In his speech in March, Collins spoke of the distinction between liberation and conquest, the need for magnanimity in victory and, above all, the choice between “righteous” force and unjustified brutality. His oratory demanded gentleness and consideration for those who surrendered, and maximum force against those who did not. Respect the enemy, Collins demanded of his troops, and ensure that “your conduct is of the highest”, but if they resist, “I want you to rock their world”.

Now Collins stands accused of rocking the world of some Iraqis rather too vigorously, after allegedly pistol-whipping a Baath Party member, shooting into the floor of his house, blowing out the tyres of looters and — in my mind the most damaging allegation of all — staging a mock execution.

To most British soldiers, and many of the inhabitants of Rumaila, the desert village where Collins’s alleged victim acted as Saddam’s chief, the British officer’s actions were not only defensible, but laudable and effectual. To his accusers, including the American officer whose complaint led to the investigation, the colonel is a violent bully and, in the light of his speech, a hypocrite.

From earliest times the rules of war have focused on the contradictory demands of utility and humanity, the need to balance what is effective on the battlefield, with what is morally acceptable. “Your deeds will follow you down through history,” Collins said. He could not have anticipated that his own alleged deeds would become part of the history of military ethics in a debate almost as old as war itself.

The Romans believed, from sheer utility, that it was not worth burning two Gallic villages and slaughtering the inhabitants where one would do, while the Greeks took the ethical step of outlawing the use of poison as a weapon of war. St Augustine argued for the protection of non-combatants while the book of Deuteronomy ruled that the enemy must be given a chance to surrender, a principle echoed by the Talmud, which held that a city should be besieged on three sides only, leaving the fourth as an escape route for the inhabitants.

In 1137 Pope Innocent II, in one of the earliest attempts to prevent the proliferation of high-tech weaponry, tried to ban the use of the crossbow — the “dastard’s weapon” — because killing from a safe distance, without declaring intent, undermined the rules of chivalry. Gentlemen (which comes from the French gendarme, “man of arms”) should not go killing Christians indiscriminately and depriving them of the opportunity for last rites; infidels, however, were another matter, and perfectly acceptable crossbow targets.

In modern times successive international laws, from the Declaration of Paris in 1846 to the postwar Geneva Conventions, have sought to codify the rules of conflict, but the chaos of modern war is less neat than legal precept, particularly when ambush is disguised as surrender, and the distinction between combatant and non-combatant is blurred. Collins may well argue that the man he is accused of beating barely fits the definition of a non-combatant since he was a known Saddam sympathiser deliberately lying about his concealed Kalashnikovs at a time when coalition forces were being sniped at.

It has often suited the brass to leave the rules of engagement somewhat nebulous, particularly for special operations. As a young commando officer during the Vietnam War, the former Nebraska Senator, Bob Kerrey, took part in the killing of at least 20 women and children in Vietcong territory, an incident that was only revealed two years ago, effectively destroying his presidential hopes. While expressing deep remorse, Kerrey nonetheless pointed to the wide latitude of his orders, while his understanding of international law at the time was vague at best.

The International Criminal Tribunal for the Former Yugoslavia and the International Criminal Court at the Hague have increased the emphasis on individual personal responsibility for wartime behaviour. But the Pentagon’s formal rules of engagement, the specific instructions on when and at whom soldiers may fire, remain classified secrets. Although there is regular ethical training in the military today, to some extent battlefield behaviour is still a matter of personal choice.

This was the thrust of Colonel Collins’s peroration, which referred to the enemy’s rights of surrender under international law, but described “life taken needlessly” as a sin — “the mark of Cain”. He advised his troops that in the coming conflict they must make their own decisions about the use of force and act according to the dictates of conscience within the demands of war. He believes he has done so himself.

The Army Special Investigations Branch seems likely to rule that, on balance, Collins behaved within the limits of what is acceptable in tense and dangerous circumstances. But the mere fact that his alleged actions seem to lie in a no man’s land, between effective military action and undue violence, suggests that the rules of war, so long in evolution, still elude exact definition.

That seems a fitting coda to the Collins speech: in an age of precision-guided warfare, the soldier’s most accurate guide is an old-fashioned moral compass.

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