Captain Mark Nutsch rode past dead and dying men, the air filled with the iron scent of blood and the acrid stench of gunpowder. Smoke hovered above the field. The horsemen charging alongside him raised their rocket-propelled grenades and fired at the enemy ahead, the resulting explosions rocking them in their saddles.

Would the plan work, or was it a death sentence? Either way, this was not how modern warfare was supposed to be fought. A cavalry charge, headlong into enemy gunfire – it was the sort of reckless risk of human life that belonged in the pages of a history book. Yet here was an elite band of US Green Berets, at the dawn of the 21st Century, in a mission so extraordinary that it has inspired a new movie, 12 Strong, starring Chris Hemsworth.

And what brought them to this desolate mountain wasteland was an act of war on America itself…

The son of a Kansas rancher, Nutsch – renamed Mitch Nelson in the movie – was the man chosen to lead the 12-strong special forces band who braved Taliban forces soon after 9/11

It was October 2001, a month after the 9/11 attacks had claimed almost 3,000 innocent lives. The Americans were fighting an air war in Afghanistan – the country’s brutal Taliban rulers had been harbouring Osama Bin Laden, the architect of the atrocity.

Without US troops on the ground to identify Taliban positions, it was proving difficult to hit the enemy.

With each passing day that planes bombed but did not kill any Taliban – not enough of them, at least – the locals grew angry and dismissive of the Americans.

Now the US Government had decided to deploy a select band of highly trained men to operate behind enemy lines. Their mission was classified: only a few people in Afghanistan and the US knew they were here.

The son of a Kansas rancher, Nutsch – renamed Mitch Nelson in the movie – was the man chosen to lead the 12-strong special forces band. Their objective was to team up with the Northern Alliance militia, headed by General Abdul Rashid Dostum, who would lead them as close as he dared to key Taliban encampments. Nutsch, 32, would then pinpoint targets for US bombers.

The key to controlling the country, Dostum explained, meant taking Kabul. The key to Kabul was taking Mazar. The key to Mazar, Dostum continued, was taking the Darya Suf river valley. And if they took Mazar, the north would fall. All six provinces. Without question.

‘The Taliban are now here,’ he said, circling a village 12 miles north. ‘From there, we will bomb the Taliban. Once the bombing starts, they will break.’

Yet for all America’s military might and high-tech arsenal, the only way the men would be able to move around this rugged terrain was on a ragged string of local horses.

For the first time in living memory, US troops would be riding into battle not in tanks or armoured jeeps but on horseback. As a gesture of goodwill, Nutsch had brought food for Dostum’s horses and vodka for his men. ‘I don’t need food for my horses,’ Dostum snorted. ‘What I need is bombs.’

‘I got more bombs than you could ever want,’ Nutsch replied. ‘But we need to see the enemy real close.’

For the first time in living memory, US troops would be riding into battle not in tanks or armoured jeeps but on horseback. As a gesture of goodwill, Nutsch had brought food for Dostum’s horses and vodka for his men

Nutsch wanted to take his entire team into action but was told there were only six available horses. ‘Who’s ridden before?’ Nutsch asked as six skinny Afghan mounts were brought into the compound. Only Vern Michaels and Bill Bennett raised their hands. ‘At summer camp,’ they said. ‘When we were kids.’

Nutsch gave his men a rundown: ‘If your horse runs off and your boot gets stuck in these stirrups and you get thrown, you’ll get dragged and you’ll die. If that happens, you gotta shoot the horse. Just reach out and shoot it in the head.’

Now he tried picking out the tallest, most handsome horse. Its rough-haired legs were knobbly at the knees. The hooves were cracked, unshod, the colour of dishwater. In height, it resembled an over-large pony, the kind children ride at county fairs. He gripped its mangy mane with one hand and held the reins with the other. He lifted a boot and jammed it into a stirrup, then jammed the other boot in and pulled himself up. He was sitting with his knees practically bent up to his ears. He wondered how he was ever going to ride it.

‘Listen up,’ Nutsch croaked. ‘Here’s how you make this thing go.’ He heeled the horse in the ribs and it walked a few steps.

‘And here’s how you turn,’ he said, pulling a rein and drawing the narrow muzzle around. The guys on the team nodded.

The mission was so extraordinary that it has inspired a new movie, 12 Strong, starring Chris Hemsworth

Nutsch kicked his horse in the flanks. ‘Cho!’ he shouted, remembering what the Afghans had shouted when they’d ridden away. The word meant ‘Giddy-up’ in Dari. The horse lurched and started towards the front gate. As they rode into the mountains, the Americans stifled groans at their saddle sores so as not to give the game away that they were novice horsemen.

The US soldiers trekked north over the following days, calling in air strikes on Taliban positions as they found them. They passed empty settlements decimated by the Islamic fundamentalists. Whole families wiped out, the men and boys dragged into the army. Their wells poisoned.

All the while they were hampered by their Afghan allies’ reluctance to allow them too close to the enemy. ‘You cannot get closer. I cannot let you get killed,’ said Dostum as they viewed a Taliban bunker from several miles away. ‘Five hundred of my men can be killed before even one of you is scratched.’

Nutsch shrugged. He reached down his shirt-front, pulled up the GPS hanging by a lanyard on his neck, and carefully read the pixelated numbers in the grey window of the device.

He did not want to give them to the pilot incorrectly, and so confuse his position with the enemy’s. These were the numbers he would radio to the B-52 overhead. He looked up, squinting. All Nutsch had to do was pick up the radio and relay the numbers. He hoped by God that he didn’t mess it up.

The bomb was 12ft long and filled with about 1,200 lb of explosives. It was tapered at its green nose to a sharp point and could fly 15 miles from drop point to target.

The US soldiers trekked north over the following days, calling in air strikes on Taliban positions as they found them. They passed empty settlements decimated by the Islamic fundamentalists (stock)

They saw the explosion before they heard it. Then came the boom – yet as the smoke cleared, Nutsch saw that something had gone wrong. The bomb had missed the compound by a mile or maybe more. It had landed between them and the target.

A second bomb also fell short. The third bomb hit closer – but was still as much as 600ft from the target. The Taliban were filing out of the bunker and looking around – up at the sky and across the desert, unsure of where the big noises were coming from. Nutsch felt as if he’d travelled back in time.

Here he was riding a horse loaded with sophisticated electronic gear and ordering bombs to be dropped from planes that were flown from Diego Garcia, 2,800 miles away in the Indian Ocean. Nutsch was getting madder by the minute. He might as well have been standing on Mars and phoning the war in.

He turned to Dostum, ready to apologise. The general’s aide, Fakir, saw the disappointment in his face. ‘Don’t worry,’ he said. ‘You have made explosions come from the sky. The Taliban are afraid!’

Through his binoculars, he looked east across a river valley controlled by the Taliban and saw the Northern Alliance horsemen, all carrying weapons, AKs and RPG tubes, glittering belts of ammo wrapped around their shoulders (stock)

Nutsch saw his opening: ‘Well, I can do a whole better than that,’ he said. Dostum wanted to know exactly how. ‘Get me closer,’ he ordered.

On October 23, 2001, four days after their arrival in Afghanistan, Nutsch and his team were to get their wish.

Through his binoculars, he looked east across a river valley controlled by the Taliban and saw the Northern Alliance horsemen, all carrying weapons, AKs and RPG tubes, glittering belts of ammo wrapped around their shoulders.

The day before, Dostum had put out the word that any man who could fight the Taliban should come to this place and be prepared to die. There were some 600 men on horses and on foot moving out on to the plain, readying for battle.

They would charge the middle, the infantry would attack the flanks, and machine guns set on adjoining hills would spray covering fire.

Then Dostum spoke into the radio: ‘Charge!’ A wave of horsemen climbed the back side of the first hill, crested it, and rode down it, quickly picking up speed. Before them lay half a mile of ground folded into hills. At the end lay the Taliban guns, eerily silent. And then they opened up.

Mortars started dropping around the riders, sending up fountains of red dirt. RPGs whizzed upward as the Taliban tried timing their impact with the arrival of the Afghans on the crest of each hill.

Dostum kicked his horse and broke into a gallop. Nutsch followed.

The noise was deafening, shells and bullets whistling over the ground at head height. Men would be riding in the saddle and then suddenly fly backward, tumble to the ground and lie motionless as more horses approached from behind and leaped over them.

Sometimes a wounded man got up and limped away or held out a hand. The remaining riders leaned out over the stretched necks of the horses, firing as they ran, the long, dark reins clamped in their teeth.

As the horsemen charged, many of the Taliban threw down their weapons and started running, their black smocks flapping as the horses thudded behind them.

The noise was deafening, shells and bullets whistling over the ground at head height. Men would be riding in the saddle and then suddenly fly backward, tumble to the ground and lie motionless as more horses approached from behind and leaped over them (stock)

The riders leaned from the saddle to reach out and club them with their rifles, then dismounted to finish them with knives.

Up ahead, Nutsch could see the Taliban line breaking in places here and there, like a sand wall crumbling. He was amazed when he saw that some of the Taliban were running toward Dostum’s men, their hands held high in surrender.

Of the 600 men who had started the charge, Nutsch guessed that there were 300 still in the fight. The remainder had been wounded, killed, or had scattered. Dostum’s men were within striking distance of victory.

One last hill separated them from the Taliban. But Nutsch sensed they were losing momentum.

The horsemen halted, uncertain what to do, trapped by gunfire. Some jumped from their saddles and crouched at the feet of their nervous horses, trying to make themselves smaller targets.

Dostum was furious. ‘We are losing!’ he screamed. ‘Attack! Attack!’

His men did not move. Nutsch watched as Dostum leaped from his horse, reached into a saddlebag, and retrieved several magazines of ammunition for his AK-47. And then he started to run. Straight down the hill towards the Taliban.

Nutsch watched Dostum as he ran and fired. He expected the commander to drop at any moment as he overtook his own men who looked amazed and, finally, embarrassed.

Galvanised by their leader’s example, they mounted their horses or took off on foot, forming a line with their general.

Nutsch could feel the battlefield swell. It had taken on new life. He watched as the Afghans coalesced as a smoky swarm, bristling with gun barrels, flashing with explosions. They descended on the enemy line with a roar.

The remaining Taliban threw down their weapons and ran. They were shot unless they surrendered first.

On the hill, one Afghan soldier reached to the ground with a knife and made a swift sawing motion.

He stood and thrust aloft a head, the head of a Taliban soldier, swinging by a fistful of black hair, a dripping pendulum, as the sun drained away. The unlikely cavalry charge had won the day.

12 Strong, by Doug Stanton, is published by Simon & Schuster, priced £7.99. Offer price £6.39 (20 per cent discount) until February 11. Order at mailshop.co.uk/books or call 0844 571 0640 – p&p is free on orders over £15.