The first thing Robert O'Neill knew about a plan to get Osama Bin Laden was a cover story that didn't seem right.

It was early 2011 and a daring raid involving exclusively SEAL Team Six, of which he was a member, was being planned. It was 'not a drill,' but there were no details.

'They had some weird story about communication cables or something,' O'Neill said. 'It was a bad story. And then they said, We found a thing, and it's in a house, in a bowl, in this mountain range. You're gonna go get it, and bring it back, and show it to us. That's how it started.

'We asked, well, what's the thing? They said, well, we can't tell you. OK...what mountain range? Can't tell you. OK... what country? Can't tell you. How do we get in there? Can't ell you. We asked how much air support, and they said, none. It didn't make a lot of sense.

After being told to go home for one day and be with their families, they worked it out for themselves - it must be Bin Laden.

Then, they were taken to a secret place in North Carolina and the commanding officer of SEAL Team Six appeared with a woman codenamed 'Maya,' the CIA analyst who tracked Bin Laden, and would later be portrayed by Jessica Chastain in the movie Zero Dark Thirty.

Fifteen years after he shot bin Laden, O'Neill remembers it like it was yesterday.

'I'll never forget it,' he told the Daily Mail. 'She said, 'The reason you guys are here is this is as close as we've ever been to Osama bin Laden.'

'It was an honor they picked us. The initial reaction was "Cool, just gonna go right now? We're good."'

It wasn't absolutely certain but intelligence pointed to Bin Laden being located inside a fortified compound in Abbottabad, Pakistan.

SEAL Team Six flew out west to another secret base and trained for the mission, becoming acquainted with stealth Black Hawk helicopters that so 'supersecret' even President Barack Obama didn't know about them. It was the beginning of Operation Neptune Spear.

'All of these variables added up to this being a one-way mission,' O'Neill, who was 35 at the time, said. 'So it was time to get your wills right, make sure your life insurance is squared away.'

Late on May 1, 23 members of SEAL Team Six, accompanied by one interpreter and one Belgian Malinois sniffer dog called Cairo, set out from a US base at Jalalabad, Afghanistan on the two stealth Black Hawks.

They were 'Dash 1' and 'Dash 2' and O'Neill was on the latter, siting in a trifold hunting chair.

'There was a real human element to it. This was a one-way mission. Off to my left on the floor was Cairo, our Belgian Malinois. Cairo was the best dog. One guy fell asleep right next to me, headphones on sleeping.'

About 10 minutes out, as he looked through the window, a quote delivered by President George W. Bush on 9/11 popped into his head.

It was from Bush's address to the nation after Bin Laden's Al Qaeda killed 2,977 innocent people that day.

'Freedom itself was attacked this morning by a faceless coward. And freedom itself will be defended.'

O'Neill said: 'I thought what an honor, wow, this is the team, we're gonna kill him.

'I was just taking mental notes, just realizing that this is it, so whatever the afterlife is, bring these memories with you.'

On the way in the tail of Dash One hit a perimeter wall and snapped off as it tried to land inside Bin Laden's compound.

Dash 2 landed outside and, from there, they went to breach an entrance at the northeast corner of the compound. But it was a fake door and when they blew it up there was a wall behind it. The existence of a fake door suggested they were in the right place.

They then headed to the carport where vehicles came and went and the team from the crashed helicopter let them in.

When he got to a guest house one of his friends had just shot two people - Bin Laden’s courier, and his wife.

'I got to the house right as my buddy had just engaged them,' he said. Then they moved on to the main house.

'Maya had told us there will be a stairwell somewhere in the house, and that means up,' he said. 'One of my friends was at the door working through a breaching problem. I watched him and I was thinking of our training together in San Diego in the 90s. I remember, every Wednesday night we used to go to a place called Hot Tuna for drinks, but didn't drink too much, because Thursday, we'd do explosive breaching. I was just like, I am so proud of you right now, let's go.'

Maya had told them they would run into Bin Laden's son Khalid, that he would be armed, and his father's last line of defense.

'She said 'If you can ace him, you get a shot at the big guy." She referred to Bin Laden as the big guy,' said O'Neill.

Khalid was behind a railing on the stairwell and the point man whispered his name until his head popped up.

'He got blasted, and then we went around him,' said O'Neill.

When they reached the second floor, some of the team fanned out to search rooms, while O'Neill followed the point man to the third floor.

There was a curtain and the point man saw two figures who could be suicide bombers, so he jumped on them.

Later, when he was asked why, his response immediately was, "I never want the guy behind me to die." That man, no one knows who he is and he should have Medal of Honor, no doubt about it,' said O'Neill.

That left O'Neill face to face with Bin Laden, about three feet away, and the terror leader had his hands on the shoulders of his wife Amal.

'I was surprised at how skinny he was,' O'Neill said. 'If I had to describe him in my mind's eye right now, 15 years later, wit would be that he seemed confused, and that's got to be just because we're very, very quiet.

'Knowing the suicide bombers might be coming, Bin Laden had less than a second to convince me not to kill him, and he did not do that.

'It seemed like he might be maneuvering. So I shot him twice, and shot him again.'

Bin Laden was hit near the left eye and part of his skull was blown off.

With the terror leader down, O'Neill moved a two-year-old boy who was in the room.

'I remember thinking, this poor kid has nothing to do with this and I moved him to the bed.'

Others then came into the room and saw the scene.

O'Neill recalled: 'One of the guys saw me and said "Are you good?" I said, "What do we do now?" And he said, "Now we find the computers."'

'My initial thought was, holy s*** we should live, I can see my kids again. Let's get our s*** together, be professional now, chop, chop, lets go. I was finding so much (computer) stuff, though, it was hard to walk away from.'

It proved an intelligence gold mine including five computers, 10 hard drives, 100 thumb drives, DVDs, mobile phones and paper documents.

O'Neill and the point man carried Bin Laden downstairs in a body bag and then were lifted out on a Chinook support helicopter.

Eighty-five minutes later the pilot announced they were clear of Pakistani airspace.

'Gentlemen, for the first time in your life, you're going to be happy to hear this,' he said. 'Welcome to Afghanistan.'