Joan Smith: Now we see what war does to those who wage it

Some combatants find war exciting. Adrenaline rushes become addictive

For the crew of an Apache helicopter gunship hovering over Baghdad in 2007, the whole thing sounds like a game. "Nice... good shooting," exclaims a voice from the cockpit as a group of men in civilian clothes lies on the ground in a cloud of dust. "Yeah, look at those dead bastards," calls out another. The co-pilot claims he can see rocket-propelled grenade launchers and AK47s near the dead and wounded. The truth is the gunner has just opened fire on two Reuters journalists, Saeed Chmagh and Namir Noor-Eldeen.

One of them is still alive and tries to crawl to safety, prompting the co-pilot to urge him to reach for a weapon: "Come on, buddy. All you gotta do is pick up a weapon." But the journalist is unarmed and dies on the street. In all, the footage from the cockpit camera lasts 17 minutes and also shows the Apache crew opening fire on civilians who arrive in a van to help the wounded, seriously injuring two children inside the vehicle.

The cockpit video has just been released by the campaigning organisation, which says it has also obtained a secret US military video showing civilian deaths in Afghanistan. Although the Apache crew has been exonerated, it is hard to believe they were following rules of engagement when they resorted to immediate and lethal force. Nor is it hard to see why so many ordinary Iraqis hate the US military as much as they loathe insurgents who kill civilians with car bombs.

But the callous exchanges inside the cockpit point to a larger problem for the US military, confirming suspicions that the wars in Iraq and Afghanistan are inflicting huge psychological damage on combatants. The Apache had been called in to support ground troops in Sadr City but was not directly at risk when the gunner asked permission to open fire. Even when someone on board realised that children had been wounded, the response was inhuman: "Well", says a voice, "it's their fault for bringing kids into a battle." Men who react like this may not have physical wounds but they suffer from terrible emotional damage, and the US military fails everyone – its own personnel and the victims of their indiscriminate violence – when it refuses to recognise what is going on.

Some combatants find war exciting. The adrenaline rush becomes addictive, which is what happens to the bomb disposal expert at the centre of Kathryn Bigelow's brilliant, harrowing film The Hurt Locker. The movie is clear-sighted about this process, unlike the Pentagon, which is struggling to keep a lid on things. There have been shootings, suicides; even incidents like that at Fort Hood last November which resulted in an army psychiatrist – Major Nidal Malik Hasan, who had treated returning soldiers with dreadful injuries – facing 13 charges of murder and 32 counts of attempted murder.

My generation grew up in the shadow of the Second World War, living with parents who had seen terrible things as young adults; I was grown up myself by the time I realised that my father suffered from undiagnosed post-traumatic stress disorder (PTSD) as a result of his experience on Atlantic convoys. Since 1945, the nature of warfare has changed radically; in recent years, British and US soldiers have been deployed for protracted periods in parts of the world where it's not always easy to tell civilians from insurgents. The scope for psychological damage is immense, with organisations supporting British veterans highlighting problems including alcohol abuse, homelessness and divorce.

In the US, there are nearly two million veterans of the Iraq and Afghanistan conflicts. An independent report published last week confirms they have high levels of mental health problems. These veterans differ markedly from survivors of earlier wars: they're older, more likely to have wives and children, and some of them have returned with devastating physical injuries. The report cites at least 40,000 cases of PTSD, along with depression, suicide, substance abuse, domestic violence, marital problems and mistreatment of children. "The mental health providers in many places are really overwhelmed with huge case loads," said Dr Albert Wu, a member of the committee which compiled the report for the Institute of Medicine. He added that some social workers are struggling to cope with case loads of up to 800 veterans.

Instead of rushing to defend military personnel accused of killing unarmed civilians, the Pentagon needs to review training and command structures which fail to identify combatants with serious psychological problems. In any conflict, soldiers have to be able to overcome the taboo against killing other humans. But this cockpit video is disturbing evidence that the wars in Iraq and Afghanistan are normalising violence.