The documents released by the Irish Justice Department said police received two anonymous telephoned warnings in the weeks before the arrival of the United States' first Irish Catholic president. A third threat went to the newsroom of the Irish Independent newspaper.
Kennedy's June 26-29 visit went ahead trouble free as he was greeted by adoring crowds in Dublin, Cork, Galway and at his family homestead in County Wexford, in southeast Ireland.
He was assassinated in Dallas five months later.
One threat claimed a sniper would target Kennedy as his motorcade traveled from Dublin Airport to the residence of the Irish president at the start of his visit. The second warned a bomb at Shannon Airport, in southwest Ireland, would detonate as Air Force One was about to depart.
According to the documents the third threat, phoned to the newspaper, indicated that Kennedy would be attacked at Dublin Airport, although the method wasn't specified.
The documents detailed police security concerns — and also reflected officials' desire to impress both U.S. visitors and onlookers in Britain, Ireland's colonial master until 1922.
In a letter, Commissioner Daniel Costigan, the commander of Ireland's national police force in 1963, described the Kennedy tour as "the most important visit to this country since the establishment of the state, with worldwide publicity. British journalists are likely to be ready to criticize any fault in arrangements."
He wrote that although unlikely, "we cannot overlook the possibility" of an assassination attempt.
Costigan said his officers would use binoculars to monitor rooftops along the route of the presidential motorcade. He said an unspecified number of police would be armed with handguns, rifles and submachine guns — an exceptional measure in a country with a largely unarmed police force — to engage any would-be sniper.
The documents indicated that 6,404 police officers were on duty the night Kennedy arrived, and 2,690 lined the U.S. president's route from Dublin airport to the Phoenix Park mansion of Irish President Eamon de Valera.