In the recent Hollywood biopic, Jackie, there is a scene that shows John F Kennedy's newly bereaved widow on November 22, 1963, talking to a group of advisers known as the 'Irish Mafia'. "We need to have the Irish Cadets," she says. "For the funeral. Jack loved them. He saw them perform in Dublin last summer."
Like most of the film's dialogue, this is based on solid fact. Although Jackie was pregnant in June 1963 and did not travel with JFK to the land of his ancestors, she knew how much the visit had moved him. For several weeks afterwards he had shown home movies from Ireland in his private White House cinema, urging everyone around him: "You've got to come and watch this!"
Although it has become a cliché, the reality is that virtually everyone alive back then can remember where they were when news of Kennedy's death came through. Equally, almost every memoir by an Irish person who saw him in the flesh tries to describe what a seminal experience it was.
Bertie Ahern watched JFK's cavalcade sweeping through Drumcondra, in Dublin, and thought he had "never seen anyone so glamorous in all my life". For Joe Duffy, the most striking feature of all was his tan: "He almost looked orange." Bob Geldof felt that: "People had gone crazy… he was for us the ultimate Irish success story. An Irishman, or as good as, who had got to be president of the USA."
At a time when the Irish desperately needed a morale boost, Kennedy gave them one by telling them this country had a great future as well as a tragic past. Grown men and women wept after shaking his hand, while in Co Mayo a 12-year-old boy called Enda Kenny began learning his speeches off by heart.
In some Irish homes, a photograph of the first Catholic US president was displayed as a Holy Trinity alongside the Pope and the Sacred Heart.
When he left Shannon Airport, his parting words were: "This is not the land of my birth, but it is the land for which I hold the greatest affection, and I certainly will come back in the spring time."
All this helps to explain why Ireland was so shocked by the news that broke on a gloomy Friday evening. Many people headed to Dublin's Pro Cathedral and other churches where masses were heard for the dead man's soul. The Tricolour flew at half-mast over public buildings, a national day of mourning was declared and all GAA matches for the following Sunday were cancelled.
By the time the Irish Independent's first edition hit news-stands on Saturday morning, the basic facts had been established. President Kennedy was shot in the head while travelling in an open-topped car through downtown Dallas with Jacqueline by his side. As the motorcade sped to Parkland Hospital where doctors laboured in vain to save him, she was heard crying: "I have his brains in my hands." Governor John Connally, seated directly in front of JFK, suffered serious wounds from the hail of gunfire but ultimately survived.
The alleged assassin was a 24-year-old ex-marine with communist sympathies called Lee Harvey Oswald. He had apparently murdered a policeman before being arrested in a cinema shortly afterwards. Although the evidence against him seemed overwhelming, he denied any involvement and yelled: "I'm just a patsy!" to reporters.
A series of iconic images has come to define that tragic weekend in Texas. Lyndon B Johnson taking the presidential oath of office on Air Force One as Jacqueline Kennedy stood by in her bloodstained pink suit. Oswald being gunned down while still in police custody by the nightclub owner Jack Ruby, who claimed that he wanted to spare Mrs Kennedy the ordeal of a public trial. Most poignantly of all, the three-year-old John F Kennedy Jr saluting his father's casket as it left St Matthew's Cathedral in Washington DC.
One week after the assassination, President Johnson created a commission led by Chief Justice Earl Warren to determine who exactly had been responsible. In September 1964, the Warren Commission delivered its 888-page report, concluding that Oswald was indeed the sole culprit. A majority of Americans could not accept this verdict and the case spawned wild and wonderful conspiracy theories.
Over the last half-century, an avalanche of books has sought to convict the FBI, the CIA, the Mafia, Fidel Castro and Lyndon Johnson himself of ordering Kennedy's death. There are even assassination buffs who claim that his Irish driver, William Greer from Co Tyrone, turned and shot the president while nobody was watching. This kind of paranoid speculation reached its zenith in 1991 with Oliver Stone's exhilarating but deeply misleading film JFK.
Since then there has been a backlash and most reputable historians now agree that the Warren Commission's conclusions were basically correct. On the 50th anniversary of the assassination in November 2013, however, a Gallup opinion poll showed that 61pc of Americans still believed Oswald was either innocent or had some help. The American author William Manchester, who was hired by the Kennedy family to write a book about the case, offered a convincing explanation for the popularity of conspiracy theories.
"There is an aesthetic principle here. If you put six million dead Jews on one side of a scale and on the other side put the Nazi regime - the greatest gang of criminals ever to seize control of a modern state - you have a rough balance: greatest crime, greatest criminals.
"But if you put the murdered President of the United States on one side of a scale and that wretched waif Oswald on the other side, it doesn't balance. You want to add something weightier to Oswald. It would invest the president's death with meaning, endowing him with martyrdom. He would have died for something. A conspiracy would, of course, do the job nicely. Unfortunately, there is no evidence whatever that there was one."
Jacqueline Kennedy got her wish about the Irish Cadets. A brigade was flown over from Dublin and took part in JFK's funeral procession on November 25. This made them the first foreign troops allowed to bear arms in the US capital since British soldiers had razed the White House in 1812.
Ireland was officially represented at the funeral by President Éamon de Valera, who had first met JFK in 1945 when the future president was working as a journalist. Jacqueline later wrote Dev a letter by hand that emphasised once again her husband's Irish heritage.
"I am only grateful for one thing in these sad days - that he did have the chance to return to Ireland as President of the United States last summer. He would never have been President had he not been Irish.
"All the history of your people is a long one of overcoming obstacles. I will bring up my children to be as proud of being Irish as he was. Already, our house is named Wexford - and they play with those beautiful animals, the Connemara pony and the deer. Whenever they see anything beautiful or good, they say, 'that must be Irish' - and when they are old enough I will bring them there."
Jacqueline proved to be good as her word, visiting Ireland with John Jr and Caroline in 1967 and giving JFK's relatives the rosary beads that he had carried in his jacket when shot. They are now on display at the Kennedy Homestead in Dunganstown, Co Wexford.
Despite her public stoicism, Jacqueline was in reality deeply traumatised by the assassination. She poured out her pain in a series of 33 letters to Father Joseph Leonard, an Irish priest who had shown her around the country during her first trip here in 1950.
"I am so bitter against God," ran a typical passage. "I think God must have taken Jack to show the world how lost we would be without him - but that is a strange way of thinking to me... I have to think there is a God or I have no hope of finding Jack again."
This correspondence did not become public until 2014, when the letters were discovered in an old safe at All Hallows College in Drumcondra, Dublin, where Father Leonard had taught.
Jacqueline's only consolation was that so many people around the world shared her grief.
The English poet Philip Larkin wrote famously: "Sexual intercourse began in 1963 between the end of the Chatterley ban and The Beatles' first LP."
Ireland lagged behind, but 1963 was an awakening. In November, the country was rocked by the youthquake that was The Beatles, who sparked a joyous riot when they played Dublin's Adelphi Theatre. The age of the teenager had arrived and it was not well received by the nation's moral guardians.
Dublin's authoritarian Archbishop John Charles McQuaid had challenged doctors and psychologists to come up with a distinctly Irish way of informing youngsters about the birds and the bees without saying too much. Naming "the two greatest needs of adolescence" as "temperance and fortitude", he said: "I am convinced that there exists the duty to supply instruction in chastity that is accurate, clear, adequate and supernatural." Properly formulated, he believed, "such an instruction can tranquillize the adolescent".
Together with The Beatles, 1963's game-changer was the lightning spread of television. Our politicians and civil servants had fought a rearguard action against a domestic TV service before conceding we needed our own wholesome, patriotic channel to counter the trash penetrating Irish homes from British overspill signals. The youngest viewers were targeted in 1963 with Daithí Lacha (David Duck), billed as "Telefís Éireann's wackiest, quackiest cartoon character". This was Stone Age TV. The duck in the striped underpants never moved. Instead, while a single static frame filled the screen, narrator Pádraic Ó Gaora would describe the action.
The Golden Boy of world politics was John F Kennedy, and he was one of ours. Nasa's victory in the Moon race would be won with a devastating sprint down the home straight after lagging behind for most of the contest. The Russians had led with a series of firsts, including first dog in space, first man, first woman, first teams and first space-walk.
On a visit to Texas in November 1963, President Kennedy rebuffed Republican calls to slash the space budget for 1964. The Irish media told with great pride that he'd quoted from the Irish writer Frank O'Connor. They reported: "Mr Kennedy related the O'Connor story of how as a boy, when he and his companions came to an orchard wall that seemed too high to climb, they took off their caps, tossed them over the wall and then had no option but to follow them. Mr Kennedy said: 'This nation has tossed its cap over the wall of space, and we have no choice but to follow it. Whatever the difficulties, they must be overcome.'"
The reports added: "Mr O'Connor said last night that he was very pleased to hear that President Kennedy had used this quotation from his autobiography. 'I think it is a very brilliant use of the quotation and I would never have thought of it myself,' he said."
The O'Connor quotation was virtually Kennedy's last word on the subject. It appeared in the Irish papers the next day, November 22, the day JFK was shot dead in Dallas.