For some of the Australian soldiers fighting in Vietnam, it was the worst day of their lives. It was also the inspiration for Redgum’s classic I Was Only 19

Bill Wilcox’s watch stopped dead at 2.20pm on 21 July 1969 and never restarted. A field engineer in 1 Squadron in the Royal Australian Engineers (RAE) in the Australian army, he’d been up in the Long Hai hills in south-eastern Vietnam for about 10 days. He and his mates were due for a break.

It had been dirty work, even by wartime standards: dropping into active tunnel systems used by the Viet Cong, at risk of underground combat or possible asphyxiation and mine demolitions.

The irony was the engineers were mostly destroying their own mines, laid two years earlier. Nearly 23,000 US M16 “jumping jacks” mines had been buried in a barrier aimed at isolating their enemy combatants in the jungle.

Facebook Twitter Pinterest Bill Wilcox served in the 1 Squadron in the Vietnam war

But the field hadn’t been properly secured. At enormous risk to themselves, with many soldiers lost, the North Vietnamese army learned to excavate and redeploy the mines against Australian forces.

Wilcox and the rest of 1 Squadron were heading back to base in a helicopter when they received the news that members of the 6th Battalion, of the Royal Australian Regiment, had strayed into a minefield in the “light green”, with one killed and many more wounded.

The “light green” was an area on the map that had been partially cleared – where defoliants including Agent Orange were used to strip the forest canopy of cover and where mines were likely to have been buried.

Facebook Twitter Pinterest Bill Wilcox’s watch stopped dead at 2.20pm on 21 July 1969 and never restarted. Its hands have since fallen off

With nowhere for the helicopter to land amid the rubber trees, Wilcox and five others, including medical officer Capt Robert Anderson, were winched down. Another was Sapper Dave Sturmer, who spotted a three-pronged stick in a tree indicating that three mines were in the area.

But only one had gone off.

After they landed, the first person Wilcox came to was Frank Hunt, later immortalised in Australian folk group Redgum’s song I Was Only 19: “Frankie kicked a mine the day that mankind kicked the moon.” Along with other members of his battalion, Hunt had been listening to a broadcast of the moon landing the previous evening.

But Hunt had survived. In the song, written by John Schumann, his name had replaced that of Lt Peter Hines. Hines’ body lay several metres away, though he too had survived the initial blast and had been giving directions until his death.

Hunt was in a bad way and was one of the first to be “dusted off” – slang for medically evacuated. “He copped it in the lower body and legs and he was smashed up real bad,” says Wilcox, now the president of the Oberon and Blue Mountains RSL sub-branches.

In the meantime, one unexploded device was located nearby. One more remained. Wilcox and company taped off safe areas, trying to clear enough space for a helipad so the remaining injured could be airlifted out.

Then the medical officer, Capt Robert Trevor Anderson, took a step outside the tape.

Jumping jacks, when disturbed, would spring from the earth into the air before detonating around waist height, but this one blew up beneath the soil, directly under Anderson. Somehow, he remained standing, still conscious, his clothes torn off.

“I was thrown probably 10 metres away, after the explosion, and I didn’t black out, I was still conscious,” Wilcox says. “I looked back and all I could see was red – like a stump – and it was Anderson.”

Facebook Twitter Pinterest Frank Hunt and his children on stage at a Sydney concert as part of the Vietnam veterans’ Welcome Home Parade concert in October 1987. Pte Hunt, a radio operator during the Vietnam war, was injured by an M16 mine. Photograph: Australian War Memorial

Cpl Johnny Needs was about 20 metres from the blast but took a single piece through the heart. He died in a comrade’s arms. Wilcox took more of the metal, mostly in his left side and knee.

Some of his own equipment saved him. “A heap of pieces went straight into a battery box, which saved my left hip, otherwise it would have smashed it as well as my knee.” His watch also took a hit for him.

Within 45 minutes, Wilcox had been dusted off himself to the military hospital in Vung Tau. With the chopper full, he was strapped to one of the landing runners. Still fully conscious, he watched for sniper fire as they lifted above the tree line.

“I thought, ‘Jeez, if I’m not dead now, I soon will be,’” he says. “I’ve got a little model at home of a chopper with a stretcher on the outside with a little dummy in it – that was me.”

Schumann was a leftwing firebrand and the singer and songwriter of Redgum, one of Australia’s most popular and political bands in the 80s. The song was written from the point of view of Schumann’s brother-in-law, Mick Storen, a veteran from the 6th Battalion. When he wrote the song, Schumann was going out with Storen’s sister, Denise – “Denny” in the song – and he figured he might have a tetchy relationship with Storen.

Facebook Twitter Pinterest Redgum’s classic song I Was Only 19 recounts the experiences of the 6th Battalion

One night Storen surprised him by coming to a Redgum gig and, after the show – “on the wings of a six-pack” – Schumann asked him to tell him his story.

Denise had warned him not to. History had not been kind to the Vietnam war or those who took part in it. “It was Mick Storen’s courage and trust to step outside the closed circle of Vietnam veterans that [propelled] 19 into the world,” Schumann says.

In 1983, after the song’s release, Wilcox was driving trucks. He was suffering from post-traumatic stress disorder and had been unable to settle into regular work. It was on long-haul shifts that he heard I Was Only 19 on the radio.

It took a while for the penny to drop as to what Schumann was singing about. “It never hit me until it was pointed out to me that it was about our set-up. It might have been weeks before I even realised. It’s still a very moving thing when I hear it.”

Anderson, who was blinded by the mine that blew under his feet, became a celebrated psychiatrist in Melbourne, served on many veterans’ committees and was the RSL Anzac of the year in 1991. He died of pancreatic cancer in 2004.

Facebook Twitter Pinterest John Schumann with the guitar he used to write I Was Only 19 on at the Australian War Memorial in Canberra in June 2016. Photograph: Rashida Yosufzai/AAP

Hunt lives on the far south coast of New South Wales. He didn’t kick the mine himself – that was Hines – but was written into the role by Schumann, with consent. “Everyone is Frankie,” he told the ABC in 2015.

These days Schumann is a little tired of talking about 19. He has written a new song, Graduation Day, about police suffering from PTSD. It hits a similar nerve to his classic, and he finds himself fielding unusual media invitations from the likes of Alan Jones and Ray Hadley.

“Having a song like 19 in your catalogue is like having five kids, and you love all of them equally, but one of them plays AFL footy – and the only kid of yours that anyone outside the family wants to talk about is the AFL footy player,” he says now.

But he’s also proud. “A songwriter gets to write something like 19, if they’re lucky, once in their life. I researched it really well and I thought about it a lot, but it was one of those songs I wrote in five minutes … I look back and I go, ‘Wow, that was something else.’”

In 2010 Wilcox revisited the site where he nearly lost his life. This year he hopes to go back on 21 July, for the 50th anniversary of something more significant than the moon landing. At 2.20pm, his stopped watch will be right again.

• This article was corrected on 26 April 2019. A previous version said Bill Wilcox was in the RAAF. He was in the Royal Australian Engineers (RAE) corps in the Australian army.