However, because of the threat of German occupation and seizure of Ireland and especially the valuable Irish ports, Plan W was developed.
Northern Ireland was to serve as the base of a new
British Expeditionary Force that would move across the
Irish border to repel the invaders from any beach-head established by German
paratroopers. In addition, coordinated actions of the
Royal Air Force and
Royal Navy were planned to repel German air and sea invasion. According to a restricted file prepared by the
British Army's "Q" Movements Transport Control in Belfast, the British would not have crossed the border "until invited to do so by the Irish Government,"
[1] and it is not clear who would have had the operational authority over the British troops invited into the State by
Éamon de Valera.
[2] The document added that most people in Ireland probably would have helped the British Army, but "there would have been a small disaffected element capable of considerable guerrilla activities against the British."
[3]
By April 1941, the new BTNI commander, General Sir
Henry Pownall extended his planning for a German invasion to cover fifty percent of the entire Irish coastline. He believed that German troops were likely to land in
Cork,
Limerick,
Waterford,
Westport,
Galway,
Sligo, and
County Donegal, i.e. on the southern or western coasts. British Army personnel also carried out secret intelligence-gathering trips to glean information on the rail system south of the border.