Nguyen and his fellow sappers were taken to within twenty miles of Saigon, to an area the Americans called The Iron Triangle, where they spent six months helping to build and equip a network of tunnels that housed hundreds of NVA and Vietcong soldiers. Deep underground were hospitals, training schools, supply stores and munitions factories. For weeks on end he never saw the sunlight. Nguyen was then put to work manufacturing home-made mines from captured US 105-millimetre howitzer shells of which the NVA had an abundant supply. The cash-rich Americans were notoriously careless with their equipment and there were crates upon crates of the shells for Nguyen and his team to work on.

One day when he was supervising a new batch of the mines a VC officer came to watch and began talking to him. The officer had been a mechanic many years before and it turned out that he’d originally worked in a garage in Hanoi not far from where Nguyen learnt his trade. The man complimented Nguyen on his work and after watching for a while longer he went away. The following day Nguyen was called to his commanding officer and told that he was being transferred to a Vietcong guerrilla unit. He’d asked what sort of unit and the officer had shrugged and said that it didn’t matter. Nguyen didn’t press it because he knew there was no point. He wasn’t surprised when he was told that he was ordered to report to the VC officer who’d been watching him earlier. That was when Nguyen had been taught to fight. And to kill.

Nguyen was told that he’d be working in a team of three, setting booby traps on trails used by the American forces. He was given a black uniform to replace his grey NVA fatigues, but he was told he was to keep his AK-47 rifle. And that was that. Nguyen spent almost a year living in fear, creeping out of the tunnels at night, planting mines, setting trip wires and doing everything possible to terrorise the Americans. He became expert at moving silently through the jungle and quickly learned to camouflage himself so effectively that he was almost invisible from a few feet away, even during daylight.

Nguyen himself gave little thought to the politics involved: he was happy to fight for his country and, besides, if he had ever expressed any reservations about what he was doing he would have more than likely been shot in the back of the head. But that all changed one night in the summer of 1968 while he was in temporary attachment to a VC training camp close to Chap Le. The camp was only thirty miles away from Dong Hoi and Nguyen was hoping to be granted leave so that he could visit his family on his father’s farm, when word reached him that his father had died. When he officially applied for leave it was refused, with no explanation. He went anyway, borrowing a battered Vespa scooter and driving through the night. When he arrived at the farm he was greeted by his tearful wife and children, and he learnt the full story.