The agreement between governments led to a revolt in Fianna Fáil when it became public,writes Stephen Collins
The Fianna Fáil government led by Jack Lynch agreed to an air corridor along the southern side of the Border which British military aircraft could use in the joint effort to combat IRA terrorism, just weeks after taking office in the summer of 1977.
When it became public two years later, the agreement to British overflights along the Border precipitated an internal revolt in Fianna Fáil against Mr Lynch's leadership, which led to his departure from office in December 1979.
A memorandum entitled "Overflights by foreign military aircraft" was brought to government by minister for foreign affairs Michael O'Kennedy on July 25th, 1977. The crucial paragraphs referred to an agreement with the British on three categories of military overflights.
The first referred to the Clonoony Salient, an area of the Republic sticking into Northern Ireland southwest of Clones in Co Monaghan. "The purpose of the flights is to facilitate the transport of men and materials, the evacuation of casualties and, in particular, the shadowing of suspect vehicles across the salient. The British authorities have standing permission for such flights and this is renewed annually. The permission is subject to notification on a regular basis of the number of crossings made," says the memo.
The second category was described as "normal" security overflights which normally came a maximum of 500 metres into Irish airspace. They were for "photographic or infra-red reconnaissance of suspect devices or buildings close to or on the Border, in order to ensure that there are no command wires or other booby trap devices awaiting the bomb-disposal team which will tackle the suspect object".
Requests for such overflights were made case by case by the British embassy in Dublin to the Departments of Justice and Defence.
The third category of overflights involved "the systematic aerial reconnaissance of those sections of the Border in which cross-Border incidents most frequently occur with a view to compiling a comprehensive record".
The British embassy stated that the purposes of such a record were:
(a) "To identify whether there are any improvised explosive devices or command wires not otherwise detected;
(b) "To trace illegal crossing points most frequently used by terrorists;
(c) "To locate potential terrorist firing positions or positions which have already been used;
(d) "To compile a full picture of the terrain to help operational planning in the North - for example in siting posts to observe illegal movements across the Border in both directions."
These flights were allowed two kilometres into Irish air space and typically lasted about 30 minutes, of which some 15 to 20 minutes were on the southern side of the Border. A programme of about 60 such flights a year was being operated at that time.
Initial permission for the scheme had been given in June, 1976 by the Cosgrave government just after the murder by the IRA of the British ambassador to Ireland, Christopher Ewart Biggs.
This permission specified that there should be no flights over or within two kilometres of Irish Army installations and that the flights would be staggered over the Border areas with no two flights over the same area in any period of about 10 days.
To remove any possible ambiguity, the Irish government had subsequently agreed that within each permitted overflight the aircraft in question might cross the Border a number of times. The memo also said that the British authorities had from time to time requested permission for "hot pursuit" overflights to enable them to maintain visual contact from aircraft with suspected terrorists fleeing across the Border.
"This suggestion has always been regarded as unnecessary and unacceptable and has always been rejected," said the memo.
"The minister for foreign affairs recommends to the government that the present arrangements in respect of overflights be continued and, in particular, that no alteration be made in the conditions under which existing permissions to overfly were granted." The cabinet agreed to the proposal.
However, a little over two years later, Lord Mountbatten was murdered at Mullaghmore in Co Sligo and Lynch's government came under fierce pressure from the newly elected British prime minister Margaret Thatcher to improve security co-operation.
Shortly afterwards, reports appeared in Irish newspapers saying that Lynch had agreed to a range of new measures, including overflights by British military aircraft along the Border. Lynch refused to confirm or deny that a deal had been done. However, a revolt orchestrated by Charles Haughey forced him to bring forward his retirement plans and he resigned in December 1979.