The threat of invasion of neutral Ireland by British forces from the north was an event that was prepared for by the Irish Government in 1940. One of the lines of defence centred around the River Boyne where a series of pillboxes were constructed on both sides of the river from Navan to Drogheda, and also in one or two places on the northern approaches. Many of them still survive; this is a photographic record of some of them - more remain to be discovered.