D-Day Planning and Execution

This page consists of a summary of the planning for D-Day in a timeline with the opportunity to discover more detail via internal or external links. all links will open as separate pages. 

D-Day in the Context of World War Two

This site concentrates on the Overlord period from May 1943 until August 1944. There is a useful timeline on the World War II foundation's website that places the preparations, and D-Day itself in the context of the 1939-45 War. Over Christmas of 1941 to January 1942 The United States and Britain had established a strategy to concentrate on the more powerful Germany before dealing with Japan. The issue became more complex with the success of Japanese forces and the lack of shipping resources to concentrate on Europe.  

Planning for an Invasion of Mainland Europe

In some respects the plans for supporting allies in Europe had begun in 1910 with the concept of the British Expeditionary Force. These plans, amended over time dealt with the detail including logistics and transportation of men to where they might be needed. This was the foundation for the British forces being sent into Belgium in August 1914 and again to France in September 1939, this time resulting in a tactical retreat to Dunkirk. 

Strategic high level plans were made for an invasion of Europe in 1942  (Operation Sledgehammer), and in 1943 to relieve pressure on the Russians. Neither of these invasions happened, but perhaps under political pressure form Russia a force was assembled to attack, and take the port of Dieppe, Operation Jubilee,  with the intention of holding until a full scale Invasion could take place. This assault was a tragic failure and is the subject of controversial debate to this day as the lives of many solders, mainly Canadians were lost and others captured. However, it did galvanise minds to concentrate on learning lessons from the tragedy.

A large naval bombardment would be needed to preceded an amphibious landing. Capturing a port, was not feasible and an understanding of the types of beaches and their defences was required in advance, together with absolute secrecy. In the absence of a port, a method of unloading large numbers of additional troops and supplies would be required after securing the beachhead.

A number of plans were drawn up and amended, culminating with Operation Roundup which concentrated on the liberation of Europe. Operation Roundup formed the basis of the eventual Operation Overload, in fact the a planning file in the UK National Archives has a heading of Roundup crossed out, and substituted for Overlord.[1]

Strategic plans were amended and even at this early stage the need for some kind of temporary port  was recognised.  

Operation Overlord: Initial Planning

Overlord was the codename for the allied liberation of France and began in May 1943, when the Washington Conference of the US & British Heads of State known as Trident set the strategic timescale for an invasion of Sicily, The invasion of France and developments in the Asia-Pacific War.

On 28th June 1943 The Overlord plan began in with a Combined Services conference Codename RAFFLE held at Largs in Scotland that included the following subject agenda in the Plan[2] below:

The RAFFLE conference marked the start of the detailed coordinated Planning which by the end of 1943 brought together a number of long term projects including, the beach assault plans, creation of artificial harbours, a fuel supply pipeline and the collection and collation of geographical and geological information and well as tackling the detailed plans to achieve strategic military goals.

Operation Overlord continued to be the overarching plan for what we know as D-Day, the Normandy landings, with Operation Neptune being the name assigned to the Naval Plan. As we will see there were a myriad of operations that were placed under the Overlord umbrella which were the ultimate responsibility of the newly appointed Supreme Commander of the Allied Expeditionary Forces (SCAEF)  General Dwight D Eisenhower. See Command & Control .

Security and Counter-intelligence 

One of several failures of The Dieppe Raid, was breaches of security. It was recognised that the Overlord Plans had to be undertaken with the utmost secrecy. The subjects in the table above give a hint as to the scope and complexity of the plan, and challenges in keeping this vast undertaking secret. As we travel through the planning stages, it is worth pausing to reflect on this; as we shall see, there were large troop movements, building programmes and training exercises, much of which was taking place very close to the coastal population.

As at the beginning of WW1 the British counter intelligence operation was very effect in rounding up spies. Secondly having spoken to some of those who were living in South East England at the time, it was obvious to the public that there was a build up of forces for an invasion, and even the enemy knew that an invasion was likely. However, when, where and how and had to remain restricted on a need to know basis.

Small snippets of information did leak out, in the form of a complex and intentional deception plan under the codename Operation Bodyguard. Information obtained too easily would be open to suspicion, but incidental information from various different sources, such as a a piece of information from fictional British agents[3] via Portugal, Spain and Switzerland all formed a complex jigsaw that when put together suggested that the British were planning an assault on Stavanger in Norway, or the more obvious area of French coast from Dunkirk south to Dieppe; an area of coastline closest to England. The dummy plans were backed up with inflatable landing craft, tanks, and aircraft at locations in Kent and Essex, Royal visits to troops at the same locations and  Fictional Armies such as the British Fourth Army Group and First US Army Group (FUSAG)  commanded by General Patton. These fake armies part of Operation Fortitude North and Operation Fortitude South consisting of numerous divisions that were moved around by means of a complex network of false radio network traffic co-ordinated from Dover Castle in Kent. There were even real bombing raids across northern France and Belgium to reinforce the idea of a Dieppe-Dunkirk landing.

The now demolished Norfolk House, St James Square in London, UK (Now 31) was the home of the Supreme Allied Commander's office and was the location for the most senior planners. Those at Norfolk House and beyond, with the highest clearance BIGOT were, except for Churchill and we presume  Allied Commander Eisenhower were prevented from leaving the UK. One now famous breach came when a Secret document containing crucial panning information flew out of the window and was retrieved by a member of the public, who assuming it must be important handed it in to the authorities.

Bletchley Park (Station X) in Buckinghamshire, now known as the centre of codebreaking and monitoring enemy radio traffic during WW2 fed High level decoded enemy traffic codenamed Ultra into the planning system. The information informed the planners of troop and aircraft movements before and during the assault and also confirmed the success of the Bodyguard deception operations.

Bletchley Park © Historic England Ref AA048017

Special Operations: C.O.P.P. and S.O.E.

The Combined Operations Pilotage Parties (COPP) were a group of specialist commandos based at Hayling Island Sailing club in Hampshire, UK during WW2.  The COPP units were involved in many operations involving secret landings on enemy beaches to carry out surveys in advance of a full military landing.

Following the Dieppe Raid it was realised that detailed intelligence about the geology of the beaches, as well as defences and hydrography of the seas around the landing sites was required to successfully get troops and equipment onto the beaches and beyond, as efficiently as possible. Additionally, it was realised that absolute secrecy was required at every level. Consequently, it has taken years to learn about the most secret aspects, including the work of COPP which had previously operated in the Sicily, gathering intelligence prior to the July 1943 landings. In 1943 alone COPP carried out 18 missions along the French and Norwegian coast 

The commandos travelled by mini submarine, landing covertly on French beaches to take soil/beach samples, survey areas of beach, and on at least one occasion even took samples of defences to test ways to overcome them. 

This information was fed back to the scientists and planners to feed into the attack plan. Following the intelligence missions COPP teams were back in action on D Day establishing landing beacons and guiding in the first waves of landing craft to ensure all subsequent craft landed in the right place.

COPP are commemorated at a Memorial at the National Memorial Arboretum, Burton on Trent, UK  and On Hayling Island.

The Special Operations Executive (SOE) [4]   was formed in 1940 to coordinate and carry out subversive action against German forces in occupied countries, including France. SOE sent agents to support resistance groups and provided them with weapons, sabotage materials and other supplies.

There was very limited cooperation between SOE and those planning Operation Overlord. The role to be played by resistance forces during the invasion was not decided until the week before D-Day, and involved disruption of key infrastructure such as railways. The instructions for these operations to start were sent in coded messages within BBC broadcasts.

SOE Headquarters was in 64 Baker Street, London, UK although there are reported to be over 80 locations in the UK with specialist responsibilities such as Training operatives, Camouflage, preparing false documents and appropriate clothing for each operating location. We have already mentioned Bletchley Park which dealt with SOE communications. Many SOE operatives were parachuted into occupied Europe by 138 (Special Duty) Squadron which carried out Supply and Agent drops from RAF Tempsford, near Sandy, Bedfordshire, UK  and  Westland Lysander aircraft operated by 161 (Special Duty) Squadron also flew from RAF Tangmere near Chichester, Sussex, UK. SOE Training took place at several locations in Beaulieu, Hampshire, UK. 

Special Equipment

Such a large assault required the maximum number of men and vehicles to be off loaded onto the beaches and immediately effective under fire. The beaches and areas beyond were protected by obstacles , which were added to when Rommel took over command of the defences. Hitler was to become taken in by the deception plan. However, Rommel was an experienced Officer who was more prone to prepare for the unexpected.

Prior to WW2, then Major General Percy Hobart was retired by the the army due to his "unconventional" approach to Armoured warfare and we believe it was during this time that he developed some of the ideas that later became known as "Hobart's Funnies". He was subsequently drafted back into the 79th Armoured Division from the Home Guard at the age of 52. 

A.T.E.A.'s (Armoured Vehicle Royal Engineer) were a series of Churchill Tanks that were adapted to; Lay a carpet roadway over areas of beach identified as soft, use a mortar to destroy bunkers or walls, Fill ditches, lay temporary bridges, and carry a flame thrower. Another development was a Sherman tank fitted with a flail for destroying mines and barbwire defences.

Such was the secrecy around these vehicles that the instructions included a line that the codenames 'C.D.L.' ; 'D.D.' and 'A.T.E.A' special Amphibious Fighting Vehicles must never include the work 'Tank' and they must not be included in any document graded lower than 'MOST SECRET' [5]  

The Duplex Drive (DD) Tank, perhaps now the most well known of these vehicles was based on a Valentine Tank with a waterproofed flexible screen which enabled it to float. The smaller lighter Sherman tank became more suited to this role which enabled the vehicle to be off loaded in deep water with a propeller drive. Once on the Beach the screen was dropped and the Tank was able to commence the assault. Valentine tanks continued to be used for training, but only Sherman DD's were used on D-Day.

Development testing of the 'Funnies' took place near Saxmundham in Suffolk, UK. The DD fresh water training took place at Fritton Lake on the Norfolk/Suffolk border from where the crews were trained to escape, maintain and waterproof the tanks. Crews were then sent to Stokes Bay in Hampshire, UK where they were trained to deploy the tanks from landing craft which took place in Osborne Bay, Isle of Wight, UK. The Salt Water training school huts were located in the area now occupied by the No:2 battery Car Park. About 150m to the east was the location of the waterproofing pit, although no traces remain. The tank, storage area was in an area now occupied by a private holiday park.

Stokes Bay and the DD Salt Water Training School is included in the Solent D-Day Tour No: 3

X-25 underway ©IWM (A 22903)

X-Craft Midget submarines were developed for clandestine use, armed with  detachable charges. A number of development craft were built before it was felt that a feasible weapon had been produced. The first operational craft was X3 (or HM S/M X.3), launched on the night of 15 March 1942 

Two X-craft were used by Combined Operations Pilotage Parties (COPP) on D- Day related operations [6] :

• X-20 was used both during reconnaissance of the Normandy beaches in early 1944 and to help guide in the D-Day invasion fleet on 6 June 1944. This boat was named Exemplar.

• X-23 was used just for beach marking on D-Day. This boat was named Xiphias.

Footnotes:

[1] ROGERS, D., 2014, Destination D-Day, P22 Helion & Co Ltd.

[2] The National Archives UK, (TNA): AIR  20/5229

[3] :BRAIN, J Dover Castle, Operation Fortitude and D-Day  https://www.historic-uk.com/HistoryUK/HistoryofBritain/Dover-Castle-D-Day/ Accessed 18 August 2024. Juan Pujol Garcia, Codename GARBO a Double Agent operating 27 fictional agents in England. A Polish officer Roman Czerniawski Codename BRUTUS who had operated from occupied France. And a Yugoslav known as Dušan Popov codename TRICYCLE.

[4] : The SOE https://holdsworthtrust.org/soe/ Accessed 18 August 2024

[5] : The National Archives UK, (TNA) WO 219/2065 (C.D.L=Canal Defence Light, D.D.=Duplex Drive and A.T.E.A.=Armoured Vehicle Royal Engineer. 

[6] : CRANE, R., COPP Survey, https://www.coppsurvey.uk/xcraft 

Page Updated: February 2025