More than 750,000 foreign troops, the vast majority from the US, have been given permission by the Government to pass through Irish airports or airspace in the past five years.

Most of these flights have also carried weapons, though some changes introduced by the Minister for Transport Shane Ross when he took office in 2016 have seen certain types of munitions prohibited from flights passing through Ireland. These are explosives classed as “dangerous goods” under aviation law.

However, Mr Ross permitted more than 1,000 overflights and landings last year, and the figures show that numbers are increasing. In the first four months of this year, permission was granted for 212 flights carrying weapons to fly through Irish airspace (one application was refused) and 190 flights were granted permission to land (one was refused).

The carriage of weapons is prohibited by air transport regulations, but the Minister for Transport is empowered to issue exemptions which were done at a rate of about 20 a week last year.

The troops are usually en route to US bases in a variety of destinations, in Europe, the Middle East and Asia, including Afghanistan, or returning to the US.

Military transports Military transports are authorised under a separate system, where the Department of Foreign Affairs has the authority to grant permission to foreign military aircraft to land here or fly through Irish airspace.

These are granted on the basis the aircraft is “unarmed, carries no arms, ammunition or explosives, is not engaged in intelligence gathering, and that the flight in question does not form any part of military exercises or operations”, the department says. However, the State does not carry out any inspections to ensure these conditions are being met. Most flights granted landing or overflight rights are from the US.

Figures compiled by the Department of Foreign Affairs last year showed that, in addition to the civilian flights, there were more than 2,000 landings or overflights by military aircraft in 2017, the vast majority from the US.