The situation of Northern Ireland within the UK in 1939-45 was unique in that it had a long land border with an independent state. The border, and Eire’s neutral status required special arrangements and planning. Overall, the defence precautions taken resembled the pattern elsewhere in Britain. The difference lay in a possible requirement for British forces in Northern Ireland to assume an offensive role in Eire, by repelling any German move by crossing the border to engage invading forces. There German ‘Plan Green’ for an invasion of Ireland as a first move on Britain. Belfast was to be the base for operations against German aggression in Eire or Northern Ireland, and this is reflected in the defences of the Province.
Northern Ireland’s stop lines (8) relied on the major river and canal systems. They effectively cut the Province in two, from Coleraine to Newry, via the River Bann and the Newry Canal. Lines covered Belfast to the north between Carnlough Bay and Lough Neagh and between Larne and Antrim. To the south, lines ran between Portadown and Dundrum, Lough Neagh and Ardmillan and the River Lagan and Hollywood. Additionally there was a complete loop line around Belfast from Green Island to Bangor. If the military situation became serious, two further defensive positions were developed on the Ards Peninsula. Belfast had further defence schemes that encircled the city similar to those of Edinburgh and London. The late date of these schemes (mid 1941) possibly means that they superseded the defence lines as Belfast’s primary defence.
Eight of Northern Ireland’s beaches were provided with defences. The most important were Magilligan, Portrush and Portstewart where defences that included pillboxes covered exit roads. The only reference to any type of nodal point was a series of ‘garrison towns’. Twenty-seven in total, most of these were located east of the Coleraine - Newry line, with only a handful to the west. Last, there was a category of defensive feature in Northern Ireland not found elsewhere in the UK, reflecting the particular needs of a land border. This was ‘border post’, of which 96 have been identified for Counties Fermanagh, Tyrone and Armagh. The function of the border posts was to control refugees from Eire in the event of German action, and to keep roads clear of traffic to enable British troops to move south.