When Admiral Mike Mullen, chairman of the Joint Chiefs of Staff and the highest-ranking American officer, was asked recently on NBC’s Meet The Press whether the United States has a military plan for an attack on Iran, he replied simply: “We do.”

General staffs are supposed to plan for even the most unlikely future contingencies. Right down to the 1930s, for example, the United States maintained and annually updated plans for the invasion of Canada—and the Canadian military made plans to preempt the invasion. But what the planning process will have revealed, in this case, is that there is no way for the United States to win a non-nuclear war with Iran.

The U.S. could “win” by dropping hundreds of nuclear weapons on Iran’s military bases, nuclear facilities and industrial centres (i.e. cities) and killing five to 10 million people, but short of that, nothing works. On this we have the word of Richard Clarke, counter-terrorism adviser in the White House under three administrations.

In the early 1990s, Clarke revealed in an interview with the New York Times four years ago, the Clinton administration had seriously considered a bombing campaign against Iran, but the military professionals told them not to do it.

“After a long debate, the highest levels of the military could not forecast a way in which things would end favourably for the United States,” he said. The Pentagon’s planners have war-gamed an attack on Iran several times in the past 15 years, and they just can’t make it come out as a U.S. victory.

It’s not the fear of Iranian nuclear weapons that makes the U.S. Joint Chiefs of Staff so reluctant to get involved in a war with Iran. Those weapons don't exist, and the whole justification for the war would be to make sure that they never do.

The problem is that there’s nothing the U.S. can do to Iran, short of nuking the place, that would really force Tehran to kneel and beg for mercy. It can bomb Iran’s nuclear sites and military installations to its heart’s content, but everything it destroys can be rebuilt in a few years. And there is no way that the United States could actually invade Iran.

There are some 80 million people in Iran, and although many of them don’t like the present regime they are almost all fervent patriots who would resist a foreign invasion. Iran is a mountainous country, and very big: four times the size of Iraq. The Iranian army currently numbers about 450,000 men, slightly smaller than the U.S. Army—but unlike the U.S. Army, it does not have its troops scattered across literally dozens of countries.

If the White House were to propose anything larger than minor military incursions along Iran’s south coast, senior American generals would resign in protest. Without the option of a land war, the only lever the United States would have on Iranian policy is the threat of yet more bombs—but if they aren’t nuclear, then they aren’t very persuasive. Whereas Iran would have lots of options for bringing pressure on the United States.

Just stopping Iran’s own oil exports would drive the oil price sky-high in a tight market: Iran accounts for around seven percent of internationally traded oil. But it could also block another 40 percent of global oil exports just by sinking tankers coming from Iraq, Saudi Arabia, and the other Arab Gulf states with its lethal Noor anti-ship missiles.

The Noor anti-ship missile is a locally built version of the Chinese YJ-82. It has a 200-km range, enough to cover all the major choke points in the Gulf. It flies at twice the speed of sound just metres above the sea’s surface, and it has a tiny radar profile. Its single-shot kill probability has been put as high as 98 percent.

Iran’s mountainous coastline extends along the whole northern side of the Gulf, and these missiles have easily concealed mobile launchers. They would sink tankers with ease, and in a few days insurance rates for tankers planning to enter the Gulf would become prohibitive, effectively shutting down the region’s oil exports completely.

Meanwhile Iran would start supplying modern surface-to-air missiles to the Taliban in Afghanistan, and that would soon shut down the U.S. military effort there. (It was the arrival of U.S.-supplied Stinger missiles in Afghanistan in the late 1980s that drove Russian helicopters from the sky and ultimately doomed the whole Soviet intervention there.)

Iranian ballistic missiles would strike U.S. bases on the southern (Arab) side of the Gulf, and Iran’s Hezbollah allies in Beirut would start dropping missiles on Israel. The United States would have no options for escalation other than the nuclear one, and pressure on it to stop the war would mount by the day as the world’s industries and transport ground to a halt.

The end would be an embarrassing retreat by the United States, and the definitive establishment of Iran as the dominant power of the Gulf region. That was the outcome of every wargame the Pentagon played, and Mike Mullen knows it. So there is a plan for an attack on Iran, but he would probably rather resign than put it into action. It is all bluff. It always was.

The second edition of Gwynne Dyer’s latest book, Climate Wars, was published recently in Canada by Random House.