Forty years ago the Provisional IRA carried out two of its most audacious attacks. In Mullaghmore, Co Sligo, they exploded a bomb on the boat of the former UK chief of defence staff and cousin to the Queen, Lord Louis Mountbatten - killing him, two teenage boys and his daughter-in-law's mother. Later that afternoon, at Narrow Water, near Warrenpoint in Co Down, the Provisionals struck again, this time exploding two huge bombs on a military convoy carrying soldiers from the Parachute Regiment.
The pathologist who arrived on the scene shortly after the attack at Narrow Water, Arthur Orr, later told the inquest into the soldiers' deaths that he had "never seen such carnage". For Orr it was "the most distressing incident" he had ever encountered in his 25 years as a coroner.
It later emerged that gardai had stopped and arrested two young men from Crossmaglen, who were riding a motorcycle on the Republic's side of the border near the detonation point in Omeath. At the Smithwick Tribunal, which investigated allegations of collusion between Irish police and the IRA, it was revealed that a forensic report recorded how, even though swabs had been taken from both men, police could not tie the suspects conclusively to the attack and they were released.
No one has ever been brought to account for the murders of the soldiers that day.
Thirty years after the Warrenpoint ambush I met one of the soldiers who survived the massacre, Paul Burns, at the launch of his memoir, A Fighting Spirit. Paul was travelling in a four-tonne truck with seven other paratroopers when the first explosion happened. A massive fireball engulfed the vehicle and he lost a leg in the blast.
"And I do not hear the bang, nor the screams that follow," he wrote. "I do not smell the stench of burning flesh, or witness the confusion. All I know is darkness."
While Paul suffered horrific injuries on that day, he would remain in the Army until 1991 and become a tireless advocate for the British Limbless Ex-Servicemen's Association (now Blesma, The Limbless Veterans).
Paul's story is like so many others I've heard about Warrenpoint. One former soldier, who had been on an earlier tour with the men killed and injured in the attack, recalls hearing the news while he was stationed in an Army camp in Antrim:
"I was in the ops [operations] room at the time and it brought back memories of '73. The IRA had that well planned, with the secondary device."
Another veteran, Parachute Regiment officer David Benest, recalled. "I was on leave. I turned up the day after to a battalion in shock. Soldiers thinking: 'Crikey, that number of people being killed in one incident?'"
Relations between the Army and RUC were badly strained by Warrenpoint. It was said that the General Officer Commanding Sir Timothy Creasey "freaked out" when he heard the news and tried to wrest back control of security operations from the Chief Constable, Sir Kenneth Newman. Recognising the discord within the security forces, Prime Minister Margaret Thatcher flew to Northern Ireland to calm tempers.
"The people of the United Kingdom will wage the war against terrorism with relentless determination until it is won," she told reporters.
Thatcher had been personally affected by the Troubles when the INLA assassinated her long-time friend and political mentor, Airey Neave, in 1978. She was renowned for taking an uncompromising public stance; after Warrenpoint she sanctioned an intelligence-led response to IRA violence.
One of the most visible signs of this new approach came when she appointed the recently retired chief of the Secret Intelligence Service, or MI6, Sir Maurice Oldfield as security and intelligence co-ordinator in Northern Ireland. He arrived in Belfast in October 1979.
Former RUC Special Branch officers have admitted to me that intelligence "coverage" was limited in south Armagh prior to Sir Maurice's arrival. One officer even suggested to me that "Oldfield's job was to hold people's hands" through a process of change.
That change was Thatcher's decision to keep the RUC in the lead against the terrorists, with the Army in support under the mantra "policy primacy".
Sir Maurice believed that the best way to deal more effectively with the IRA was to turn its own members against the group. To "start a cancer and watch it spread", as one veteran RUC spymaster put it. In this Sir Maurice had some success.
The "supergrass" trials of the early 1980s were part of his legacy after his retirement from the post; so, too, was the comprehensive infiltration of the Provisionals by agents. The direction given to these moles was to disrupt IRA activity and to help move the group down a political path.
Sir Maurice also believed - as did Thatcher - that the only way to tackle IRA terrorism was to work closely with the authorities in Dublin. The Irish border had long been porous and IRA members and smugglers crossed it with ease, despite the presence of a number of crossings manned by security forces on the northern side.
Interestingly, Omeath, where the Provos responsible for Warrenpoint had detonated their bombs, would become a key hub of IRA activity over the coming years. It was the place where the Provisionals' internal security unit (or "nutting squad") once took suspected "touts" for interrogation. And it was the place where the IRA also kept a major bomb-making factory in the 1980s. These borderlands were synonymous with the political dispute at the heart of the Troubles.
As we remember the 18 soldiers and one civilian killed near Warrenpoint four decades ago, it is also worth keeping in mind how it represents a Pyrrhic victory for the IRA.
Within a decade of the killings the group came under intense pressure from the security forces and had even moved towards secret talks with the British aimed at ending its armed campaign.
Nowadays some republicans have desecrated the poppy wreaths left by the roadside to commemorate the soldiers who died at Narrow Water.
But attempts to dismantle the visible symbols of their past atrocities can never fully eradicate the memories of such evil deeds, nor of militant republicanism's ultimate strategic surrender.
⏭ Dr Aaron Edwards is the author of UVF: Behind The Mask (Merrion Press, 2017). He is currently writing a new book for Merrion on Britain's secret intelligence struggle against the Provisional IRA.