D-Day, 75 Years on: how it was planned

6 June 2019 marks the 75th anniversary of D-Day, code-named Operation Overlord, when Allied forces launched the greatest land, air and naval operation in history – a massive amphibious assault to retake Nazi-occupied France during the Second World War.

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Landing supplies at Omaha beach, Normandy. Public Domain.

156,000 soldiers – British, American, Commonwealth and other allied troops – landed on the beaches of Normandy, together with thousands of vehicles and tons of supplies.

Aerial photograph of Royal Navy ships massing off the Isle of Wight prior to the invasion © IWM A23720A.

The seaborne attack – Operation Neptune – involved nearly 7,000 vessels, including warships, destroyers, minesweepers, landing craft and merchant ships.

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Allied paratroopers over France. Public Domain.

In the air, 18,000 Allied paratroopers dropped in the invasion zone, along with glider-borne soldiers, while Allied air forces flew over 14,000 sorties in support.

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Two Commonwealth War Grave Commission headstones marking the graves of five Allied aircrew – four RAF and one Royal Australian Air Force. Bayeux War Cemetery, Normandy.
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German Military Cemetery, La Cambe, Normandy. Public Domain.

D-Day marked the start of the long campaign to liberate north-west Europe from German occupation and laid the foundations for the eventual Allied victory in the West. However, the Normandy campaign came at great human cost. It is estimated over 425,000 Allied and German servicemen were killed, wounded or reported missing.

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Remains of a slipway used by American troops for embarkation to the Normandy beaches, Torquay, Devon. Listed Grade II*. Public Domain.
Remains of dummy concrete landing crafts, Braunton Sands, Devon, built for the US Army to rehearse disembarking soldiers and vehicles during practice invasion assaults. Newly Listed Grade II © Historic England DP248202

Evidence of D-Day planning, rehearsal and action is all around us, on our coastline and in our waters. To commemorate the D-Day anniversary, a number of sites have been granted protection: four have been newly scheduled and one listed in recognition of that momentous event.


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German forces fixing posts to prevent Allied assault craft from coming ashore © Schwoon

In 1944, the tide was turning against Germany.  Britain’s allies, the Russians, were attacking from the east, and British and American forces (who had entered the war in 1942) were advancing north from Italy.

But France was still an occupied nation. In anticipation of an Allied invasion, German forces had heavily fortified France’s north-west coast as part of Hitler’s ‘Atlantic Wall’ that stretched from Norway to Spain: a 2000 mile chain of gun emplacements, obstacles, minefields and tank traps.

Meeting of the commanders of the Supreme Allied Expeditionary Force, London, 1 February 1944. Pictured centre General Dwight D. Eisenhower with General Sir Bernard Montgomery to his left © IWM TR1541

Prime Minister Winston Churchill first mooted the idea of an invasion in 1940, but it was not until 1943 that President Roosevelt committed America to Operation Overlord, targeted for the following year. General Dwight D Eisenhower was Supreme Commander and General Sir Bernard Montgomery Commander-in-Chief.

Secret Intelligence

The Allied Central Interpretation Unit, RAF Medmenham, Buckinghamshire. D-Day forces were briefed with the aid of rubber models of the landing sites based on aerial photographs © IWM CH16106

Precise intelligence was needed to pinpoint potential invasion sites. spitfires flew aerial reconnaissance missions, covert surveys of potential landing beaches were made by divers and midget submarines, the French Resistance provided details of troop movements and defences, and the British public was even asked to send in holiday photos and postcards. The data was forensically analysed down to each pillbox and gun emplacement. A 100 kilometre stretch of Normandy coast was identified as having weaknesses in its defences.

Dummy inflatable Sherman tank © IWM H42531

Deceiving the Enemy

Crucial to D-Day was fooling the German command into thinking that the Allies would invade around Calais, the nearest French coast to Britain. Fake radio traffic, dummy landing craft and vehicles, double agents spreading false information and a fictitious ‘First US Army Group’ helped divert attention away from Normandy and contribute to the impression that the invasion force was far bigger than it actually was.

Colossal Logistics

The building of infrastructure in Britain to facilitate a massive seaborne invasion was key. Camps, depots and new roads were built along the south coasts of England and Wales to facilitate the accommodation and movement of troops and equipment.

These sites stored thousands of vehicles and tons of supplies ready to go by sea. Harbours and ports were filled with ships of every type and beaches were given hard surfaces known as ‘embarkation hards’ to enable the direct loading of vehicles from sand to ship. British factories hugely increased production. Nearly 1.5 million servicemen arrived from America, along with millions of tons of supplies.

Mulberry Harbours

Artificial harbours being constructed at Surrey Docks, London, 17 April 1944 © IWM H37067

The Allies needed to rapidly land enormous amounts of supplies and equipment in Normandy during the invasion, but all of the French ports were in German hands.  Prior to D-Day, in a colossal engineering project, British manufacturers pre-fabricated two artificial ‘Mulberry Harbours’, mainly on the River Thames in London and on the River Clyde in Glasgow. The enormous component parts were towed by tugs across the Channel on the afternoon of D-Day and assembled by the military.  Each harbour was the size of Dover.

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The design of each Mulberry Harbour included 10 kilometres of flexible roadways, floating on pontoons and capable of taking the weight of tanks from ship to shore.

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These were sheltered by 146 massive semi-sunk concrete ‘Phoenixes’, each weighing up to 6,000 tonnes and armed with anti-aircraft guns and barrage balloons, along with lines of 60 metre long floating breakwaters and scuttled obsolete merchant vessels.

Fuelling the invasion

Fuel pipes wound round a giant drum, a ‘Conundrum’, ready to be laid on the sea floor by specialised cable-laying vessels. The first fuel pipeline was laid under the Channel from the Isle of Wight to Cherbourg, France, August 1944 © IWM T54

Operation Pluto (Pipe Line Under the Ocean) was a complex operation to construct oil pipelines to provide fuel for vehicles and tanks for Operation Overlord in an attempt to relieve the dependence on oil tankers that were vulnerable to U-Boat attack.

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Former Brown’s golf course pavilion, Sandown, Isle of Wight. Enlarged during the Second World War to provide power for Pluto. Listed Grade II © Simon Hawkins
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Former Brown’s ice cream factory that secretly housed a Pluto pumping station. Sandown, Isle of Wight © Simon Hawkins.

The Pluto project was carried out in the utmost secrecy, with pipeline channels across land dug at night out of sight of enemy aircraft. The pumping stations and their power supplies were disguised by camouflage or hidden in everyday buildings. Fuel was stored on the Isle of Wight before being gravity-fed into the pumping system and sent 60 miles under the Channel to France.

Header Image: American infantry landing on D-Day at Omaha beach, Normandy. Public Domain. 

Written by Nicky Hughes.

Further Reading

1 responses to D-Day, 75 Years on: how it was planned

  1. Maria Holm says:

    Thank you for this excellent post. As a Dane, I am so grateful for the heroic action of D-Day by the allies.

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