AUSTRALIAN soldiers fought many savage battles in Vietnam but none against such odds, with such ferocity, in such a short space of time, with such heroism and so decisive an outcome as Long Tan.

Fifty years ago on Thursday August 18, 105 soldiers of Delta Company, 6th Battalion of the Royal Australian Regiment (6RAR) plus three New Zealanders patrolled into the Long Tan rubber plantation, unaware that they would shortly bump into a force of some 2000 North Vietnamese and local Viet Cong soldiers.

The ensuing battle started at 3.40pm, was fought wholly in torrential rain and was all over by 7pm when the relief force arrived.

As waves of enemy assaulted scattered Australian positions, their ranks were shredded by almost 3500 rounds of artillery, fired with astonishing accuracy from the Nui Dat base about five kilometres away.

Grovelling in the red mud as enemy fire cracked low over their heads, the Australian soldiers of the besieged Delta Company fired more than 10,000,000 rounds from their rifles and machine guns.

The Battle of Long Tan had its genesis in the early hours of August 17 when Viet Cong gunners opened fire on the Australian base, wounding 24 soldiers, one seriously. Australian and New Zealand guns returned fire and the next morning 6RAR's Bravo Company was dispatched to find the enemy firing point.

Delta Company was sent out to relieve Bravo Company around midday on December 18. The soldiers were disappointed - they would miss out on a concert with Little Pattie and Col Joye to be held on the base that night.

A group of Viet Cong blundered into the Australian formation and soldiers of 11 Platoon opened fire and gave chase, thinking this was a small local force.

"Then all hell broke loose,” one soldier later recalled, and 11 Platoon took many of its casualties in that opening moment as massed fire from a very large enemy force. About this exact time, the rain started, turning the ground into red mud and cutting visibility to about 50 metres.

The situation was dire but Delta Company had a few factors in its favour.

Most importantly, Long Tan was within optimum range of Australian, New Zealand and US artillery at Nui Dat. With fire directed by New Zealand forward artillery observer Captain Morrie Stanley, shells began to obliterate the enemy formations.

Because the Australian platoons and sections were so scattered, enemy commanders never really figured just how few they were up against. Every time they lined up to attack one position, they came under fire from another direction.

As the fighting progressed, Delta Company started to run low on ammunition. Two RAAF helicopters flew through driving rain, hovered over the treetops and dropped boxes of ammunition right into Smith's headquarters position.

Shortly after 6pm, the last units had linked up with the headquarters, placing all the Australians in one position for the first time.

Human wave assaults were smashed by artillery with shells landing just 30 metres in front of the Delta Company perimeter.

Just as it seemed one more massed assault would break through, the relief force of seven M-113 armoured carriers arrived and within minutes it was all over as enemy units withdrew, taking with them many of their dead and wounded.

In the evening darkness, the cost seemed exorbitant with a third of Delta Company dead, wounded or missing. It was decided to withdraw and return the next morning.

Australian War Memorial senior historian Ashley Ekins said they didn't realise they had achieved a great victory.

"It was only when they began to see the devastation and count the bodies or pieces of bodies, they realised they had inflicted a huge loss on the enemy. They stopped counting at 245,” he said.