WITH its deafening explosions, searing fires, dismembered corpses and stench of death, war pushes everyone it touches to the brink. Most recover naturally. Some, though, suffer psychological injuries that do not heal. The names of these injuries have changed. Once they were known as shell-shock; then as battle fatigue; then as combat stress reaction. Now, the preferred term is post-traumatic stress disorder. But whatever they are called, they are worryingly common. About 17% of American troops returning from Iraq and 11% of those coming back from Afghanistan suffer from them.

The most common treatment is known as exposure-based therapy. This asks those afflicted to imagine the sights and sounds that traumatised them, and helps them confront those memories. It often works. But not always. And it would undoubtedly be better if troops did not develop the condition in the first place.

With this in mind, a team of engineers, computer scientists and psychologists led by Skip Rizzo at the University of Southern California propose a form of psychological vaccination. By presenting soldiers with the horrors of war before they set off to fight, Dr Rizzo hopes to inure squaddies to anything they might witness on the field of battle.

The idea of doing this developed from Dr Rizzo’s work using virtual reality to help with exposure-based therapy. Such VR enables the sights, sounds, vibrations and even smells of the battlefield to be recreated in the safety of a clinic, and trials suggest it can help those who do not respond to standard exposure-based therapy. The success of such simulation led Dr Rizzo to wonder if a similar regime, experienced before actual battle, might prepare troops mentally in the way that traditional training prepares them physically. His preliminary results suggest it might.

The virtual training course Dr Rizzo and his team have developed leads soldiers through a tour of duty that includes seeing and handling human remains, experiencing the death of virtual comrades to whom they have become emotionally close, and watching helplessly as a child dies. Unlike a real battlefield, though, a virtual one can be frozen, and events occurring there discussed at leisure. When that happens, a virtual mentor emerges from the midst of the chaos to guide the user through stress-reduction tactics he can deploy. These may be as simple as breathing deeply, or as sophisticated as objectively recognising normal reactions to stress, and thus realising that your own reactions are normal too.

To monitor what is going on Dr Rizzo’s colleague Galen Buckwalter tracks physiological markers of stress, such as the reactions of participants’ pupils to what their eyes are seeing, their electrocardiograms and their galvanic skin responses. Dr Buckwalter hopes that as his charges become more psychologically prepared for battle, these markers will change in recognisable ways. This will allow officers to identify who is, and is not, ready for combat.

That would be an obvious boon. But it could also create problems, for it is a long-standing belief of most armed forces that, with proper training, anyone can become a warrior. Dr Buckwalter’s work would undermine this philosophy if it showed that no amount of training was ever going to change some people’s markers.

If that were the case, should such soldiers then be excused active duty? As things stand, those with physical limitations who apply to serve in America are still recruited, but are given only work that they are physically capable of doing. Should applicants with psychological limitations be treated similarly?

Perhaps they should. For if it does prove possible to sort those who are likely to become inured to war’s horrors from those who will not, one result would be a more effective fighting force. A second would be the consequential elimination of one of those horrors—the psychological wounds that are often regarded by soldiers who suffer them as worse than physical ones.