If he dwells on it, Lt Col Harry Smith can still see, vividly, the blood on the trees on the enemy’s escape path. There was so much blood. In the days after the three savage hours that was the battle of Long Tan, his soldiers were finding body parts, carnage and corpses spread across the battlefield. But it was that blood, “the blood of all the others that were dragged away, wounded, suffering”, that affects him the most. “That worries me more than a dead body.” In the eerie silence, in the pervasive gloom, among the smell of the dead in the Long Tan rubber plantation, latex ran down trees punctured by bullets and mingled with the blood.

Long Tan had been a battle fought against almost impossible odds. A ferocious battle, a defining action of the Vietnam war. On the afternoon of 18 August 1966, a single infantry company of 108 mostly inexperienced Australian and New Zealand soldiers engaged with a regiment of 2,500 battle-hardened Viet Cong and North Vietnam army troops. Almost surrounded, outnumbered 10 to one, they withstood Viet Cong attacks in cyclonic rain.

Now, 86, Smith is sitting on the patio of his Sunshine Coast home as he recalls that desperate day, 53 years ago, now the subject of the feature film Danger Close. A small, wiry, compact man, there is still something indomitable about him. Age has not wearied him. He was 33 when he commanded his company of early 20-year-olds from south Queensland in the battle for their lives.

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The Australians had recently established a stronghold at Nui Dat, in the middle of Viet Cong supply routes in Phuoc Tuy province. “But they didn’t have enough troops to protect the base,” says the film’s producer, Martin Walsh, who also made the documentary Battle of Long Tan.

Smith believes that Brigadier Oliver Jackson had intelligence that there was a regiment massing on the other side of the rubber plantation, 5km from base. “And he didn’t pass it on to my commanding officer, Col Townsend, he held it at the headquarters and didn’t tell us. His excuse was that he didn’t think it was the enemy in force, he thought it was just reconnaissance. You have to ask what he thought the reconnaissance was for.” Had he known, says Smith, “There is no way in the world I would have sallied forth into the rubber plantation with 100 men to face an enemy regiment with 2,000 or more soldiers.”

On the afternoon of 18 August, the focus was on a concert being given by the Australian singers Col Joye and Little Pattie. To their chagrin, Delta Company 6RAR weren’t at the concert; they were out on patrol on the edge of the rubber plantation. Smith recalls it being “deathly quiet”. He believes the enemy “were on their way to attack Nui Dat on the night of the concert. We just happened to get in the way”.

Facebook Twitter Pinterest Lt Col Harry Smith was the officer commanding Delta Company 6th Battalion Royal Australian Regiment at the battle of Long Tan. Photograph: Rob Maccoll/The Guardian

The company halted just under a rise in the ground. It would protect them in a defensive position, with the bullets going just over their heads. “And to our advantage, they were silhouetted in the gunfire smoke, making easy targets for my machine gunners and riflemen.” At about 4pm all hell broke loose. 11 Platoon, which was out in front, took heavy casualties. The enemy were firing with machine guns, the monsoon hit in full force, with thunder and lightning, turning the ground into liquid mud, reducing visibility to almost nothing. The rain came down so hard on to the red earth that it kicked up a mist, which helped camouflage them. At 4.25 Smith called the commanding officer, Townsend, requesting that reinforcements be helicoptered, but was refused. Neither reinforcements or helicopters were available. In his book The Battle of Long Tan: The Company Commander’s Story, Smith wrote: “As though we were all at a ladies’ tea party in downtown Toorak, Townsend instead proposed an Alpha Company reinforcement force would come out in armoured carriers ‘later that afternoon’!”

By 4.40pm, 11 Platoon were under attack on three sides and separated from the other two platoons. Major Morrie Stanley from the Royal New Zealand Artillery was working off grid references from platoon commanders trying to read muddy maps, relaying them to the artillery guns 5km away, who were landing them with deadly accuracy only 50 metres in front of the beleaguered soldiers, six rounds a minute. “The artillery fired 3,500 rounds of high explosives which took a terrible toll on the enemy and saved us from annihilation.” And still the enemy kept coming and coming and the soldiers kept firing and firing. The noise was incredible, the tracers lit up sky.

Smith kept moving his platoons into strategic positions, at times without radio communication, to within metres of the enemy. It was all business. “I was too bloody busy to be frightened,” he says. “Everything I did was an automatic reaction, your mind just tells you what to do. I was giving orders to my platoon, talking on the radio, I didn’t have five minutes to sit down and be scared. Afterwards I thought, shit, why am I alive?”

Running out of ammunition Smith requested RAAF helicopter resupplies. He didn’t know that this was being delayed by arguments at Nui Dat over standard operating procedure of air staff not being allowed into unsafe conditions. Chopper pilots Bob Grandin and Frank Riley who had been there to deliver Little Pattie and Col Joye overheard this, and knew 6RAR was in desperate trouble. Riley stepped forward. “I am the captain in charge of my aircraft and I am going out.” They didn’t ask for permission so that no one could say no. They just went. The soldiers were down to just a few rounds of ammunition each when the choppers took off, with 50-metre visibility, flying at treetop level. Overloaded with ammunition, they struggled to get the choppers off the ground. It was a suicide mission but it was the right thing to do.

Facebook Twitter Pinterest Harry Smith (left): ‘Wars are never going to cease as long as the world is the world.’ Photograph: Big Sky Publishing

The armoured personnel carriers (APCs carrying infantry) had been held back for nearly an hour. Brigadier Jackson had intelligence that there was another Viet Cong regiment north-west of the base, and was concerned that Long Tan was a ruse to draw the Australians out and leave the base unprotected. Just as 6RAR was preparing for a huge final assault from the enemy, the APCs arrived more than three hours after the battle had begun and an hour and a half after Smith had requested reinforcements. The enemy retreated, and the only sound in the plantation was the ticking as the engines cooled down.

Seventeen Australian soldiers had been killed and 25 wounded; one died nine days later. Because of medic Phil “Doc” Dobson, who had rudimentary first aid training and like all medics was in the army band in peace time, not one of the horribly wounded in the ditch died. The Vietnamese left 245 dead on the battlefield, but Smith believes the toll was much higher.

He says the men didn’t talk about it much after the battle. “There wasn’t a lot of confession afterwards. Platoon commanders talked with their section commanders, I put in a patrol report. But it wasn’t ever discussed in detail. I think the senior officers were embarrassed that we had been sent out but not told that the enemy was there. They didn’t want to prolong the agony by discussing it.” In those three-and-a-half crowded hours there had been some exceptional acts of bravery. In May 1968 the members of Delta 6RAR were awarded the US Presidential Unit Citation for gallantry by Lyndon B Johnson for extraordinary heroism in action against an armed enemy. South Vietnam awarded them the equivalent.

But in Australia, Smith would fight another epic battle to have his men recognised and decorated. “Vietnam was a case of out of sight, out of mind,” he says. “I don’t think that many people in Australia recognised the war was going on or what was happening on the ground.” Says Walsh more bluntly: “They were treated like shit when they came back. They wouldn’t let them join the RSL, they were called baby killers. At the time when this battle happened the protests had barely begun.” When he began talking to the veterans for his documentary released in 2006, Walsh says, “Most of these men had not talked about it, even to their families. It would have been a travesty to bury these men’s sacrifice and history.”

Some of Smith’s “nastiest” battles have been with civil servants in his own government. “The medal system is another battle I fought after the 30-year secrecy period because they cut the allocation of medals that I had recommended in half, and of that half they downgraded them in status. I initially recommended 20 of my men.” He fought for decades, through three government inquiries – “Now we are the most decorated company of the Royal Australian regiment.” But “it left a nasty taste in my mouth.”

Smith stayed in the army for 10 years after Long Tan, “I went to One Commando in Sydney, jumping out of aeroplanes, ambitious exercises, boats, all sorts of things like that. Not getting shot at.”

Facebook Twitter Pinterest Danger Close: The Battle of Long Tan is now showing in cinemas. Actor Travis Fimmel plays Major Harry Smith during the Battle of the Long Tan . Photograph: @jasinboland/Suppled

In his book he admits he was “a changed man” after Vietnam, “and blotted it out”. Official records were not released until 1993, a long time to carry it alone.

He was diagnosed with PTSD “years ago. I keep it under control. I have been lucky that I have been sailing over the last 25 years, sailing to Cape York for six months of the year. That was my outlet. That keeps me involved in other things. I am sure if I dwelled on what happened in Vietnam I would probably go gaga but I am not prepared to do that. When you have more time on your hands your mind dwells on nasty thoughts and pieces of bodies.”

He adds: “In 2016 I had an evening with former enemy at a restaurant in Vietnam, we got on very well. They were very friendly, as we were, and we talked about the battle. Their biggest problem was that they didn’t know where we were and they didn’t know how many of us there were. They couldn’t understand why we were able to withstand their assaults. They had bad weather, they couldn’t see very well through the monsoon rain, [but] we could see them.”

The battle of Long Tan is portrayed in Danger Close in almost real time and takes the audience on to the ground, into the mud, the noise, the confusion, the adrenaline of battle. (Kriv Stenders directs the film and Travis Fimmel plays Smith, who says “overall … I would rate it eight out of 10”.)

Once your heart rate returns to normal, you are struck by how young those boys were, and by the relentless brutality, madness, adrenaline, courage and futility that is the anatomy of war. “Wars are never going to cease as long as the world is the world,” says Smith. “There have been wars since the world was formed. There has always been some conflict somewhere, there always will be. It is just like a couple of fellas arguing, except they argue with bullets.”

Danger Close: The Battle of Long Tan is now showing in cinemas