When an Irish assistant postmistress called in her nightly forecast from a lighthouse weather station on Co Mayo’s wild Atlantic coast, she had no idea of the crucial role it would play in the Allied victory in the Second World War. At 1am on June 3 1944 – her 21st birthday – Maureen Flavin noticed a sharp drop in the barometer, the first sign of an incoming storm. After waking Ted Sweeney, the lighthouse keeper and her future husband, to confirm the reading, she reported it to the Irish Met Service. Later that day, after a woman with an English...