They were ambushed by terrorists firing automatic rifles as they were about to take delivery of pizzas before catching a flight to Helmand.
The ruthlessness of the shootings which rocked the peace process and shocked political representatives in Belfast, London and Dublin, left two other soldiers badly wounded. Two delivery men were also hit, one critically.
Security chiefs believe the gunmen were prepared to murder all six in front of the main gates of the Massereene Barracks at Antrim. At one stage the killers stood over their victims and fired a second volley.
Chief Constable Sir Hugh Orde who had earlier called in undercover soldiers to carry out surveillance operations in a bid to thwart a heightening threat against his officers, ruled out putting troops back on the streets.
But the planning and execution of this double-murder after a series of failed attacks over the past two years will mean an immediate and urgent review of security measures.
There are an estimated 200-300 dissident republicans active in Northern Ireland, and even though no more than a dozen may have been directly involved, detectives believe the two masked gunmen who opened up before being driven off in a getaway car on Saturday night were clearly experienced in the use of high powered weaponry.
Sir Hugh said: "This was an act by an increasingly desperate small group of increasingly desperate people who are determined to drag 99% of this community back to where they don't want to go."
Prime Minister Gordon Brown and the Irish Taoiseach Brian Cowen insisted the killings would not disrupt the peace process. However the Northern Ireland First Minister Peter Robinson and the deputy First Minister Martin McGuinness have delayed a planned visit to the United States which was due to end next Tuesday with a St Patrick's Day meeting with President Obama at the White House.
The names of the dead soldiers have been withheld until all their relatives have been informed. They were due to fly out of RAF Aldergrove, just a few miles away from their base in the early hours of today.
It departed with four empty seats, and even then the flight had to be held up until investigating police officers finished interviewing other soldiers who were near or close to the main gates at the time of the attack.
The gunmen were obviously aware that soldiers at the Massereene Barracks followed a regular routine on Saturday nights when as many as 20 separate orders were made for pizza to be delivered.
They waited until the troops, all dressed in desert fatigues, emerged through the gates to pick up the food. One burst of automatic fire was followed by another just seconds later as the four soldiers and the two delivery men - one of them was Polish - lay wounded on the ground.
All sides in Belfast denounced the attack, and even though Sinn Fein's condemnation stopped short of expressing sympathy for the soldiers and their families, Mr McGuinness, a former IRA leader in Londonderry, demanded the dissidents call off their campaign.
Chairman of the Northern Ireland Policing Board Professor Sir Desmond Rea said: "It is with horror and sorrow that I learned that two men have been killed and four others injured in the gun attack at Massereene Army base. On behalf of the Board I unequivocally condemn this vile attack and those who are responsible for it.
"Our thoughts are with the families of those killed and injured."
Martin McGuinness added: "I was a member of the IRA, but that war is over now. The people responsible for last night's incident are clearly signalling that they want to resume or re-start that war. Well, I deny their right to do that."
Mr McGuinness, MP for Mid-Ulster, told the BBC: "I will stand for all democrats against their attempts to plunge us back into conflict; to see soldiers on the streets; to see more checkpoints on the roads; to see houses being raided and to see people being dragged back to interrogation centres. Those days are over. They can never come back again."
The last soldier to be killed in Northern Ireland was in February 1997 - just over a year before the signing of the Good Friday peace agreement - when the IRA shot dead Lance Bombardier Stephen Restorick, 23, in south Armagh.
That particular area as well as parts of Tyrone, Londonderry and especially south Fermanagh, is where the dissident threat is at its highest.
They came dangerously close to killing police officers in four separate gun and bomb attacks in Derry, Dungannon, Castlederg and Rosslea and last month a 300lb car bomb on its way to an army base at Ballykinler, near Newcastle, Co Down was abandoned in a hurry near a school.
But this shooting, according to authoritative security sources in Belfast, represented a "step change" by the terrorists belonging to the Real IRA and Continuity IRA, many of whom quit the Provisional IRA after becoming disillusioned with Sinn Fein's peace strategy. No organisation has claimed responsibility.
One security source said: "They would have been quite happy to have killed all six at Antrim. Civilians didn't matter, and that's a sign of just how desperate and determined they've become.
"As targets go, they didn't come much softer than this. They achieved their objective, but I wonder how much greater the impact on the public here (Northern Ireland) might have been had they been police officers rather than British soldiers?"
The chief of police in the Irish Republic, Garda Commissioner Fachtna Murphy whose officers are heavily involved in countering the dissident threat in border areas is to meet with Sir Hugh in Dublin on Thursday.
They spoke by telephone in the hours after the Antrim attack. Sir Hugh confirmed later he has no plans to bring troops back onto the streets as operational support for the police, or call up more military resources for undercover duties.
After the Real IRA bomb atrocity in Omagh in August 1998 which claimed the lives of 29 people, including a mother pregnant with twins, the dissidents more or less went to ground.
But in the last three years the level of activity has gradually picked up, even though virtually all of their attacks ended in failure or were foiled.
The republicans suspected of orchestrating the violence are effectively under round the clock surveillance, especially one based in south Armagh and another in Fermanagh.
There was no advance intelligence of any threat at the Massereene Barracks, one of the lesser known military installations in Northern Ireland where the Engineers Regiment had been based since last summer