As noted, Cork was the suspected target of an invasion because it was the nearest landfall between Luftwaffe bases in north-western France and the island of Ireland. Northern Ireland was to serve as the base of a new British Expeditionary Force, that would move into the State to repel the invaders from any beach-head that was established. Troops of the 53rd Division in Belfast were held in readiness for the advance. A brigade of Royal Marines stationed at Milford Haven were also prepared to seize a bridge-head in Wexford the moment the Germans landed. Officers at the headquarters (HQ) of British troops in Northern Ireland, Thiepval Barracks, Lisburn, County Antrim estimated that the Germans could embark five divisions by sea to Ireland although "not more than 2 to 3 would reach land". Up to 8,000 German airborne troops could be flown into the State, some of them by seaplanes which would land on the lakes. The British striking force of 53 Division, later augmented by the 5th Battalion, Cheshire Regiment, were to concentrate on the west of Down and Armagh borders, then drive across the border and race towards Dublin along three main roads – the Belfast – Dublin coastal road through Dundalk, Drogheda and Balbriggan, the inland road through Ardee and Slane, and the Castleblayney — Carrickmacross — Navan road. It is not clear who would have had the operational authority over the British troops invited into Ireland by de Valera, but it is assumed the British would retain command.