It was another hot, sunny day and Ben Barry was looking to kill time.

Wearing his T-shirt, shorts and trainers, he was crossing the dusty scrubland to the gym with a couple of friends, when the first mortar shell fell. “We heard a whishing sound and then the alarm went off and there were rockets and mortars going over. We were about 100 metres from cover and we just had to run back,” he recalls. “That one was pretty close.”

Mortar attacks were part of life at Basra Palace, on the outskirts of Basra in south-east Iraq. Sometimes, there would be one every night for a fortnight; sometimes it would go quiet for as much as a week. Fortunately, most were wide of their target, and those that did hit rarely caused much damage.

The palace was home to 9th12th Royal Lancers, part of the Royal Armoured Corps. But Lance Corporal Barry differed from most of the other soldiers quartered in Saddam’s former stronghold: while they were regular soldiers, he was a member of the Territorial Army (TA), a part-time soldier. Back on Civvy Street, he was a teacher.

Ben, 27, had joined the TA as a teenager, taking a year’s break after university before rejoining in 2004. But while it may once have been seen as a legitimate excuse to run about the woods at weekends, increased overseas involvement means about 13,000 of the 32,000 members of the TA have served in Iraq and Afghanistan. For Ben, by then a maths and technology teacher at The County High School in Leftwich, Cheshire, the call-up came in July 2005. “I always thought I would get used, and it was something I wanted more than anything. I wanted to be able to say that we were doing all this training for a reason,” he says.

After medical checks and extra training in Germany, he flew to Iraq in October 2005. He says it was only then that the nerves hit. He had been told to take a deep breath during the stopover in Qatar, and when he got off the helicopter in Iraq he realised why. “It was the smell, it was everywhere, like rotting rubbish.”

Ben’s role in Basra was an intelligence Non-Commissioned Officer, briefing patrols on likely threats. He also took part in patrols, on foot and in armoured Land Rovers. “I’d have my head sticking out of the roof, although when you have a rifle it is slightly comforting. It was the threat of getting blown up I didn’t like.”

During one of these patrols, his Land Rover got bogged down in the sand next to 20,000 Iraqis celebrating a Muslim festival. “We had to dig ourselves out but luckily another patrol came over. When we counted how many rounds we had we realised we were not going to make it if it came to a fight,” he says.

Living conditions in Basra Palace were basic, despite its former opulence: 14 men in bunk beds in an area smaller than a normal classroom. Fresh water was intermittent, scavenged wood was made into shelves and cardboard boxes doubled as bedside tables. The mornings after mortar attacks involved patrolling the grounds, checking for any unexploded devices. Evenings were spent in the gym, watching DVDs, reading and playing chess. No one left the camp except on patrol.

Ben’s tour of duty ended last May. After a weekend off, he started supply teaching, before returning to The County High School in September. “I’d been looking forward to getting back to teaching and when I was in the classroom I just switched on again.” But his experience has had a lasting effect: “I value life more now,” he says. It has also shown his pupils another side to their teacher. “My form loves it. It is odd for the pupils to think a teacher has got another life, but they love asking questions, and they love the idea that you are someone else as well as a teacher.”

David Stanhope completed two tours of duty in just 18 months. A geography teacher at Woodside Middle School in Bedford when first called up, he served in Iraq from April to November 2005, and then in Afghanistan from May to October last year. He resigned from his job before he left for Iraq.

“I didn’t want the school to plan for me to be back in case anything happened,” he says.

He served as a platoon commander with the Princess of Wales’s Royal Regiment, based at a logistical base a few kilometres from Basra. The platoon’s main role was to escort convoys all over the British zone. Then lieutenant - he was promoted to captain between tours - he was also responsible for the welfare of 24 men.

“I thought being a teacher I was pretty well prepared for that, but there were a lot of welfare issues. It’s hard when somebody is upset because they’re away from home for a long time, or their child has to go into hospital for an operation.”

David took responsibility for teaching the company to speak Arabic, putting lesson plans together after studying a CD Rom language course. He also tried to make use of his teaching experience. He says: “If I was trying to get across a particular point about patrolling, I would almost treat it like a classroom situation. I always tried to carry teaching materials around, such as laminated card and whiteboard markers. People used to say: ‘There is the combat teacher’, but it got results.”

His tour in Iraq came before hostilities escalated: most patrols were in soft-topped vehicles, and the battalion cultivated a good relationship with the locals. But there were always reminders of potential danger - another patrol was ambushed by an Improvised Explosive Device hidden in a camel, although nobody was hurt.

On his return to the UK, after two months’ post-operational leave, he was looking for another teaching post when the opportunity came up to help train the Afghan army. David leapt at the chance. “I felt it was an opportunity to teach foreign forces and be involved in fighting drugs and I just couldn’t turn it down. A lot of my friends said I was bonkers, but I felt I could really make a difference.”

He became part of the Operational Mentoring and Liaison Team, stationed at Camp Tombstone, a US base in Helmand province. After a spell teaching administration skills within the base, he was sent to train Afghan soldiers on operations, near the Kajaki dam, home of a power station that supplies electricity to southern Afghanistan. It was there he went through what he describes as some of the most horrendous times of his life.

He spent eight weeks at the mountain base, the only officer with about 30 British and the same number of Afghan soldiers. “It was probably the most beautiful place I have ever been, but the situation was terrible. The only connection was the odd Chinook flight, and apart from that, we were completely surrounded by the enemy. It was scary, but you couldn’t afford to be scared,” he says.

Skirmishes took place regularly, but it was the events of one particular day, September 6, 2006, which are etched most firmly on his memory. A group of British soldiers was patrolling on the other side of the mountain, when David heard an explosion: one of the men had trod on a mine and his leg was blown off. A group of soldiers went to his aid, but another soldier trod on a mine and lost a limb.

As the remaining soldiers tried to evacuate the casualties, Corporal Mark Wright, the patrol leader, trod on a mine. A medical orderly began treating him, but another mine exploded, injuring both Cpl Wright and the orderly.

There were a total of seven casualties, three of whom lost limbs. Cpl Wright died of his wounds in the rescue helicopter. “I could hear mines going off and I knew people were being injured, but I just felt utterly powerless and unable to do anything about it,” David says. “It was something I never expected to go through.”

David returned to the UK in October. He was reluctant to go back into the classroom straight away, and works for the TA as part of what the Army terms a “decompression package” (a period that allows troops returning from the front line to adjust and cool off), although he plans to resume his teaching career.

“It does affect you a lot. You realise that the things that used to matter beforehand don’t matter at all. What matters are the fundamentals of life.

When people are injured and killed it really focuses your mind,” he says.

“If I’ve made the smallest change to some of these people, I’ve done my bit. That is why a lot of teachers go into teaching, to make a difference to people’s lives, and whether it’s teaching in Britain or in the depths of Afghanistan, you are doing effectively the same thing, making a difference.”