It could take the Army up to two hours to deploy specialist soldiers to Dublin in the event of a terrorist attack.
The Sunday Times reports that the Army Ranger Wing, based in the Curragh in Kildare, does not have 24-hour access to helicopters.
Those that are available can only transport a small number of fully equipped soldiers at a time.
Gardaí and Defence Forces took part in a training exercise in the capital during the week, but response times for the rest of the country have not yet been tested.
People are being assured that armed Gardaí would be at the scene within minutes.