Iran's most potent weapon is its ability to block oil supplies
Robert Tait in Tehran
In The Persian Puzzle, an absorbing and detailed history of Iran's troubled relationship with America, Kenneth Pollack, the former Clinton administration foreign policy adviser, recounts having a flash of insight into the mindset of the Iranian leadership.
It was 1989, shortly after the conclusion of Iran's gruelling - and unsuccessful - eight-year war with Saddam Hussein's Iraq and Pollack, then a military analyst at the CIA, was studying Iranian priorities and expecting to find it frantically preparing for renewed conflict with its western Arab neighbour. He found something else entirely.
Rather than re-arming, Iran's Islamic leadership was bogged down in time-consuming negotiations with small-arms makers. Nor did they appear intent on redressing the failings that had undermined the war effort with Iraq.
'They were buying mostly weaponry intended for naval warfare; anti-ship missiles, medium-range strike aircraft, fixed surface-to-air missiles and the like,' writes Pollack.
'They were not arming to defend themselves against Iraq - the state that had invaded their country and just obliterated their armies - they were arming to defend themselves against us, the United States.'
Seventeen years on, Pollack's realisation is being shared by the rest of the world. For the past week, in a series of high-profile war games, Iran has been staging a demonstration of military muscle in the Persian Gulf unambiguously directed at the US and its western allies as they ratchet up the pressure over the Islamic regime's suspected nuclear weapons programme.
In a series of exercises, Iran's naval forces have test-fired an impressive array of hardware - including a stealth missile that can evade radar, a flying boat, and what they claim is the world's fastest underwater missile.
It is not the first sabre-rattling mock manoeuvre the Islamic Republic has staged. But with the clock ticking on last week's 30-day deadline issued by the UN Security Council for Iran to abandon uranium enrichment activities, its message to the west is clear: if you want a fight, we're ready.
'After weeks of psychological warfare, they expected that we would back down and give up our rights,' General Mohammed Hejazi, head of Iran's Basij (Islamic volunteer force) told state television.
'Not only did we not do that, we showed our capabilities through these manoeuvres. The enemies must know that they should play with fire.'
The setting for this bellicose exhibition, the Strait of Hormuz, has been carefully chosen. Situated at the mouth of the Gulf, it is a strategically vital waterway through which two-fifths of the world's oil is transported. By displaying its capacity to disrupt the shipping carrying these supplies, Iran is sending a veiled warning that it has the ability to send oil prices soaring and devastate the world economy.
The US affects to be unimpressed, citing a supposed Iranian trait to exaggerate its capabilities.
Yet while defence analysts are equally sceptical of the tangible worth of Iran's newly demonstrated hardware, there is acknowledgement that its true value may be psychological.
'You don't actually need lots of weapons to close the Strait of Hormuz, you just need lots of threats,' said Tim Ripley, an analyst with Jane's Defence Weekly Magazine.
'You don't even have to sink a ship, you just have to double the insurance rates for shipping and it has a knock-on effect on the price of oil.'
Much of Iran's sea defence weaponry has been supplied by China. Iran is also the only nation in the Gulf to operate attack submarines - three Russian-built Kilo class diesel-electric vessels.
If Iran's fixation with America has led it to focus on naval matters, it has certainly not neglected its ground forces. The regular Iranian army is estimated at 325,000 troops, with another 100,000 in the Revolutionary Guard armed forces.
The Iranians have also re-equipped their army with weapons largely bought from China.