Then taoiseach Seán Lemass authorised searches of Cuban and Czech aircraft passing through Shannon after the Cuban missile crisis in 1962 at the request of the United States. Details of searches were secretly passed on to the US authorities for the following eight years, writes Stephen Collins, Political Editor
Mr Lemass personally gave the go-ahead for the aircraft inspections and the data handover to embassy officials following a direct approach from US ambassador Mathew McCloskey, who called to see him in the taoiseach's office.
Previously classified files opened to the public for the first time from this morning show that details about aircraft cargo and weight, and about passengers and their nationalities, were handed over along with details of overflights.
On December 6th, 1962, the government announced a ministerial order had been made invoking the power to search aircraft for "munitions and implements of war".
The files show US assistance was first sought in October at the height of the crisis. A stand-off between the United States and the Soviet Union had arisen out of the decision of Soviet premier Nikita Khrushchev to arm Fidel Castro's regime in Cuba with nuclear missiles capable of striking targets in the US.
In October 1962 president John F Kennedy imposed a naval blockade designed to prevent any more missiles reaching the island. The confrontation led to the biggest crisis of the cold war and brought the world the closest it had come to a nuclear war.
When the US ambassador in Dublin sought an appointment with the taoiseach in October, a US embassy counsellor, Mr Sweeney, visited the Department of External Affairs and said Mr McCloskey would raise previous inquiries concerning the Shannon stopover involving Prague-Havana flights.
Mr Sweeney "spoke about these flights and the data the US administration were anxious to have", according to Con Cremin, secretary of the department, in a November 2nd memo.
"He made it clear Washington has been worried about the extent to which the traffic through Shannon may have helped in the build-up in Cuba, and in particular in the transport of technical personnel and possibly of arms.
Mr Cremin said Mr Lemass rang him to record that he had told the ambassador the aircraft would be searched and if any "warlike" material was found, Ireland would consider refusing rights of transit.
"We will supply such manifest data as becomes available in respect of future flights and are prepared to make available similar data in respect of a reasonable past period, going back if necessary to the initiation of the service," Mr Lemass told him.