The Government attempted to withdraw blanket landing and overflight rights for unarmed US military aircraft in 1970 and to grant permission on an annual basis only.
In November 1969, a US navy aircraft overflew Ireland without giving the customary notice to air traffic controllers at Shannon.
The Government issued a note of protest to the American embassy in Dublin and the embassy apologised for the lack of communication with Shannon.
However, in Washington, state department officials found a 1959 letter from Frank Aiken, then minister for External Affairs, agreeing that unarmed military aircraft carrying only passengers and cargo could overfly Ireland, adding that "this permission will be subject to reconsideration in the event of a serious deterioration in the international situation".
An internal state department document in May 1970 suggests that the US should seek to have the Irish note of protest withdrawn and ask the Government for an apology for having falsely accused the US navy aircraft of breaching the agreement.
Three years earlier, the Government told Washington that nuclear-powered naval vessels and ships carrying nuclear weapons would not be welcome at Irish ports.
In November 1967, however, the American embassy in Dublin reported that Hugh McCann, secretary of the Department of External Affairs, had suggested a "don't ask, don't tell" policy.
"Mr McCann said that in future that when the embassy asked for permission for a visit of naval vessel, Extaff [ the Department of External Affairs] would assume that nuclear weapons and power plants would be on board without our having actually to give such assurance. The tacit agreement would be government-to-government and confidential and there would be no reason for it to become public property," the report said.
US policy was not to reveal which of its ships carried nuclear weapons, but a American embassy official in Dublin suggested that Washington might employ a little deception.
"Not obviously nuclear-weaponed ships may be sent to Dublin, leaving us uninformed about such weapons, and we would ask for clearance on the assumption that they were not on board," he wrote.
Washington rejected the suggestion, concluding that if Ireland banned nuclear vessels, no large US warships could call at Irish ports.
"Under no circumstances, however, would we wish to deceive the Irish by leaving the embassy in ignorance . . . and thereby implying that we were abiding by Irish wishes, when in fact we were not," the state department said.
