WASHINGTON, May 17: Those who planned the secret mission to get Osama bin Laden in Pakistan knew there was no room for error, and it nearly went terribly wrong.

The US deliberately hid the operation from Pakistan, and predicted that national outrage over the breach of Pakistani sovereignty would make it impossible to try again if the raid on Bin Laden's suspected redoubt came up dry.

Once the raiders reached their target, things started to go awry almost immediately, officials briefed on the operation said.

Adding exclusive new details to the account of the assault on Bin Laden's hideout, officials described just how the SEAL raiders loudly ditched a foundering helicopter right outside Bin Laden's door, ruining the plan for a surprise assault.

That forced them to abandon plans to run a squeeze play on Bin Laden --- simultaneously entering the house stealthily from the roof and the ground floor. Instead, they busted into the ground floor and began a floor-by-floor storming of the house, working up to the top level where they had assumed Bin Laden (if he was in the house) would be.

They were right, according to the officials.

The US raiders came face-to-face with Bin Laden in a hallway outside his bedroom, and three of the Americans stormed in after him, the officials said on condition of anonymity.

The decision to launch the attack on that particular moonless night in early May came largely because too many American officials had been briefed on the plan. US officials feared if it leaked to the press, Bin Laden would disappear for another decade.

US special operations forces have made approximately four forays into Pakistani territory since the Sept 11, 2001, attacks, though this one, some 145km inside Pakistan, was unlike any other.

The job was given to a SEAL Team 6 unit, just back from Afghanistan, one official said. This elite branch of SEALs had been hunting Bin Laden in eastern Afghanistan since 2001.

Five aircraft flew from Jalalabad, Afghanistan, with three school-bus-size Chinook helicopters landing in a deserted area roughly two-thirds of the way to Bin Laden's compound in Abbottabad, two of the officials explained.

Aboard two Black Hawk helicopters were 23 SEALs, an interpreter and a tracking dog named Cairo. Nineteen SEALs would enter the compound, and three of them would find Bin Laden, one official said, providing the exact numbers for the first time.

Aboard the Chinooks were two dozen more SEALs, as backup.

The Black Hawks were specially engineered to muffle the tail rotor and engine sound, two officials said. The added weight of the stealth technology meant cargo was calculated to the gram, with weather factored in. The night of the mission, it was hotter than expected.

The Black Hawks were to drop the SEALs and depart in less than two minutes, in hopes locals would assume they were Pakistani aircraft visiting the nearby military academy.

One Black Hawk was to hover above the compound, with SEALs sliding down ropes into the open courtyard.

The second was to hover above the roof to drop SEALs there, then land more SEALs outside, plus an interpreter and the dog, who would track anyone who tried to escape and to alert SEALs to any approaching Pakistani security forces.

If troops appeared, the plan was to hunker down in the compound, avoiding armed confrontation with the Pakistanis while officials in Washington negotiated their passage out.

The two SEAL teams inside would work towards each other, in a simultaneous attack from above and below, their weapons silenced, guaranteeing surprise, one of the officials said. They would have stormed the building in a matter of minutes, as they'd done time and again in two training models of the compound.

The plan unravelled as the first helicopter tried to hover over the compound. The Black Hawk skittered around uncontrollably in the heat-thinned air, forcing the pilot to land. As he did, the tail and rotor got caught on one of the compound's 3.6-metre walls. The pilot quickly buried the aircraft's nose in the dirt to keep it from tipping over, and the SEALs clambered out into an outer courtyard.

The other aircraft did not even attempt hovering, landing its SEALs outside the compound.

Now, the raiders were outside, and they'd lost the element of surprise. They had trained for this, and started blowing their way in with explosives, through walls and doors, working their way up the three-level house from the bottom.

They had to blow their way through barriers at each stair landing, firing back, as one of the men in the house fired at them. They shot three men as well as one woman, whom US officials have said lunged at the SEALs.

Small knots of children were on every level, including the balcony of Bin Laden's room.As three of the SEALs reached the top of the steps on the third floor, they saw Bin Laden standing at the end of the hall. The Americans recognised him instantly, the officials said.

Bin Laden also saw them, dimly outlined in the dark house, and ducked into his room.

The three SEALs assumed he was going for a weapon, and one by one they rushed after him through the door, one official said.

Two women were in front of Bin Laden --- yelling and trying to protect him, two officials said. The first SEAL grabbed the two women and shoved them away, fearing they might be wearing suicide bomb vests, they said.

The SEAL behind him opened fire at Bin Laden, putting one bullet in his chest, and one in his head. It was over in a matter of seconds.

Back at the White House situation room, word was relayed that Bin Laden had been found, signalled by the code word “Geronimo”.

As the SEALs began photographing the body for identification, the raiders found an AK-47 rifle and a Russian-made Makarov pistol on a shelf by the door they'd just run through. Bin Laden hadn't touched them.

They were among a handful of weapons that were removed to be inventoried.

It took approximately 15 minutes to reach Bin Laden, one official said. The next 23 or so were spent blowing up the broken chopper, after rounding up nine women and 18 children, to get them out of range of the blast.

One of the waiting Chinooks flew in to pick up Bin Laden's body, the raiders from the broken aircraft and the weapons, documents and other materials seized at the site.

The helicopters flew back to Bagram Air Base in Afghanistan, and the body was flown to a waiting US Navy ship for Bin Laden's burial at sea, ensuring no shrine would spring up around his grave.—AP