The American Marines who allegedly murdered 24 Iraqi civilians in Haditha, in what a US official described as "a total breakdown in morality and leadership", have disgraced their uniform, their flag and their country. They have polluted the reputation of the hundreds of thousands of allied troops who conducted themselves honourably while on duty in Iraq. They have defamed the memory of the Allied soldiers who have fallen in combat.
Worst of all, by making it much harder for peace and decency to prevail, they have increased the risk that those who sacrificed their lives may have done so in vain. If any officers or senior NCOs were involved in this atrocity, they should pay for their crimes with their lives.
Especially as they are Marines. The US Marines are an elite force. Indeed, they think that they are the elite force, which can irritate other soldiers. But they are good (almost as good as the average Scottish soldier; no one could pay a higher compliment than that). The Marines pride themselves on their discipline, resilience and courage. Their battle honours prove that this is no empty boast. They have now had a battle dishonour. Throughout the corps, in the ranks of those who served in the corps, in the families who had a son, husband, father in the corps whose grave they now visit - there will be shame, grief and anger. Without in any way excusing what happened, it is possible to offer explanations. This may also be a useful exercise, if it points the way to corrective measures.
Soldiers are trained for high-intensity warfare. On the battlefield, the rules of engagement are simple, and tersely put by a Scottish colonel in one of John Buchan's books. "Ye see those lads on yon hill? If ye dinna kill them, they'll kill you." Throughout the history of warfare and whatever the rules, soldiers who surrender after giving their enemies a desperately hard battle did not find it easy to be taken prisoner. The Geneva Convention is often obscured in the red haze of a fire-fight's immediate aftermath.
Equally, civilians who launch sneak attacks on soldiers are not entitled to the same latitude as legitimate combatants. It is permissible to have francs-tireurs shot out of hand.
The problem is that those rules and traditions are of little use in dealing with guerrillas who can rely on support from sections of the local population. Robert Maxwell and Alan Clark argued that the IRA should be treated as francs-tireurs. They probably did not expect to be taken seriously, and they were not. There is no escape route to sanguinary simplicity. In dealing with guerrillas, armies are condemned to subtlety and stress.
Even if more dangerous, the battlefield can be more manageable than a theatre of guerrilla conflict. It is easier to deal with an enemy when you can establish a location and then demonstrate your firepower than if he is invisible, striking by roadside bombs, and never allowing you the satisfaction of returning fire. The resulting strain helps us to understand why those Marines went berserk.
But not to condone it. Many senior officers will argue that there is no such thing as a bad soldier: only a badly trained or badly led soldier. The Marine Corps now has to re-establish its reputation. It can only do that by scrutinising its training methods and the quality of its NCOs and officers.
In that regard, the Marines share some problems with the rest of the US military. It is easy to make jokes about Americans in uniform. Before the war, an American flagship once sailed into Hong Kong harbour. The Admiral sent a signal to his British counterpart: "Good morning. How is the second biggest navy in the world?" "We are fine," came the reply: "How is the second best?"
Soldiers of other nationalities have often made such patronising comments, partly as a defence mechanism in the face of overwhelming American superiority in technology and firepower. But we should always remember that without those patronisable Yanks, there would be no free world.
Yet in two respects the Yanks could learn from the British army. The first is initiative. We expect a lot of it from junior officers and indeed NCOs. They are given responsibility and are required to exercise it. The American system is much more rigid and hierarchical. Paradoxically, this may make it harder to control the men. A system based on initiative is more flexible, while soldiers accustomed to take responsibility are more likely to act responsibly.
The second is training. Partly because of 30-odd years in Northern Ireland, the British army is used to operating in sensitive political-military contexts, in which the battle for hearts and minds is at least as important as the battle to eliminate terrorists. Some of our soldiers who have served beside Americans in Iraq and Afghanistan have been surprised at their reluctance to get out of their armoured vehicles and their body armour, they have sometimes been alarmed at the brusque way in which the Yanks treat the locals.
There is a ghastly piece of jargon which is indispensable for studying high-intensity warfare: species pseudo-differentiation. If you regard the enemy across the battlefield as a sub-species, it is easier to kill him. On the battlefield, that may have its uses. In Iraq, it is disastrous.
Just because one group of American soldiers betrayed their country, it would be foolish to conclude that the entire military system is flawed. It would be equally foolish to shirk from hard lessons.