The remote Irish lighthouse that changed the course of the Second World War

On the western edge of Europe, flanked by a pretty fishing village, pristine beaches and dramatic mountains, a historic lighthouse monitors the Atlantic Ocean. It is small and unremarkable in appearance. Yet Ireland’s Blacksod Lighthouse has an extraordinary legacy tied to one of the most important days in history.

In 1944, at the height of the Second World War, more than 150,000 lives depended on an Irish couple working in this building. Visitors can now tour the lighthouse where Maureen and Ted Sweeney changed the course of history by delivering crucial weather reports that convinced the Allies to delay the D-Day invasion of Normandy.

That change of plans prevented a probable disaster and ultimately helped the Allies end the war. Now, visitors can learn this rollicking tale during guided tours of the still-active lighthouse in Mayo, a county embellished by the kind of raw natural scenery that entices so many tourists to Ireland.

“This is one of the most remote places in the country,” says guide William Duffy as he shows my tour group through the lighthouse, which is three hours drive from the nearest city, Galway. “The storms here in winter are very fierce. Nowadays this lighthouse is pretty warm and comfortable. But many generations ago it would have been a cold and pretty lonely place for lighthouse keepers. It was a tough job.”

Maureen and Ted Sweeney, who would later marry, were working together at the lighthouse in June 1944 Duffy explains as we stand in the building’s small museum. Unbeknown to the couple, the Allies of the US, UK and Canada were secretly preparing a mass invasion of France via its Normandy beaches. Their aim was to drive the Nazis out of France.

One of the most ambitious amphibious military invasions ever planned, it was to involve boats delivering about 156,000 soldiers on the sands of Normandy. Conceiving such a grand strategy was one thing. Executing it was infinitely more difficult.

Once the Allies hit French shores, they would collide with the Nazis’ infamous Atlantic Wall, a 3,800-kilometre-long roadblock along the western edge of mainland Europe that consisted of millions of landmines, bunkers and turrets. The success of this invasion relied heavily on two factors — secrecy and favourable weather. While the Allied commanders handled the former, the latter was largely left up to the Sweeneys at Blacksod.

The Allies went to great lengths to deny the Nazis advance warning of their invasion. Having taken nearly a year to meticulously plan, they could not afford for the German forces to be waiting for their troops at Normandy. So they dispersed misinformation, leading the Nazis to believe the invasion would occur elsewhere. With their foes distracted, the Allies decided to strike. June 5, 1944, was the date.

But, as the lighthouse museum explains, on June 3 the Sweeneys calculated weather reports that showed a storm was rolling across the Atlantic and would besiege Normandy on the day of the invasion. This could have caused a catastrophe. Had the plan gone ahead, the Allied troops would have been in shambles, trying to steer their boats through rough waters and clamber onto the beach in driving rain and whipping winds.

Instead, the Sweeneys’ reports convinced the Allies to invade on the following day, when far gentler weather would offer them smooth passage. Had this Irish couple not predicted that storm, the D-Day campaign may well have failed, the path of the Second World War would have changed, and the entire world might look very different right now. So significant were the Sweeneys' efforts that last year the US government awarded Maureen Sweeney, then 98, a special US House of Representatives honour.

Yet few people outside of Ireland are familiar with this incredible tale that unfolded in Mayo. Duffy says he hopes this will change now the lighthouse has been turned into a tourist attraction. Its 45-minute tours can be booked in advance via the Blacksod Lighthouse website. They take visitors through most of the building, from its ground-floor museum to its top-floor beacon, while a knowledgeable local guide explains its history.

Visitors are fortunate to get such access, as the lighthouse remains a key piece of infrastructure. It helps not just to guide vessels through the neighbouring seas, but also acts as a helicopter landing site and a refuelling base for the Irish Coast Guard. This tour also pays respect to four rescue workers who died near the lighthouse in 2017 when their helicopter crashed after assisting in the recovery of a lost fisherman.

Those deaths loom over this corner of Mayo like the nearby peaks of Achill Island. Learning of this tragedy is a jarring experience for tour participants who have been delighted by the rousing tale of the Sweeneys’ triumph. Together, these contrasting events represent the brutality, volatility and majesty of a wild swathe of Ireland edged by the ferocious Atlantic Ocean. And watching over all of this is Blacksod lighthouse.