The number of US troops who passed through Shannon airport on commercial aircraft in the first three months of this year has increased by more than 20,000 compared to the same period last year.
Figures released by the Department of Transport show that from January to March this year, 116,450 US troops passed through Shannon on civilian aircraft.
The comparable figure for the same period in 2005 was 95,984.
Since the beginning of this year, the department has received 492 applications for permission for commercial planes to land with US troops on board.
All were granted. The busiest month so far was January, when 41,413 troops, an average of 1,336 a day, used the airport.
A spokeswoman for the department said that in considering requests, the department consults the Departments of Foreign Affairs and Justice, as well as the Irish Aviation Authority. The Department of Defence is also informed.
"If any of those agencies objects to the exemption being given, then the department will refuse to grant an exemption."
The transport of troops adheres to instructions laid down by the International Civil Aviation Organisation, she added.
Before each flight, the US military and the commercial airline carrying the troops must request official permission from the Department of Transport.
When this is granted, a note is sent by the department to Shannon airport authorities to notify them of the landing.
Permission must also be sought for all weapons being transported through the airport, an airport spokeswoman said.
Last year 330,000 US troops used the airport, more than double the figure of 121,943 for the previous year.