The German constitutional court has just made a decision on the Lisbon treaty and clarified what it says about an EU-wide army. The findings are available here -
http://www.nationalplatform.org/lisbon-treaty/german-constitutional-court.html
What is relevant for Ireland is this particular passage:
384
(2) The wording of the Treaty of Lisbon does not oblige the Member States to provide national armed forces for […]