree.
"Both sides are engaged in heavy posturing right now," said Reva Bhalla, director of strategic intelligence for U.S.-based consultancy Stratfor. "Iran is focused right now on highlighting its deterrence tools in the Persian Gulf ... This, of course, increases the risk of miscalculation."
Whilst some analysts believe the Islamic Republic may already worry it has overreached itself, others worry that pulling back may become increasingly difficult politically.
The conventional military mismatch between Iran and its enemies remains colossal.
As well as the Abraham Lincoln, the United States routinely retains a second carrier in the Indian Ocean - currently the USS Carl Vinson - within easy striking distance.
Between them, the two battle groups have the capacity to carry well over 120 aircraft, while escort ships will be carrying dozens if not hundreds of Tomahawk cruise missiles. Then there are U.S. combat aircraft based in the Gulf and Afghanistan, together with other well-equipped local air forces, particularly that of Saudi Arabia, not to mention Israel.
Long-range stealth and other bombers based either in the continental United States or the British Indian Ocean territory of Diego Garcia could also hit Iranian targets with virtual impunity.
"Closing Hormuz is a myth. Iran tried to do that for eight years during the (1980s) Iran-Iraq war, and it wasn't successful even for one hour," said Mustafa Alani, head of Security and Terrorism Studies at the Gulf Research Center.
"They put mines, hit ships, but traffic through the strait continued. They were hit very hard and learned their lesson when they hit an American ship. The U.S. president ordered the U.S. navy to attack, and two-thirds of the Iranian navy was destroyed in one day. We saw that and we know their limitations," he said.
"This is why there are clear statements coming from Saudi Arabia and the UAE (United Arab Emirates) saying, indirectly, that they will replace Iran's oil."
"ASYMMETRIC WARFARE" THREAT
Iran's functional air force is limited to perhaps as few as a few dozen strike aircraft, either Russian or aging U.S. models acquired before the 1979 Iranian revolution and for which Tehran has long struggled to find spare parts.
The conventional Iranian Navy (IRIN) is also weak by modern standards. In any war, its corvettes and relatively advanced three Russian-built Kilo diesel electric submarines -- the pride of its navy -- would almost certainly be destroyed.
Its missile, torpedo and sea mine-equipped mini submarines are also seen as likely to be sunk within days.
More of a worry to Western strategists and shippers are the hardline Iranian Revolutionary Guard Corps Naval Forces (IRGCNF) with their focus on "asymmetric warfare" designed to work around Tehran's conventional military inferiority.
Firing their truck-mounted missiles directly at a warship or commercial vessel would be swiftly judged an act of war and prompt the immediate U.S. destruction of coastal batteries. But hundreds of Iranian small boats - believed to include suicide craft modeled on those once used by Sri Lanka's Tamil Tigers -would offer more options.
Operating in international waters, they can perform threatening passes of both commercial and military shipping, perhaps even firing warning shots and essentially daring international forces to respond. Individual craft could even conduct damaging and perhaps deniable attacks.
For many -- including the insurance companies nervously watching Gulf waters as they determine premiums -- the key question is whether such forces are under responsible control.
"Whereas the IRIN (Iran's mainstream navy) is a conventional military force and likely to be under tight control, the same is not true of the IRGCN," said John Cochrane, senior global risk forecaster at Exclusive Analysis, a London-based consultancy advising foreign firms in the region, including insurers.
"We assess there is a higher risk of a low-level IRGC small boat commander taking unsanctioned action - or just making a mistake - that would result in an incident in which lethal force was used by one side or the other."
Many of the commercial ships passing through Hormuz now carry their own often heavily armed private security details to protect against Somali pirates in the wider Indian Ocean.
Already accused of sometimes shooting unnecessarily at fishing boats, some worry that private security units could spark wider confrontation by inadvertently firing the first shots against Iranian forces.
But ultimately, many believe, wiser heads would probably prevail before matters spiraled out of control.
Such action would not be without precedent.
After frigate USS Samuel B Roberts was heavily damaged by an Iranian mine during the so-called "tanker war" in 1988, the U.S. military launched a limited retaliatory strike that wiped out much of Iran's navy.
But outright war was avoided, as it was again a month later after the USS Vincennes shot down an Iranian airliner, killing 290 in what Washington said was a tragic accident.
"I think it's unlikely to escalate -- Iran has too much to lose... and our forces are too professional to let any kind of a localized event blow up into a larger conflict," said the senior Western naval officer.
"If there is an incident, we will quickly get our forces into our respective corner, establish a defensive posture - albeit ready to go on the offensive if directed... - and wait to see what Iran's next move on the chessboard will be."
(Additional reporting by William Maclean in London and Joseph Logan in Dubai; Editing by Mark Heinrich)