Victims of the Miami Showband massacre are suing the Ministry of Defence and PSNI over alleged collusion with the loyalist killers, it's been revealed.
Writs issued by survivors and relatives of two murdered group members include claims for assault, trespass, conspiracy to injure, negligence and abuse of public power.
Both aggravated and the more punitive form of exemplary damages are being sought.
The High Court proceedings centre on the collaboration between terrorists and military personnel to carry out the infamous killings.
The action comes after the release of a book by former journalist Anne Cadwallader detailing alleged collusion in dozens of murders by a gang including serving police and UDR members in the 1970s.
Three members of the popular band were taken from their tour bus and shot dead on a country road after a gig in Banbridge, Co Down, in July 1975.
They were travelling home to Dublin when a fake Army patrol made up of UDR and UVF members stopped them at a bogus checkpoint outside Newry.
Band members were made to line up at the side of the road while attempts were made to hide a bomb on the bus.
The device exploded prematurely, killing some of the would-be bombers.
The other gunmen then opened fire on the band, murdering lead singer Fran O'Toole, guitarist Tony Geraghty and trumpeter Brian McCoy.
Two other band members, Des McAlea and Stephen Travers, were injured but survived the atrocity.
In 2011, a report by the Historical Enquiries Team raised collusion concerns around the involvement of an RUC Special Branch agent.
It found that UVF commander Robin 'The Jackal' Jackson had been linked to one of the murder weapons by fingerprints. Jackson claimed in police interviews he had been tipped off by a senior RUC officer to lie low after the killings.
He went on trial charged with possession of a silencer attached to a pistol used in the murders but was subsequently acquitted.
Two serving members of the UDR were, however, eventually convicted for their part in the attack.
Based on documents uncovered by campaign groups, the legal action is being taken by Mr McAlea, Mr Travers, and the families of Fran O'Toole and Brian McCoy.
Their solicitor, Michael Flanigan, confirmed that writs have been issued against both the MoD and Chief Constable.
It is expected to be next year before the case is heard in the High Court.