A Royal Marine in southern Afghanistan threw himself onto an exploding grenade to save the lives of his patrol.

Miraculously, Lance Corporal Matt Croucher, a marine reservist from Birmingham, survived the blast with little injury when his rucksack and body armour took the force of the blast. He is expected to receive one of the highest awards for gallantry.

The story of his courage emerged last week in interviews with marines occupying a forward operating base near Sangin in Helmand province. They are preparing to leave after serving for six months at the centre of some of the fiercest fighting in Afghanistan. The outpost, Forward Operating Base Inkerman, is better known to troops as "FOB Incoming".

Croucher's action occurred just before dawn on February 9, as the reconnaissance troop from 40 Commando, operating to the south of Sangin, was searching a compound it suspected was being used for making bombs to attack British and Afghan troops.

Walking in the darkness among a group of four men, Croucher stepped into a tripwire that pulled the pin from a boobytrap grenade. His patrol commander, Corporal Adam Lesley, remembered Croucher's shout of: "Grenade!"

As others dived for cover, Croucher, 24, did something nobody expected. He lay down on the grenade to smother the blast. Lesley got on the ground, another man got behind a wall, but the last member of the patrol was still standing in the open when the grenade went off.

"My reaction was, 'My God this can't be real'," said Lesley. "Croucher had simply lain back and used his day sack to blunt the force of the explosion. You would expect nine out of 10 people to die in that situation."

Then they waited. "It felt like a lifetime," said Lesley. When the grenade went off it blew Croucher's rucksack more than 30ft and sent a burning radio battery fizzing into the air. As the noise died down, one of the patrol, Marine Scott Easter, was standing "just completely frozen" and untouched. Croucher was in deep shock but, apart from a bloody nose, had few injuries. "He had shrapnel in his helmet, in the plate of his body armour, but he was basically okay," said Lesley. "His day sack had taken the blast."

Croucher told the News of the World: "All I could hear was a loud ringing and the faint sound of people shouting 'are you ok? Are you ok?'

"Then I felt one of the lads giving me a top to toe check. My head was ringing. Blood was streaming from my nose. It took 30 seconds before I realised I was definitely not dead," he added.

The troop commander, Captain Dan Venables, said they decided to exploit the incident. "I made the decision that after the grenade went off, the Taliban would come to see what had happened. So we lay in wait and ambushed them."

Croucher's actions prompted his colleagues to pass a citation to the Commanding Officer of 40 Commando, Lieutenant Colonel Stuart Birrell, to recommend him for the Victoria Cross.

"It's a pretty unusual thing but the lads put me forward for the VC themselves.

"It's entirely out of my hands. But if it was to happen it would be a massive honour, not just for me but for the regiment and all my comrades,” he told the News of the World.

Yesterday, fellow marines were reluctant to play up the incident. "Such has been the ferocity of the fight 40 Commando has endured these past few months, this has been one remarkable incident among many," said one senior Royal Marines officer as they prepared to hand over to the Parachute Regiment. Their experience highlights the danger faced every week by many of the 7,700 troops in Afghanistan. Inkerman, an exposed hilltop compound, is a heavily contested position.

Since the marines arrived last October it has been attacked 57 times, including twice while I was there with the photographer Nick Cornish. Inkerman stands on the edge of what the military call the "green zone", a fertile strip of land along the Helmand River which, in front of the base and for nearly 20 miles north, is almost entirely in Taliban hands.

The garrison's role is to draw enemy fire from Sangin three miles to the south — a job similar to what Sergeant James Liepa, 30, did for his men in January when his patrol was ambushed. Liepa and seven fellow marines were pinned down behind a bank of mud by Taliban fighters they could not spot. Liepa tried to get a bearing on where the gunfire was coming from but as the rounds cracked around him, he realised it was impossible.

"They were literally trying to shoot my hand off," recalled Liepa. "I thought, 'If we stay here more than a couple of minutes we'll be dead'." Liepa told his comrades he was going to stand up and make himself the prime target. "That meant I was going to jump and run so all firing points would shoot at me," he said. The idea was to give everyone else a chance to spot where the Taliban were firing from — and return fire. Liepa, from Barnstaple, Devon, gave his men a 30-second countdown. Then he got up and the bullets flew.

Liepa's bravery turned the battle around. "There are a few people who would do something like that, but not many," said Corporal George Alford, 27, a marine who was there. "The truth is that someone had to do it or we'd have been killed."

Liepa says he had no choice. "For me to tell someone else to stand up and run while everyone shoots at them just felt like sending someone to their death, so I decided to do it myself."

On his second step Liepa fell face first. As he did so, arcs of fire from at least three Taliban machineguns met above his head. "I lay there half a second and thought, 'They know where I am, I'm dead,' but I got up and ran again and the bullets were everywhere, bar me, which was nice." His men drove off the Taliban and all got out alive.

Interviewing the marines of Alpha Company, 40 Commando, it became clear the toll has been heavy: several serious injuries and the death of a much-respected corporal, Damian "Dee" Mulvihill, 32.

We met them after stepping into the choking, hot dust from a helicopter ramp. Their home was a sandy, square compound of flapping canvas and thick walls made from wire and cloth cages packed with earth.

The marines sleep under the thin protection of parachute silk or roofs made from a patchwork of ponchos. Urinals are metal tubes hammered into the sand.

We did not have to wait long to witness the dangers. The day after our arrival, Inkerman's mortars were booming away at Taliban men in front of the base. Apache helicopters strafed ditches where the enemy was hiding.

Two days later we joined an Alpha Company patrol as it headed north in Viking armoured vehicles. The plan was to head into the desert and then sweep back into the "green zone" for a surprise attack. The Taliban were waiting in ambush.

The first clue of imminent combat was the sight of men, women and children fleeing their homes as the marines approached a ridge-line. "The Taliban are actually pretty concerned to get civilians out of the way," said Captain Ian Preece, second-in-command of Alpha. Then, with marine snipers and reconnaissance troops dismounted, the enemy opened fire with a volley of machinegun fire and rocket-propelled grenades. One struck an old fort on the hilltop where Liepa and a team of snipers were hiding.

The response was ferocious. Machinegunners on the Vikings opened fire, a French jet dropped a 500lb bomb on a compound and artillery back at Inkerman fired a barrage of shells against a tree line.

Next came the Apaches came circling overhead. The Taliban, who hate these helicopters, lay low, challenging the British to descend from the ridge. With their ambush so well prepared, Major Adrian Morley, Alpha's commander, declined the offer.

Twice more the Taliban struck — a bang to the right and a cloud of black smoke announced another close by. Then a rocket came whizzing over the ridge, landing behind us. The Apaches struck back with rockets.

However, for the marines at Inkerman, named after a British victory in the Crimean war, the most ferocious fighting took place five months ago. Alpha company calls November 9 their "9/11". Returning from a foot patrol in the green zone, the marines were ambushed in open ground and ran for the shelter of a compound. It was a trap. Both the entrance and the roof were raked by enemy fire. Four men were wounded and had to be evacuated by helicopter and the troops were able to withdraw only under a barrage of artillery and mortar fire.

Marine Gary Ogden, 26, a company medic, remembers lying behind a mud bank when he felt a tug on his leg. "I glanced back at the compound entrance," he said, "and I could see a figure screaming 'medic'." The man was Captain Paul Britton, the officer who co-ordinated artillery, mortars, Apaches and air strikes. "I remember rounds hitting the doorway all around him and wondering why they weren't hitting him," said Ogden.

With the air filled with the crack and thump of bullets, Ogden charged into the compound. Propped up on the floor was Corporal Simon "Sy" Greening, with a bullet wound to his chest. Ogden patched him up, but soon there was another cry of "medic".

This time, an RPG had blasted two men from the compound roof. One, Marine David Fletcher, had serious wounds to his legs. Ogden stabilised Fletcher, but as he did so, he noticed bullets that had come straight through the open door were still thumping into walls around him.

"As I was chatting to Sy, an RPG streaked over and arched down into the compound and hit the wall I was facing. Then I saw a body drop."

It was a signaller, Corporal Dave Watts, with a shrapnel wound. Meanwhile, a huddle appeared around another man. Britton had at last been hit, but despite the shrapnel lodged in his arm, the captain opted to stay and fight rather than be evacuated.

While the group was holed up, a troop of Alpha company was dashing south through the cornfields and ditches, trying to secure a landing zone for a rescue helicopter. With the entrance under constant fire, a "mousehole" was blown in the compound wall to make an escape route. For a long time, a twin-bladed Chinook rescue helicopter had been circling round waiting to land.

"The [helicopter] was holding off because it just looked at a storm of rounds going in and out," said Ogden. "Mortars were going down and artillery was smashing the place. The Apaches were waiting to come in."

As the Chinook finally dived down to land, its two Apache escorts swerved ahead and rocketed the tree lines. "It was like a scene from Apocalypse Now," said one marine watching from Inkerman.

For the Chinook, the continuing gun battle made it a hot landing zone, a helicopter pilot's worst fear.

"The Apaches asked if the landing zone was secure," another marine recalled. "We said it was as secure as it could be."

On the ground with four casualties to evacuate, Ogden recalls a doctor running down the ramp of the helicopter and having to be dragged into cover as bullets streaked by. Without the daring rescue, said Ogden, the two most seriously injured, Greening and Fletcher, who are now recovering well in Britain, might not be alive.

When the helicopters pulled away, the troops began to pull back to the base, covered to the rear by a barrage of mortar and artillery fire. When they returned, it was dark.

The next day, Ogden and other medics were back in action as the Taliban began a month of ferocious attacks with enemy fighters coming within 100 yards of the base. Three men were injured, blown backwards and raked with shrapnel as a rocket struck the front of their firing position on the base's walls. November and December saw more than 33 attacks on the base. Commanders believed the Taliban were concentrating attacks on bases such as Inkerman to divert the British from their manoeuvres to take the Taliban stronghold of Musa Qala further north.

Since then attacks have been lighter, but new threats have emerged, such as a spree of mines laid nearby. One killed Mulvihill, from near Plymouth, who was 32 and engaged to be married, when it detonated under his Viking. A few days later a marine sniper team exacted vengeance. Operating at night, the group lay in wait in old Soviet hilltop trenches, and fired a missile at two men laying mines. The marines, now preparing to leave, realise it will be difficult to adjust to home. Among the hardest things to explain to their families will be what made them act as they did.

Liepa said: "All that happens is you look left and right and think, 'We're dead unless you do something now'," he said. "You just do what your brain tells you is the right thing."

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