The shattering blast from the rocket-propelled grenade forced us to dive into a ditch. A second round exploded almost immediately, leaving a swirl of black cloud overhead. Then after a moment came long, raking bursts of machine-gun fire from the poppy fields. We were pinned down in the mud. What followed was hours of fierce, rolling, close-quarter combat against the Taliban fighters in the heart of the Afghan badlands. This was Operation Kapcha Salaam or "Cobra Salute", the furthest south that a British combat mission has ever gone in Afghanistan.
In this highly dangerous Taliban-controlled area in the deep south of Helmand province lie the supply routes that keep the insurgency watered and armed, as well as the "blooding ground" where young jihadists cut their teeth. The joint British and Afghan offensive, which included armour and warplanes, was part of efforts to pave the way for the forthcoming US surge, which Nato chiefs hope can turn the tide on a war they are far from winning.
Just last week, Afghanistan's electoral authorities announced that the presidential poll would be postponed by four months to give forces time to improve security to a level where people can safely vote. Any doubt about how tenacious the Taliban insurgents are was quickly snuffed out in Cobra Salute. Fighters used farmhouses and irrigation channels in repeated attempts to ambush British and Afghan troops with Kalashnikov fire, while a second tier further back sent over salvos of mortar shells and grenades in an attempt to cut off the line of retreat. Garmsir, the main urban centre, dubbed "the snake's head" because of its topography, has been taken back and lost again in almost continuous fighting. The British lack of manpower - one attempt to wrest back control was undertaken by just 17 British troops alongside 10 Estonians and 200 Afghans - has made it hugely problematic to drive the enemy entirely from the area or hold the ground gained.
This time around the force numbered 350 from Battlegroup South, and The Independent accompanied troops from D Company of 2 Royal Gurkha Rifles and B Company of 1 Rifles as they left Garmsir last Tuesday heading south towards Koshtay and Lakari. The two towns are home to enemy bases housing bomb-making equipment, as well as opium markets which provide crucial revenue streams for the militants.
As the mass of troops began moving out, intercepted communications revealed the Taliban were waiting. Local leaders could be heard calling for more ammunition, while the movement's shura (council) at Quetta in Pakistan urged the "faithful" to head for Garmsir. "Intelligence shows the enemy is well armed, as well as Afghans there are Pakistanis and Chechens as well. We can expect attacks," said the officer commanding, Captain Wesley Hughes of the Gurkhas.
The first attack was a massive roadside bomb which exploded just 50 metres from a patrol of 12 soldiers. Captain Thomas Bennett, a bomb disposal expert with the Royal Logistics Corps, also found a "daisy chain" of five mortars lined up next to the 6ft- deep hole gouged out by the blast.
"It seems the plan was for the vehicle the troops were travelling in to be blown up by the IED [improvised explosive device]. There was enough explosive there to cause damage to a heavy vehicle. The mortars would have been detonated remotely as the men got out of the vehicle. I don't think many would have survived," he said.
The troops continued on their way, and by Wednesday the town of Koshtay had been taken. But there is a sense of Groundhog Day about the attempts to sweep militants from around Garmsir. Last year, in the first sign on the ground of the Americanisation of the war in southern Afghanistan, around 2,000 US Marines launched an operation which cleared the town and its surrounding districts of Taliban forces. But the insurgents moved further south, regrouped, and now the battle is being played out all over again.
President Barack Obama has pledged to focus on Afghanistan and one of his first military acts will be to approve a surge of US forces. Most of the 30,000-strong reinforcement will be stationed in the south, in Helmand and Kandahar. That, as well as the expected arrival of around 3,000 more troops from the UK, would, according to American officials, provide enough boots on the ground for a push to the Pakistani border. Company Sergeant-Major Dalindra Chetri, of D Company, a veteran of 18 years, said: "I think most of us know this is not just about fighting, but politics. In Nepal we had the Maoists fighting for a long time and now they have joined the political system. Maybe that will happen over here with the Taliban one day. But I also think that we will be coming back to Afghanistan many, many times."
On Thursday, just after midday, Afghan and British troops entered their next target, Lakari, to find the town near-deserted. As they turned into the market place, travelling along potholed roads, they were met by 107mm rockets. Major Andy Watkins, mentoring the Afghan forces, had the Taliban commander in the sight of his SA80 rifle. "I could see him quite distinctly; he was in a black dishdash and wearing a dark turban. He was gesticulating and men were following his orders. I looked hard, but could not see any weapons," he explained. "Under the rules of engagement on this op I wasn't in a position to fire."
I was accompanying British troops led by B Company, 1 Rifles, who had been sent to cut off the retreating militants. But now we were the ones under attack with shots from a variety of directions. On a ridge, Viking fighting vehicles of the Royal Marines returned fire and this silenced the militant attack, but only briefly. We clambered over a wall and fell on a farmer rolled up against the other side.
"Ask him about the Taliban," Lance Bombardier Ben Wosik shouted at one of the interpreters. The man said he knew nothing. Later, as we crouched under renewed fire, he said his family were trapped in a nearby house and his children were terrified.
The previous day the Gurkhas had been repeatedly approached by locals. Outside Koshtay, Haji Mohammed Amin came up to complain that "Talibans and bandits" were preying on residents. "They come at night and ask us to feed them, sometimes they ask for money; they are not Afghans, they are Pakistanis. We have had 30 years of war and it still continues. Where is our government? Why don't they help us? We hardly have enough to eat." Another, Ahmed Jan, complained: "This is our land, we need this land to live. And you and the Taliban are using it to fight your wars. We want to be left in peace. You are here but then you will go away and the Taliban will come back."
We moved into the next irrigation channel, slipping and sliding around in the ankle-high mud, another prolonged burst of Kalashnikov fire came in from the front and seemed to be getting closer. "They are in the ditch in front of us, they are actually in the ditch," exclaimed Lieutenant Simon Burkill, shaking his head.
Air and ground strikes were called in an attempt to deal with the continuous mortar fire ahead from another compound. A Harrier roared through low with the Taliban opening up at it with their AK-47s. Minutes later an American B1 bomber dropped a 500lb bomb, a deafening noise, followed by another, equally loud, as a round from a mortar struck home. It seemed implausible anyone could survive that, but the Taliban were heard on the radio reporting "they have dropped a bomb on us".
British troops were eventually forced to call a halt to the attack after literally "going off the map". They were around three miles beyond Lakari and their operational maps did not indicate what lay ahead. "We simply did not expect to be so far south," said Captain Tom Bewick.
The return to the safety of the Viking vehicles was a hurried affair. As we fell back, the militants advanced along the ditch, spraying fire which intensified as we ran, without cover, across an open field. On the way I glimpsed the farmer, standing silently at the doorway of his farm, his children crowded around him, watching the departing troops.