The German machine gunner blasted away at the Australians. The advancing infantry fell down before the murderous fire until finally the survivors hurled themselves against the sandbags. The machine gunner finally raised his hands in surrender: "Kamerad!"

The German machine gunner blasted away at the Australians. The advancing infantry fell down before the murderous fire until finally the survivors hurled themselves against the sandbags. The machine gunner finally raised his hands in surrender: "Kamerad!"

"Too late, chum!" replied the enraged Australian infantryman as he plunged his bayonet into the German's stomach.

The above story - apocryphal or not, it has the ring of truth - has been taught to generations of graduates of the British Army Staff College as an object lesson in three things: first, how difficult it can be to surrender; second, the realities of men in battle; and last, the niceties of the law of armed conflict.

This issue has been brought sharply into focus by the extraordinary camera footage of what appears to be a US Marine shooting a wounded Iraqi. Civilian reaction has been mixed from "disgraceful" to "what do we expect in a war?". Military reaction has generally been one of defensive embarrassment.

The propaganda victory for the enemies of the coalition is theoretically immense.

And yet we have seen nothing new. For centuries men have been casually slaughtering each other on a thousand battlefields. What is different here is that for the first time since Vietnam we can see the reality of war via the "embedded" front-line cameras of both commercial news teams and military combat cameramen. The military realises that the presentation of combat is far too important to be left to the media, even though it has no control over what goes on in the editing suite.

The irony is that, by revealing the awfulness of the legalised killing that we call combat, the networks have done us a favour. They have forced us to confront the key problem of battle: at what point does the "fighting" end? It is a very grey area. While all training manuals are agreed that an attack takes in several phases, "fighting through the objective" is by far the least well-defined, even by the US Infantry's Field Manual 7-8. For this is the endgame of battle, the brutal teamwork by small groups of soldiers trying to kill their enemies at close quarters without getting killed themselves, a bloody mayhem of screams, smoke, explosions, terrifying noise and, above all, bowel-watering fear. A moment's indecision can spell mutilation or death.

And when the objective has been taken, it must be "consolidated". Who knows when a wounded man may rise up and fire into the backs of the advancing troops? Who knows when a wounded man may roll over to reveal a lethal grenade and kill his rescuers? FM 7-8 is clear: "Treatment of casualties normally begins at the conclusion of the engagement..." But who decides when the fighting is "concluded"?

We have already entered the lawyers' pedantic clutches in the issuing of little yellow cards to soldiers setting out their "rules of engagement" on what a soldier may or may not legally do. However, such bureaucratic niceties have little place in the mind of a frightened young man clearing a house full of suicidal Islamic fighters, dangerous as snakes in a pit. Battle is legalised killing. In such circumstances the rule is "Shoot first and ask questions later" - and always has been.

Embedded cameras have allowed us a peek into this brutal world. Our liberal civilian instinct is to reach for the courts. Ironically, that is the correct decision in this case: not to protect the fighters of Fallujah, but to protect the hapless soldiers fighting in our name in an unpopular war.

For the key question in that soldier's mind must be clarified once and for all in law. Was he an enraged Marine out of control and taking revenge for the slaughter of his comrades by "ragheads"? Or was he in genuine fear of a suicidal grenadier and protecting himself and his comrades?

Only a court martial can rule in a test case. The civilian legal apparatus should then confirm that ruling under the Hague Conventions and national laws. Then, finally, our soldiers will be sure that they are protected by the law and "obeying the rules" in the butchery and mayhem of "clearing the objective". But of one thing today's soldiers can be certain: there will never be human rights lawyers or health and safety executives in the front line. It's far too dangerous.

John Hughes-Wilson is an author and broadcaster. He served as an infantry officer in the Sherwood Foresters before transferring to the Intelligence Corps. His latest book is 'Puppet Masters: the Secret History of Intelligence'