D-Day, 75 Years on: how the Allies prepared

Between midnight on 6 June (D-Day) and 30 June 1944 an Allied invasion force of over 850,000 troops landed on France’s Normandy beaches, together with nearly 150,000 vehicles and 570,000 tons of supplies.

‘Operation Overlord’, as the almost three month campaign was known, was supported by a massive airborne assault and the deployment of 7,000 vessels, known as ‘Operation Neptune’.

D-Day was the start of the long campaign to liberate occupied north-west Europe, leading to the eventual Allied defeat of Nazi Germany.

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Troops storm ashore from Landing Craft Assault (LCAs) during Exercise Fabius, a major invasion rehearsal on the British coast, 5 May 1944 © IWM H38244

Planning for what was the largest and most complex land, air and sea operation in history began as early as 1942. British, American, Commonwealth and other allied forces took part in months of intensive military training at sites across Britain, including large scale invasion rehearsals on English beaches, often under live fire to make them as realistic as possible.

Exercise Smash

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One of seven Valentine tanks lost during Exercise Smash in April 1944, lying under 15 metres of water, Poole Bay, Dorset. Newly Scheduled © Paul Pettitt

Six weeks before D-Day on 4 April, troops gathered at Studland Beach in Dorset, which had similar features to the beaches of Normandy, to rehearse an assault. This stretch of coastline was  considered vulnerable to a German invasion and had already been heavily fortified. Thousands of men took part in the exercise and live ammunition was used, as well as rockets and bombs.

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Fort Henry, Studland Bay, Dorset. Listed Grade II © Derelict Places

The exercise was watched by Churchill, Montgomery, Eisenhower and King George VI from Fort Henry, an observation post built on a small cliff overlooking the bay.

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Modern memorial to the six soldiers who drowned during Exercise Smash, erected 2004 © Derelict Places.

A new type of amphibious vehicle, a modified Valentine tank, was tested during the practice assault. They were launched too far from the shore and seven sank. Tragically six men drowned.

Exercise Tiger

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This American Sherman tank sank during Exercise Tiger at Slapton Sands in Devon. It was raised from the seabed in 1984 and is now a memorial to those who died. Public Domain.

The United States Army and Navy used Slapton Sands in Devon from 22-30 April 1944 to secretly practice the Normandy landings. This comprehensive rehearsal involved 30,000 servicemen and meant that 3,000 local residents were given six weeks notice, without explanation, to leave their homes.

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American troops landing during Exercise Tiger rehearsals.

The first practice assault was on the morning of 27 April and included live ammunition and a naval bombardment. Due to a catastrophic mix up in communications, the seaborne troops came under friendly fire and an estimated 300 Americans were killed.

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Aerial view of the aftermath of Exercise Tiger showing three ships lying off Lyme Bay, Devon, two landing craft to the left, plus the destroyer HMS Onslow diverted to the rescue of survivors and retrieval of dead bodies © Historic England 11169-700

The next day, 28 April, an Allied convoy on its way to the rehearsal was attacked in Lyme Bay by heavily armed, fast attack German E-boats, resulting in 198 US Navy and 441 US Army dead or missing.

The disaster was hushed up and the truth only revealed 40 years later when the Sherman tank was raised from the seabed.

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Multi-beam swath bathymetry ‘depth map’ of the seabed showing the ghostly outline of the bow section of landing craft LST-507 which split in two as a result of the German attack. This section of the ship has landed on the seabed upside down © UK Hydrographic Office

6 June 1944: D-Day

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Aerial photo of the British Army’s 50th Infantry Division during the D-Day assault on Gold Beach, Normandy © IWM CL3947

The D-Day invasion took place on five codenamed Normandy beaches. British and Canadian forces attacked on the east at Sword, Gold and Juno, whilst the Americans landed on the two western beaches: Omaha and Utah.

Tanks & Bulldozers
Submerged tank from a group of armoured vehicles lost en route to Juno Beach 5 June 1944 when an LCT capsized, Selsey, West Sussex. Newly Scheduled. © Historic England

The amphibious Allied D-Day landings were preceded by extensive aerial and naval bombardments and an assault by thousands of airborne troops. Infantry landing on the beaches faced heavy fire and the shoreline was mined and covered with obstacles.

Casualties were high on both sides: 4,414 Allied servicemen were killed and there were an estimated 4,000 to 9,000 German casualties, whilst thousands of French civilians also lost their lives, many as a result of Allied bombing.

From D-Day to 30 August 1944, the end of the Battle of Normandy, the Allies had gained a vital toehold in Europe, forcing Germany to fight on two fronts, and leading to her eventual defeat in Europe less than a year later on 7 May 1945.

Written by Nicky Hughes.

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