A bright orange and red flash, a crack and then a huge blast shattered the heart of the country on a warm summer’s evening.
Journalist Frank Khan, among the first on the scene, recalled walking into ‘Dante’s Inferno’ as dust and debris fell over blood and scattered limbs.
The cries and screams of survivors pierced the eerie silence that suddenly dropped over Dublin’s city centre at 5.28pm on Friday, May 17, 1974.
Then the wailing sirens of fire engines, ambulances, garda cars and the chimes of shards of glass dropping from shop windows. About 90 seconds after the first explosion ripped through Parnell Street, wiping out 11 lives, a second car bomb 300m away tore up Talbot Street killing 14 people.
Broadcaster and journalist Vincent Browne was another who saw what had happened.
"Three or four bodies were strewn across the pavement outside Guiney’s store. A human torso protruded from a shop window. In one store front there were two bodies — a man and a woman, both alive — but only just," he wrote.
Esma Crabbe, a 15-year-old girl who was a volunteer with St John’s Ambulance, was called to a man lying motionless by a Fiat car on Parnell Street.
"I took his pulse, and he was dead. Then I was called to a man covered by a plank. When I lifted it up, one of his legs was missing and lying nearby," she said.
"One side of his head was completely ripped away and was lying on the ground."
On the south side of the River Liffey crowds rushing to catch trains at Pearse Station met a third explosion, killing two people at the junction of South Leinster Street and Lincoln Place.
Then at about 7pm, about 120km north, the calm summer evening in the small border town of Monaghan was shattered by another car bomb, killing five people initially with another two dying from their injuries.
Survivors lifted bodies of the dead and injured, wrapped them in coats and bundled them into cars, vans and buses to get them to the nearest hospital.
Some 33 civilians and one unborn child died as a result of the four explosions while around 258 people were injured.
No one has been arrested or convicted of involvement in the single greatest act of mass murder in the history of the Troubles.