As a young woman growing up in County Kerry, Maureen Flavin Sweeney dreamed of moving to the United States. However, Belmullet in County Mayo, on Ireland’s Atlantic coast, was as far west as she got. There, she worked as a postal clerk and, on June 4, 1944, made a weather report that changed the course of history. She was 21 years old.
Constructed in 1866, the lighthouse at Blacksod might not offer commanding views of the vast ocean, but its geography at the very western edge of Europe made it crucial for D-Day planners in England. Maureen Sweeney’s weather reports from Blacksod would be the first to confirm any change in the weather impacting Europe.
Ireland was officially neutral during WW II. At the outbreak of the war, despite being an island nation, its “navy” consisted of two fisheries protection vessels and six motor torpedo boats unsuited to ocean patrols; the Irish Air Force comprised four obsolete Gloster Gladiator biplane fighters and 16 maritime patrol aircraft. Yet despite this, Ireland did provide significant aid to the Allies, including allowing Allied aircraft to overfly the Republic of Ireland in what became known as “the Donegal Corridor” to save vital fuel, sharing information on German espionage activity in Ireland and, as it turned out most importantly, weather information.
D-Day, also known as Operation Overlord, was the largest seaborne invasion in history and marked the turning point against Nazi Germany. To be successful, Operation Overlord required specific conditions: a rising tide shortly before dawn, following a full moon-lit night. These requirements limited the potential landing dates to May 21-23, June 5-7, June 18-20, and July 3-5, 1944.
Dates in May were eliminated as the required forces and supplies would not be ready. On the night of June 2-3, Maureen Sweeney reported approaching severe weather with a rapidly falling barometer and a force six wind. This report, forwarded from the Irish Meteorological Service to Allied headquarters in southern England, prompted an unusual callback. A woman with an English accent asked for confirmation. Sweeney rechecked her figures and confirmed their accuracy. Maureen did not know then that this call was made at the request of Group Captain James Stagg, the chief meteorological officer for D-Day. Stagg used the report to advise the Overlord planner to postpone the invasion by 24 hours. “The whole situation from the British Isles to Newfoundland has been transformed in recent days and is now potentially full of menace,” Stagg told General Dwight D. Eisenhower.
For the Allied troops waiting under canvas across southern England and already embarked on troop ships in the English ports, the weekend of June 3-5 brought strong winds, low clouds, rough seas, and seasickness. On June 3, Eisenhower gave the order to postpone.
Eisenhower and his commanders faced a dilemma: launch in bad weather and risk failure or delay with the risk that the invasion plans would be leaked. On June 4, crucial information came through from Blacksod. Maureen Sweeney reported: “Heavy rain and drizzle cleared, cloud at 900 feet and visibility on land and sea very clear.”
At 04:15 on June 5, 1944, Eisenhower met with his senior staff and declared: “OK, We’ll go.” The rest, as they say, is history
Had the invasion been postponed until the next available date, June 18, 1944, the results could have been disastrous. That week, the worst storm in 40 years hit the English Channel, making the landings impossible. The delay would have increased the risk that the plans of the invasion would become known to the Germans and given them another month to prepare their already formidable defenses.
In 1961, while heading to his inauguration, President John F. Kennedy asked Eisenhower what had given him the edge on D-Day. He replied: “We had better meteorologists than the Germans.” Those meteorologists relied on Maureen Sweeney, carefully watching the weather on Ireland’s rural west coast.
In 2020, Maureen Flavin Sweeney, then 98, received a special US House of Representatives honor for her part in the war. She passed away on December 17, 2023.
Neil F. Cosgrove, Historian