Strategic analysis: There is a point in every war when the tide turns

On Saturday, after 16 days of continuous military operations, the dam of Iraqi resistance burst. Both sides in this latest conflict could be likened to water, as Sun Tzu said of armies in the 4th century BC: avoiding the heights and hastening to the shallows – or into the cracks. The Iraqi attempts to counter US and British military power by drawing them into urban jungles may have diverted the first trickles of the flood a little, but the message is clear. The weight of water is overwhelming. And at the weekend, it broke through. Après moi, le déluge.

The Iraqis avoided a head-on collision with the Americans and British because they knew they would lose any first-division, pig-iron contest with them in the open desert. Instead, they let the Allies roll over them, and put their faith in a guerrilla-type strategy, popping up behind the lines and attacking their vulnerable supply routes. As Tariq Aziz said six months ago, Iraq's cities would become its swamps and its buildings its jungles. An example of how a clever combatant avoids the heights, again.

Such "asymmetric" solutions are usually the preserve of the weaker side. But there was a great deal more water on the other side this time. It found the start of a big crack at Baghdad airport. The Iraqis said they would plug the hole with "non-conventional" action, but whatever they planned to use, little evidence of it has appeared so far.

On Saturday the Americans broke through into the Iraqi capital. Whatever setbacks lie ahead, it is hard to imagine the Iraqis closing that gap now. Like the Mediterranean breaking through what is now the Dardanelles and flooding the hollow that became the Black Sea (a possible source of the Great Flood story), with the US 4th Division now moving up behind the 3rd, the surge looks pretty much unstoppable.

Napoleon once said that battles are won or lost in 15 minutes. The way the tide turns, to use the water metaphor, again is mysterious. At Singapore, in 1942, the Japanese were at the absolute limit of their supply lines and were really struggling when the British Imperial forces gave in. Many parallels have been drawn with the battles for Baghdad and Basra: Berlin and Stalingrad, even Warsaw in 1944 with its doomed rising. But Singapore may prove a truer analogy than any.

Most casualties occur in battles after one side breaks and runs. On Saturday, a US colonel, David Perkins, estimated that about 1,000 Iraqis had been killed in the aggressive incursions into the capital for the cost of one American tank commander. The former figure is speculative, but it is the kind of balance that occurs after an enemy breaks. Many examples are available: Agincourt, Culloden, the 1991 Gulf War.

The desired "end state" in this strategic campaign has been unclear. When you plan a war, you start with the desired political "end state". You then give it to the joint commanders (based in the US and UK), who work it backwards, identifying the "centre of gravity" (Baghdad, obviously) and the "decisive points", which are the stepping stones on the way to that "centre of gravity". The detailed operational planning is done by the Joint Force Commander, in this case General Tommy Franks of US Central Command in Qatar and his British National Component commander, Air Marshal Sir Brian Burridge. In a properly run campaign plan, the people at the top of the food-chain (the politicians) indicate their intent but let the experts get on with planning. In this case, many reports have been heard that one politician in particular, Donald Rumsfeld, has been getting seriously down into the weeds.

You would not expect the US and British governments to advertise the desired political "end state" yet, but suspicions have been aroused that they didn't have one, apart from "get rid of Saddam Hussein and up to a score of other people around him". Baghdad is undoubtedly the seat of the centre of gravity, but its precise location and fate is unclear. An interesting development yesterday was the switch of attention to targets around President Saddam's home territory of Tikrit.

The Americans' strategy in this war, like their helmets, looks very German. During the First World War the nearest the German High Command got to an "end state" was: "we punch a hole: the rest follows." In contrast, the much-maligned Field Marshal Douglas Haig (who had been to Oxford) had a more sophisticated plan: smash a hole in the German fortified front to restore the element of manoeuvre which brings about relatively rapid victories. He won, in the end. The Germans, in spite of their stunning offensive in March 1918, lost.

The military concepts taught at US and British staff colleges have been in clear evidence. The first one is "find, fix, strike – and exploit". The finding was pretty easy: the US had achieved "transparency of the battlespace" with satellites, total air control, and 24-hour vision using image intensification and other night-vision equipment. It is no coincidence that most of the rapid Allied advances in the past couple of weeks have taken place at night, when the US and British can see pretty much as in daylight (apart from having to deal with the green light, as if under a stagnant pond, that attends night vision). The Iraqis, on the other hand, saw nothing.

The fixing operation was probably Basra. The oil fields and terminals had to be secured: Iraq's second city merely needed to be screened, while the main thrust headed for the centre of gravity: Baghdad. The strikes have been concentrated on the Republican Guard. And, for once, the oft-forgotten need to exploit has been in evidence. Saturday and Sunday's "incursions" into Baghdad clearly exploited an enemy which was thrown off-balance. If there's nothing in the way, why stop?

The larger-scale picture of the US advance from Kuwait, for 300 miles to Baghdad, looks terribly like that of the Germans into France and Belgium in 1940. Audacious to the point of rashness. Heading for the Channel, the German advance could have been cut off by the British counter-attack south from Arras. That counter-attack just failed, but it shook the Germans, including Rommel. A combination of aggression, energy and superior use of air power carried the Germans through. It was a close-run thing, and the advance on Baghdad will probably prove to be similar. This time, however, US information dominance was so overwhelming that they could see just about anything coming.

When the "tip" occurs, however, it is psychological – "when your weapons are dulled and your ardour damped, your strength exhausted and your treasure spent" (in Sun Tzu's words). Wars are fought by people, most of whom – and never forget this – do not want to be there. They do not fight for principles or political parties. They fight for their friends, their families, their mates.

As long as the fear of failure, and of the disciplinary machinery around them hold sway, they fight. The Allied thrusts into Baghdad, psychological operations and the realisation that Saddam Hussein is not going to be around much longer are the fulcrum on which the scales tip. When the majority of the other guys decide "this isn't worth it", you've won. Whatever you think of the reasons for going to war, it looks as if the tide has turned. Remember King Canute.

The writer is professor of military science and doctrine at Cranfield University