Bernard McGinn (41), of Castleblayney, Co Monaghan, was given life sentences at Belfast Crown Court yesterday for the murder of three British soldiers in south Armagh.
He was also jailed for a total of 490 years for a list of IRA crimes, including making the bombs used in London at Canary Wharf, the Baltic Exchange and Hammersmith Bridge.
McGinn and three co-accused, Michael Caraher (31), of Cullyhanna, Martin Mines (30), of Silverbridge, and James McArdle (29), of Crossmaglen, were also each given 20 years for conspiracy to murder and 20 years for weapons possession.
The Northern Ireland Lord Chief Justice, Sir Robert Carswell, said McGinn had admitted to police that he had made explosives north and south of the Border on an almost daily basis, "like a day's work".
McGinn, although not the "trigger man", was convicted of murdering Lance Bombardier Stephen Restorick, who was shot by a sniper at a checkpoint in the village of Bessbrook, Co Armagh, in 1997.
He also received life sentences for the murders of Lance Bombardier Paul Garrett in Keady, Co Armagh, in 1993, and former UDR soldier Thomas Johnston, who was shot dead in Keady in 1978.
Lance Bombardiers Restorick and Garrett were victims of an IRA Border sniper unit which made single-shot attacks on the security forces using a powerful American-made Barrett "Light 50" long-range rifle.
Caraher was sentenced to another 25 years for the attempted murder of RUC Constable Ronnie Galway, who was injured in a sniper attack in Forkhill, Co Armagh, in 1997, and jailed for 20 years for having the weapon used in that attack.
The judge said: "Weapons of death and destruction have been used to lethal effect on all too many occasions, and possession of them must be considered a grave offence."
A fifth man, Mr Michael Anthony Kearns (58), from Crossmaglen, was found not guilty of making a hayshed available to terrorists.
All the men were arrested when troops swooped on Mr Kearns's farm in 1997 and uncovered the Barrett rifle and an assault rifle hidden in a secret compartment in the bottom of a trailer.
Police also seized mobile phones, CB radios and a car which had been adapted as an armour-plated firing platform.
Convicting the men, the Lord Chief Justice said he was satisfied they were all at the farm preparing an operation to murder yet another soldier.
The RUC man who led the investigation branded the terrorist team as "undoubtedly one of the most vicious, callous and ruthless" ever recruited, trained and activated in south Armagh.
The four defendants, all of whom refused to stand up and recognise the court when sentenced, laughed and shouted to friends as they were led away handcuffed by prison officers.
Ms Rita Restorick, mother of Stephen, watched yesterday as the gang was convicted.
Her son, the last soldier to be killed in Northern Ireland before the Belfast Agreement, was hit by a bullet from a Barrett rifle as he spoke to a local woman, Ms Lorraine McElroy, as she went through the Bessbrook checkpoint.
Ms Restorick said after yesterday's hearing that she thought justice had been done, but she called for a rethink over the early-release scheme because of the seriousness of the offences.
She said they would be released in just over a year's time, and considering the seriousness of the crime, and also the fact that the Taoiseach, Mr Ahern, had said the killers of a garda would not be eligible for early release, "I believe the same consideration should be given for this case."
However, she said she would still support the early-release scheme if paramilitaries started giving up their weapons. "At the moment we, as victims' families, are being asked to give everything," she said.
"We are seeing the people found guilty of our loved ones' murders walk free early, and it's time the paramilitaries gave that little bit towards decommissioning. They have to make a move."
Mrs Restorick said what she wanted from the Belfast Agreement was that "no more mothers, no matter on what side, have to face the death of a son." Lance Bombardier Garrett's father, Gladstone, said: "If the process towards peace works I will think Paul has made a little contribution."