Irish neutrality during World War II

The policy of Irish neutrality during World War II was adopted by the Oireachtas at the instigation of the Taoiseach Éamon de Valera upon the outbreak of World War II in Europe. It was maintained throughout the conflict, in spite of several German air raids by aircraft that missed their intended British targets and attacks on Ireland's shipping fleet by Allies and Axis alike. De Valera refrained from joining either the Allies or Axis powers. While the possibility of not only a German but also a British invasion were discussed in the Dáil, and either eventuality was prepared for, with the most detailed preparations being done in tandem with the Allies under Plan W, De Valera's ruling party, Fianna Fáil, supported his neutral policy for the duration of the war.

This period is known in the Republic of Ireland as the Emergency, owing to the wording of the constitutional article employed to suspend normal government of the country.

Pursuing a policy of neutrality required attaining a balance between the strict observance of non-alignment and the taking of practical steps to repel or discourage an invasion from either of the two concerned parties.

Despite the official position of neutrality, there were many unpublicised contraventions of this, such as permitting the use of the Donegal Corridor to Allied military aircraft, and extensive co-operation between Allied and Irish intelligence, including exchanges of information, such as detailed weather reports of the Atlantic Ocean. For example, the decision to go ahead with the D-day landings was decided by a weather report from Blacksod Bay, County Mayo.

...
Wikipedia