Much of the huge advantage enjoyed by the US aircraft and troops driving deep into the capital stems from superior technology -- air-conditioned tanks that fire at great distance while on the go, night-vision goggles, devastatingly precise bombs and missiles dropped from the air.

The Iraqis, in contrast, have been striking back with guerrilla tactics and the occasional suicide attack -- the classic "assymetric warfare" of an outclassed force that turns to desperate measures to inflict casualties on a seemingly unstoppable enemy.

That imbalance has been dramatically highlighted by the fighting in and around Baghdad.

The US Third Infantry Division, an 18,000-man strong contingent with over 500 tanks and armoured fighting vehicles, closely backed up by many of the tens of thousands of Marines deployed in Iraq, thrust into the city Monday with close air cover.

Iraq's much-vaunted Republican Guard divisions, hit by days of aerial bombardment, were in little evidence and apparently unable to stop the invaders. US commanders say they have decimated the six active Guard divisions that once collectively totalled 60,000 men.

As elsewhere, the 300,000 or so soldiers that made up the rest of Iraq's demoralised and underfunded regular army have put up little real fight. Many are said to have deserted, others have been crushed by the US onslaught, but a few fight on under threat of Iraqi death squads.

Paramilitary units fanatically loyal to Iraqi President Saddam Hussein -- the feared Fedayeen among them -- are believed to be scattered throughout the city, however.

The presence of a few hundred of these fighters in the southern city of Basra held off the 30,000 British Marines and soldiers positioned in the region for more than two weeks.

Two suicide attacks using bomb-laden cars at US checkpoints north and south of Baghdad have shaken the US-led forces and provoked greater tensions every time coalition troops and Iraqi civilians have to approach each other.

Although US political and military leaders have congratulated themselves on the rapid advance on Baghdad, including the taking of the city's airport, they continue to be wary of scenarios of urban combat that many analysts have predicted could yet ensue.

That possibility has been underscored by the welcome Iraqi civilians have given US and British forces along the way.

Lukewarm at best, often ambivalent, sometimes hostile, the scenes have fallen far short of the wildly cheering crowds greeting their "liberators" that Washington and London had hoped for.

US Commanders have ordered the doubling of their forces in Iraq, to more than 200,000 troops, including the Fourth Infantry Division which has started arriving in Kuwait.

At the same time, Marines and the 101st Airborne Division are providing stepped-up protection for the 600-kilometre (400-mile) long supply line stretching from Kuwait to near Baghdad.

The US strategy to leapfrog towns and cities still in Iraqi hands had exposed the relatively vulnerable truck convoys to hit-and-run attacks.

But Washington's belief is that, once Baghdad has fallen, its forces will prevail over the rest of Iraq, leaving the Middle East, and indeed the rest of the world, in no doubt about the might of the US military.

SPACE.WIRE