We are only now beginning to understand how war affects soldiers. Spielberg's film covers the Normandy landings where much modern combat research began. Studies of US soldiers showed that 98 per cent of fighting men cracked after 35 days of active front-line fighting. Only 2 per cent of soldiers actually enjoyed battle and did not crack. Military doctors considered them aggressive psychopaths.
In the First World War, the diagnosis of "shell shock" proved that soldiers who suffered breakdowns were not malingerers. Lord Moran, later Churchill's doctor, served as a medical officer. In his book Anatomy of Courage, he describes a Sergeant Turner who was unable to speak and trembled, although "trying to keep his limbs still... It was plain to me the game was up and he was done. When this sort of thing happens to a good fellow it is final". Moran knew Turner to be a man of exemplary courage.
A remarkable discovery by US researchers in the Second World War was that many "stable" men could not kill - soldiers who went into battle yet never fired their weapons. Lieutenant Robert G Cole was in charge of the 502nd Parachute Infantry, considered one of the best units in the US army. Yet when they were being attacked along the Carenton Causeway on 10 June 1944, he found it impossible to make his men fire: "Not one man in 25 voluntarily fired. There was no cover; their only protection was to continue a fire which would make the enemy keep his head down. They all knew this but could not force themselves to act upon it."
A Korean War study of the US Air Force's famed 51st Fighter Wing, known as the MiG-killers, revealed that half their pilots had never fired their guns - and of the half that fired, only 10 per cent had hit anything.
Fear in fiction is usually a few beads of sweat. Fear in real battle is often debilitating. In a study of US combat soldiers in 1944, more than half admitted they became sick to their stomachs, felt faint and lost control of their bowels in battle.
The Anglo-Saxon Chronicle reports on a battle in 1003 between English and Danish armies. Aelfric, the English commander, became violently ill and began to vomit. He couldn't continue, and the Danes routed their adversaries.
Soldiers do run away; it's a fact of war, and a good commander knows that a frightened unit can undermine an army. In 480 BC, Leonidas was in command of a force of Spartans holding the pass of Thermopylae. He realised that some troops, shaken in earlier action, were likely to break. Herodotus wrote that Leonidas "dismissed them when he realised they had no heart for the fight" and that, when the battle was about to start, two soldiers claimed that they were suffering from an "acute inflammation of the eyes" and retreated to the rear. One returned to the front line, but the second, Aristodemus, "finding his heart failed him", stayed in safety. After the battle, he "found himself in such disgrace that he hanged himself".
Soldiers can develop combat reactions within seconds. At the battle of Eylau, in 1807, a Russian cannonball ripped past a French officer, knocking off his hat. The shock paralysed the officer in the middle of the fight. Eventually the battle moved elsewhere, and the officer's horse calmly walked away, taking its paralysed passenger to safety. He came out of shock later.
Battle exhaustion is the first level of psychological stress. During the Normandy campaign the British army had battle exhaustion units just behind the lines. For every 1,000 men with physical wounds, "combat stress" affected a further 200 - though 60-65 per cent of soldiers could be returned to their units after 10 days, according to Dr Desmond Murphy, a veteran and leading military psychiatrist.
An analysis of psychiatric casualties of D-Day that appeared in The Lancet of August 1944 did not exactly show an enlightened attitude. "Of 100 psychiatric casualties received from the beachhead during the first 10 days, six were severe chronic neurotics, five could be regarded as cases of pure physical exhaustion, two were schizophrenics and the rest men with a history of childhood neurosis who had adjusted superficially in maturity."
There is now a mounting body of evidence that suggests that most front- line veterans will suffer psychological scarring. We are only now beginning to understand the effects of battle. Post-traumatic stress disorder (PTSD) has been defined only in the last 20 years.
Jack Daniel, a gunner in the Desert Rats (who fought Rommel in North Africa), estimated that "about 50 per cent of my mates hit the bottle upon returning. I had nightmares after the war. It wasn't done to consult a `trick cyclist'. If you went to the doctor, it was about a related symptom, like not sleeping."
One research project on Dutch resistance veterans showed that PTSD symptoms grew worse after retirement. Elite units are not immune. Studies of paratroop regiments that fought in the Falklands showed that, five years on, 22 per cent of men still serving had full-blown PTSD symptoms.
The technology of mass slaughter has raised the stakes. It was no coincidence that, with the advent of the machine gun and the sustained artillery barrage, shell shock was finally recognised. Richard Gabriel, in his book No More Heroes, says: "To understand the development of war is to recognise a single indisputable fact: not only is war becoming more lethal in terms of its ability to kill and maim, but it is far more destructive in its ability to drive soldiers mad."
What keeps soldiers returning to the front line is camaraderie. As Jack Daniel recalled: "I remember being sent away from the front on a task. I can't tell you the pleasure of sleeping in a bed... But I felt I had to get back as quickly as possible to rejoin my mates. It was this team spirit that kept you fighting when you wanted to run away - you just couldn't leave your mates."