Life-saver: Maureen Sweeney, at just 21, prevented the loss of thousands of soldiers’ lives on the beaches of Normandy

A 96-year-old retired Irish postmistress has recalled how she unwittingly helped to save the world - by pinpointing a storm which could have devastated the D-Day landings.

On June 3, 1944, the night of her 21st birthday, Maureen Sweeney, was taking pressure and temperature readings at Blacksod weather station on Ireland's west coast as part of her duties as a post office assistant.

Her extraordinary - and largely unknown - role in altering the course of World War II is detailed in a new RTÉ documentary - 'Storm Front in Mayo - The Story of the D-Day Forecast' - which will be shown on Thursday, June 6, at 10.15pm.

Although Ireland was neutral in the war, the documentary sheds light on how Éamon de Valera sanctioned the passing of weather readings to the allies.

The readings from Mayo were crucial as they were the first sign of weather coming across the Atlantic two days in advance.

General Eisenhower had planned D-Day for June 5 but it was delayed after Maureen reported a dramatic drop in pressure pointing to a coming storm over the beaches.

In the documentary, Maureen examines her notes, commenting: "I'm very, very happy about it that we did give the right readings. I felt proud that it was from Blacksod."

One of the country's best known weather forecasters, Ger Fleming, reveals how Maureen took down the crude readings at 1am. "She's out on her 21st birthday at one in the morning doing a weather observation and what does she spot but the change in pressure, the pressure falling away was the red flag."

The documentary reveals how Eisenhower had no choice but to stall the invasion force of 160,000 troops on nearly 7,000 ships, along with thousands of airmen, as stormy conditions and poor visibility would have played havoc with their landing.

D-Day veteran Joe Cattini (96), said: "We owe a lot to Maureen of the west of Ireland, us who invaded France on D-Day, because if it hadn't been for her reading of the weather we would have perished in the storms."

Maureen reveals in the documentary that she answered an ad for a post office assistant in Blacksod but she only realised when she got to Mayo that part of her duties was to carry out weather observations.

"It was only every six hours pre-war but then they found out our weather reports in (Blacksod) were the first indication of good or bad weather coming in and they made it hourly," she said.

Maureen had to record the pressure, the temperature and the water vapour and transmit it from Blacksod to Ballina. It then went to the meteorological office in the UK.

Maureen's updated readings were passed to Eisenhower, who gave the signal to invade on June 6. Critically, the Germans' information was not as accurate.

"The information they had basically suggested a big storm was coming and it would be impossible for any allied armada to land anywhere in northern France," said Robert Gerwart, professor of modern history at UCD.

Irish Independent