Think back to the fabled battles of the Vietnam War. Which ones come to mind?

Long Tan? The Tet Offensive? Khe Sanh?

But Australia's largest battle in Vietnam is one you probably haven't heard of.

It's known as Coral-Balmoral.

The Australian War Memorial describes the 26 days of intermittent fighting at Coral and Balmoral as Australia's "largest, most sustained and arguably most hazardous battle of the Vietnam War".

Twenty-six Australians died and 100 were wounded.

It is estimated at least 300 North Vietnamese soldiers were also killed.

This year marks the 50th anniversary of the battles, which began in the early hours of May 13, 1968.

Vince Dunn was one of the troops deployed to the region, about 45 kilometres north-east of Ho Chi Minh City, to establish several fire support bases in the area.

Vince Dunn (centre, back) with three other Charlie Company boys at Nui Dat. ( Supplied: Vince Dunn )

The bases were designed to provide firing points for artillery and mortars and give cover for foot patrols targeting enemy forces withdrawing from the city.

But a deadly combination of poor reconnaissance, a lack of accurate intelligence and bad planning on the part of their superiors led to delays and confusion during the deployment.

The troops didn't arrive until late in the day on May 12 and had only partially established and secured the base at Coral by sundown.

Mr Dunn said they were completely unaware of the number of North Vietnamese troops in the area.

"We were placed into a position north of Saigon to allegedly hammer dispirited troops retreating from Saigon and heading back north," he said.

"That's what we were told; they'd be a dispirited lot, just a gaggle of troops ... disheartened and out of gas."

The Australians' defences were frail. They had no barbed wire, no infantry, no mines and were only partially dug in.

"It's all we could manage before dark," Mr Dunn said.

Vince Dunn served in the 102 Field Battery, Royal Australian Artillery, and later as a forward observer in C Company. ( Supplied: Michele Dunn )

Early the next day, around 3:30am, the base was attacked by a brief but intense rocket and mortar barrage.

The North Vietnamese Army (NVA) exploited the disorganised defence to penetrate the Australian perimeter.

The 1RAR mortar platoon position was over-run.

A frantic call for help was made and with the aid of US air support, the attack was eventually suppressed.

A captured gun pit was retaken around 6:30am with the gun still inside.

Mr Dunn said the enemy troops were far from the tired soldiers their superiors had anticipated.

"They were fresh North Vietnamese on their way to Saigon," he told ABC Radio Melbourne's Jon Faine.

"They were professionals."

Four key battles interspersed with multiple smaller firefights make up the Battle of Coral-Balmoral.

The two bases, Coral and Balmoral, were only 4.5 kilometres apart.

Recovery vehicle 'Tunza Guts' sustained damage during one of the North Vietnamese Army assaults. ( Supplied: National Vietnam Veterans Museum )

Although the fighting continued until early June, it's that first battle on May 13 which sticks in Mr Dunn's mind the most.

"After the first night at Coral we were reinforced with the tanks, but during the first battle there was no support whatsoever," he said.

"Had they [the North Vietnamese troops] not walked into the mouths of the guns we would have been slaughtered."

As it were, 11 Australians died that night.

On a clearing patrol the next morning, 52 NVA soldiers were dead in front of the Australian guns.

Drag marks on the ground suggested there had likely been more.

"That clearing patrol was probably the first time I'd seen a body and they were obviously in a dreadful state. Artillery does dreadful things to human bodies," Mr Dunn said.

"Our boys were being loaded onto the chopper — our dead — as we were clearing the front area and I just kind of came to the realisation that it was Mother's Day.

"I kept thinking of my own mum and mothers in Australia who within the next few hours are going to have someone knocking on the door to tell them what we already knew, that their sons were dead.

"That's been a very difficult thing to deal with over the years."

Later that day a road convoy carrying support arrived at Coral, but it was too late to help those killed and injured in the fiasco the night before.

Why don't we know much about Coral-Balmoral?

In 1968 the Vietnam War was "on the nose" with the Australian public.

Mr Dunn said the information that made its way back to Australia was that there had been light casualties and it was "no big deal".

In fact, it was Australia's largest battle since World War II.

Mr Dunn said he wanted to share the story on behalf of all the men who served at Coral and Balmoral, especially those who never came home.

"We have lost a lot of our boys already and my concern is that Australia doesn't know about Coral and Balmoral," he said.

Bell helicopters, nicknamed Hueys, drop supplies at Coral. ( Supplied: National Vietnam Veterans Museum )

An exhibition at the National Vietnam Veterans Museum on Victoria's Phillip Island is trying to change that.

Air Force veteran and exhibition organiser Bob Woods said it happened at a time when the war was increasingly unpopular and governments were starting to prepare for peace talks.

"There was a lot of secrecy about the whole deal because there was a lot of poor reconnaissance," he said.

"It wasn't a popular thing to talk about people getting killed. It wasn't a popular war and that wasn't a popular time."

Mr Wood said many people still did not understand the significance of the battle or the gallant fighting carried out by Australian troops under testing circumstances.

"It's the 50th anniversary so it's time to try and get the story out. It's a good opportunity to educate people."

The 50th anniversary of the Battle of Coral and Balmoral exhibition runs until October 26.