Here we have a story of desertion that is marked heavily by fighting.

This is more than a flippant observation because combat forms the very core of Charles Glass's compelling reportage. The author seeks to paint the scene before examining those who exit it.

This is a book that has to be painted in lurid colours, particularly in terms of the awful violence. However, it is finely, almost delicately, drawn when it comes to personalities and to the internal forces that conspire to make men run.

Glass recounts the tale of three soldiers in his successful attempt to open up what was once a subject shrouded in shame.

The heroes – and this is a considered usage – are Private Steve Weiss, a Brooklyn soldier who left the front line and fought for the French resistance; John Bain, who fought with the Gordon Highlanders in Africa and Normandy before buckling; and Alfred Whitehead, a private from the American South, who deserted and became involved in gangsterism in wartime Paris.

They are different personalities, with different lives before the war. Weiss was the son of a soldier, eager to join up. Bain had both the sensibilities of the poet and the physical presence of a professional boxer. Whitehead, who came from a life of poverty, found an existence of almost luxury in the army with a clean bed and regular food.

They were broken in similar ways, though. More than 150,000 Allied troops deserted during the war and Glass gently but inexorably pushes the reader to consider not why the men ran but why they stayed in position.

Hungry, exhausted, with their senses battered by incessant shelling and their nerves destroyed through the witness of extraordinary trauma, hundreds of thousands of men stayed in their foxholes, ran towards machine guns or jumped into planes with an increasingly probable death only seconds away.

They ran because they had had enough. It is baffling why this limit was not reached until months or even years had passed.

At the core of their desertion was disillusion. Bain, who changed his name to Vernon Scannell and became a fine poet, suffered a crisis that can only be described as existential. War was a senseless outrage to him, an intellectual and spiritual problem he could not solve. His only possible response was to walk away. He ended up in a military prison.

Weiss, his preconceptions blasted away by the reality of war, found his superiors arrogant, insensitive and incompetent. He decided he could not serve them and left to fight with the French resistance.

Those who lazily describe deserters as cowards must note that Weiss was awarded the Bronze Star, three US battle stars, the Second World War Victory Medal and the Southern France D-Day Landing citation by the US Army. France honoured him by naming him an officier in the Legion d'Honneur and gave him two Croix de Guerre.

Bain, too, fought bravely before deserting and Whitehead was wilfully belligerent, dangerous even in his life as a black market gangster.

They survived to try to make some sort of sense from their experience. The epiphany for Weiss came when, after he was court-martialled and sentenced to hard labour for life, a psychologist told him: "You do not belong here. You should be in hospital."

Bain, in the guise of his alter ego Scannell, made his journey to discovery through poetry.

Whitehead found later life difficult, perhaps impossible. He drank heavily, confided in no-one and a trip back to his hunting ground of Paris ended in violence.

Each chapter is headed by a quote from Psychology For The Fighting Man, a wise manual compiled during the Second World War whose truths were rarely spoken. Thus the soldier was condemned to face a desperate fate with officers unwilling or unable to provide succour in terms of spirit or psychology. Their confusion was physical and psychological.

The exemplary, cool work of Glass shows, however, that no survivor escaped without wounds, physical and psychological. The price of war is extracted daily from those who witnessed what is innocuously dubbed "action" and are condemned never to forget it.

Deserter: The Last Untold Story Of The Second World War

Charles Glass

HarperPress, £25