“The most clichéd but accurate metaphor for the sound of incoming shells in flight is that of an old-fashioned steam express train rushing past a few feet away. Depending on their distance,speed and angle, shells tunnelling through the air make slightly different noises, so a heavy barrage weaves itself into a bewildering cacophony of sounds; but the rushing always ends the same way, with a thunderclap detonation – sscchiiiii…boom! Hollywood’s microphones fail to convey either the sharpness or the loudness of battlefield explosions; and the visual effects normally used to simulate shellfire – with plastic bags of petrol and aluminium silicate – are equally misleading………………….

The most obvious sign of primary injury is rupture of the eardrums, which may occur when air pressure rises to anything between 5 and 15 pounds per square inch; war memoirs offer many instances of men killed by blast who appear peacefully asleep apart from tell-tale bleeding from the ears. The lethal internal damage caused by pressures of 50psi and upwards do not present dramatic outward signs (though shellfire casualties typically suffer multiple injuries).

It is the gas containing organs which sustain immediate and often fatal damage from the pressure wave: the lungs and occasionally the colon suffer catastrophic injury from the instantaneous compression effect of the blast. Large blood-filled cavities are formed in the spongy alveoli of the lung, and fatal air embolisms are released into the arterial system; les often, the bowels may rupture as – in a few cases – may the spleen and liver.

Secondary injuries will be more obviously dramatic. When a shell bursts the steel case breaks up into fragments of all shapes and sizes, from tiny beads to twisted chunks weighing several pounds. These – together with stones, pieces of weapons and equipment, and even large bone fragments from casualties nearer the blast – whirl outwards from the centre at different speeds. sometimes a man is unaware that he has been pierced by a small splinter until somebody else points out the bloodstained hole in his clothing. Larger fragments, cartwheeling unevenly through the air edged with jagged blades and hooks, can dismember and disembowel.

In many cases the evidence confronting an eyewitness is all too vivid. In others the immediate reaction is one of simple puzzlement: blast and steel can play such extreme games with the human form that the observer does not understand what he is looking at. When some random physical reference point suddenly jerks the whole image into a comprehensible pattern, the shock of recognition can be appalling. The results of massive destruction – the ruined hulk of a torso, the crimson rack of ribs, the glistening entrails, limbs ripped away and scattered, a severed head – have a charnelhouse squalor that denies all human dignity.

On chilly evenings at Dien Bien Phu the warm, gaping body cavities steamed visibly, and the opened-up bowels gave off a stink of faeces.