Families of those killed and injured in the Dublin/Monaghan bombings are in a Belfast court as an attempt is made by the military and police to strike out their claim for damages.
The families allege serving soldiers and Royal Ulster Constabulary (RUC) members were among the loyalist gang which carried out the 1974 atrocities.
Some 34 people were murdered and more than 250 others were injured when four bombs went off - three in Dublin and one in Monaghan - on the evening of 17 May.
It remains the single greatest loss of life on any single day of the Troubles.
The families also allege that the authorities colluded in facilitating the bombings.
They have been pursuing damages in Belfast High Court since 2014.
Now lawyers for the Police Service of Northern Ireland, the successor to the RUC, the Ministry of Defence and Secretary of State have applied to the High Court in Belfast to throw the damages claim out.
Barrister Paul McLaughlin KC acting for the military, police and the UK government said the damages claim contained broad allegations of collusion which were not accompanied by the necessary supporting facts.
He said without such facts the army and police could not be expected to defend itself in the civil action.
Mr McLaughlin said it was unfair to ask the military and police to challenge the claim unless they knew specifically what was being alleged and against whom.
"The key facts in the statement of claim don't meet the requisite standard," he said.
Mr McLaughlin said the families cited various sources including accounts of investigative journalists, which he submitted could not be relied upon.
"We say you should strike the proceedings out," he told the judge.
A number of family members of those killed and some of the injured in the bombing made their way to Belfast for the case.
Marion Bolger was injured in the blast in Talbot Street. She said the damages claim was not about the money and that those taking it hoped it would establish as much truth as possible about the circumstances of the attack.
Kevin O'Loughlin's 51-year-old mother Christina was murdered in the explosion at South Leinster Street.
He said he was pursuing justice in her memory.
The civil action will stand or fall on the decision of the Belfast judge in this case.
It will not be affected by the UK's controversial Legacy Act which only guillotines Troubles-related civil actions begun after May of 2022.
The judgement is likely to be reserved to be delivered at a later date.
A barrister for Patrick Askin whose 48-year-old father was murdered in the Monaghan bomb said the attempt to throw out the case "defied common sense".
Brian Fee KC said the plaintiffs could not be criticised for not providing more detailed information when that information was only to be found in military, police, and government archives.
"The defendants know the case they have to meet.
He said: "We allege that serving soldiers and policemen, former soldiers and policemen and informants were part of a gang - the Glenanne Gang - which carried out the Dublin and Monaghan bombings along with a huge string of other horrendous crimes.
"We say the defendants knew that this gang comprised people in these categories and knew that they were carrying out horrendous crimes and instead of taking effective action to stop them - they facilitated it."
Mr Fee said the Dublin/Monaghan families had provided the names of soldiers and police officers who had been members of the Glenanne Gang.
"We say this is a million miles away from a bare assertion of the case."
"We have gone to considerable lengths to provide as much information as we can and it would be frankly outrageous for the defendants to avoid this case by relying on a technical point," he added.
