I can spot him - though sometimes it is her - from about 50 metres away, usually in railway stations. He stands out from the crowd because I know what to look for. He has arrived in good time and is waiting for the platform to be called. The kitbag is the first giveaway, either the Nato standard black holdall or a camouflage daypack. If the pack fabric is the latest coloured pattern, then he has been over there within the past year or so. He is possibly back here on R&R if he looks suntanned, gaunt and perhaps a little hungover.

Haircut is next. That tells you if he is serving, or out of the forces but still clinging to the kit. Touch of facial stubble and clothes that seem tight: he's out and is missing the daily physical exercise and constant discipline. Hair length is a good indicator of rank. Shaved close, and he is probably a non-commissioned officer. He values uniformity and hygiene above the elan of an officer's swept-back side parting.

The armed forces might be small and getting smaller - the Ministry of Defence announced 17,000 redundancies from the current troop strength of 186,360 in October last year - and those who do the fighting are an even tinier proportion of our society, but they are all around us. The conflict in Afghanistan has been going on for so long that there is a danger that we begin to take it as routine, and possibly take what they do for granted.

When I leave home on a given day, the mental checklist is simple: wallet, mobile phone, keys. Leaving a checkpoint for a foot patrol in Helmand Province, soldiers are thinking: rifle, radio, morphine and a litany of other items that will keep them going in a fight.

The level of violence in parts of Helmand last summer, when I spent about two months there researching a book, was astonishing. You get used to gunfire waking you up, accompanying the morning shave and pinging off the sentry towers for hours on end. Foot patrol entails a sacramental adherence to the counter-IED drills, and the hope not to get shot at too much on the ground. Back at base, the insurgents sometimes like to throw in a night shoot for good measure. Late in their tour, many soldiers will say that they are quite happy if they never have to fire their rifle again.

Soldiers now compare previous tours, which were "kinetic" - or violent, in layman's terms, with current ones, when a combined force of British and Afghan troops and policemen might not call in artillery or a bombing run for half a year (as the Scots Guards achieved last summer - one round of smoke fired for effect in six months). The emphasis today, Nato says, is on talking rather than shooting.

There is an explicable human reason for wanting to think that the Afghan war is at last going well: past sacrifices of life, and the hope that the casualties will stop coming and the tours stop rolling round every 24 months. Soldiers also quite like winning. This optimism can be exhausting. In his memoirs of his time as Britain's ambassador to Afghanistan (2007-2009) and then the Foreign Secretary's Special Representative for Afghanistan and Pakistan, Sir Sherard Cowper-Coles writes of officials who regularly announced that "progress has been made, but challenges remain". They certainly do. One thing has changed recently: previous errors are now discussed openly.

After the British military lull in Afghanistan from 2002 to 2006, the troops who broke into the south-western region of Helmand that summer were too few, too late. According to Michael Clarke, director general of the Royal United Services Institute for Defence and Security Studies (RUSI) in London, there was "no strategically literate group in British government who could intervene in the momentum of the process. At no point did anybody say: 'Should we do this or not?'"

Before the British arrived in 2006, Helmand was a province about which our armed forces knew little. "We used to say there would be a reaction to our size 12 boots going in to Helmand," Ed Butler, commander of the first UK brigade to deploy there, told the Commons defence select committee in March, "whether from the Taliban, from the opiate dealers or from the warlords, because we were threatening their very existence." The plan was that the initial British deployment of 3,150 troops - which translated into a mere 650 infantrymen - would remain in Helmand for a three-year stabilisation mission. This modest force was to be based between the province's two principal towns and the newly built Camp Bastion.

However, almost immediately the force was thinned across a network of little bases spread across northern Helmand. The decision was never put to cabinet - because it was ostensibly not a strategic one - but rapidly triggered a doubling of the British presence.

RUSI's Michael Clarke tells me that when the implications of the move became clear, one minister asked a colleague: "How did we get ourselves into this position? How did we go charging up the valley [to Sangin in Helmand] without it ever being put to cabinet?"

“There was a conspiracy of optimism that somehow it would be OK," Clarke says, "and because it sounded like a local tactical move - 'We're going up to forward operating bases in the north' - it sounded straightforward. But the strategic impact of that move was huge."

Yet, despite the increase in commitment, the British had no overall strategy. Isolated troops became "fixed" in bases that could not then be abandoned. They fought tenaciously against waves of attackers.

The need to accede to opaque Afghan political imperatives speeded up the move north. In June 2006, the then governor of Helmand, Mohammed Daoud, asked the British to rescue the injured son of the district governor of Sangin. The envisaged snatch mission turned into a four-year-long British presence in Sangin. By the time it was handed over to the US marine corps in September 2010, the district had claimed nearly a third of all British casualties.

While resources continued to pour in, a regrettable pattern was set, whereby different brigades would arrive for their six-month tour, shake things up, devise new priorities and plans, and then leave again. According to Theo Farrell, a professor in the department of war studies at King's College London: "What you had in the British part of the campaign was a succession of, basically, six-month campaigns."

For instance, Operation Herrick 5, in 2006-2007, deployed mobile operations groups (flying columns of vehicles) to attempt to tease the insurgents out of the green zone along Helmand Valley. By Operation Herrick 8, in 2008, the mantra was to "go deep rather than go broad" and to focus on the local people rather than the enemy. This switching of strategies by consecutive brigade chiefs hampered progress; by October 2008, the outgoing British commander, Brigadier Mark Carleton-Smith, was willing to concede to the press: "We're not going to win this war. It's about reducing it to a manageable level of insurgency that's not a strategic threat and can be managed by the Afghan army."

In time, the momentum of the campaign switched back to development in central Helmand. "Six-month syndrome" became less of a factor as brigades realised the utility of building on previous successes. Farrell points to the arrival of General Stanley McChrystal as US commander in Kabul in June 2009 as the point when "you get more coherence being driven down into the campaign itself, which didn't exist previously".

In the summer of 2010, while I was in Helmand, the aim was to connect with the local people in spite of a determined and sophisticated insurgency. Vets dewormed livestock and local contractors upgraded roads to connect people better to markets. "If you look at the trend over time," says Prof Farrell, "the British shift from a focus on combat and very crude means . . . to developing more focus on 'non-kinetic effects' and 'influence operations'. They have become much more sophisticated."

The unofficial motto of the British army is to "improvise, adapt and overcome". It does this, on the whole, very well. Yet if a fourth commandment - "anticipate" - had been thrown in, many of the initial mistakes could have been avoided. Scarcity of resources, at least in the early days of the war, pushed the emphasis very much on to "improvise". James Fergusson's account of the fighting season of 2006, A Million Bullets, records men suffering acute weight loss through lack of food, as well as a shortage of working radios, and soldiers rigging defences from cardboard boxes filled with pebbles.

The government was forced to provide an embarrassment of riches once such stories became public, although the system still fails occasionally - what with the variety of vehicles used, a lack of spare parts is often an irritant. But now, though there are few luxuries in Helmand, the bases are secure and life is manageably austere; a frequent observation by soldiers is that you sleep in, eat from, shower beneath and defecate into a series of bags.

What stood out for me was quite how hard the junior soldiers work. They rarely sleep through the night, as sentry duty is frequent. Early mornings are taken up with foot patrols, resupplies or, occasionally, large operations to clear areas of improvised explosive devices or insurgents - all while carrying roughly 35kg of kit. Midday is indescribably hot. I remember walking past a thermometer that read 39° Celsius and thinking: "Oh good, it's cooling down at last." It is easy to become listless at best, dangerously heat-exhausted at worst. But there is no scope for switching off: there are no weekends, no days off.

As an outsider, I found listening in to the conversation at mealtimes hard at first. Each checkpoint has its own code of in-jokes and nicknames, built around the troops like a second layer of defence against the harshness of daily life. At night, the junior guys will sleep eight to ten to a tent. Sometimes even in sleep there is no true rest. I remember lying awake one night, listening to a guardsman reliving the day as he slept. "Fuck, fuck," he moaned, thinking he was still being shot at in his sentry tower.

War is over

What of the veterans? Tens of thousands of servicemen and women have been in Afghanis­tan. Many have done multiple tours. My time out there was modest - two months - but a year on, I have a depth of feeling about "over there" that leads me to believe that soldiers who have endured long periods of time in Helmand will be changed permanently by their service.

Where the system stands out today is in processing casualties. US and British helicopter crews are seemingly fearless as they swoop
to pick up wounded comrades. The hospital system works. One soldier who had made the journey from firefight to Camp Bastion, and then on to Selly Oak and Headley Court Military hospitals, told me of his amazement at quite how good the process was. It was the only part of the army he had seen in his career that was properly resourced.

Flying in to RAF Brize Norton knowing that Afghanistan is over for you for a while feels good. Oxfordshire compares well to Helmand. The baggage reclaim is odd - 250 near-identical kitbags. Once his bag is found, the soldier is up and out and heads to Oxford station by coach. From there, he takes the train home, becoming isolated as his friends peel off on various branch lines. He stands out from the crowd if you know what to look for.

Max Benitz's "Six Months Without Sundays: the Scots Guards in Afghanistan" (£16.99) will be published by Birlinn on 11 November. To buy it for £13.99 (free post and packaging) call 0845 370 0067 and quote the reference: NS11