They had come to the gates of their Masserene base in Co Antrim to collect pizza when they were ambushed by terrorists firing automatic rifles.
Four other people were wounded in the attack including a Polish national who is critically ill in hospital. The killers even stood over their victims and fired a second volley.
Last night, a Dublin-based newspaper had a call supposedly from the Real IRA claiming responsibility for the attack, using a recognised codename.
Gordon Brown declared that "no murderer will be able to derail the peace process" but there was anxiety that the killings might generate either political recriminations or retaliation from extreme loyalists. The Prime Minister said: "The whole country is shocked and outraged at the evil and cowardly attacks on soldiers serving their country. We will do everything in our power to make sure that Northern Ireland is safe and secure, and I assure you we will bring these murderers to justice."
Martin McGuinness, of Sinn Fein, said: "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 restart that war. Well, I deny their right to do that."
Security sources said the planning and execution of the attack showed an increasing sophistication among the dissidents, as well as growing evidence of collusion between republican groups. Monitoring of communications presented a "confusing and complex" picture in which members of the two main groups, Real and Continuity IRA, appeared to be speaking to each other while the groups themselves were split into as many as six sub-groups.
There was also evidence that the dissidents have been acquiring weaponry including semi-automatic rifles, machine-pistols and, mechanisms for detonating pressure-plate explosive devices of the type British forces face in Afghanistan and Iraq. But security sources deny reports that a 300lb car bomb found at Castlewellan, Co Down, had, as it was reported at the time, an advanced anti-handling device.
Though it seems there were no prior indications of the Saturday night attack, security was already unusually high because of an increased threat from a variety of small-scale but lethal republican dissidents opposed to the peace process. This month, the threat level was upgraded from "substantial" to "severe", and sources revealed that MI5 spends 15 per cent of its resources on countering terrorism in Northern Ireland. Chief Constable Sir Hugh Orde recently requested support from the Army's Special Reconnaissance Regiment to help with surveillance.
The weekend victims had gone to meet a mobile Domino's Pizza takeaway which had arrived with food for the soldiers. The gunmen obviously knew of the regular routine on Saturday nights when as many as 20 orders of pizza were delivered. They waited until the troops emerged through the gates to pick up the food. The ambushers then stepped forward from the shadows and sprayed bullets with sustained bursts from semi-automatic weapons, hitting four soldiers and two Domino employees.
A senior police officer said: "The gunmen, having fired an initial volley of shots, moved forward when people were on the ground and fired additional shots at those people on the ground, so it was a very, very callous and very ruthless attack."
Maverick republican splinter groups have for some time publicly proclaimed their ambition to kill members of the security forces as part of a strategy to restart the Troubles and return to large-scale conflict. They have injured several police personnel in gun and bomb attacks but security force members have escaped with their lives, sometimes by luck.
Northern Ireland's First Minister Peter Robinson said there must not be retaliation for the attack, declaring: "Can I urge all of those who may be angry within the Unionist community; this is a matter to be left entirely with the police and the authorities to deal with."
Frankie Gallagher, a member of a political group which has links with the paramilitary Ulster Defence Association, echoed this, saying: "This cowardly attack has created considerable anger in unionist communities but there must be no retaliatory actions. This situation must be dealt with entirely by the police."
Mr Robinson and Mr McGuinness have delayed a planned visit to the US which is due to end with meeting President Barack Obama at the White House.
Sir Hugh Orde added: "This was an act by an increasingly desperate small group of increasingly desperate people who are determined to drag 99 per cent of this community back to where they don't want to go."