Introduction The war had been over for thirteen years when at breakfast tables around the country a small group of former comrades opened the morning post to find a letter from their old chief. He had a favour to ask. The Admiralty was preparing a report on a controversial operation in which they had all been intimately involved when they worked together at Combined Operations Headquarters. He enclosed a draft of the text concerning their part in the drama. ''I cannot help feeling that this does not tell the whole story,'' he wrote. He invited suggestions as to how it might be amended ''to put the responsibility . fairly and squarely where it belongs'', which, he made clear, was not with him or them. He signed off, ''Yours ever, Dickie''.

The writer was Louis Mountbatten and the action in question was Operation Jubilee, the August 1942 raid on Dieppe. The appeal got a generous reception. The old comrades rallied round, and under the supervision of Lord Louis produced a version to his liking. When the Admiralty published its report, the account followed closely the Mountbatten team''s narrative of events. These exchanges took place in the summer and autumn of 1958 when Mountbatten was First Sea Lord and in charge of the Royal Navy. He was officially a great man, created Earl Mountbatten of Burma for his services to victory in South East Asia, and the uniforms he loved to wear were almost ludicrously encrusted with decorations and orders. He was about to take over the newly created post of Chief of the Defence Staff, making him the professional head of the armed forces at a time of great upheaval, and it might be thought that he had little time to waste on the historiography of what in the context of a world war has been seen as only a minor episode. This was just one example of Mountbatten''s attempts to hijack the Jubilee narrative.

From the day the operation ended until the close of his life, he hammered away at the construction of a legend that presented Dieppe as a calculated sacrifice in which the losses (which he routinely downplayed) taught hard lessons which were triumphantly justified on D-Day. He made the case so often that it sometimes seemed that the main person he was trying to convince was himself. Bernard Montgomery, another key player, also kept his sharp blue eyes focussed on accounts of his role in the story, intervening brazenly when he thought his reputation was threatened. In books and interviews he often expressed astonishment at the decision to do without an aerial bombardment before the raid, a move which was later held to have helped to doom the enterprise. Yet it was he who chaired the meeting at which the fateful choice was made. Mountbatten and Montgomery believed themselves to be men of destiny and had been building their own myths virtually since the day they first put on uniform. Dieppe marred the heroic canvas depicting their wartime achievements, and it was perhaps to be expected that they would take every opportunity to touch up the picture. Yet their interest concealed deeper concerns.

Dieppe was more than just another painful station on the calvary of failure that preceded the Allies'' change of fortunes. It was a defeat but also a great human tragedy that to those most closely involved in it seemed to require not just vindication but absolution. In the summer of 1942 the last thing the Allies needed was another disaster. In the Dieppe raid, that is what they got. The news of the attack produced first surprise, then dismay and finally bewilderment. ''What I don''t understand is why Dieppe?'' puzzled Major General Percy Hobart in a letter to the military historian and expert Basil Liddell Hart. ''A raid is either "to obtain information" and destroy some worthwhile objective or it is to train one''s own troops. In the latter case one would not select a strongly defended sector.

In the former, what was the objective? Evidently we did not reach it. It all sounds pretty Passchendaele to me.'' The reference was to the notorious 1917 battle on the Western Front when thousands of Allied troops, many of them Canadians, floundered to their deaths in an ocean of mud. Some of the Jubilee survivors reached for a different episode from British military history to describe what they had endured. It was, they said, ''just like the Charge of the Light Brigade''. The difference was that in this case 6,000 - mostly Canadians - had been sent into the jaws of death, rather than the 670 or so who had charged the Russian guns at Balaclava in 1854. Soon no comparisons were necessary and Dieppe stood in its own right as a metaphor for bloody futility. Hobart''s questions have never been properly answered.

In the thousands of official documents generated by the preparations for Jubilee the military objectives of the raid are laid out clearly enough. There is very little that reveals the higher purpose. Almost all the explanations and justifications supplied by those who planned and mounted it came afterwards. The hole in the story where a clearly stated intention should be has subsequently been filled by several theories. Some have sought to uncover a secret motivation that clears up the mystery, or to explain it through the malign behaviour of a principal actor or actors. This book, while making its own contribution to what we know about why things happened as they did, offers a broader explanation. Dieppe provides in miniature a display of the way that human qualities, failings and passions that are held in check by the constraints of peacetime tend to run free in times of war. Those at the top were driven by a complicated and sometimes contradictory combination of motives of the sort that only the strange moral ambience of wartime can produce: patriotism and duty, yes, but also reckless ambition.

Jubilee might have been small compared with what was to come but it was big at this stage in the conflict, the largest amphibious assault that Britain had attempted since being driven from the continent. Much more than straightforward military considerations were at stake. Britain was at a crucial new phase of its war, seeking to both impress and restrain its new American allies while managing a tortuous partnership with the Soviet Union. It was having to learn the deference due to powers on whose resources victory ultimately depended. Jubilee was intimately linked to those realities. Its outcome showed how the pressures of high politics could override military common sense to generate action at almost any price. In Jubilee the line connecting Churchill''s need to keep Stalin and Roosevelt happy and a shambles of smoking tanks and crumpled bodies on a French beach is stark and clear. The losses at Dieppe were, proportionately, among the worst suffered in a single operation in the Allied war in Western Europe.

Of roughly 6,000 ground troops who took part, 3,625 were killed, wounded or captured. This would have been considered nothing on the Eastern Front. During the months of July, August and September 1942 the Red Army lost through death, capture, injury and sickness an average of 27,256 every day . That did not make the Dieppe losses less shocking. The scale of the operation meant it carries an intimacy and imaginability that the Russian battles can''t convey. They are just too enormous, too distant and too horrendous to comprehend. But standing on a summer morning by the sea wall beneath the gardens that run down to the narrow little beach at Puys where the Royal Regiment of Canada came ashore, it is very easy to summon up the horror of that day; the demonic rip of bullets pouring from the defenders'' MG34 machine guns at a rate of fifteen rounds a second, the whistle and thud of mortars and the humped khaki shapes, swaying face down in waves clouded with blood. That the victims were mostly Canadians is one of the elements that gives the story its heavy tinge of tragedy.

The deference which the British were forced to show to the Russians and Americans did not apply to Dominion family members. Despite the blood debt owed by Britain to Canada for its support in the previous war, the old habits of condescension and the assumption of unquestioning obedience died hard. Just as at Passchendaele, the Canadians would pay the price for British mistakes. Their leaders too had a share in the blame. If, as some said, the troops were martyrs, then those who commanded them had done much to determine their fate. In this book, as with all my books, my primary interest is in the participants and their experience, be they British, Canadian, American, French or German. Each project is an attempt at resurrection. The challenge is to bring back to life the faces smiling out from the monochrome snaps and show them as they were.

We can''t know the story without knowing the actors; the stuff they were made of and the forces that drove them on. I come to the task with some knowledge of war from a former life as a foreign correspondent reporting on conflicts around the globe. The first war I covered was the 1982 recapture by British troops of the Falkland Islands. I went ashore with 42 Royal Marine Commando huddled in a Second World War-style landing craft. Mercifully there were no Argentinian machine-gunners waiting for us as the bow door clattered down and we stepped thigh-deep into the sea. But I can still recall the slap of spray on my face and the metallic tang of fear on my tongue as we ran in, a tiny taste of what the attackers must.