D-Day at 80, how a tiny Scottish isle was key to Operation Overlord

Yet, as unsullied by the horror of conflict as the Inner Hebridean coastline may be, the island would play a crucial role in events on Normandy’s beaches, where the sand would become stained with blood as it bore witness to the largest seaborne invasion in history.

A pivotal moment on the road to victory, it would be magnificent men in flying machines - daring RAF crews who embarked on perilous missions from Tiree far into the skies above the North Atlantic – and a persuasive Scottish weatherman who would hold the key to the D-Day landings and help usher the Second World War to its conclusion.

Tiree's coastline, where RAF Squadron 518 left for its weather watch sorties across the Atlantic (Image: Getty)

Events of 80 years ago will soon be marked across the country with poignant events to mark the Normandy landings.

Much of the focus in the UK will be on Portsmouth where thousands of spectators are expected to join D-Day veterans, Armed Forces personnel and VIP guests for a Royal Air Force flypast, military bands and moving tributes.

Across the country, lamps and beacons will be lit to mark the anniversary, while equally poignant gatherings are planned in France. Among them, a deeply touching evening vigil at the Bayeux War Cemetery when 4,500 graves of fallen fighters will be illuminated and a piper's tribute to 'mad piper' Bill Millin who, dressed in his kilt, played his bagpipes on Sword Beach while comrades fell.

Piper Bill Millin plays his bagpipes, as Allied troops wade through the sea to the Normandy shore during the D-Day landing of June 1944 (Image: PA)

It will be a chance for millions to pay respects to the handful of surviving D-Day veterans and to those who perished, and to reflect on the remarkable coordinated effort of 13 countries in a massive joint invasion that would eventually repulse the German forces eastwards.

The date is carved in the timetable of Second World War history: 6 June, 1944.

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But it could all have been so different had it not been for vital data gathered by Tiree-based 518 Squadron and delivered to Group Captain James Martin Stagg, chief meteorological adviser to Operation Overlord, the name given to the Normandy landings.

Without their input, D-Day would have happened 24 hours earlier or two weeks later: potentially sending tens of thousands of troops straight into weather conditions that could have left them woefully exposed and vulnerable.

Tiree’s role in events are often dwarfed by the bigger picture of the largest military naval, air and land operation ever attempted.

More than a year of planning had gone into the assault that would see the simultaneous landing of tens of thousands of troops on five separate beaches in Normandy.

Allied Supreme Commander Dwight Eisenhower and his colleagues needed a full moon to illuminate landing places for gliders and to highlight obstacles, and a low tide at dawn to expose German underwater defences.

What they didn’t need was high winds and rough seas, thick cloud cover that could hinder air support and wet weather that might could hamper the army.

Dr John Holliday, a local historian on Tiree wrote about 518 Squadron as part of a project for An Iodhlann, the island’s historical centre.

He recalls: “For what they hoped would be their final push from the north, the Allies made preparations for the largest seaborne invasion in history, with 700 warships, 4,000 landing craft and over 150,000 troops prepared for a beach landing.

“There were also elaborate dummy plans, codenamed Operation Bodyguard, to fool the German high command into believing that an invasion would take place in the autumn or at other points along the coastline.

Air crew of 518 Squadron at RAF Tiree in the Hebrides (Image: Newsquest/unknown)

“Commanders argued over the timing. A pre-dawn landing was a given, but naval top brass pushed for low water so that captains could see the sunken beach defences laid by the Germans, while army generals preferred high tide to reduce the distance their troops must run under gunfire.

“The RAF wanted clear skies and a full moon to help pilots hit their targets and to release 24,000 airborne troops over the correct drop zones. They settled on a window between the 5th and 7th of June, when the moon and tides were suitable.

“General Dwight Eisenhower, commander of the Allied Forces in Europe, chose 5 June.

“One thing they could not predict,” he adds, “was the weather.”

The RAF’s 518 Squadron had been formed at RAF Stornoway in July 1943 and equipped with four-engined Handley Page Halifax bombers.

Within weeks they had transferred to Tiree where, with their aircrafts’ bombing equipment stripped out to enable them to fly further for longer, they became daring weather watchers, embarking on long flights deep over the Atlantic to gather weather data.

Some sorties would take the crews 700 miles from land, with each flight beginning with a fly-past of the 148-foot high Skerryvore Lighthouse to calibrate the aircraft’s altimeter, before heading off on what could be ten to 12 hours of data gathering.

In flight, they kept an eye out for German U-boats and collected information on temperature and barometric pressure, humidity, cloud and wind velocity.

The information they accumulated would be sent back to base every half hour in code and wartime cypher.

And there was a relentless flight schedule: the squadron flew every day during 1944 apart from just two when the runway was consumed by a thick fall of snow.

Plane failure and the wild weather were their enemies: it was not uncommon for aircraft to limp home with only three engines running, and sometimes, just two.

An aerial view of the D Day landings taken by the RAF over Western Europe in the Second World War (Image: PA)

Wind speeds could soar to 150mph, ice built up on the aircraft and they sometimes were confronted by St Elmo’s fire: bright, sudden flashes of apparent lightning.

The pilots and their crews displayed fantastic navigational skills, but accidents happened.

In January 1944, eight men died when their plane got into difficulties in bad weather and smashed into cliffs at Bundoran in Donegal.

Later that year, a miscommunication resulted in two aircraft entering the airspace above the Tiree airfield at the same time. It was a dreadful error; the two Halifax Mk V aircraft collided and burst into flames, killing all 16 on board.

No fewer than ten aircraft were lost that year alone with the loss of 54 lives.

The squadron, its associated personnel and two radar stations on the island saw Tiree’s wartime population swell by around 3,000, mostly from the UK but boosted by others from Canada, New Zealand, Australia and Poland.

As D-Day approached and success hinging heavily on the surprise assault, the information gathered by Tiree’s weather watchers would become crucial.

Group Captain James Martin Stagg, originally from Dalkeith near Edinburgh, was the chief meteorological adviser to Operation Overlord.

Based in the south of England at the centre of Allied Supreme Command, he gathered data from the Tiree base and others and drew up his weather forecast.

Despite calm weather over Portsmouth on 4 June, 1944, information from his weather watchers - among them an Irish postmistress Maureen Flavin Sweeney who had reported observing stormy weather - Stagg and his British colleagues persuaded Eisenhower to put the invasion plans on hold.

Dr Holliday recalled: “By this stage in the war, the Allies controlled the North Atlantic giving them the advantage of being able to gather meteorological readings from as far afield as Iceland.

“The Germans, pushed back as they were, had limited weather information; in fact, their forecasters predicted a fortnight of rough weather, meaning many German troops were deployed inland on exercise.”

Tiree airport on the isle of Tiree (Image: Andrew Milligan - PA Archive/PA Images)

Having postponed plans to mount the Allied assault on June 5, Stagg analysed data from the westernmost weather stations, including the Tiree squadron.

They suggested a lull in the storms, enough, they argued, to allow for an invasion on June 6.

It was a hard sell: by now the command centre was in the grip of the storm. But opting not to go ahead would mean delaying D-Day for nearly two weeks.

Stagg’s insistence persuaded Eisenhower to go ahead on June 6, a crucial move that saw took the enemy by surprise and kick-started the liberation of German-occupied France, and later Europe, from Nazi control.

Had he chosen not to follow Stagg’s weather prediction, D-Day would have been delayed by two weeks when, as it turned out, more storms would have thrown the plan into chaos.

Today, the airfield is the island’s airport: travellers can pause outside the terminal building to pay respects at a memorial dedicated to the crews of the two Halifaxes that crashed there in 1944.

“After the war 518 Squadron was awarded its crest, the only one in the RAF to be in Gaelic,” adds Dr Holliday.

“A hand holds aloft a key with the motto ‘Tha An Iuchair Againn-Ne’ - We Hold the Key.”