The division was initially headquartered at Dublin, but shortly after at Carton House, Maynooth for the duration of the war; tasked with defending the Northern Ireland border.

[2][3] Following the declaration of state emergency by the de Valera government in 1939, efforts were made for military expansion.

[4] Prior to the outbreak of war in December 1937, it was estimated that a force of three divisions would be necessary to defend Ireland in the event of an invasion.

Experienced with training from the United States and head of the Temporary Plans Division, MacNeill was regarded as a "forward-thinker".

Being from Northern Ireland, MacNeill was ardently anti-British and, in the 1930s, was among other army leaders in calls for a war with Britain - and even approached German intelligence on several occasions.