The Great War of 1914-18 caused the military to acknowledge the psychological problems caused by war. For the first time, psychiatrists were sent into battle with the troops - a practice maintained today - and 100,000 soldiers later received a pension as recompense for "shell shock".

Many others were not so lucky. Pte Harry Farr was just 25 when he was shot at dawn for refusing to fight. Despite his history of shell shock and the five-month spell he spent in hospital trembling so severely he could not hold a pen, the court martial took just 20 minutes to find him guilty of cowardice.

Pte Farr's family, along with many others, have spent years fighting to clear his name.

Throughout the 20th century, the link between mental illness and combat proved the subject of repeated debate. In 1922, the Shell Shock Commission decreed it was due to poor leadership and training and a question of poor morale. Seventeen years later, at the beginning of the Second World War, the Horder Committee banned all psychiatric labelling, treatment and pensions.

But the number of mental health problems became too obvious to ignore and a more liberal attitude was taken. By 1942, it was the military psychiatric services which started using group therapy for the first time.

The Vietnam war in the 1960s and its images of traumatised veterans, beamed around the world, proved the turning point for care of those who had suffered the horrors of battle.

Groups of anti-war psychiatrists lobbied long and hard to get the problem of post-traumatic stress disorder acknowledged. In 1980 the American Psychiatric Association conceded that PTSD was not just an acute illness but a chronic problem caused by war.

In Britain, events such as the King's Cross fire and the Hillsborough stadium crush brought PTSD to the fore, and by the 1991 Gulf war, the military was sending more psychiatric workers into battle than ever before. Nevertheless, in 2001 veterans from the Gulf war as well as the Falklands brought a class action for PTSD against theMinistry of Defence. The Government won, but limited liability was established.

Today, mental health problems have become an acknowledged side-effect of battle, yet still many feel let down. In particular, the Territorial Army and reservists, who make up one sixth of all forces, have not received care from the military since 1995.

But, as the court found in 2001, the only real way to prevent PTSD is to not send men and women to war.