The Government received over 700 requests * last year for waivers allowing them to transport * firearms and dangerous materials through Shannon Airport.
Of those, about 15 per cent related to a non-specific category of objects that may include explosives and gas canisters.
However, according to the secretary general of the Department of Foreign Affairs Niall Burgess, requests of that nature would have been recommended for refusal.
Addressing the Oireachtas committee on Public Service, Oversight and Petitions , Mr Burgess said the issue of of US military flights landing in Shannon was one reflecting strong relations between the two countries.
Strict procedures exist on the transportation of arms through Ireland, both on military and civilian aircraft carrying troops, although the Department of Transport may grant waivers in the case of personal firearms so long as they are stored out of reach, the committee heard.
"The bottom line is, it's fair to say, that some department of this Government has given permission to 2.3 million US marines to come through Shannon [in recent years] with their weapons stored," said the committee chairman, Sinn Féin TD Padraig Mac Lochlainn.
Mr Burgess said while he could not comment on the specific number, “exemptions are routinely granted as a matter of Government policy”. The amount of such requests has been falling year on year.
In 2013, 50,000 troops passed through Shannon.
Landing facilities have been made available to US military aircraft since 1959 although the “vast majority” of troops landing in Shannon during recent conflicts have done so on chartered civilian aircraft, Mr Burgess said.
Regarding military flights, he said, the overriding factor is one of sovereign immunity. Foreign governments are requested to guarantee these planes carry no arms or ammunition and must not be part of military operations. “It has been the practice of successive governments to accept in good faith that details provided by diplomatic missions to all government departments are accurate,” he said.
Independent TD John Halligan said: "It would be naive now of very many of us to think that just because the CIA are telling you there are no arms or munitions on a plane that you would believe them."
Mr Burgess had said the approach was in accordance with international practice and reflects the principle of sovereign immunity.
"Information provided to other states by Irish diplomatic missions seeking diplomatic clearance for flights undertaken by the Air Corps is similarly accepted by those countries to be accurate," he said.
* This article was edited on Thursday, December 4th, 2014
