In the third episode, we discover the surprising roles that lighthouse keepers played in both World Wars. As the First World War raged around Ireland’s coast, our lighthouse keepers acted as unofficial coastguards, keeping detailed logs of their observations. In the Second World War an Irish lighthouse keeper played a decisive role in the outcome. We travel to Blacksod Bay, Co. Mayo where in 1944 lighthouse keeper Ted Sweeney took a weather reading which was to determine the entire timing of the allied invasion on D Day.