Weather warning from Ireland saved 10,000 D-Day lives

Irish Daily Mirror

05-06-2025

The Allies landed 160,000 soldiers on five beaches in Normandy on this day, 81 years ago.
It's known as D-Day and was the largest land, sea and air invasion in military history and a pivotal moment in World War II, on June 6, 1944.
Allied forces - American and Canadian - landed in the Nazi-occupied France gaining a foothold and pushing inland.
But one of D-Day's biggest secrets for years was that the landings had been delayed 24 hours as Ireland - officially neutral - had passed on a crucial storm warning from Blacksod Bay lighthouse, on the Co Mayo coast.
The readings of one young woman, a Kerry-born postmistress Maureen Flavin Sweeney, averted potential disaster and saved countless thousands of lives.
Her unexpected weather recordings from Blacksod Bay lighthouse, routinely transmitted to Dublin changed the course of history.
This part of story begins on the morning of June 3 at 1am, coincidentally the morning of Flavin Sweeney's 21st birthday.
At that point, the Blacksod barometer was showing a slight drop in air pressure, which - combined with a 7m/ph south-westerly and slight drizzle was indication of an approaching storm.
It was a routine post or so she thought...
However, a little later, she received an unusual phone call. It was the Irish Meteorological Office in Dublin, asking her to check again.
Confirming her first reading was right, Dublin then asked for further reports on the hour to 7am.
These following weather reports would show a continuing drop in pressure and the wind shifting to storm force 6, the wind having got up to 25-31m/ph.
This was data being simultaneously - and secretly - fed to the Allies preparing for a June 5 Normandy invasion. It set off near-panic as specific weather conditions were needed for the landing, codenamed Operation Overlord.
It was such vital information that at 11am that morning, the British Met Office threw protocol aside and phoned the Blacksod Bay telephone number directly.
To establish the messages hadn't been tampered with on route, they asked: "Were those Blacksod readings correct? And could Maureen check one last time?"
Operation Overlord required specific conditions in place shortly before dawn, good weather, no cloud cover, a full moon and a rising tide.
When planning began in 1943, it was deemed there were just four possible windows in 1944, but June 5-7 was the only really suitable one.
If the summer opportunity had been missed, focus would have turned to landings in the south of France in the Autumn which may have stretched the war to 1946.
The data suggesting there would be a storm on June 5 and a respite on June 6 was relayed to General Eisenhower, the Supreme Commander of the Allied Expeditionary Forces (SHAEF) who postponed D-Day to June 6.
The day's delay saw the Allies land successfully on all five beaches.
Mary Flavin Sweeney's readings saved an estimated 10,000 June 6 D-Day lives.
President John F. Kennedy, on the way to his inauguration in 1961, asked Eisenhower what had given the Allies the edge on D-Day and was told: "Because we had better meteorologists than the Germans."
Yet for the 21 year-old postmistress, there would be very little recognition in the immediate post-WWII years and she was only told of her role by British authorities in 1956.
The world learned further details in 2004, while the full extent of Flavin Sweeney's part was not released by the British War Office until 2012. Latterly, the USA awarded her the Congressional Medal of Honour in 2021, their highest award available to civilians.
The secrecy at the time surrounding the weather reports from Blacksod Bay was understandable.
Ireland, officially neutral in the Second World War, was nonetheless pursuing a policy of mild cooperation with the Allies.
This, for instance, allowed stranded Allied airmen and naval personnel return via Northern Ireland while, at the same time, similar Axis personnel were interned.
Ireland also consented to Allied weather/air sea-rescue aircraft based at RAF Castle Archdale on Lough Erne - Catalina and Sunderland flying boats which doubled as reconnaissance aircraft - avail of a four-mile 'fly zone' between Beleek and Ballyshannon to access the Atlantic.
More famously, and following a massive Luftwaffe bombing raid on Belfast in the early hours of April 16 1941, Taoiseach Eamon De Valera had dispatched 13 units of the Dundalk, Drogheda, Dublin and Dun Laoghaire Fire Brigades to Belfast.
He further sent the Great Northern Railway to Belfast to evacuate some 3,000 people to Dublin.
If the Donegal Corridor narrowly avoided being an act of war, gaining tacit German approval as flights were meant to be restricted to just air/sea rescue, the sending of uniformed men across the border to firefight and supply aid was, unambiguously, an Act of War.
Just as was the clandestine sharing of weather information.
The Irish Meteorological Office in Dublin's passing data on from their 10 stations to the British Met Service - run by the British Ministry of Defence until as recently as 2011 - was in clear contravention of Irish neutrality.
D-Day is now celebrated as a spectacular triumph. However General Eisenhower, who had been working 20 hours a day, smoking four packs of unfiltered Camels each day, was not even so sure of its success.
Late into the night of June 5, he reached for a notepad and pencil and drafted a statement, headed by the words 'In Case of Failure'.
Now housed in the Eisenhower Museum in Abilene, Kansas, it read: "Our landings in the Cherbourg-Havre area have failed to gain a satisfactory foothold and I have withdrawn the troops. My decision to attack at this time and place was based upon the best information available."
That information had come directly from Mary Flavin Sweeney, a young Irish woman based in one of the most western points in Europe - Blacksod Bay.