The Balcombe Street gang, as they became known after the dramatic siege of a flat in Balcombe Street, London, in December 1975, was part of a specialist IRA unit which sometimes numbered as many as 20. It was described as "the most violent, ruthless and highly-trained unit ever sent to Britain by the Provisional IRA".
The description did not come from a prosecuting barrister but from the Press Association on February 11th, 1977, the day after Mr Justice Cantley, sitting at the Old Bailey, sentenced Edward Butler, from Limerick; Hugh Doherty, from Carrigart, Co Donegal; Harry Duggan, from Feakle, Co Clare, and Martin Joseph O'Connell, from Kilkee, Co Clare, to 47 life sentences.
Mr Justice Cantley described the four as "criminals who call themselves soldiers". He recommended that each serve at least 30 years.
The life sentences were imposed for the deaths of seven people: broadcaster and journalist Ross McWhirter; explosives expert Capt Roger Goad; cancer specialist Prof Gordon Hamilton-Fairley;
Robert Anthony Lloyd, who died in a Hilton Hotel bombing; Graham Ronald Tuck, who was killed in a Piccadilly explosion; and Audrey Edgson, who died in an explosion at Walton's Restaurant, Mayfair, and John Francis Bately at Scitts Restaurant, Mount Street.
The charges related to a bombing in Oxford Street; bombings at the Hare and Hound public house in Maidstone; a car bomb attack in Connaught Square; and two firearms charges relating to the attack on Goff's restaurant on the night of the Balcombe Street siege, December 6th, 1975.
The bombings were described as a "reign of terror" perpetrated by the IRA in the two years prior to 1975.
Between them, including additional sentences, they were sentenced to more than 600 years in prison.
The unit was, ironically, modelled on the British army unit, the SAS. The training they received produced a team which was so closely integrated that police experts at the time of the trial said they believed it unlikely that another such unit could ever be recruited.
As the bombing campaign progressed, it was targeted by Scotland Yard's anti-terrorist branch. On December 6th, the four were chased through London by the Metropolitan Police after they fired an automatic weapon at a restaurant in Mayfair. Having driven into a cul-de-sac, they ran through the open door of a house, holding Mr and Mrs John Matthews hostage in a first-floor flat.
The siege ended after six days with the hostages being released. The gang gave itself up.
In addition to being unknown to other members of the wider Irish republican community in London, the four were remembered in their home districts as quiet men.
Harry Duggan was one of four children of Mr and Mrs Harry Duggan, of Feakle, Co Clare. He was born in Kilburn, London, before returning to Co Clare with the family when he was three. He left school at 14 and became a carpenter in a local factory. He became active in Sinn Fein when the troubles started in the late 1960s and in 1972 his family was told he was "killed in action". His father searched a graveyard in Scarriff, Co Clare, after gardai had said his son had been buried secretly.
It was during the Balcombe Street siege that fingerprints from Ireland confirmed his identity. His father, who said he had not heard from his son for two years before the siege, described him as "a nice quiet boy at home who never gave us any trouble".
Edward Butler's family lived in a small cottage in Castleconnel, Co Limerick. He is one of seven children and worked as a labourer with Limerick County Council. He sold republican newspapers outside his local church before leaving the area a year before the siege. Butler's father was formerly a private in the Defence Forces.
Martin Joseph O'Connell, known as Joe, lived with his parents in a small bungalow beside their farm in Co Clare until 1974. His mother, Ms Annie O'Connell, said after his arrest: "I don't know how he got mixed up with such people."
In 1996, O'Connell wrote from jail to Sinn Fein's An Phoblacht newspaper, declaring the IRA ceasefire to be "the most stupid, blinkered and ill-conceived decision ever made by a revolutionary body".
Hugh Doherty was born in Glasgow but his family came from Co Donegal, where his relatives still live. After leaving school, he worked in various parts of Britain as a labourer on road building contracts. His brother Pat is a vice-president of Sinn Fein.
The four are currently on leave from Portlaoise Prison and will return on Wednesday to be formally released.
Meanwhile, the Police Federation of England and Wales has protested at the early release of the fifth man yesterday, Irish-American William (Liam) Quinn, who was released from Portlaoise Prison.
Quinn (51) was jailed for life in 1988 after being extradited from the US for shooting dead PC Stephen Tibble in Hammersmith, west London, 13 years earlier. He was repatriated in May of last year.
Labour's Sen Joe Costello has given a warm welcome to the release of the sixth man. He said he always believed John Kinsella was an innocent man.
Kinsella, originally from Ballyfermot, Dublin, was sent to prison in 1993 for involvement in a bomb attack on Warrington gas works. He was repatriated in December to Wheatfield Prison. He would have been due for release in 2004.