The INLA bombing of the Droppin Well bar in Co Derry in 1982 was almost called off at the eleventh hour.
A day before the attack, which was to claim the lives of six civilians and 11 British soldiers, an INLA member and his girlfriend were ordered to pick up a charger for the bomb from a safe house in Buncrana in Co Donegal.
When they arrived from Derry, they found nothing had been left for them. The operation was almost abandoned but later that Sunday the INLA man decided to return to the town and this time the charger was ready.
He took the device back to Derry where the bomb was being made.
Small by standards of the time, it is believed to have consisted of 10 pounds of Frangex explosives.
The following night, Monday December 6, it was left beside a pillar at the Droppin Well bar in Ballykelly. When it exploded at 11.15pm, it collapsed the roof of the crowded bar, killing 17 people and injuring another 30.
Ballykelly had always been a garrison town. Just two miles from Limavady on the main Derry road, it was home to one of the biggest British army bases in the north with housing estates also providing married quarters behind security fencing.
The Droppin Well was selected because it was a known favourite for off-duty soldiers.
The huge loss of life ensured that 1982 was the first time the INLA killed more people than the Provisional IRA. The bombing also came after a long period of relative inactivity by the Derry INLA.
In claiming responsibility, the paramilitary group described the civilian women killed in the massacre as "consorts".
In a statement the INLA said: "We believe that it is only attacks of such a nature that brings it home to the people in Britain and the British establishment. The shooting of an individual soldier, for the people of Britain, has very little effect in terms of the media or in terms of the British administration."
It later emerged that the INLA may also have targeted Ballykelly because it believed it was part of Nato's radar and communications network.
In June 1986 four people were jailed for life for the massacre while a fifth received a 10-year sentence.
Anna Moore (40) and her sister Helena Semple (29), from Derry's Bogside, were given life sentences along with Semple's partner Eamon Moore (25) and Patrick Shotter (40), who was the boyfriend of Anna Moore's daughter Jacqueline Ann Moore (19).
Jacqueline Ann Moore was given a 10 years for manslaughter when the court accepted she had been forced into involvement.
In court Anna Moore revealed that the INLA had carried out reconnaissance missions to the Droppin Well to see if there were enough soldiers to justify the possibility of civilian casualties.