When I paid my first visit to the front lines of the conflict in Afghanistan in 2009, I was confronted with an eternal truth about warfare: it's a young man's business. When I looked around the interior of the Chinook helicopter which was taking me into the heart of Taliban territory, at the fresh faces of the infantrymen on their way into action, it looked like a sixth-form geography field trip. With guns.

I was to find the conduct of this collection of teenagers and twenty-somethings enormously impressive over the next few days. When I was their age I was a university student, and my chief concerns were avoiding lectures and consuming vast quantities of beer. These young people were carrying almost their own bodyweight in kit, in temperatures of up to fifty degrees centigrade, through a territory filled with invisible threats.

They had to be extremely disciplined, and permanently aware of the possibility of ambush, or of stepping on an IED. They had to make very grown-up decisions about when to fight and when to hold.

When they were shot at, they couldn't just follow their instincts and shoot back. First they had to judge whether or not any local civilians might be hurt if they brought their firepower to bear. Helmand continues to be an extremely challenging environment, which requires soldiers to be, above all, psychologically tough.

So it was awful to learn that over the Christmas and new year period, and within a couple of weeks of each other, three of the young soldiers involved in that operation had chosen to take their own lives.

One had been constantly reliving the traumas of Helmand - to the extent that he was convinced that the roast lamb lovingly prepared by his mother for Sunday lunch was the burning flesh of a dead comrade. One found the uncertainties of civvy street, after the routine of army life, so difficult that he lost himself in alcohol abuse. I was told that another found it impossible to cope with a permanent sense of guilt about the things he'd done as a soldier.

Their families always proudly display a photograph of their boy's finest moment - when he passed infantry training and first wore the uniform of his chosen regiment. To think that such sunny optimism could be replaced by a dark absence of hope is profoundly, unspeakably, sad.

Helmand Province, Afghanistan. Credit: Reuters

Over the last few weeks I've been looking at what help there was available for these young veterans. It's clear to me that the armed forces are working hard to maintain the mental health of their service personnel.

During active operations, they try to identify individuals who have been involved in traumatic incidents and who are likely to be at risk as a result. There have been a number of campaigns to encourage soldiers to come forward, and not be put off by the stigma which surrounds mental health issues across society. Once a soldier has been identified as having a problem, the Ministry of Defence says they are given access to the highest quality mental health care.

Our research has found that such care can be patchy, and can vary greatly depending on where in the UK the sufferer happens to be living. Then there is the question of young people who have left the armed forces - known in the military as 'Early Service Leavers'. It is all too easy to lose track of these people. If they are in danger of descending into despair, it cannot be just the MoD's responsibility to make sure they are helped out. Local GPs, social services and charitable organisations all have to be involved in keeping an eye on these guys.

It's the military covenant we are talking about here. In terms of the relationship between the government, and the young people who risk life, limb and mental health in its name, it's almost sacred stuff. There have been huge advances over the last ten years in the care of soldiers who come home from Afghanistan with physical injuries - society owes just as big a debt to those who return with a damaged mind.