WHEN writing his monumental history of the British army, Sir John Fortescue devoted just two paragraphs to the military implications of the Union. He noted that Union greatly simplified British military affairs in general and that this was an excellent thing for historians, driven to distraction by the confusing archival situation produced by the pre-Union military relationship of the two countries. The Irish military historian, Sir Henry McAnally, was equally succinct, merely remarking that `military matters had not bulked largely in the Union debates'. In ways they were both right. Although none of the eight articles of the Union refer to the army, it was understood that the assimilation principle, which regulated other branches of the public service and the church, would apply to the army. Yet, beneath and perhaps because of the delusive brevity of these bare facts, lies a seriously under-researched subject with wider ramifications, both in the short and longer term. Before these issues can be developed, it is first necessary to set the context by describing the pre-Union military background Ireland and then outlining the formal changes wrought by the Union.